Axial and Centrifugal Compressors Application Guide

Axial and Centrifugal Compressors Application Guide
GE Oil & Gas
Axial and Centrifugal Compressors
Application Guide
Bently Nevada* Asset Condition Monitoring
Contents
1.Disclaimer........................................................................................................................................................................................................3
2.Purpose............................................................................................................................................................................................................3
3.Scope................................................................................................................................................................................................................3
4.References.......................................................................................................................................................................................................4
5.Protection/Management...............................................................................................................................................................................4
6.Types of Centrifugal Compressors...............................................................................................................................................................4
6.1 Process Centrifugal Compressors........................................................................................................................................................................................................... 4
6.2 Package Centrifugal Compressors (Integrally Geared Compressors).................................................................................................................................... 5
7.Typical Malfunctions......................................................................................................................................................................................5
7.1 Compressor Surge and Stall....................................................................................................................................................................................................................... 5
7.2 Anti-surge control and recycle valves................................................................................................................................................................................................... 7
7.3Choke.................................................................................................................................................................................................................................................................... 8
7.4 Thrust Force:..................................................................................................................................................................................................................................................... 9
7.5 Fluid-Induced Instability.............................................................................................................................................................................................................................. 9
7.6Unbalance........................................................................................................................................................................................................................................................... 10
7.7Misalignment.................................................................................................................................................................................................................................................... 12
8.Transducers��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 12
8.1 Selection of Transducers and Locations�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������12
8.2 Proximity Probes���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������12
8.3 Shaft Radial Vibration�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������13
8.4 Axial (thrust) Position�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������13
8.5 Keyphasor Sensor�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������14
8.6 Accelerometers (seismic transducers)��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������14
8.7 Temperature Sensors������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������15
8.8 Speed Sensors��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������15
All drawings and diagrams contained herein were produced by GE and cannot be
reproduced or copied without GE’s express consent.
application guide
application guide
9.Bently Nevada 3500 Series Machinery Protecting System�������������������������������������������������������������������������������������������������������������������� 15
9.1 3500 System Overview������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 15
9.2 System Copmonents Selection��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 16
9.2.1 Instrument Rack��������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 16
9.2.2 Power Supplies����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 16
9.2.3 Trasnient Data Interface Module������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ 17
9.3 Monitor Module Selection�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 16
9.3.1 Vibration Monitors���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 17
9.3.2 Keyphasor/Speed/Overspeed Monitors���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 18
9.3.3 Temperature Monitors�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 20
9.3.4 Relay Modules������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 20
9.3.5 Alarm Setpoints���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 21
9.6.6 Vibration Instrumentation diagram for Dual Flow Centrifugal Compressor���������������������������������������������������������������������������������������������������������� 23
9.6.7 Vibration Instrumentation diagram for Axial Flow Compressor���������������������������������������������������������������������������������������������������������������������������������� 24
9.6.8 Vibration Instrumentation diagram for Integrally Geared Compressor (3 or 4 stage)�������������������������������������������������������������������������������������� 26
10. The Industrial Internet������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ 28
11. Management with System 1* Software�������������������������������������������������������������������������������������������������������������������������������������������������� 28
11.1 Outline of System1���������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 28
11.2Thermodynamic Performance����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 29
11.3Automated Machinery Diagnostic Functionality����������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 29
11.4 Centrifugal Compressor RulePak������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ 30
11.5 Axial Flow Compressor RulePak�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 30
11.6 Integral Gear Compressor RulePak������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 31
12. SmartSignal Integration��������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 31
APPENDIX 1 System 1 Software and Network Connectivity������������������������������������������������������������������������������������������������������������������������������������������������������������������ 32
APPENDIX 2 Process Inputs for the RulePaks������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ 34
APPENDIX 3 OptiComp* BN����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 35
APPENDIX 4 Data Required for Thermodynamic Performance������������������������������������������������������������������������������������������������������������������������������������������������������������� 37
APPENDIX 5 Discussion of 3500 Thrust Measurement and API 670 Compliance������������������������������������������������������������������������������������������������������������������������� 38
APPENDIX 6 Voting Truth Tables for Normal AND and True AND voting������������������������������������������������������������������������������������������������������������������������������������������� 40
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Integrally Geared
Compressor type
Axial
Centrifugal
1 Disclaimer
TRANSDUCERS



Radial Vibration (X/Y)



Axial Position (Thrust)



Casing Accelerometers (Gearbox)



Keyphasor* and Speed



Temperature



PROCESS INPUTS (DCS)



Pressures



Flows



Temperatures



Speed



Machine State (SU/SD, Steady State)



MACHINERY PROTECTION SYSTEM
(MPS)



3500 Local Display



The American Petroleum Institute (API) 617 style compressors are
typically found in refinery and petrochemical applications.
3500 Rack



3500 Power Supplies



GE strongly recommends the continuous collection, trending and
analysis of the radial vibration, axial position, and temperature
data using a machinery management system such as System 1*
software. Use of these tools will enhance the ability to diagnose
problems and analyze the performance of the compressors.
3500 TDI Module



3500 Monitoring Modules



3500 Relay Modules



MACHINERY CONDITION
MANAGEMENT SYSTEM (MCMS)



System 1 Core



System 1 RulePaks - Integrally Geared
Compressors



System 1 RulePaks - Centrifugal
Compressors



System 1 RulePaks - Axial
Compressors



Bently Performance
(Thermodynamics)



