AVR UPGRADES
Jussi Rantoja
AVR UPGRADES
Technology and Communication
2014
VAASAN AMMATTIKORKEAKOULU
Sähkötekniikan koulutusohjelma
TIIVISTELMÄ
Tekijä
Opinnäytetyön nimi
Vuosi
Kieli
Sivumäärä
Ohjaaja
Jussi Rantoja
AVR Upgrades
2014
englanti
36
Vesa Verkkonen
Wärtsilän installaatioissa on yhä käytössä vanhoja automaattisia jännitteensäätäjiä (AVR), joita ei enää ole saatavilla. Nämä vanhentuneet jännitteensäätäjät
tullaan ennemmin tai myöhemmin korvaamaan uusilla. Opinnäytetyön tarkoituksena oli luoda ohjeistus päivitysprosessin tueksi.
Ohjeistuksen teko aloitettiin tutustumalla aiheeseen ja perehtymällä AVR:n toimintaan manuaalien, piirustusten ja muun aiheeseen liittyvän materiaalin avulla.
Aiheen ymmärtämiseksi tuli myös tutustua generaattorin sekä sitä pyörittävän
moottorin toimintaan eri kuormitustilanteissa. Työ oli pitkälti selvitysluontoista ja
siinä tutkittiin mitä ominaisuuksia uusi AVR tarjoaa ja mitä mahdollisuuksia olisi
vielä käyttämättä. Työ sisälsi myös runsaasti Ethernet-liitynnän kautta tapahtuvaan Modbus-protokollapohjaisen kommunikoinnin tarjoamiin ominaisuuksiin ja
mahdollisuuksiin perehtymistä.
Lopputuloksena syntyi ohjeistus, jossa on esitetty päivitysprosessin kannalta
oleellisimmat asiat kuten päivitysprosessissa tarvittavat tiedot alkuperäisestä installaatiosta, eroavaisuudet kytkennöissä ja toiminnallisuuksissa sekä uuden laitteen parametrien asettelu. Lisäksi ohjeistuksessa on esitelty uuden laitteen tarjoamia ominaisuuksia, joita voidaan mahdollisesti ottaa käyttöön päivityksen myötä.
Avainsanat
ohjeistus, automaattinen jännitteensäätäjä, päivitys, Modbus-protokolla
VAASAN AMMATTIKORKEAKOULU
UNIVERSITY OF APPLIED SCIENCES
Sähkötekniikan koulutusohjelma
ABSTRACT
Author
Title
Year
Language
Pages
Name of Supervisor
Jussi Rantoja
AVR Upgrades
2014
English
36
Vesa Verkkonen
The obsolete automatic voltage regulators (AVR) are still being used in several
Wärtsilä installations. Because of the old AVRs are not available anymore, they
will be replaced with the new model sooner or later. The purpose of this thesis
was to create the work instructions for the upcoming upgrade projects.
The making of the instructions was started by getting familiar with the subject and
the functionality of the AVR by reading the manuals and analyzing drawings. To
understand the subject, getting familiar with the operation modes of the generator
and the engine was also required. The thesis included largely sorting out which
features of the new AVR has already taken and which features could possibly be
taken into use. The thesis also included studying the features and possibilities
provided by the Modbus protocol based communication over the Ethernet interface.
As a result the work instructions were created. The instructions represents the
most essential points such as required information from the original installation,
the functional and connection differences caused by the upgrade and the setting
the parameters for the new AVR.