SmartSignal Integration



Machine State



This application guide is intended to provide guidance only. The
procedures provided will not apply to all situations, and may vary
based on different circumstances such as government or industry
regulations, customer-specific requirements, and public safety laws
and regulations.
GE assumes no responsibility for errors or omissions that may
appear in this document and reserves the right to change this
document at any time without notice. This document is not to be
construed as conferring by implication, estoppel, or otherwise
any license or right under any copyright or patent, whether or not
the use of any information in this document employs an invention
claimed in any existing or later issued patent.
2 Purpose
The purpose of this document is to establish guidelines for the
selection and installation of GE’s Bently Nevada transducers
and protection and monitoring systems on axial and centrifugal
compressors with fluid film bearings – classified as critical
machines. These recommendations apply to both new machines
and existing machine installations targeted for retrofit.
3 Scope
Compressor asset management best practices indicate the use of
the following items:
• Proper transducer suite
• Corresponding 3500 machine protection system
• System 1 asset monitoring platform
• Thermodynamic performance
• Automated machinery diagnostic functionality (RulePaks)
The table to the right provides a more detailed view of the specific
components.
Best Practice Components
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application guide
4 References
6 Types of Centrifugal Compressors
1.API Standard 670 Fifth Edition, November 2014
2.API Standard 617 Eight Edition, Axial and Centrifugal
Compressors and Expander-compressors for Petroleum,
Chemical and Gas Industry Services, September 2014
3.API Standard 613 Fifth Edition, Special Purpose Gear Units for
Petroleum, Chemical and Gas Industry Services
6.1 Process Centrifugal Compressors
Horizontally Split – Horizontally split compressors are
used primarily for low and medium pressure applications
in ethylene and fertilizer plants refineries, liquid natural
gas (LNG) for refrigeration, air compression, and so on.
5 Protection/Management
Protection Solution - The recommended protection system for
axial and centrifugal compressors follows the API 670 Standard for
Machinery Protection Systems.
Management Solution - The recommended management solution
for centrifugal compressors includes the protection solution with
the addition of System 1* trending and analysis software. The
table above shows recommended protection transducers on a
centrifugal compressor. Each item is discussed in detail in the
Transducer Selection section of the document.
Note: It is recommended that the management solution include
the pre-packaged diagnostics and performance applications (if
applicable) to manage issues before the protection system must act
(i.e. the Integral Gear Compressor application package).
Barrel – Vertically-split barrel compressors are used primarily for
high-pressure applications such as ammonia, urea and methanol
synthesis, refinery recycle, natural gas compression and injection,
and hazardous gases.
Additional Measurements - Many measurements, such
as thermography and oil analysis, can be made on API 617
compressors. In many cases, new or emerging technology
enables the online implementation of these parameters. As the
robustness and value proposition of these technologies prove out,
these measurements may be included in future Bently Nevada
Best Practices from GE. Separate application notes provide
transducer, monitor, and installation recommendations for these
measurements. For a copy of these application notes, please
contact your local account manager.
Instrument Diagnostics:
Extensive self-testing is performed continuously on each of GE’s
Bently Nevada 3500 or 3701 instrumentation packages. Self-test
failures are displayed to the end user in several ways, including:
the green OK LED being extinguished, the instrument rack OK relay
(normally energized) changing state, a note in the operator display
(if supplied), and a note in the monitor events list. It is extremely
important that end users are aware of and take advantage of
these self-test indicators so that instrumentation problems can be
addressed before there is a false or missed alarm event.
Integrated Compressor Line – Integrated compressor line (ICL)
is designed to achieve balance between productivity and the
environment, power demands and space limitations, performance
goal and maintenance requirements, reliability, and availability.
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application guide
pinion-shaft. Optimal impeller speed and the ability to inter-cool
compression stages supports very high efficiency. A large variety
of gases can be handled by this compressor line with appropriate
construction materials, seal and control systems. Sometimes these
machines are referred to as four-posters (for four stages) or simply
as air machines, because the most common service is general plant
compressed air supply.
7 Examples of Centrifugal Compressor
Malfunctions
Overhung Single Stage – Overhung compressors are mainly
used as boosters in petrochemical applications or for recycle in
polypropylene and polyethylene plants. The single-stage overhung
configuration is simple and easy to maintain. Almost all gases
can be handled by this type of compressor with appropriate
construction materials and seal systems.
Pipeline – These compressors are specifically designed for pipeline
compression stations. They are used for low and medium pressure
ratio pipeline service and in recycle applications such as those
performed in methanol plants, etc.
7.1 Compressor Surge
Surge is the point at a given operating speed when the compressor
cannot increase gas pressure to overcome the system resistance or
backpressure. This causes a rapid, cyclic flow reversal. As a result,
thrust reversal causing high axial vibration, temperature increase
because of recompression of the same portion of gas are common
symptoms and some radial vibration also can occur. In centrifugal
compressors these occurrences can damage the interstage/eye
labyrinth seals, impellers, couplings, and the compressor driver.
Most compressors are designed to withstand occasional surging.
However, if the machine is allowed to surge repeatedly over a long
period of time, or if it is poorly designed, prolonged periods of
surging can result in a catastrophic failure.
The incipient surge (i.e. before flow reversal develops) can be
detected in the radial vibration signal as subsynchronous vibration
at a frequency of approximately 0.10X to 0.20X (10 to 20 percent
of the rotor speed). Fully developed surge is self-excited vibration
characterized by flow reversal and causes low frequency, high
amplitude axial vibration, typically in the 0.3 Hz to 3 Hz frequency
range. Some radial vibration at the same frequency can also be
observed due to coupling of axial and radial vibration, but the levels
may be insufficient to cause alarm.
6.2 Package Centrifugal Compressors
(integrally geared compressors)
These machines are produced as a package with the entire machine
mounted on a common foundation. The machines are integrally
geared, and used in several refineries, petro chemical plants and
applications, either for low pressure/high-flow, or low-flow/high
pressure conditions. This type of compressor has from one to four
high speed pinions and the bull gear can be driven directly by an
electric motor or by a turbine (gas or steam). One or two impellers,
open or closed, tri- or bi-dimensional type can be mounted on each
The above figure can be used to illustrate the surge cycle as follows:
• The compressor reaches surge point A and loses its ability to make
pressure.
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application guide
• Suddenly pressure at the discharge drops, causing pressure at the
discharge line to be higher than compressor discharge pressure.
The compressor surges, the flow reverses, and the compressor
operating point goes to point B (negative flow).
• The result of the flow reversal is that the pressure at the discharge
goes down, so now there is less negative flow. The operating point
goes to point C.
• The system pressure is going down, and the compressor is
again able to overcome pressure in thedischarge line. Thus, the
compressor “jumps” back to the performance curve and goes to
point D.
• Forward flow is re-established. The compressor starts to build
pressure and follows the pressure-flow characteristic curve,
toward surge. Point A is reached. The surge cycle is complete.
Note: Surge is a coupling effect between the compressor and the
network (for example: resistor, capacitor). The working point is the
intersection between the compressor performance curve and the
network. Physically, the pressure ratio fixed by the upstream and
downstream pressures of the network will determine the flow.
Figure: Surge event on shaft relative vibration, half spectrum waterfall.
Compressor surge is typically controlled by detecting when
the compressor is nearing the surge line on the compressor
characteristic curve and modifying the compressor operation to
avoid entering into a surge cycle. In air compressors, surge control
can be accomplished by opening a discharge end bypass valve and
venting air to the atmosphere. This increases the flow, with an
accompanying loss of pressure, and avoids the potentially harmful
surge cycle. However, continuous operation in this manner is costly
and inefficient and the root cause of the reduced flow needs to be
identified to allow corrective action to be taken to re-establish the
compressor on an optimal operating point.
Process compressors use a recycle valve to allow some of the high
pressure compressed product to be reintroduced into the low
pressure compressor inlet (after appropriate cooling if necessary),
thus maintaining flow below the surge line with some loss in
process efficiency. Again, the root cause of the reduced flow needs
to be determined and the compressor brought back to its design
point as soon as practical.
An anti-surge device is a common part of most centrifugal
compressors control systems. However, the operation of most
systems depends on the experimentally identified stable operation
limit on compressor characteristic. When the compressor
characteristics change in time (due to some wear or failure)
the anit-surge system may not react properly on real surge
conditions. The OptiComp* compressor control suite is GE’s latest
comprehensive software package for controlling centrifugal and
axial compressors. It improves upon the standard industry antisurge control and protection algorithms and effectively and safely
matches compressor performance to process demand within
the operational constraints of the compressor, its driver, and the
process. In addition, OptiComp uses a specially developed algorithm
for detection of real surge events based on thrust position
measurements from the 3500 monitoring system. The presence
of surge condition is detected before single full cycle of reversal
occurs.
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application guide
Figure: Surge event (detected and controlled before full cycle occurs) from thrust position movement.
7.2 Compressor Stall
Stall is a local disruption of flow within the compressor that
continues to provide compressed flow but with reduced
effectiveness. The boundary layer of the flow moving along a
diffusing passage, such as impeller and diffuser, may be retarded
enough by the static pressure gradient to bring it to rest and to
reverse it, causing the flow to separate from the wall. Stall can
create a single rotating cell or multiple rotating cells in one or
several stages.
The aerodynamic instability due to impeller stall typically causes
forward subsynchronous rotor vibration at a frequency of “less than
1X”, typically 0.6X to 0.8X (60 to 80 percent of the rotor speed).
Diffuser stall is often accompanied by forward subsynchronous
rotor vibration at a low frequency of around 0.2X to 0.4X (20 to
40 percent of the rotor speed). And the disturbances in the area
between stationary and rotating channels (for instance, due to axial
misalignment) can produce a forward subsynchronous component
from the 0.4X to 0.6X range. Flow reversals do not occur, and axial
vibration at the above frequency or significant movement is not
detected. The energy level of stall phenomena is not significant
and it is not proven that stall condition can cause any damage
to machine elements; however the occurrence of stall can be
considered an operational problem because increased vibration
may reach trip limits. Additionally, if the process is within limits
that in the past were not causing stall, then there is likely some
change in the geometry of channels (such as flow obstruction, blade
damage, or fouling), indicating that stall can be a consequence and
symptom of another problem.
Figure: Subsynchronous component at approximately 0.2X and accompanied orbit/timebase plot,
caused by stall in the stationary channels.
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application guide
Figure: Full size sample orbit for stationary channel (diffuser) stall.
7.3 Unbalance
Mass unbalance occurs when at given section of the rotor, the
geometric center and the mass center of a rotor do not coincide.
While there is always some remaining unbalance in the real
rotors, the problem starts if there is an excessive one – because
the unbalanced centrifugal forces are forcing excessive 1X rotor
response. The result is elevated 1X vibration that is forward in
precession and with a circular or, more typically, elliptical orbit
shape. Centrifugal force is not changing if the speed is constant;
this means that the elliptical orbit shape is changing because of the
supporting stiffness (bearing, bearing supports) that is typically
anisotropic (different in different radial directions). It is worth
noting that the 1X vibration response depends proportionally on
the magnitude of unbalance force but inversely proportionally on
synchronous dynamic stiffness, so not every situation in which
1X vectors are increased is related to increase in unbalance force.
Consider for instance the situation in which the bearing clearance
is increased causing lower bearing stiffness. Or consider that the
stiffness is reduced because the bearing was unloaded as result of
misalignment. The shaft relative vibration will increase then, for the
unchanged level of unbalance force.
Therefore, before claiming an unbalance problem, it may be
beneficial to measure the absolute casing vibration (because
the compressors are typically not equipped with this type of
measurement the portable data collector with temporary installed
velocity transducers can be used) to confirm the elevated level of
the forces transmitted to the bearing. Another important aspect
is to recognize that rotors for critical, high-speed machinery
are typically well balanced in the whole range of speed, before
installation. So even if unbalance is confirmed on an operating
compressor, the historical data should be analyzed to help
understand when the unbalance first appeared, whether it is
changing in time, what the potential source could be, and so on.
Coupling damage, a missing coupling bolt, or a cracked impeller