Keywords
Instructions, automatic voltage regulator, operation mode,
Modbus communication
CONTENTS
TIIVISTELMÄ
ABSTRACT
1
INTRODUCTION ............................................................................................ 7
1.1 Wärtsilä ..................................................................................................... 7
1.2 Employer ................................................................................................... 7
1.3 Purpose of the Thesis ................................................................................ 8
2
THEORETICAL BACKROUND .................................................................... 9
2.1 Synchronous Generator ............................................................................. 9
2.1.1 Stator ........................................................................................... 10
2.1.2 Rotor............................................................................................ 10
2.1.3 Brushless Excitation .................................................................... 11
2.1.4 Excitation Power Supplies .......................................................... 12
2.2 AVR ........................................................................................................ 13
2.3 Operation of the Generating Set ............................................................. 14
2.4 Engine Operation Modes ........................................................................ 16
2.4.1 Speed Droop Control .................................................................. 16
2.4.2 Isochronous Load Sharing........................................................... 18
2.4.3 kW Control .................................................................................. 19
2.5 Generator Operating Modes .................................................................... 19
2.5.1 Voltage Droop ............................................................................. 19
2.5.2 Voltage Droop Compensation And Cross Current Compensation
19
2.5.3 Power Factor And var Control .................................................... 20
4
BACKGROUND ............................................................................................ 21
4.1 ABB Unitrol 1020 ................................................................................... 21
4.2 Purpose of the Instructions...................................................................... 22
4.3 Making of the Instructions ...................................................................... 23
4.4 Testing..................................................................................................... 23
5
CONTENTS OF THE INSTRUCTIONS ...................................................... 25
5.1 Initial Information ................................................................................... 25
5.2 Basic Setup And the New Setup ............................................................. 26
5.3 Settings And Parameters ......................................................................... 27
5.4 New Functions And Features of the ABB Unitrol 1020 ......................... 29
5.4.1 CMT 1000 ................................................................................... 29
5.4.2 Ethernet Interface / Modbus Communication ............................. 30
5.4.3 Time Synchronization ................................................................. 31
5.4.4 Rotating Diode Monitoring (RDM) ............................................ 31
5.4.5 Limiters ....................................................................................... 32
6
CONCLUSION .............................................................................................. 33
REFERENCES...................................................................................................... 35
6
LIST OF FIGURES
Figure 1.
Stator steel plates
p. 10
Figure 2.
Cylindrical (left) and salient pole rotors
p. 11
Figure 3.
Block diagram of the simple basic AVR
p. 14
Figure 4.
Power triangle
p. 15
Figure 5.
Speed droop
p. 17
Figure 6.
100 % and 50 % loads at 3 % droop setting
p. 18
Figure 7.
ABB Unitrol 1020
p. 22
7
1
INTRODUCTION
1.1 Wärtsilä
Wärtsilä is a global provider of the power solutions for the marine and energy applications. The company has approximately 18 700 employees in nearly 70 countries around the globe. In 2013 Wärtsilä net sales totaled 4,7 billion Euros.
Wärtsilä is divided into three different units: Ship power, Power plants and Services.
Ship power acts in the field of marine, oil and gas. In 2013 the net sales of Ship
power was 1325 million Euros. Along with the engines, Ship power supplies for
example propulsion equipment, control systems and sealing solutions. Power
plants supplies power plants up to 600 MW (megawatts). Plants are for several
purposes: peaking, reserve, industrial self-generation and load-following. The
product range covers also LNG (liquefied natural gas) terminals and distribution
systems. In 2013 its net sales was 1459 million Euros. Services are providing
lifecycle support for Wärtsilä installations by providing maintenance, service, reconditioning as well as efficiency and performance optimizing and customer training. The Services has a global service network for both, power plant and marine
installations. In 2013 Services net sales was 1842 million Euros. /27/
1.2 Employer
This thesis was made in 2014 for Plant Automation, which is a part of Technical
Service. It is a proactive organization which supports Wärtsilä and its customers
in technical issues regarding the secondary controls in the field of electrical and
automation. It continuously maintains, refreshes and develops its technical
knowledge, and aims to improve the ways of distributing the knowledge for those
who need it.