blade are examples of an unbalance source that would not be
appropriate to treat by balancing. In addition, not every 1X forcing
change is caused by mass unbalance. For instance, rotor bow due to
a rub generated hot spot or due to transverse crack development
can also look like simple unbalance until historical data is properly
analyzed. Finally, the compressor rotors do not always have field
accessible balancing planes so field balancing is often limited to
weight placement on coupling flanges.
Field balancing is a valid tool in the diagnostic toolbox – provided
that the balancing decision is made based on firm evidence of the
problem. Direct and 1X filtered orbits, transient and steady-state
vector changes for the 1X component (Bode and polar plots, trends,
both for shaft relative and casing absolute vibration), and shaft
centerline position changes should always be analyzed before
making a decision to perform balancing.
Figure: The full spectrum waterfall shows step change in the forward precession 1X vibration of
the compressor stage. This type of step-like “change of mass distribution” was not a candidate for
a balancing attempt. The fatigue crack on the impeller disc was diagnosed as the result of sonic
excitation of the disc mode (sound wave resonance) due to recent modernization of the stage.
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application guide
7.4 Electrostatic Discharge
For an example of another 1X vibration problem that is not
unbalance related, see the vibration trend below.
Figure: The electrostatic discharge case shows both data and inspection results.
The gradual increase of vibration was compared with the position in
the bearing and the apparent increase in bearing clearance found.
The increase in vibration is 1X related, however the unbalance
force is constant and the synchronous dynamic stiffness is
reduced. The chaotic spikes observed on orbit/timebase plots
allowed a conclusion of the electro static discharge (ESD) problem.
Replacement of grounding brushes stopped the change in vibration;
however the bearing had to be replaced at the closest opportunity.
Bearing inspection confirmed ESD damage. It took only six weeks
to wear the bearing pad more than 20 mils (0.5 mm) deep.
7.5 Misalignment
Machine alignment can be defined as proper positioning of bearing
supports (external alignment such as between machines in the
train) measured at the coupling; and alignment between rotating
and stationary parts (internal alignment measured as available
clearance around a rotating part at a given location). Misalignment
can be be defined as excessive error in alignment, whether external
or internal, that results in excessive radial preloads (for example,
static radial forces acting on rotor and bearings).
The effects of misalignment (and generally any other excessive
preload) can include overloading of the bearing causing premature
damage or unloading of the bearing that may lead to instability;
and cyclic stress on rotating elements leading to fatigue. For
most compressors, the damage is typically fastest at the coupling
elements, designed as a weak link, but a crack in the shaft is also a
possible result. Extreme change in the position can lead to contact
between the rotor and a stationary part (or rub).
With deformation of the casing, the clearance position is changed
or the shape of clearance can be deformed, and flow asymmetry
can generate high fluidic preloads. Therefore, thermal changes in
bearing position, limitations in thermal expansion, piping stress,
and soft foot issues fall into the same category of problems
because their effect is the generation of preload forces. And, even
if machine alignment was ideal there could be many reasons it
changed during the period of operation or due to changes related to
a specific condition.
The detection of excessive preloads is important, and can be
ensured by combining information from several sources. Any
change in radial loads acting on the rotor will cause a change in
bearing reaction that will result in a change to the position of the
shaft in the bearing. Therefore, a shaft centerline position plot is
extensively used for evaluation of alignment/radial preload changes.
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application guide
Figure: Shaft centerline position plots suggesting misalignment between bearing 2 (turbine) and
bearing 3 (compressor).
A change in preload will also change the support stiffness in
particular radial directions (for example, a change anisotropy of
stiffness) and as a consequence in flatness or in orientation of 1X
filtered orbit. Flatness of orbit can be tracked in full spectrum plots
(for instance, trended in full spectrum waterfall). The change in 1X
vectors (amplitude and phase) can be observed in trends or in an
acceptance region plot (a variation of polar plot for tracking steady
state data). While a flat 1X orbit can be considered a symptom of
misalignment, care should be taken because the orbit could also
be flat for other reasons, such as an operation close to resonance
speed. Proper diagnosis must consider several types of data to
confirm the problem.
Because excessive preload, which moves the rotor closer to
clearance boundary, causes higher dynamic stiffness, shaft relative
vibration amplitudes can go down. Conversely, a higher load on the
bearing causes an increase in absolute vibration. When this occurs,
other symptoms of excessive preload can be observed such as
abnormal casing absolute to the shaft relative vibration ratio.
Additionally, a higher load on the bearing results in a change of
bearing metal temperature and bearing oil temperature. Because
the former is a localized measurement, if the bearing is preloaded
at a position distant from where the temperature sensor is
normally installed, the readings can be lower than normal values.
This indicates that any change from normal bearing temperatures,
up or down, should be investigated.
Finally, for some types of couplings (for instance, gear coupling
and grid coupling), the misalignment can produce 2X and other
harmonics of 1X. This can be explained by vibration coupling
elements (for instance, teeth) with two stress cycles for shaft
revolution. In such situations, the amplitude of the 2X component
rises with the power transmitted, but because the load of the
compressor is often controlled by rotating speed change the
relationship between speed and amplitude is often observed. As a
result of this 2X component, some typical orbit shapes like “banana”
or “figure eight” are often quoted as misalignment symptoms.
However, they are present only for specific types of couplings and a
similar pattern can be obtained due to nonlinearity in stiffness (rub,
looseness, nonlinear behavior of oil film), therefore they should not
be used as a primary indicator of an alignment problem.
7.6 Rubs
Rub occurs when a rotating part is in contact with a stationary
part that is not designed for such contact. The only parts designed
for contact are bearings and some seals. In the fluid bearing, the
contact should be maintained through a film of oil. In the types of
seals that allow some contact by design – either constantly during
operation (oil seals) or occasionally (carbon seals, brush seals, and
honeycomb seals), the latter category will show symptoms of rub
contact as a part of normal behavior.
Because there are many possible rub scenarios, it is often called a
multi-face phenomenon. Rub varies depending on contact forces,
friction coefficients, material hardness, and so on.
A short list of rub symptoms includes:
•Changes in 1X vibration amplitude and phase due to a change of
orbit shape and size.
•Changes in 1X due to a contact spot temperature increase and
generated bow.
-A spiral vector change on a polar plot, or limited cycle can be
observed due to contact spot migration (known as Newkirk
type rub).
-A similar (or identical) pattern can be the result of Morton
effect, but this phenomenon is without surface contact.
Morton effect is caused when oil in the fluid bearing sharing
generates slight difference of temperature on both sides of
the journal that results in a configuration with a significantly
overhung mass. The generated bow increases the effect of the
unbalance of the overhung part and 1X vibration in the bearing
increases the temperature differential on two sides of the
journal.
-Subtle differences in some situations make it possible to
differentiate between the Newkirk and Morton effect, but such
details are beyond scope of this overview.
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application guide
• Changes in direct orbit shape due to any of the following:
-Heavy rub can reduce vibration in some directions and result in
a characteristic D-shape orbit.
-Light rub tends to re-bounce the shaft and increase vibration in
the direction of contact. If the friction forces are high enough,
the normally forward motion of the orbit reverses for part
of the cycle, resulting in external loop on the orbit. It is also
possible for 1X to become reversed for some speed range,
typically in the resonance regions.
•Changes in transient 1X response characteristics due to
increased stiffness at the rub location, cause the resonance
frequency to be shifted up.
• Harmonics of 1X due to the truncation of the normal sine wave.
•Exact fractional components generation (such as ½ X, 1/3 X, and
so on) and their harmonics are generated due to re-excitation of
rotor resonance at specified speed ranges. When rotor speed is
slightly above n-times resonance speed the 1/n X component can
be generated.
•A similar effect and very similar orbits will be generated due
to looseness in the support when 1/n X components can be
generated when operating slightly below n-times resonance
speed. This is called Mathieu type rub (or looseness) condition
and the effect is due to periodic change in system stiffness
during the vibration cycle. Since rub is increasing stiffness, and
looseness is reducing this for part of the cycle, the resonance
condition for the average value of stiffness will be above n-time
resonance speed for rub and below n-times resonance speed
for looseness. Taking into account the typical ratio of operating
speeds to resonance speeds, the most typical situation is
excitation of exactly ½ X. This is an exactly fractional component
contrary to instability situations that were characterized by some
subsynchronous but not exactly fractional components. It can be
easily observed on orbit/timebase plots, where Keyphasor dots
are locked at the same location on orbit for particular revolutions
of the shaft (compare with plots for stall or fluid instability, earlier
in the document).
Whether identification of rub symptoms is normally relatively easy
because of multiple but characteristic patterns, the localization
of the rub requires combining vibration and position data with
information about machine design, especially the position of seals,
clearance data, and so on.
Because rub is a secondary phenomenon, the primary cause must
be identified before the problem can be solved. The rub can be due,
and only due, to:
•Anything that causes excessive relative vibration levels, such
as unbalance, fluid induced instability, or oversized bearing
clearance.
•Anything that causes extreme shaft position – excessive preload,
internal or external misalignment, casing deformation, limitation
in thermal expansion, piping stress, and so on.
•Anything that causes limited clearance such as thermal
expansion, assembly, manufacturing or design errors, or deposit
formation.
•Any combination of the above that leads to rotor to stationary
part contact.
After detecting the rub symptoms, the vibration, position, and
process data are analyzed to identify the conditions leading to rub
and to track the primary source of it.
Figure: Rotating 1X vector on polar plot due to
Newkirk type rub in the carbon seal. Note that the
similar picture can be due to the Morton effect.
Figure: Sample orbit/timebase plots for rub condition. The orbit on the left shows 1X
and higher frequency components, the 1X precession is reversed. In the orbit on the
right (the same case, another measurement speed) there is exact ½ X present. The
full spectrum for the same condition is shown below the orbits.
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application guide
7.7 Malfunction Review Summary
From the brief review above, some conclusions can be drawn.
Because the detection of machine problems requires proper data,
the first, necessary condition is the installation of the proper suite
of transducers at the right machine locations and in the correct
manner. Next, the signals can be connected to the monitoring and
protection system. Some information about this process is provided
in sections 8 and 9 of this document. The conversion of data into
actionable information is a complex task that requires proper
diagnostic software as well as knowledge and skills (refer to the
overview of System 1 software in section 11 for more information).
To facilitate data interpretation, real-time, continuous, automated
diagnostic capabilities are offered by RulePaks, which use a rule
processing engine to evaluate collected vibration, position, and
process data to detect typical rotating machinery malfunctions.
About GE’s Bently Nevada Marchinery Diagnostic Service
For more in-depth analysis, both in-situ and remote diagnostics are
offered by GE’s Bently Nevada Machinery Diagnostic Service (MDS),
with more than 130 diagnostic engineers available worldwide. The
same diagnostic methodology used by MDS is offered as diagnostic
training courses available to customers:
Machinery Diagnostics – This course covers the solid basics of
data interpretation by teaching causes, effects, and indicators
of typical machine malfunctions for fluid film bearing supported
rotating machinery.
Machinery Fundamentals/Applied Diagnostics – This
intermediate-level course provides additional information about
design machinery (for instance, compressors, electric motors,
and steam and gas turbines). Learning occurs primarily through
the completion of workshop tasks in which students perform
diagnostic analysis based on data from real-world cases.
Advanced Machinery Dynamics – The highest level course
provides a deep dive into the details of machine design and their
influence on machine dynamics. It connects calculation (rotor,
bearing system modelling), measurement (radial and torsional
vibration of rotating machinery, structural analysis) and machine
design expertise (rotors, couplings, bearings and seals) approaches
to solve some of the most demanding diagnostic cases.
Refer to http://ge-energy.turnstilesystems.com/
MachineryDiagnosticians.aspx for more information about MDS
courses.
8 Transducers
8.1 Transducer/Location Selection
Sensors are installed in or on the machine to make appropriate
measurements such as vibration, position, speed, and pressure.
API 670 standard, Machinery Protection Systems, should be
followed for selection of transducers. The transducer types and
methodologies described here apply to axial, centrifugal and
integrally-geared compressors.
Typically, each radial bearing requires a pair of X-Y proximity probes
to monitor shaft vibration and shaft centerline position. Each thrust
bearing requires two proximity probes to monitor the axial position.
A Keyphasor* probe is required to obtain a phase reference (and
can provide speed measurement although a multi-tooth wheel
may be required for higher resolution speed measurements) from
each shaft. Accelerometers are required on integrally-geared
compressors to measure gear-related vibrations.
8.2 Proximity Probes
A 3300 XL 8 mm proximity transducer system is typically used,
consisting of three components: a 3300 XL 8 mm probe with 3/8-24
UNF threaded body, a 3300 XL extension cable (when required), and
a 3300 XL Proximitor* sensor. These components comprise a tuned
system, and must be selected to achieve a combined standard
electrical length for proper operation. Often a 5-meter system
with a 5-meter Proximitor sensor is used. A 9-meter system with
a 9-meter Proximitor sensor can be used if longer physical length
is needed between probe and Proximitor. When possible, the
consistent use of one electrical length is desired for simplicity and
standardization.
The 3300 XL 8 mm proximity transducer system provides up
to 80 mils (2 mm) of linear range with an output of 200 mV/mil
(7.87 V/mm) when observing AISI standard type 4140 steel. This
addresses the majority of compressor monitoring applications
for radial vibration, axial (thrust) position, speed, and Keyphasor
measurements. Shaft materials other than AISI 4140 steel require
a modification to the Proximitor sensor to preserve the standard
200 mV/mil (7.87 V/mm) scale factor. The system should be provided
with hazardous area and country certifications appropriate to the
installation. The gap between the probe and the shaft should be
adjusted to approximately mid-range (approximately -10 volts) for
optimal use of the full linear range when monitoring radial vibration.
Axial position monitoring requires a precise setup for the expected
motion of the thrust bearing.
Intrinsic safety barriers or galvanic isolators are required for
sensors located in some areas classified as hazardous. These
should be supplied in accordance with the user’s general
instrumentation standard and selected to ensure compatibility with
the transducer system and associated monitor modules. Refer to
the monitoring system’s field wiring diagrams and instructions for
details.
For all proximity probes, an “external” probe mounting arrangement
is often preferred, as it allows adjustment or removal of the probe
without disassembly of the machine. This method uses a part
number 31000 or 32000 Proximity Probe Housing Assembly and a
reverse-mount style probe. The Probe Housing Assembly should
be mounted to a structural component of the machine that firmly
positions the probe to accurately represent the movement of
the shaft relative to the corresponding bearing. If this mounting
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application guide
location is a distance from the shaft surface of 15 inches or more, a
bracing support at the tip of probe sleeve must be installed so that
it the probe tip does not vibrate laterally relative to the observed
surface of the shaft. Lateral vibration could fatigue the probe sleeve
and possibly introduce measurement errors. Also, this method
of installation often introduces thermal error in shaft centerline
position measurements because of movement of the fixture in
relation to the bearing. By fixing the probe to the bearing as close to
the probe tip as possible, the quality of the data used for diagnostic
purposes can be improved.
A variant of the external arrangement is the PROXPAC XL* proximity
transducer assembly. This modular proximity transducer system is
a 31000 housing that contains a special 3300 XL Proximitor sensor
and uses a 1-meter reverse-mount proximity probe (no extension
cable is needed between the probe and Proximitor sensor).
When the external mounting arrangement is dimensionally
unworkable, or a stable external mounting location cannot be
found, an “internal” mounting arrangement can be used. This
arrangement positions the probes inside the machine case or
underneath the bearing cover using standard or custom mounting
brackets. The cables are routed through the cover or case using
cable seals. When this arrangement is used, it is recommended
that a second set of X-Y radial proximity probes, and a spare
axial (thrust) probe and Keyphasor probe be installed, preferably
in the locations described in API Standard 670 guidelines. The
extension cables for these spare probes should be routed to where
the Proximitor sensors for the primary probes are located, for
connection to a Proximitor sensor should they be needed.
Note: All brackets should be designed to minimize the possibility
of thermal deformation causing error in shaft centerline position
readings.
The shaft surface observed by the probe should be smooth and free
of plating, scratches, residual magnetism, and shoulders or edges.
Radial probes should observe a probe target area on a circular
shaft that is concentric to the bearing journal. Axial probes should
observe a flat surface. The probe’s eddy current field should not
interact with metal surfaces alongside the probe tip or the field
from adjacent proximity probes. When mounting space is tight or
the observable shaft surface area is small (such as in integrallygeared air compressors), consider using the 3300 5 mm or 3300 XL
NSv* (narrow side view) proximity transducer systems, which have
a ¼-28 UNF threaded body.
Note: Refer to API 687 for additional information about
measurement path preparation and verification.
A transducer system verification check should be performed before
and after installation to ensure system integrity. The Bently Nevada
TK-3 instrument enables the installer to perform a calibration check
and exercise (loop test) the transducer and monitor system prior to
installing the transducer in the machine. Recalibration based upon
the TK-3 calibration graph is not recommended. This is because
all probes, cables and Proximitor sensors are factory calibrated
using precision instrumentation and field recalibration may have
an adverse effect on the interchangeability of components if it
becomes necessary to replace a part.
8.3 Shaft Radial Vibration
GE’s recommendation for radial vibration measurements is two (2)
vibration transducers mounted coplanar and 90 degrees apart (X
and Y) within 3-inches (75 mm) of the bearing. This X-Y configuration
provides a complete picture of the shaft centerline vibration
and radial position within the bearing clearance. The probes are
mounted perpendicular (within ±5°) to the shaft centerline with an
angular separation of 90°±5°. Typical probe orientation is 45° left
and 45° right, referenced to vertical (up) and viewed from driver to
driven end of the machine train. Where practical, a consistent probe
orientation should be used for all radial bearings on a machine case
or train to simplify diagnostics and balancing.
On integral geared compressors used for air compression service,
a single probe per bearing is acceptable when space constraints
prevent two probes in the X-Y configuration.
8.4 Axial (thrust) Position
Thrust bearing failure is considered a catastrophic failure and
typically leads to an immediate catastrophic failure of the
machine. Two (2) thrust probes should be used for redundancy to
ensure reliable machine protection. When the internal mounting
arrangement is used, a third (spare) probe and extension cable is
recommended. For installations requiring SIL 3 compliance, a third
probe is installed to provide a 2 out of 3 voting scenario. Position
measurements utilize the DC component of the transducer signal.
Mount the probes at the thrust bearing end of the machine and
within 12 inches (300 mm) of the thrust bearing to minimize the
effects of shaft growth due to thermal expansion. For example, 12
inches (300 mm) of 4140 steel with a temperature change of 100°F
(38°C) will grow 0.008 inches (0.2 mm). Therefore, the measurement
could show 8 mils of apparent thrust motion that is due only to
thermal growth if all else remains fixed. This must be considered
when establishing thrust alert and danger setpoints.
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application guide
A Keyphasor transducer should observe each output shaft of
the driver or (if present) gearbox. A spare Keyphasor transducer
is recommended and is especially important when the probes
are mounted internal to the machine. If possible, Keyphasor
transducer(s) should observe each pinion shaft of an integrallygeared compressor. Ideally, Keyphasor transducer(s) should also
observe the input shaft of the compressor to provide a dedicated
and consistent phase angle reference for the compressor despite
replacement or rework of the driver or gearbox. Keyphasor
probe and notch/projection locations and orientations should be
documented for future reference.
The preferred mounting arrangement for the thrust probes is
directly through the thrust bearing, but the machine design does
not always permit this. Thrust probe installation may also be
engineered to observe the end of the shaft within 12 inches
(300 mm) of the thrust bearing, or another collar on the shaft
within a similar proximity to the thrust bearing. If all probes cannot
observe the same plane, one of the two probes can be mounted to
observe the end of the shaft, and the other to observe the thrust
collar.
Due to the compact design of some integrally geared compressors,
manufacturers may elect to provide a single axial proximity
displacement transducer on the blind end of each pinion shaft
instead of the bullgear. This is acceptable per API STD 672, section
7.10.8. (This is an exception to the best practice of using dual
axial positon transducers and is driven by the space available for
the sensor installation). Specialty sensor designs such as “button
probes” may be employed for this purpose when the geometry of
the machine prohibits conventional sensors.
Keyphasor probes should be mounted radially; axial Keyphasor
probes observing the end of a shaft should be avoided, but may
be the only option on integrally-geared compressor pinion shafts.
The notch or projection observed by the Keyphasor transducer
should be intentionally designed into the shaft, should avoid high
torque areas and utilize radiuses to minimize stress concentrations,
and should be located and/or dimensioned such that axial shaft
movement due to thermal growth or rotor float does not affect the
Keyphasor measurement.
The minimum width and length of the notch should be one and
one-half times the diameter of the probe tip, and the minimum
depth should be 0.06 inch (1.5 mm). Except for small edge radiuses,
the notch or projection should present a well-defined step that
results in a Proximitor output voltage change of no less than 7 volts.
Note: It is a recommended practice, where possible, to input the
Keyphaser signal(s) into one channel(s) of a 3500/42 monitor to allow
capture of the Keyphasor signal waveform(s).
8.5 Keyphasor Sensor
The Keyphasor probe provides a once-per-turn phase reference
voltage pulse that is combined with vibration measurements to
derive synchronous (1X, 2X, nX, etc.) amplitude and phase angle
of vibration values. It is necessary for diagnostics and balancing,
and is required by the System 1 condition monitoring platform for
synchronous sampling.
8.6 Accelerometers (seismic transducers)
An accelerometer mounted to the gearbox can provide indications
of progressive damage to gear elements. Specific mechanical fault
symptoms related to gear wear or sudden damage can be detected
using the accelerometer’s increased sensitivity to higher-frequency
vibrations.
The 330400 accelerometer is suitable for most gearbox monitoring
applications, and the user should verify that the frequency
14
application guide
response of the chosen accelerometer is capable of detecting
the gear-related frequencies of interest. The 330400 has an
upper amplitude range of 50 g peak. Alternatively, the 330425
accelerometer has an amplitude range of 75 g peak for installations
where higher amplitudes are expected.
Accelerometers should be mounted on a flat surface of sufficient
area to provide full contact with the accelerometer’s base. The
surface should have a maximum roughness of 16 micro inches
(0.4 micrometers) Ra (arithmetic average roughness). A hole for
the accelerometer mounting stud should be drilled and tapped
perpendicular to the mounting surface (±5 minutes of an arc) in
the center of the mounting surface that will accommodate the
accelerometer stud thread, and to sufficient depth to prevent the
stud from bottoming out in the hole. Neither the mounting stud nor
any housing used should interfere with full and complete contact
of the accelerometer base with the gearbox surface described
above. A thin layer of coupling grease (such as silicone grease)
applied between the accelerometer and the mounting surface is
recommended. The accelerometer manufacturer’s minimum and
maximum torque requirements should be followed to prevent
accelerometer looseness and damage. Cable and connector
characteristics should meet the physical and environmental
requirements of the installation. Refer to API Standard 670 and
the accelerometer manufacturer’s installation manual for detailed
information.
For integrally-geared compressors, two accelerometer transducers
should be installed on the bull gear housing. The transducers
should be located on each side of the casing, and be mounted
radially on, or adjacent to, the bearing boss with axis aligned as
close as practical to the principal load direction (OEM should advise
recommended mounting orientation). If bearing bosses are not
available, the accelerometers should be mounted horizontally at a
location that provides direct transmissibility of bearing vibration
from the bearing support to the transducer. The accelerometers
should be mounted below the split line unless otherwise specified.
This placement allows the machine to be disassembled without
requiring removal of the instrumentation.
measured are preferred. Sensors that are potted into place should
be avoided, as this complicates replacement.
For radial bearings, depending on the length to diameter ratio,
installations should use one or two sensors at the calculated
maximum load deflection point on the bearing under normal
conditions. For thrust bearings, the end user should install
temperature sensors in each of two shoes in both the normally
active and normally inactive thrust bearings, with equal
angular separation between sensors. Dual element sensors are
recommended, with one lead connected to the monitor and the
other serving as an installed spare. Refer to API Standard 670 for
further details and requirements.
8.8 Speed Sensors
Speed is considered a primary measurement, and compressors
and their drivers typically have continuous speed indication in
revolutions per minute (rpm). Machine speed measurements
can come from a Proximitor sensor or magnetic pickup. Optical
speed sensors are typically used for temporary diagnostic
instrumentation only.
For permanent installations, the Proximitor sensor is
recommended. All of these transducers can observe a single or
multiple number of events-per-revolution of the shaft. Either
signal can be used for the speed indication, but the multi-event
per revolution signal, such as on a gear or toothed wheel, provides
better resolution at speeds below 300 rpm. Speed wheels are
typically located on the shaft of the driver, with once-per-turn
Keyphasor signals providing speed for driven shafts. Specific sensor
requirements for speed and overspeed detection are described