8
The job of the Plant automation is to make field tests, site surveys and to arrange
trainings. It also handles the technical requests, software backups and distribution
of the plant automation related software development tools. /26/
1.3 Purpose of the Thesis
The purpose of the thesis was to create the instructions for the AVR upgrade projects. The main target of the instructions was a replacement of an obsolete Basler
DECS 125-15 type AVRs with the new ABB Unitrol 1020. To the customer it
will be more economical to update the legacy AVRs to the new and secure the
spare part availability before the old AVRs will break. It will of course ease the
work of Wärtsilä as the replacement solutions could be offered and realized systematically at the same time. The output of the project, the work instructions are
meant to support the whole replacement project all the way from the sales to design and commissioning.
9
2
THEORETICAL BACKROUND
2.1 Synchronous Generator
The generating set comprises a diesel or gas engine and a generator. The engine is
a prime mover which produces a mechanical energy that rotates the generator
connected to the engine. For example in 50 Hz system the Wärtsilä 16V34DF engine is rotating 750 rpm and it produces rated power of 7200 kW to the generator
which produces electrical power of 6920 kW. /28/
Electric generators are rotating machines that convert mechanical energy to electrical energy. Mechanical energy comes down from a prime mover. The prime
mover is a device, for example a steam turbine or in this case, a diesel or gas engine connected to the generator shaft and thus rotating it to produce electricity.
Synchronous machine is a device whose rotor is rotating at the same speed as the
rotating magnetic field. For comparison, in asynchronous machines the rotor and
the magnetic field are rotating with different speeds. /4, 7/
The frequency of the generator is depending on the rotating speed and the number
of the poles of the generator which can be seen from the next equation:
݂=
௣௡
଺଴
(1)
where f is the frequency of the induced voltage, p is a number of the pairs of poles
on the rotor and n is speed of the rotor. The constant 60 converts rpm to revolutions per second. If the engine is rotating at 750 rpm in the 50 Hz system the
number of the pairs of the poles can be calculated by solving the p as follows:
‫=݌‬
௙∗଺଴
௡
(2)
By placing the given frequency and speed to the equation the number of the pairs
of poles is 4 which is received as a result. /10/
10
2.1.1
Stator
In the synchronous generator there are two main parts. The stationary
tationary part is
called the stator and inside the stator is the rotating part of the generator, called
the rotor. The stator is constructed by laminating thick insulated steel plates tot
gether (Figure 1).
). This kind of construction minimizes the losses caused by eddy
currents.
Figure 1. Stator steel plates /18/
As shown inn Figure 1 there are slots on the inner circumference of the stator plate.
The 3-phase
phase armature winding
winding is wound inside these slots. The stator windings
are further on connected to the generator terminals. /14/
2.1.2
Rotor
The rotor
otor is the rotating part of the generator and it is built on the shaft. The synchronous machine has two different rotor types, cylindrical
cal and salient pole (Fig(Fi
ure 2).
11
Figure 2. Cylindrical (left) and salient pole rotors /5/
Generators with the cylindrical rotors are typically used with higher speeds, 1500
rpm and above. A typical application for cylindrical rotors is a steam turbine. The
diameter of the cylindrical rotor is smaller due to mechanical forces caused by the
higher speed.
Salient pole rotors are used in the lower speed applications, such as hydroelectric
power plants and diesel- or gas-powered medium- and slow-speed engines. The
rotor is constructed from the laminated plates, just like the stator, to reduce the
eddy current losses. The salient pole rotor has the T-shaped poles. The field winding or excitation winding is wound around the poles of the rotor.
Direct current (DC) is supplied to the rotor field windings with different polarity
on the North (N) and South (S) poles (Figure 2). The current in the field windings
creates a flux. When that flux rotates according to the rotor, it induces sinusoidal
3-phase voltage to the stator windings. /14/
2.1.3
Brushless Excitation
In the conventional excitation system the exciting current is supplied to the excitation windings with the coal brushes and slip rings. Coal brushes, slip rings and
commutators of the DC excitation system require maintenance which is eliminated by brushless excitation.