separately in the best practices for the driver machine.
9 Bently Nevada 3500 Series Machinery
Protection System
8.7 Temperature Sensors
Temperature measurements provide immediate and corroborating
indications of bearing wear and damage due to vibration,
misalignment, high load, lubrication problems, and other
malfunctions. Bearing metal temperatures in compressors and
gearboxes should be monitored using resistance temperature
detectors (RTDs). Thermocouples (TCs) may be used if dictated
by user preference. Temperature elements of varying styles are
available from several manufacturers.
For best temperature detection, the sensing elements should be
embedded in the metal backing of the pads, as close as possible
but not penetrating into the babbitt. Spring-loaded temperature
elements that hold the sensor tip against the surface to be
9.1 3500 System Overview
The 3500 system provides continuous, online protection for critical
and highly-critical machinery applications. This system complies
fully with API 670 and provides our best technology, developed over
50 years of experience, for protection of your most critical assets.
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application guide
In addition to the solid foundation, many options exist to further
increase fault tolerance such as SIL-rated modules and redundant
power and signal pathways. The 3500 system also serves to capture
all information for online condition monitoring and feeds directly
to System 1 software for diagnostics and monitoring via separate
digital pathways.
The system’s highly modular design consists of:
• 3500/05 instrument rack (required)
• One or two 3500/15 power supplies (required)
• 3500/22M transient data interface (required)
• 3500 rack configuration software (required)
•One or more 3500/XX monitor modules (required) (The
available 3500/XX are discussed below)
Rack Mount – This rack format mounts the 3500 rack on 19-inch
EIA rails. Wiring connections and I/O modules are accessible from
the rear of the rack.
Bulkhead Mount – This rack format mounts the rack against a
wall or panel when it is not possible to access the rear of the rack.
Wiring connections and I/O modules are accessible from the front
of the rack. The 3500/05 Mini-Rack is not available in this format.
Note: Please see the latest 3500/05 Instrument Rack data sheet for
more information (www.ge-mcs.com).
The power supplies and TDI module must occupy the far left rack
positions. The remaining 14 rack positions (7 rack positions for the
mini-rack) are available for any combination of modules.
Best Practice Recommendation
•One or more 3500/92 communication gateway modules
(optional)
For highly critical and critical machinery, each 3500 monitoring and
protection rack should contain modules for only a single machine.
This allows dedicated monitoring and protection functions for an
individual machine and provides the following benefits:
•Internal or external intrinsic safety barriers, or galvanic
isolators for hazardous area installations (where required)
•Service carried out on the 3500 rack will not affect other
machines
9.2 System Component Selections
•Failure of any component of the 3500 will not affect other
machines
The 3500 Series monitoring and protection system has several
required components to create a functioning system.
•Configuration changes can be carried out without affecting
other machines
• One or more 3500/32 or/33 relay modules (recommended)
• Required for various functional safety certified configurations
9.2.2 Power Supplies
9.2.1 Instrument Rack
The 3500/05 system rack design holds all 3500 monitor modules
and rack power supplies. It allows the various 3500 modules
to communicate with one another and the power supplies to
distribute power to each module as required.
3500 racks are available in two sizes:
Full-size Rack – 19-inch EIA rack with 14 available module slots
Mini-Rack – 12-inch rack with 7 available module slots
3500 racks are available in three formats:
Panel Mount – This rack format mounts to rectangular cut-outs
in panels, and secures to the panel using clamps supplied with the
rack. Wiring connections and I/O modules are accessible from the
rear of the rack.
The 3500/15 power supplies are half-height
modules and must be installed in the specially
designed slots on the left side of the rack.
The 3500 rack can contain one or two power
supplies (any combination of AC and/or DC)
and either supply can power a full rack. The
second supply is highly recommended and
acts as a backup for the primary supply. When
two power supplies are installed in a rack, the
supply in the lower slot acts as the primary
supply and the supply in the upper slot acts as
the backup supply. Removing or inserting either
power supply module will not disrupt operation
of the rack as long as a second power supply is
installed.
The 3500 power supplies accept a wide range of input voltages
and convert them to voltages acceptable for use by other 3500
modules. Three power supply versions are available with the 3500
Series machinery protection system as follows:
• AC power
• High voltage DC power supply
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application guide
• Low voltage DC power supply
Note: Please see the latest 3500/15 Power Supply data sheet for
more information (www.ge-mcs.com).
Best practice recommendations
•Use two power supply modules with separate power feeds for
highest failure tolerance. In this scheme, the rack will continue
monitoring in the event of loss of a single power feed, or loss of
a single power supply module due to failure or removal of the
module.
•Use of two power supply modules with a single power feed
coupled to both inputs is also possible, and is a suitable
solution when the single power feed is from an uninterruptable
power supply (UPS). In this case, the benefit of having two
power supply modules is for continued operation if a single
module fails or is removed from service.
9.2.3 Transient Data Interface Module
The 3500/22M transient data interface (TDI) is the interface
between the 3500 monitoring system and GE’s System 1
machinery management software.
The TDI operates in the RIM slot of a 3500 rack in
conjunction with the M series monitors (3500/40M,
3500/42M, and so on) to continuously collect steady-state
and transient waveform data and pass this data through
an Ethernet link to the host software. Static data capture
is standard with the TDI, however using an optional
channel enabling disk allows the TDI to capture dynamic
or transient data as well. The TDI features improvements
in several areas over previous communication processors
and incorporates the communication processor function
within the 3500 rack.
Although the TDI provides certain functions common to
the entire rack, it is not part of the critical monitoring path
and has no effect on the proper, normal operation of the
protection function of the monitoring system. Every 3500
rack requires one TDI, which always occupies Slot 1 (next
to the power supplies).
check this is by using System 1 software to monitor startup
plots (bode plot and direct/1X trends).
•TM should also be enabled for shutdown to prevent unwanted
alarms.
•Rack reset input contacts should be connected to the
control system to allow remote reset of rack alarms after
acknowledgement from the operator/engineer.
•Rack OK contacts should be connected to the control system
to alert the operator when a rack fault exists or certain other
events warrant operator attention.
9.3 Monitor Module Selection
9.3.1 Vibration Monitors
As a key indicator of compressor condition, vibration is
critical to understand how the compressor is running and
whether or not it is running safely. The 3500 Series has two
choices for vibration monitors.
3500/40M Proximitor Monitor – The 3500/40M
Proximitor Monitor is a 4-channel monitor that accepts
input from Bently Nevada proximity transducers, conditions
the signal to provide various vibration and position
measurements, and compares the conditioned signals with
user-programmable alarms. The user can program each
channel of the 3500/40M with the 3500 rack configuration
software to perform any of the following functions:
• Radial vibration
• Axial (thrust) position
• Differential expansion
•Eccentricity
Note: The monitor channels are programmed in pairs and can
perform up to two of these functions at a time. Channels 1 and 2 can
perform one function, while channels 3 and 4 perform another (or the
same) function.
The primary purpose of the 3500/40M monitor is to provide:
Note: Please see the latest 3500/22M TDI data sheet for
more information (www.ge-mcs.com).
•Machinery protection by continuously comparing monitored
parameters against configured alarm setpoints to drive alarms.
Best practice recommendations
•Essential machine information for both operations and
maintenance personnel.
•Security of the TDI module should be configured to comply
with local site regulations and best practices.
•Trip multiply (TM) input contacts should be connected to
the control system to inform the 3500 system of a startup
condition so that normal channel alarms can be given
“headroom” during startup. This prevents trips during transient
events such as passing through first and second critical (where
applicable). The TM factor should be set to bring alarm levels
above normal transient vibration peak levels. The best way to
Each channel, depending on configuration, typically conditions its
input signal into various parameters called “static values.” The user
can configure alert setpoints for each active static value and danger
setpoints for any two of the active static values.
Note: The 3500/40M has no 4/20 mA recorder outputs.
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application guide
3500/42M Proximitor Monitor – The 3500/42M
Proximitor/seismic monitor is a 4-channel monitor that
accepts input from proximity and seismic transducers,
conditions the signal to provide various vibration and
position measurements, and compares the conditioned
signals with user-programmable alarms.
The 3500/42M contains the functions of the 3500/40M with
some additional features, including support for seismic
transducers and configurable 4-20mA recorder outputs.
Note: Refer to the latest 3500/40M and 3500/42M data
sheet for more information (www.ge-mcs.com).
The user can program each channel of the 3500/42M using
the 3500 rack configuration software to perform any of the
following functions:
• Radial vibration
• Thrust position
• Differential expansion
•Eccentricity
•Acceleration
•Velocity
• Shaft absolute
• Circular Acceptance Region
•Smax is available if requested by the end user (usually
dependent on regional geographical preference)
Note: The monitor channels are programmed in pairs and can
perform up to two of these functions at a time. Channels 1 and 2 can
perform one function, while channels 3 and 4 perform another (or the
same) function.
The primary purpose of the 3500/42M monitor is to provide:
•Machinery protection by continuously comparing monitored
parameters against configured alarm setpoints to drive alarms.
•Essential machine information for both operations and
maintenance personnel.
Each channel, depending on configuration, typically conditions its
input signal to generate various parameters called “static values.”
The user can configure alert setpoints for each active static value
and danger setpoints for any two of the active static values.
Best practice recommendations
Either the 3500/40M or 3500/42M should be used for protection
and monitoring on compressors covered in this document. The
3500 rack will need to contain enough modules to cover the number
of installed radial vibration and axial (thrust) position probes.
Although the 3500/42M card has 4-20mA recorder outputs, it is
always recommended that relay outputs are used for alarming/
protection services. Refer to the relay card information section
below for further information.
WARNING: Barriers/Isolators in Hazardous Areas
Double check whether transducers are installed within
hazardous areas. If so, the transducers should be certified
for the required zone/division, and barriers or isolators will
be required to isolate the transducers (hazardous area)
from the monitoring system (safe area). If unsure about the
requirements, contact GE’s Bently Nevada Technical Support
([email protected]) and specify the instruments used
(such as probes and monitors), the site hazardous rating, and
any other information requested by Tech Support.
9.3.2 Keyphasor/Speed/Overspeed
Monitors
The 3500 Series has two choices for Keyphasor measurement and
two choices for speed measurements. The 3500/53 is an overspeed
detection system (ODS). An alternative to the 3500/53 ODS is
the 3701/55 emergency shutdown device (ESD) that also provides
overspeed detection. A general overview describing the
capabilities of the two choices follows.
3500/25 Keyphasor Module – The 3500/25 enhanced
Keyphasor module is a half-height, 2-channel module used
to provide Keyphasor signals to the monitor modules in a
3500 rack. The module receives input signals from proximity
probes or magnetic pickups and converts the signals to
digital Keyphasor signals that indicate when the Keyphasor
mark on the shaft coincides with the Keyphasor transducer.
The 3500 machinery protection system can accept up to
four Keyphasor signals for normal configuration and up to
eight Keyphasor signals in a paired configuration.
Note: A Keyphasor signal is a once-per-turn pulse from a rotating
shaft or gear used to provide a precise timing measurement. This
allows 3500 monitor modules and external diagnostic equipment
to measure shaft rotative speed and vector parameters such as 1X
vibration amplitude and phase. The installation of a spare Keyphasor
sensor is highly recommended because the Keyphasor is a vital
element in performing machine management and diagnostics.
Note: Refer to the latest 3500/25 Keyphasor module data sheet for
more information (www. ge-mcs.com).
3500/50M Tachometer Module – The 3500/50M tachometer
module is a 2-channel module that accepts input from proximity
probes or magnetic pickups (except as noted) to determine shaft
rotative speed, rotor acceleration, or rotor direction. It compares
these measurements against user-programmable alarm setpoints
and generates alarms when these setpoints are violated. The
3500/50M tachometer module is programmed using the 3500 rack
18
application guide
configuration software and can be configured with four different
options:
•Speed monitoring, setpoint alarming, and speed band alarming
•Speed monitoring, setpoint alarming, and zero speed
notification
•Speed monitoring, setpoint alarming, and rotor acceleration
alarming
•Speed monitoring, setpoint alarming, and reverse rotation
notification
Note: Refer to the latest 3500/50M Tachometer module
data sheet for more information (www.ge-mcs.com).
The 3500/50M can be configured to supply conditioned
Keyphasor signals to the backplane of the 3500 rack for
use by other monitors, thus eliminating the need for a
separate Keyphasor module in the rack. The 3500/50M
also has a peak hold feature that stores the highest speed,
highest reverse speed, or number of reverse rotations
(depending on channel type selected) that the machine has
reached. These peak values can be reset by the user.
Best practice recommendation
For highly critical and critical compressors, Keyphasors
must be installed following transducer recommendations.
It is recommended that the monitoring system should use
the 3500/50 tachometer module to bring in Keyphasor and
high resolution speed (where available).
3500/53 Overspeed Detection Module – GE’s Bently
Nevada electronic overspeed detection system for the
3500 Series machinery detection system provides a highly reliable,
fast response, redundant tachometer system intended specifically
for use as part of an overspeed protection system. It is designed to
meet the requirements of API 670 and 612 standards pertaining to
overspeed protection.
3500/53 modules can be combined to form a 2-out-of-2 or
a 2-out-of-3 (recommended) voting system. The overspeed
detection system requires the use of a 3500 rack with
redundant power supplies. ODS is only applicable to the
driver, not the driven machine.
Note: The 3500/53 product has been included in this
application guide to support our existing installed base
of these units. The 3500/53 is no longer available for new
installations and 3701/55 ADAPT* ESD should be considered
for all future Bently Nevada overspeed detection and
emergency shutdown applications.
3701/55 Emergency Shutdown Device – The two types of
modules in a 3701/55 ADAPT ESD are processor modules and
relay modules. Three of each type of module are inserted into
the terminal base. Processor modules fit into the slots on the left
side of the terminal base and perform system wide supervisory
functions, including maintaining an event and alarm list. Relay
modules fit into slots on the right side of the terminal base. The
3701/55 ADAPT overspeed and emergency shutdown device is
certified for use as a microprocessor-based logic solver in a SIL 3
certified safety system.
The 3701/55 operates by receiving input signals (speed pulses) from
field sensors, applying pre-programmed logic to these inputs, and
then outputting the results of this logic to relays. The relays, in turn,
operate final control elements such as an actuator shutdown valve
and other emergency shutdown devices. Each processor module
controls relay channels on one of the relay modules. Each processor
module/relay module pair operates independently and separately.
This redundancy increases the availability of the 3701/55. The three
processor/relay module sets can be configured to operate as a 2
out of 3 (2oo3) triple module redundant device. Each of the three
relay modules in a 3701/55 contain five relays – one protection fault
relay (OK relay) and four programmable relays. The logic that drives
these programmable relays is identical for each module and is
programmed using the ADAPT ESD monitor configuration software.
The contacts for all five relays are on the side of the relay module.
All relays are single pole/double throw (SPDT) relays and the
connectors use standard labels (NO, ARM, and NC). Normally open
(NO) and normally closed (NC) refer to the contact condition when
the relay is not energized.
The protection fault relay indicates the status of the processor/
relay pair. This relay is normally energized. An asserted protection
fault relay indicates that the protection function for the channel
(transducer input, monitor and relay) has been compromised.
The protection fault relay indicates the operating status of the
processor /relay pair and is not programmable.
Note: The output of the protection fault relay should always be
connected into an operator warning system so that any fault can be
immediately addressed and repaired by the end user.
Caution: Due to the extremely open and unrestricted
configurability of the 3701/55 ESD overspeed detection
system, it is imperative that the specific logic configuration of
the trip function be completely understood, documented, and
tested. Thorough validation is necessary to be certain that
the system responds as desired to all possible input scenarios
under all machinery operational conditions.
Refer to the separate Overspeed Detection System Application
Guide for more details on ODS.
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application guide
9.3.3 Temperature Monitors
As a key indicator of compressor condition, temperature is
important to understand how the compressor is running and
whether or not it is running safely. The 3500 Series offers
the following choices for temperature monitors.
3500/60 and /61 Temperature Monitors – The 3500/60
and 3500/61 modules provide six channels of temperature
monitoring and accept both resistance temperature
detector (RTD) and thermocouple (TC) temperature inputs.
The modules condition these inputs and compare them
against user-programmable alarm setpoints. The 3500/60
and 3500/61 provide identical functionality, except that
the 3500/61 provides recorder outputs for each of its six
channels, while the 3500/60 does not.
3500/65 Temperature Monitor – The 3500/65 monitor
provides 16 channels of temperature monitoring and
accepts both resistance temperature detector (RTD) and
isolated tip thermocouple (TC) temperature inputs. The
monitor conditions these inputs and compares them against
user-programmable alarm setpoints.
Note: Refer to the latest 3500/60, 3500/61 and 3500/65
Temperature Monitor data sheet for more information (www.
gemcs.com).
The monitor is programmed using the 3500 rack
configuration software. The 16-channel temperature
monitor can be configured to accept isolated tip
thermocouples, 3-wire RTD, 4-wire RTD, or a combination of
TC and RTD inputs.
Best practice recommendation
Temperature sensors should be connected directly to the
3500 rack if possible. If not possible, information from the
DCS can be provided digitally to System 1 software, or via
analog output cards into the 3500 rack inputs.
9.3.4 Relay Modules
The 3500 Series has three choices for relay modules to serve
different annunciation requirements. A general overview
describing the capabilities of the primary two modules (the
third is a TMR module and not listed here) follows.
3500/32 Relay Module – The 4-channel relay module
is a full-height module that provides four relay outputs.
Any number of 4-channel relay modules can be placed in
any of the slots to the right of the transient data interface
module. Each output of the 4-channel relay module can be
independently programmed to perform needed voting logic.
Each relay utilized on the 4-channel relay module includes
"alarm drive logic." Programming for the alarm drive logic
uses AND/OR logic, and can use alarming inputs (alert
and danger statuses), Not-OK, or individual PPLs from
any monitor channel or any combination of monitor channels
in the rack. Users program this alarm drive using the 3500
rack configuration software to meet the specific needs of the
application.
3500/33 Relay Module – The 16-channel relay module is a
full-height module that provides 16 relay outputs. Any number
of 16-channel relay modules can be placed in any of the slots
to the right of the rack interface module. Each output
of the 16-channel relay module can be independently
programmed to perform needed voting logic.
Each relay used on the 16-channel relay module includes
"alarm drive logic." Programming for the alarm drive logic
uses AND/OR logic, and can use alarming inputs (alert
and danger statuses), Not-OK, or individual PPLs from any
monitor channel or any combination of monitor channels
in the rack. Users program this alarm drive using the 3500
rack configuration software to meet the specific needs of
the application.
Note: Refer to the latest 3500/32 and 3500/33 Relay Module
data sheet for more information (www.ge-mcs.com).
Best practice recommendations
(for relay annunciation or trip)
Radial Vibration - Radial shaft vibration is monitored with
orthogonal X/Y paired proximity sensors. The vibration shutdown
system is field configurable to shut down when either a single
sensor exceeds the danger alarm setpoint (one-out-of-one logic
(1oo1)) or when both sensors are exceeding their danger alarm
setpoints (two-out-of-two logic (2oo2) or dual voting logic). The end
user must make an informed decision to use single logic or dual
voting logic based on a risk analysis and the economic impact of
a missed shutdown compared to a false shutdown. An excellent
discussion of this trade-off consideration is presented Section 7.4.1
of API 670.
Note 1: Voting a radial vibration X/Y pair increases the risk
of failing to shutdown on high vibration if the machine is
experiencing a severely elliptical orbit which can occur due to a
heavy preload condition.
Note 2: When 2oo2 dual voting is applied, if one channel
shows an alarm and the other does not, the end user should
immediately determine the root cause of the alarm and take
appropriate corrective action.
Note 3: When 2oo2 dual voting is selected, a channel Not-OK
with one of the vibration signals demands immediate action
from the end user to rectify the cause of the Not-OK condition.
Failure to rectify this condition may have the consequence of
either having unprotected operation or reverting to a single
logic protection (1oo1) based on the remaining OK channel. Field
changeable options allow the end user to establish the correct
response based on their operational needs.
Note 4: End users need to be aware that logically OR-ing the
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application guide
channel Not-OK with the channel alarm in relay logic could
lead to false shutdown if an event causes a momentary Not-OK
condition on one channel (if 1oo1 voting is applied) or both
channels (if 2oo2 voting is applied). A nearby lighting strike or
other fast electrical disturbance could cause this condition. The
input spike event is capable of exceeding the channel OK limits
nearly instantly, while that same channel’s alarms may not be
driven due to the momentary nature of the disruption combined
with the inherent measurement delay, and the configured alarm
time delay. The Not-OK response of the channel has no delay.
(See Appendix 6 for further discussion on voting.)
Timed OK Channel Defeat – This feature defeats the channels
alarm capability when the transducer is in a Not-OK state. When
the transducer returns to an OK state, a 30 second delay occurs
before the channel alarm capability becomes active. The OK
channel defeat provides additional immunity to false alarms or
trips due to a detectable fault that may occur in the sensor and
monitor path such as intermittent field wiring. This option is
available only if the OK mode is set to non-latching. The OK LED on
the front of the monitor will flash at 2 Hz (two times per second) to
indicate that the monitor has been in a Not-OK state. The end user
should immediately investigate this to determine the cause of the
temporary Not-OK state to avoid the initiation of a false trip. The
end users’ operating practices will best dictate when this option is
selected.
Note: This feature is not available for axial thrust monitoring.
Axial (thrust) Position – Many years of field experience have
shown that the best practice is dual voting thrust (2oo2) for
shutdown. This voting requires both sensors to exceed their danger
set-point to initiate a shutdown. API 670 Section 7.4.2 covers this
consideration in detail. API 670 makes an allowance for end users
to choose single logic (one-out-of-two or 1oo2) for axial position
shutdown based on needs and preferences.
Note 1: When dual voting is applied, if the two channels
show a different reading, immediate action should be taken
to determine the root cause driving the difference and then
corrective action should be taken.
Note 2: When dual voting thrust is applied, a channel Not-OK
caused by a transducer fault will drive that channel’s alarms,
resulting in a vote for shutdown. A second vote from the
remaining channel will activate the shutdown relay. (Refer to API
670 7.4.2.5 b).
Note 3: The end user is encouraged to thoroughly understand
and verify voting logic at the time of commissioning and after
any change in configuration.
(See Appendix 6 for more information about voting.)
Temperature – Temperature alarms should be annunciated via
relay contacts to the control system for operator intervention.
Note: All alarms should be set to latching mode. In this mode,
when an alarm is triggered, it will remain in this state until it is
reset by the operator/engineer. If latching is not enabled, alarms
may disappear and the operator may miss the annunciation.
9.3.5 Alarm Setpoints
This section provides general guidance on the processes that
service engineers can use to obtain alarm set-point levels in the
absence of any other procdures. This information is not intended to
define alarm levels or recommend any machine limits.
Alarm setpoints are generally obtained by:
•OEM limits established in machine datasheets or OEM direct
recommendations
• Site-specific monitoring philosophy and experience
•Relevant ISO/API standards or standards applicable to the
jurisdiction
In the absence of the above sources of information, and as a good
starting point to determine approximate alarm levels, API 617:
Axial and Centrifugal Compressors and Expander-Compressors for
Petroleum, Chemical and Gas Industry Services provides reference
calculations to determine the acceptable vibration limits for OEM
testing. These calculations can be used as a guideline when no
other information is available. In any case, alarm set-points and
relay logic configurations should be checked and signed off by site
management.
Radial Vibration Alarms
When normal operating levels and limits have been defined – alert
(H) and danger (HH) levels – the radial vibration channels should
be set to alarm based on these levels. End users may elect to use
either single logic or dual voting logic to initiate radial vibration
alarms. The same considerations concerning alarm voting that
were presented above, when discussing shutdown voting, apply to
vibration alarms indication (see Notes above).
Note: When dual voting is applied, if one channel shows an alarm
and the other does not, immediate action should be taken to
determine the root cause driving the alarm.
Radial Position (Gap) Alarms
When normal operating levels and limits of gap voltage have been
defined – gap high alert (H) and gap high danger (HH) set-points,
and gap low alert (L) and low danger (LL) setpoints – the radial gap
channels should be set to alarm based on these levels. End users
may elect to use either single logic or dual voting logic to initiate
radial gap alarms. The end user must make informed decisions
concerning voting as explained in the Notes above.
Axial (Thrust) Position Alarms
When normal operating levels and maximum bearing clearances
have been defined – alert (H) and danger (HH) levels, and alert (L)
and danger (LL) levels – the axial position channels should be set to
alarm based on these levels. Because of the rapid nature of many
thrust failures, alarming only on thrust position is rarely used. Many
years of field experience has shown that the best practice is dual
voting thrust (2oo2) for shutdown. This voting requires both sensors
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application guide
to exceed their danger set-point to initiate a shutdown. API STD 670
Section 7 also covers this consideration in detail.
Additional monitors can be chosen based on required measurement
capabilities. The following list of available monitors covers needed
functions for centrifugal and axial flow compressors.
3500/25
3500/40M
3500/42M
3500/45
3500/50
3500/53
3500/60/61/65
3500/62
Monitor Modules
Phase reference