12
Brushless excitation is based on a small AC (Alternating Current) generator
mounted on the generator shaft. Compared to the main generator, the construction
of the exciter is inversed. The DC field current is supplied to the stator creating a
static flux. When the shaft is rotating it induces 3-phase AC voltage to the armature windings that are rotating in the rotor of the exciter. This alternating current
is then rectified by the diode bridge and supplied to the field windings of the main
generator. /19/
2.1.4
Excitation Power Supplies
The permanent magnet generator (PMG) is an independent generator mounted on
the generator shaft to produce excitation power when the generator is rotating.
The PMG excitation power supply gives a reliable voltage build-up on starting
situations. Because the PMG is not affected by the load circuits of the generator, it
gives the same excitation power even in short circuit situations where the generator voltage drops near to zero.
Excitation from a potential source takes the excitation power from the potential
transformers on the generator output. This kind of excitation supply is depending
on the generator voltage and it requires a separate supply for the short circuit situations. This short circuit excitation is taken from appropriate boost current transformers to maintain the sufficient excitation when the generator voltage drops.
With this kind of excitation system the voltage build-up is dependent on a residual
voltage. If there is not enough residual voltage to build up the voltage, the generator must be excited with a separate battery or by using field flashing. The field
flashing is the function of the voltage regulator for exciting the machine with no
residual voltage.
Auxiliary windings are wound into the same slots as the armature winding but it
has mounted in a different way to work more like a current transformer. Like the
PMG, the auxiliary windings are producing sufficient excitation power under
13
short circuit situations. However, the voltage build-up also requires the residual
voltage. /14/
2.2 AVR
AVR (Automatic Voltage Regulator) is a device controlling the excitation current
of the synchronous generator and therefore the output voltage of the generator. It
keeps the generator operation inside the allowed limits, thus preventing situations
that can be harmful to the generator. AVR rectifies the AC received from the
PMG, auxiliary windings or PTs (Potential Transformer) and regulates it to suitable level. Then the AVR supplies the DC to the exciter field and thus further on to
the excitation winding.
To understand the basic functionality of the AVR, a simplified AVR block diagram is shown in Figure 3. Voltage measurement from the generator output is
compared to the reference voltage to get the error, difference between the actual
voltage and setpoint. The error signal is amplified in the operational amplifier
which together with the firing gear controls the thyristors to regulate the excitation
current to the required level. Stabilizing is a function which prevents voltage from
hunting. A block diagram of a modern AVR is much more complicated as this
model comprises voltage control only. /14/
14
Figure 3. Block diagram of the simple basic AVR /6/
2.3 Operation of the Generating Set
The generator supplies both active (P) and reactive (Q) powers. The active power
is the power that is required for purely resistive loads, such as an ideal heater. A
purely resistive load means that there is no phase shift between the voltage and the
current. It is required to produce the same amount of the active power as it is consumed. Otherwise the frequency starts to increase or decrease.
The reactive power is the power that is oscillating between the load and the generator. An inductive reactive power is needed for example to create a magnetic field
for the electric motor. In inductive reactive power, the current lags behind the
voltage. If considered the pure inductive load, the current lags 90 ° behind the
voltage. The reactive power can also be capacitive which means that the current is
leading the voltage. The capacitive reactive power is required to the long power
transmission lines which form a huge capacitor with the earth. Also the production of the reactive power must meet the consumption. Otherwise the voltage increases or decreases.
15
The combination of the active and reactive power is called apparent power (S).
(S)
The apparent power does not take the phase angle difference between the current
and voltage into account. The relationship between P, Q and S can be visualized
with the power triangle (Figure 4.).
4.). The relationship can also be represented by
the next equation:
ܵ ଶ = ܲଶ ൅ ܳ ଶ
(3)
The cosine
osine of the angle θ between the P and S is a power factor.. The power factor
represents the ratio of the active and reactive power. /14, 19/
Figure 4. Power triangle /3/
The generating
enerating set can operate either in an island mode or parallel with the grid.