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

Radial vibration (proximity probes)








Radial position (proximity probes)








Axial position (proximity probes)








Eccentricity (proximity probes)








Seismic vibration (velocity/
accelerometers)








Shaft absolute (proximity and seismic)








Differential expansion








Ramp differential expansion








Complementary differential expansion








Valve position








Rotor speed








Rotor speed rate-of-change (acceleration)








Rotor zero speed (turning gear
engagement)








Overspeed








Temperature (direct/average/differential)








Process variable signals
(4–20 mA, 1–5 vdc, etc.)








Measurements
3500 Series
Measurement Capabilities
22
application guide
9.3.6 Vibration Instrumentation Diagram for Dual Flow Centrifugal Compressor
KP
TM
X/Y
Thr
TM
TMX/Y
Key
KP
KeyPhasor – Redundant
X/Y
Radiat Proximity Probes – Dual
TM
Temperature Probes
Thr
Axial (Thrust) Position
AC
Accelerometers – Single
23
application guide
9.3.7 Vibration Instrumentation Diagram for Axial Flow Compressor
TM
KP
X/Y
Thr
TM
X/Y
TM
Key
KP
KeyPhasor – Redundant
X/Y
Radiat Proximity Probes – Dual
TM
Temperature Probes
Thr
Axial (Thrust) Position
AC
Accelerometers – Single
The following is the recommended rack layout for centrifugal and axial flow compressors:
Note: For details about the configuration of the various modules and settings, please refer to the 3500
Installation and Setup manual.
24
application guide
Slot No.
SLOT 2
SLOT 3
SLOT 4
SLOT 5
SLOT 6
Transducer Location
Transducer Type
Compressor Inboard Radial Y
3300 XL Proximity Probe
Compressor Inboard Radial X
3300 XL Proximity Probe
Compressor Outboard Radial Y
3300 XL Proximity Probe
Compressor Outboard Radial X
3300 XL Proximity Probe
Compressor Thrust A
3300 XL Proximity Probe
Compressor Thrust B
3300 XL Proximity Probe
(Empty Channel)
N/A
(Empty Channel)
N/A
Compressor Keyphasor A
3300 XL Proximity Probe
Compressor Keyphasor B
3300 XL Proximity Probe
(Empty Channel)
N/A
(Empty Channel)
N/A
Compressor Inboard Radial Temperature A
RTD Sensor (or T/C)
Compressor Inboard Radial Temperature B
RTD Sensor (or T/C)
Compressor Outboard Radial Temperature A
RTD Sensor (or T/C)
Compressor Outboard Radial Temperature B
RTD Sensor (or T/C)
Compressor Active Thrust Temperature A
RTD Sensor (or T/C)
Compressor Active Thrust Temperature B
RTD Sensor (or T/C)
Compressor Inactive Thrust Temperature A
RTD Sensor (or T/C)
Compressor Inactive Thrust Temperature B
RTD Sensor (or T/C)
(Empty Channel)
N/A
(Empty Channel)
N/A
(Empty Channel)
N/A
(Empty Channel)
N/A
(Empty Channel)
N/A
(Empty Channel)
N/A
Monitor Type
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/50M Tachometer Module
or 3500/25M Keyphasor Module
3500/60 or 3500/61
Temperature Monitor
3500/60 or 3500/61
Temperature Monitor
Table 1. Axial flow and centrifugal compressors
Note: All possible transducers are shown in table above, but not all transducers may be installed in any given installation.
25
application guide
9.3.8 V
ibration Instrumentation Diagram for Integrally Geared Compressor
(3 or 4 stage)
KP
KP
TM
X/Y
TM
X/Y
AC
KP
TM
X/Y
TM
X/Y
Thr
TM
TM
X/Y
AC
Thr
TM
TM
X/Y
Thr
TM
Key
KP
KeyPhasor – Redundant
X/Y
Radiat Proximity Probes – Dual
TM
Temperature Probes
Thr
Axial (Thrust) Position
AC
Accelerometers – Single
Recommended rack layout for integrally-geared compressors
Note: For details about the configuration of the various modules and settings, please refer to the 3500
Installation and Setup manual.
26
application guide
Slot No.
SLOT 2
SLOT 3
SLOT 4
SLOT 5
SLOT 6
SLOT 7
Transducer Location
Transducer Type
Compressor Bull Gear Inboard Radial Y
3300 XL Proximity Probe
Compressor Bull Gear Inboard Radial X
3300 XL Proximity Probe
Compressor Bull Gear Outboard Radial Y
3300 XL Proximity Probe
Compressor Bull Gear Outboard Radial X
3300 XL Proximity Probe
First Stage Compressor Bearing Radial Y
3300 XL Proximity Probe
First Stage Compressor Bearing Radial X
3300 XL Proximity Probe
Second Stage Compressor Bearing Radial Y
3300 XL Proximity Probe
Second Stage Compressor Bearing Radial X
3300 XL Proximity Probe
Third Stage Compressor Bearing Radial Y
3300 XL Proximity Probe
Third Stage Compressor Bearing Radial X
3300 XL Proximity Probe
Fourth Stage Compressor Bearing Radial Y
3300 XL Proximity Probe
Fourth Stage Compressor Bearing Radial X
3300 XL Proximity Probe
First/Second Stage Compressor Pinion Thrust A
3300 XL Proximity Probe
First/Second Stage Compressor Pinion Thrust B
3300 XL Proximity Probe
Third/Fourth Stage Compressor Pinion Thrust A
3300 XL Proximity Probe
Third/Fourth Stage Compressor Pinion Thrust B
3300 XL Proximity Probe
Compressor Bull Gear Thrust A
3300 XL Proximity Probe
Compressor Bull Gear Thrust B
3300 XL Proximity Probe
(Empty Channel)
N/A
(Empty Channel)
N/A
Compressor Bull Gear Accelerometer A
330400 Accelerometer
Compressor Bull Gear Accelerometer B
330400 Accelerometer
Compressor Bull Gear Accelerometer A (Integrated) 330400 Accelerometer
Monitor Type
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/40M Proximitor Monitor
or 3500/42M Proximitor/Seismic
Monitor
3500/42M Proximitor/Seismic
Monitor
Compressor Bull Gear Accelerometer B (Integrated) 330400 Accelerometer
SLOT 8
(Upper)
Compressor Bull Gear Keyphasor
3300 XL Proximity Probe
First/Second Stage Compressor Pinion Keyphasor
3300 XL Proximity Probe
SLOT 8
(Lower)
Third/Fourth Stage Compressor Pinion Keyphasor
3300 XL Proximity Probe
(Empty Channel)
N/A
Compressor Bull Gear Inboard Radial Bearing
Temperature
RTD Sensor (or T/C)
Compressor Bull Gear Outboard Radial Bearing
Temperature
RTD Sensor (or T/C)
Compressor First Stage Radial Bearing
Temperature
RTD Sensor (or T/C)
Compressor Second Stage Radial Bearing
Temperature
RTD Sensor (or T/C)
Compressor Third Stage Radial Bearing
Temperature
RTD Sensor (or T/C)
Compressor Fourth Stage Radial Bearing
Temperature
RTD Sensor (or T/C)
SLOT 9
3500/50M 3500/25M Keyphasor
Module (Upper)
3500/25M Keyphasor Module
(Lower)
3500/60 or 3500/61
Temperature
Table 2. Integral Gear Compressors
Notes:
•All possible transducers are shown in the table above, but not all transducers may be installed in any given installation (thrust
measurements are shown on the two pinion gears, but are not configured in the table above.)
•When only one or two Keyphasor transducers are installed per rack, the 3500/50M tachometer module could be used.
27
application guide
Best practice recommendations (cabinets)
11 Management with System 1 Software
Best practice for the installation of 3500 racks is placement in
a standard industrial Rittal TS-8 series cabinet (800w x 800d x
2200h). The cabinet should be located inside a clean, climatecontrolled room. Refer to document GEA-17562 for further
information on 3500 installation, cabinets and integration.
11.1 Overview of System1 Condition
Monitoring and Diagnostics Platform
10 The Industrial Internet
Widely used across many industries, System 1 condition monitoring
software enables plant personnel to quickly identify important
events, evaluate the situation, and respond. These abilities lead to
increased equipment availability, enhanced reliability, and reduced
maintenance costs.
System 1 is GE’s patented condition monitoring software platform
for real-time optimization of equipment and selected processes,
condition monitoring, and event diagnostics. Similar in concept to a
process control system that allows users to understand, diagnose,
and control their process conditions in real time, the System 1
platform provides this capability for the assets that drive your
process.
GE’s new focus is about the convergence of the global industrial
system with the power of advanced computing, analytics, lowcost sensing and new levels of connectivity permitted by the
Internet. It's about how the deeper meshing of the digital world
with the world of machines holds the potential to bring about
profound transformation to global industry, and in turn to many
aspects of daily life, including the way many of us do our jobs. It’s
fundamentally about data – Big Data – and how it transforms and
even revitalizes the dirty work of manufacturing, transportation,
and energy production.
Following is typical layout showing how System 1 software interrelates with other devices in a plant environment network.
Section 7 of this document references typical machinery
malfunctions associated with compressors, including System 1
software plots that are used to identify the various malfunctions.
Refer to Appendix 1 for further information regarding System 1
software and network connectivity .
For additional technical details regarding System 1 software, please
consult the Installation Quick Start Guide (Part Number 181136,
Rev. J (03/12)).
28
application guide
11.2 Thermodynamic Performance
Early phase degradation of critical process compressors is
determined by thermodynamic machine performance. GE’s
Bently PERFORMANCE* SE* software extends System 1 software
system functionality by providing online, real-time continuous
calculation of machinery performance parameters. A graphical user
interface displays performance cures and calculated performance
parameters. Thermodynamic performance monitoring helps:
• Improve overall production capability
• Control costs through optimized maintenance activities
• Improve diagnostics and decision making
• Automate data analysis and advisories
• Provide fast and easy combustion problem diagnostics
Bently PERFORMANCE SE software integrates with System 1
software to display information about the condition of machines in
combined mechanical and thermodynamic data presentations.
11.3 Automated Machinery Diagnostic
Functionality
Pre-configured diagnostic RulePaks automate the compressor
failure mode and anomaly detection process within the machinery
management system. A RulePak is a set of extraction, calculation,
and diagnostic rules that work together to analyze static and
dynamic data in real time. This real-time analysis provides
continuous asset health feedback to the user.
Designed specifically to work with System 1 software, the RulePaks
present System 1 supplied mission critical data in an actionable
format. Conceptually, a RulePak can be thought of as a black box,
with inputs coming in on one side and diagnostic results coming
out the other. When an event occurs, these diagnostic results can
trigger notifications to machine operators that indicate how severe
the issue is, and provide suggested actions to mitigate the issue.
The Compressor Performance Module is available in versions
suitable for single and multi-stage centrifugal compressors, axial
compressors, and blowers. Gas calculations are performed using
industry accepted computational methods with real gas equations
of state for single gases and complex gas mixtures. Compressors
with side load and side stream flows can be accommodated with
section performance calculations as required. Design performance
data is used to create a database from which expected
performance is calculated and compared with actual performance.
Available compressor performance indicators are isentropic and
polytropic head, discharge pressure, and pressure ratio for variable
speed and inlet volume flow. Isentropic and polytropic efficiency
and gas (internal) power are also calculated for current operating
conditions and compared to expected values.
29
application guide
11.4 Centrifugal Compressor RulePak
11.5 Axial Flow Compressor RulePak
The centrifugal compressor advanced RulePak contains algorithms
that help diagnose the following machine malfunctions:
The axial compressor advanced RulePak contains algorithms that
diagnose the following machine malfunctions:
Anomaly
Description
Anomaly
Description
Compressor Surge
The compressor is operating at flow
rates significantly below the design flow
rate, causing vibration and possible flow
reversals
Compressor Surge
The compressor is operating at flow
rates significantly below the design flow
rate, causing vibration and possible flow
reversals
Compressor Near
Surge
The compressor is operating near surge
limits, based on pressure ratios and
flow
Compressor Near
Surge
The compressor is operating near surge
limits, based on pressure ratios and
flow
Compressor Stall
The compressor is operating at flow
rates significantly below the design flow
rate
Compressor Stall
The compressor is operating at flow
rates significantly below design flow
rate
Whirl
Fluid induced instability is causing
lateral rotor vibrations
Whirl
Fluid induced instability is causing
lateral rotor vibrations
Whip
Severe fluid induced instability is
causing lateral rotor vibrations at one or
more resonances
Whip
Severe fluid induced instability is
causing lateral rotor vibrations at one or
more resonances
General Radial
Preload
A unidirectional, steady-state force on a
rotor is causing rotor operation at high
eccentricity within the seal or bearing
clearance boundaries
General Radial
Preload
A unidirectional, steady-state force on a
rotor is causing rotor operation at high
eccentricity within the seal or bearing
clearance boundaries
1X Runout
The slow roll vector magnitude exceeds
the recommended level, indicating a
non-concentric rotor surface at the
plane of measurement
1X Runout
Slow roll vector magnitude exceeds the
recommended level, indicating a nonconcentric rotor surface at the plane of
measurement
Sub-synchronous
Rub
Rotor contact with a stationary part
excites sub-synchronous radial
vibration characteristics
Sub-synchronous
Rub
Rotor contact with a stationary
part excites sub-synchronous radial
vibration characteristics
Super-synchronous
Rub
Rotor contact with a stationary part
excites super-synchronous radial
vibration characteristics
Super-synchronous
Rub
Rotor contact with a stationary part
excites super-synchronous radial
vibration characteristics
Synchronous Rub
Thermal rotor bow is induced by
rotor-to-stator rub (Newkirk effect) or
differential viscous shearing within the
bearing (Morton effect)
Synchronous Rub
Thermal rotor bow is induced by
rotor-to-stator rub (Newkirk effect) or
differential viscous shearing within the
bearing (Morton effect)
Loose Rotating Part
Changes in the synchronous behavior
of the rotor due to rotating elements
coming loose
Example: Shrink fit elements losing the
frictional force required to keep them
locked onto the shaft
Loose Rotating Part
Changes in the synchronous behavior
of the rotor due to rotating elements
coming loose
Example: Shrink fit elements losing the
frictional force required to keep them
locked onto the shaft
Synchronous Rub or
Loose Rotating Part
Non-specific determination of either a
synchronous rub or a loose part
Synchronous Rub or
Loose Rotating Part
Non-specific determination of either a
synchronous rub or a loose part
High Synchronous
Vibration
Excessive vibration at running speed
High Synchronous
Vibration
Excessive vibration at running speed
Misalignment
Misaligned rotors between coupled
machines
Misalignment
Misaligned rotors between coupled
machines
Rotor Bow
Bent rotor shaft
Rotor Bow
Bent rotor shaft
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application guide
11.6 Integral Gear Compressor RulePak
The integral gear compressor (IGC) RulePak contains algorithms that diagnose the following machine malfunctions:
Anomaly
Description
Compressor Surge
The compressor is operating at flow rates significantly below the design flow rate, causing vibration and
possible flow reversals
Compressor Near
Surge
The compressor is operating near surge limits, based on pressure ratios and flow
Compressor Stall
The compressor is operating at flow rates significantly below the design flow rate.
Gear Mesh
High vibration occurs at the frequency of the gear tooth mesh
Whirl
Fluid induced instability is causing lateral rotor vibrations
Whip
Severe fluid induced instability is causing lateral rotor vibrations at one or more resonances
General Radial Preload
A unidirectional, steady-state force on a rotor is causing rotor operation at high eccentricity within the seal or
bearing clearance boundaries
Radial Preload—IGC
Pinion Shaft
A unidirectional, steady-state force on a rotor is causing rotor operation at an irregular shaft centerline
position
Rotor 1X Runout
Slow roll vector magnitude is greater than 40 percent of the compensated 1X vector, indicating a nonconcentric rotor surface at the plane of measurement
Sub-synchronous Rub
Rotor contact with a stationary part excites sub-synchronous radial vibration characteristics
Super synchronous
Rub
Rotor contact with a stationary part excites super-synchronous radial vibration characteristics
Synchronous Rub
Thermal rotor bow is induced by rotor-to-stator rub (Newkirk effect) or differential viscous shearing within
the bearing (Morton effect)
Loose Rotating Part
Changes in the synchronous behavior of the rotor due to rotating elements coming loose
Example: Shrink fit elements losing the frictional force required to keep them locked onto the shaft
Synchronous Rub or
Loose Rotating Part
Non-specific determination of either a synchronous rub or a loose part
High Synchronous
Vibration
Excessive vibration at running speed
Misalignment
Possible Misalignment
Misaligned rotors between coupled machines
Rotor Bow
Bent rotor shaft
12 SmartSignal Integration
Performance
Efficiency Loss
Bearing Failures
Rotating Part Failure
Lubrication
Mech Damage/Wear
Leakage/Seal Failures
Fouling
Process Deviations
Intercooler
Key Equipment Failure Modes
Centrifugal Compressors










Axial Compressors










Integrally Geared Compressors










(Gearboxes)










SmartSignal Early
Warning for Compressors
Machine Type
As part of any plant-wide monitoring
solution, we recommend that compressors
be tied into GE’s SmartSignal predictive
analytics software for the earliest possible
notification of changes that indicate
operation outside of normal parameters.
Because SmartSignal software uses
similarity-based modeling to warn of the
smallest changes in machine behavior in
any area (process, vibration, or electrical),
it is an important tool underlying the
foundation of the condition monitoring
program. Note that SmartSignal software
is an early warning/detection tool, while
System 1 software is a detailed
diagnostics tool.
31
application guide
APPENDIX 1 System 1 Software and Network Connectivity
System 1 communication across Network layers
The customer’s information technology (IT) department typically defines network layers. Layers are often separated by functionality. Here
is one example of a layer scheme:
• Layer 3 network for machinery monitoring/control equipment
•Layer 2 network for customer business needs like file sharing,
corporate email, and Intranet applications
•Layer 1 network for the customer’s Internet access, public
websites, and business-to-business applications
Network devices such as routers, firewalls, and switches are
common solutions used to physically separate the network layers.
These devices may impose restrictions on the types of network
communications allowed to cross the network layers. For example,
between Layer 2 and Layer 1 (as shown above) the restrictions
may only allow HTTP (web access), SMTP (email access), and FTP
(file transfer) communication. This list is not comprehensive, but
outlines some common restrictions in use on firewalls and/or
routers.
Network Address Translation (NAT) – NAT is a technology to
mask the IP address in network communications. The source and
destination IP addresses are changed based on some pre-defined
rules.
TCP/UDP Port Blocking – Some network devices have the ability
to block traffic according to which port number it is using. If port 80
is blocked at a router, typical web browsing would not be possible
as all requests for port 80 passing through the router would be
discarded.
One-way Communication Rules – Some network devices have
the ability to restrict network communication in a single direction
– from Network Layer 2 to Layer 1, but not from Network Layer 1 to
Layer 2.
32
application guide
Network Broadcasting – Network broadcasting involves
network communication without a specific target destination. The
requesting application asks a blanket statement such as “Are there
any SQL Servers on my network?” It is common to prohibit this type
of behavior across network layers.
Firewalls – A firewall is a system designed to prevent unauthorized
access to or from a private network. Firewalls can be implemented
in both hardware and software, or a combination of both. Firewalls
are frequently used to prevent unauthorized Internet users from
accessing private networks connected to the Internet, especially
intranets. All messages entering or leaving the intranet pass
through the firewall, which examines each message and blocks
those that do not meet the specified security criteria. To control
the flow of traffic, numbered ports in the firewall are either opened
or closed to types of packets. The firewall typically considers the
following transmission details for each packet:
• Destination port
• Source IP address
• Destination IP address
Some firewalls also consider protocol. If the firewall is configured to
accept the specified protocol through the targeted port, the packet
is allowed to enter.
UDP and TCP/IP
Some frequently used terms in this section include the following:
User Datagram Protocol (UDP) – This is a connectionless protocol
that, like TCP, runs on top of IP networks. Unlike TCP/IP, UDP/IP
provides very few error recovery services, offering instead a direct
way to send and receive datagram packets over an IP network. It's
used primarily for broadcasting messages over a network.
Transmission Control Protocol/Internet Protocol (TCP/IP) –
This suite of communications protocols is used to connect hosts
on the Internet. TCP/IP uses several protocols, and the two main
ones are TCP and IP. TCP/IP is built into the UNIX operating system
and is used by the Internet, making it the de facto standard for
transmitting data over networks. Even network operating systems
that have their own protocols, such as Netware, also support TCP/
IP.
Directional Reference (Inbound Vs. Outbound) – In this
document, inbound connections refer to the connections from
the un-trusted side of the firewall to the trusted side. Outbound
connections refer to the connections in the opposite direction –
from trusted to un-trusted.
33
application guide
APPENDIX 2 RulePaks Process Inputs
The following table defines the process measurement inputs used by the RulePaks:
Measurement
Value
Req
Inlet Pressure
Pressure
Inlet Pressure Backup
Pressure
Discharge Pressure
Pressure
Discharge Pressure Backup
Pressure
Control Setting Angle
Degrees or Radians Closed
✔
Inlet Flow Rate
Volumetric Flow
✔
Inlet Flow Rate Backup
Volumetric Flow
Opt
✔
✘
✔
✘
✘
Bearing Metal Temperature
Temperature
Bearing Metal Temp Backup #1
Temperature
✘
Bearing Metal Temp Backup #2
Temperature
✘
1
✔
Note: System1 Software provides all the information for a qualified diagnostician to perform the analyses performed in the RulePaks above.
1
Metal temperatures for each bearing
34
application guide
APPENDIX 3 OpitComp*-BN
The OptiComp-BN integrated turbine and compressor control
solution delivers advanced compressor surge control, process
performance control, load sharing/balancing, auto sequencing, and
other auxiliary controls. In many cases, mechanical measurements
of the radial vibration and axial vibration and displacement of the
compressor rotor can show a clear indication of surge and incipient
surge. Therefore, correlating the appearance of mechanical signs of
surge with the process instability can help differentiate between
normal operation and surging, significantly improving detection of
surge and incipient surge.
monitoring.
OptiComp-BN combines thermodynamic and mechanical
measurements in one integrated system. These measurements are
used in algorithms designed to detect surge and incipient surge.
OptiComp-BN can detect incipient surge when it is not visible by
monitoring only the thermodynamic signals. Moreover, monitoring
rapid changes in both radial and axial vibration and displacement
signals, combined with any indication of process instability,
significantly increases reliability in detecting surge cycles and
surge severity. OptiComp-BN is applicable to GE’s turbomachinery
control, monitoring, and protection systems, which include
the Speedtronic Mark* platform and Bently Nevada vibration
•
No need to cause compressor surge to establish field
mapping of surge points: Lower risk of compressor damage
during commissioning; detect “stall” before surge
OptiComp-BN provides the following benefits relative to traditional
surge and incipient surge detection systems:
•
More reliable surge detection: Mechanical and process
monitoring enable you to avoid unnecessary process
interruption.
•
Reduced risk of surging compressor and process
shutdown: Rotating stall detected and operators alarmed
early; choose real-time manual or automatic response.
•
Risk assessment for continued operation: Determine
potential mechanical damage resulting from compressor surge.
OptiComp-BN Functional Diagram
35
application guide
I/O Points typically used in the OptiComp-BN system
I/O Point Description
Notes
Process (Thermodynamic) Signals (per compressor section)
1
Differential Pressure from Flow
Measuring Device
Typically, most sensitive to compressor load changes. Used in anti-surge control algorithms,
surge detection, performance calculations, diagnostics
Mandatory (see Note 1)
2
Discharge Pressure
Used in anti-surge control algorithms, surge detection, performance calulations, diagnostics
Mandatory
3
Suction Pressure
Used in antisurge control algorithms and surge detection, performance calculations,
diagnostics
Mandatory
4
Discharge Temperature
May be used in antisurge control algorithms. Used for performance calculations, diagnostics
Highly Recommended
5
Suction Temperature
May be used in antisurge control algorithms. Used for performance calculations, diagnostics
Highly Recommended
6
Compressor Shaft Rotating
Speed
Used for start/stop sequencing, diagnostics
Mandatory for variable speed drives
7
Motor Power
Applicable only to electric motor drive units. Used for start/stop sequencing, diagnostics
Mandatory for constant speed motors (see Note 1)
Mark VIe Outputs
Modulating Output to Recycle
(Blow-off) Valve
Typically, 4/20mA signal proportional to valve position
Mandatory
Solenoid Control of the Air
to Recycle Valve Actualtor/
Positioner
Used to override modulating control signal and open to recycle valve
Optional
Unit trip on Multiple Surge
Detection
Used to trip the unit if multiple surge cycles are detected within short period of time
Optional
Mechanical Signals (per compressor case)
1
NDE Radial Vibration, Horizontal
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
2
NDE Radial Vibration, Vertical
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
3
DE Radial Vibration, Horizontal
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
4
DE Radial Vibration, Vertical
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
5
Axial Displacement
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
6
Axial Vibration
Used by BN-3500 for alarm/trip. Used by OptiComp-BN to detect non-synchronous vibration
Mandatory for OptiComp-BN stall/surge detection
7
Key Phasor
Mandatory for BN-3500
BN-3500 outputs for OptiComp
Discrete Output: Rotating Stall
Detected
Used to signal rotating stall detection from BN-3500 to Mark VIe.
Discrete Output: Surge Detected
Used to signal surge detection from BN-3500 to Mark VIe.
36
application guide
Appendix 4 Thermodynamic Performance Required Data
Air Compressors
Process Compressors
Online Process Data:
Online Process Data:
• Ambient Pressure
• Ambient Pressure
• Ambient Temperature
• Ambient Temperature
• Relative Humidity
• Suction Volume Flow
• Inlet Filter Delta Pressure
• Suction Pressure
• Wet Bulb Temperature (Optional)
• Suction Temperature
• Suction Volume Flow
• Discharge Volume Flow
• Suction Pressure
• Discharge Pressure
• Suction Temperature
• Discharge Temperature
• Discharge Volume Flow
•Speed
• Discharge Pressure
• Discharge Temperature
Composition of Gas Mixture:
•Speed
• Gas Constituent #1
• Gas Constituent #2
Composition of Gas Mixture:
• Gas Constituent #3
• Gas Constituent #1
• Gas Constituent #2
Motor Data:
• Gas Constituent #3
• Input Power
• Input Voltage
Motor Data:
• Input Current
• Input Power
• Input Power Factor
• Input Voltage
• Motor Efficiency
• Input Current
•Speed
• Input Power Factor
• Motor Efficiency
•Speed
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application guide
Appendix 5 3500 Thrust Measurement and API 670 Compliance
The design of a monitoring system must strike a careful balance
between false trips of the machine and missing conditions where
the machine should be tripped. Obviously missing a machine trip
can be a serious event, but it must be recognized that incorrectly
tripping a machine is also an event that could compromise safety,
especially considering the complex processes that most of the
machinery covered by API 670 supports. In both missed trip and
false trip cases safety may be compromised and there is the risk of
potential negative financial impact to the end user.
API 670 Requirements
API 670 outlines requirements for axial position measurements,
calling for paired channels. The requirement allows for one
transducer signal (single voting logic, 1oo2) or two transducer
signals (dual voting logic, 2oo2), to exceed the danger set point to
initiate shutdown relay actuation. Specifically, with regard to 2oo2
dual voting logic applications, the standard indicates that shutdown
relay actuation should occur when:
• Both axial position transducers or circuits fail
•One channel has failed and the other has exceeded its danger
set point
• Both channels exceed the danger set point
Transducer System Faults
The axial position measurement is distinct from other
measurements covered by API 670 due to the critical nature of the
measurement and the possibility that the transducer element can
be destroyed under extreme machinery conditions. In this case,
there is the possibility that the probe target can shift suddenly
in the direction of the probes with sufficient magnitude to make
contact with, and destroy the transducer. This may occur before
the monitoring system measurement is capable of detecting the
sudden shift and generate a trip signal.
In this scenario, if the protection system were to defeat alarming
upon probe failure, the alarming capability would be defeated at the
time that the machine is experiencing what is highly likely to be an
operating condition requiring shutdown – the very type of situation
that the measurement is put in place to protect against. The
possibility that the loss of a transducer is very likely to have been
caused by the machine resulting in the overall protection function
being defeated is what is fundamentally behind the standard’s
requirement to trip upon loss of protection circuit function.
Monitoring System Faults
The design of the 3500 monitoring system thrust channel type
considers the protection circuit outlined in API 670 section 5.4.3,
to only include the probe and transducer system which are
susceptible to machine-induced faults. The 3500 system is capable
of differentiating between faults that occur with the transducer
system and those that occur in the monitoring system itself. While
the system drives for trip in the case of a transducer system fault,
a fault at the monitoring system does not. Rather than driving for
machine trip, the system design annunciates the fault, providing
an opportunity for plant personnel to respond to the problem
condition.
A protection system designed such that it generates a trip signal in
the event of a system fault condition has a significantly increased
tendency for false tripping of the machine, unless the fault can
credibly be linked to a machine emergency condition such as is
the case with axial position transducers. If those elements of the
monitoring system that are “out of harm’s way” were to drive a
trip relay actuation upon failure (single logic), or drive a vote for
trip in dual voting logic, the system would contribute significantly
to reducing machinery availability. This is especially relevant
considering the relative complexity of a typical monitoring system’s
architecture.
In effectively all cases, a fault at the monitoring system will not
coincide with, nor be driven by a safety critical machine operating
condition. Unlike the transducer portion of the protection path,
there are no known credible cases where the machine is capable
of compromising, or generating a fault in the monitoring system.
Therefore, to drive for a trip in the event of a monitoring system
fault will result in a false machine trip in effectively all cases for
single logic applications, and have serious potential negative impact
on the availability of the machinery in dual logic cases.
To accommodate for the possibility of monitoring system faults,
the monitoring system has extensive diagnostic capability to
self-diagnose and annunciate internal faults. In the event of an
internal monitoring system fault, the system responds by providing
visibility to the condition by means of a number of mechanisms
to annunciate the condition. This provides for a more effective
alternative response to a fault than simply tripping the machine
or voting to trip. Visibility mechanisms include, monitor LED
states, monitor channel states (available in Modbus registers,
local and remote system displays, and in System 1), 4 mA to 20 mA
outputs, and the 3500 rack OK relay. These allow plant personnel
to immediately be visually informed of a protection system
malfunction so they can quickly attend to the problem. In the
case of a single point monitoring system fault, the second channel
supporting the recommended dual channel 1oo2 configuration
continues to protect the machinery without the user suffering
a false trip of the machinery and the associated safety risk and
process interruption.
38
application guide
Summary
The axial position measurement is critical and is adapted to the
application-specific possibility of a probe fault being induced
by a catastrophic machinery condition. Due to this possibility,
API 670 requires that a transducer system fault results in that
path’s protection relay actuation or voting for trip in dual logic
applications. The 3500 system meets these requirements by driving
for trip in the event of a transducer system malfunction.
The possibility of a catastrophic machinery condition compromising
the protection function does not extend to the monitoring system
portion of the protection path. Therefore the 3500 system does
not generate a trip signal in the case of a monitoring system fault.
The 3500 system configured for thrust measurement is capable of
differentiating between a fault at the transducer level and one that
occurs within the monitoring system itself. This allows the system
to avoid false trips that may otherwise result from monitoring
system malfunctions. The 3500 monitoring system internal
diagnostic coverage and numerous fault annunciation methods all
support the availability of the protection function by making the
status of the monitoring system channels known to plant personnel
in real time. The protection function is maintained without
potentially compromising the availability of the monitored machine
and associated process.
The Bently Nevada 3500 system’s axial position measurement is
compliant to API 670 4th edition requirements.
39
application guide
Appendix 6 Voting Truth Tables for Normal AND and True AND voting
A. True AND Voting - Radial Vibration
Trip logic: CHAdanger AND CHBdanger = Trip
Channel A
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
NOT OK
NO ALARM
DANGER
DANGER
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
NO ALARM
NOT OK
DANGER
NO ALARM
B. True AND Voting - Radial Vibration with Not OK
Trip logic: CHAdanger OR CHANot OK AND CHBdanger OR CHBNot OK= Trip
Channel A
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
NOT OK
ALARM
DANGER
DANGER
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
ALARM
NOT OK
DANGER
ALARM
40
application guide
C. Normal AND Voting - Radial Vibration
Trip logic: CHAdanger AND CHBdanger = Trip
Channel A
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
NOT OK
ALARM
DANGER
DANGER
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
NO ALARM
NOT OK
DANGER
ALARM
D. Normal AND Voting - Radial Vibration with Not OK
Trip logic: CHAdanger OR CHANot OK AND CHBdanger OR CHBNot OK= Trip
Channel A
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
NOT OK
ALARM
DANGER
DANGER
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
ALARM
NOT OK
DANGER
ALARM
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
DANGER
ALARM
DANGER
NOT OK
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
ALARM
NOT OK
DANGER
ALARM
E. Normal AND or True AND Voting - Thrust Position
Trip logic: CHAdanger AND CHBdanger = Trip
Channel A
41
application guide
F. Normal AND or True AND Voting - Thrust Position with Not OK
Trip logic: CHAdanger OR CHANot OK AND CHBdanger OR CHNot OK= Trip
Channel A
Channel B
Result
OK
OK
NO ALARM
OK
NOT OK
NO ALARM
OK
DANGER
NO ALARM
DANGER
OK
NO ALARM
DANGER
NOT OK
ALARM
DANGER
DANGER
ALARM
NOT OK
OK
NO ALARM
NOT OK
NOT OK
ALARM
NOT OK
DANGER
ALARM
3500 RV and TP Voting Observations
1.Four truth tables define voting an RV XY pair and two truth tables define voting a TP pair. These are:
A.RV True AND
B.RV True AND OR-ed with channel OK
C.RV Normal AND
D.RV Normal AND OR-ed with channel OK
E.TP True AND as well as TP Normal AND (note: these are identical)
F. TP True AND OR-ed with channel OK as well as TP Normal AND OR-ed with channel OK (note: these are identical)
2.Timed OK Channel Defeat (TOKCD) prevents a trip on simultaneous loss of OKs (such as lightening) for voted RV channels when OK is not
OR-ed for both True and Normal voting (see Truth Tables A and C).
3.If RV is OR-ed with the channel OK, a Trip occurs (see Truth Tables B and D).
4.The nature of the TP measurement does not allow TOKCD to be applied to that measurement (see Appendix 5).
5.If TP is OR-ed with the opposite OK, the OR-ed OKs will trip upon a momentary instantaneous loss of OK (see Truth Table F). A long term
loss of OK – for approximately 0.1 seconds or longer – will cause a trip as shown in the truth table.
6.If TP is not OR-ed with the OK (see Truth Table E), a momentary instantaneous loss of both transducer OKs will most likely not cause a
trip because of the time required by the monitor to calculate perceived axial position shift and the normal 0.1 second TP time delay. A
long term loss of both transducer OKs, greater than the 0.1 seconds, will result in a trip (see Truth Table E).
1631 Bently Parkway South
Minden, Nevada USA 89423
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GEA31971A (01/2016)
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