In the island mode the generating set is typically producing electricity for the ini
dustrial plants,, ships or to the other relatively small networks where even one
generating set can have an influence on the system frequency. In the island operation the frequency is controlled
controlled by controlling the speed of the prime mover and
the voltage is controlled by regulating the excitation current.. Active and reactive
powers are produced by the level of consumption. Generating sets can produce
electricity to the network operating as a single unit or operating parallel with other
units. When operating parallel in the island system,
system there are special operation
modes for sharing the load with the other units. /26/
When the generating set is operating parallel with the grid, it is basically
basical connected to a relatively large grid. A large grid consists of the numerous power plants
connected to the same network,
network for example the nation-wide
wide grids.
grids In a large grid,
the frequency is such a strong variable that a single generating set or even a whole
power plant cannot increase or decrease it. Instead of controlling the frequency
16
and the voltage, the amounts of the produces active and reactive powers are controlled. /23/
Before synchronous generators can be connected to the parallel operation, they
must be in synchronism. The synchronization comprises that the generator must
meet the following conditions:
1. Phase sequence must be matching between the generator and busbar
2. Voltages must be in phase
3. Frequency must be the same as the busbar frequency
4. Voltages must be equal
After the previous conditions are met the circuit breaker between the generator
and the busbar can be closed to start parallel operation. After the synchronization
the generator field current is sufficient to maintain the voltage and the prime mover produces sufficient mechanical power to cover its rotational losses. After that
the engine and field excitation can be governed to produce the wanted active and
reactive power. /19/
2.4 Engine Operation Modes
To cover the different loading situations and demands the engines must have different operation modes. The engines are controlled according to the need of the
active power and frequency. The control takes place by controlling the fuel supply.
2.4.1
Speed Droop Control
“Speed droop is a governor function which reduces the governor reference speed
as fuel position (load) increases.” /20/ Droop as a notion means the amount of the
speed or frequency drop that appears when the engine load increases from 0 % to
100 %. For example, the engine with rated speed of 750 rpm and the droop value
is set to 4 %. When the engine load changes from no-load to full-load the speed
17
will decrease
crease 4 % of 750 rpm which means that the speed decreases 30 rpm. Thus
the actual speed at the 100 % load is 720 rpm. An example of the droop curve is
shown in Figure 5, where the active power is as a function of the frequency.
Figure 5. Speed droop /12/
The droop is a function that stabilizes the engine in situations where the load
changes. Without the droop the speed would continue fluctuating over and under
the reference speed as the consequence of the load change. The speed
peed droop mode
is usually a backup mode in case the other control modes cannot be used. In an
island operation the active load is shared between
between parallel units. The load is equal
with all parallel units if the speed references and droop values are the same.
When operating in the speed droop mode in parallel
par
with the grid,, the frequency is
determined by the grid.
grid Increasing or decreasing the speed reference does not
cause a change in the system speed but it determines how much load the engine is
carrying. The loading percent can be seen as an intersection point of a droop line
and a dashed 60 Hz system speed line (Figure 6). The intersection point of the
droop line and the vertical axis shows the speed reference. As it can be seen, the
increment in the reference speed causes the load to increase. The speed droop is
18
usually used as a backup mode in case the other control modes cannot be used.
/20, 21/
Figure 6. 100 % and 50 % loads at 3 % droop setting /20/
2.4.2
Isochronous Load Sharing
Despite the load isochronous load sharing is intended to maintain the system
speed precisely. It can only be used in the island system for parallel operating
units to share the load with each other. The units are sharing the load via load
sharing lines. If there are different size units, the load is shared proportionally.
If there are several units running in isochronous mode, it is able to set one unit to
speed droop mode for base loading. Base loading means that one unit is in the
speed droop mode maintaining a certain output power while the isochronously
running units are maintaining the frequency. /21/
19
2.4.3
kW Control
The kW control maintains the constant output of the generator set. It does not control the speed and it is not influenced by the frequency fluctuations. The kW control can only be used when the generator set is operating parallel with the grid. It
is used in the base load applications because of the constant output power can be
maintained. /21/
2.5 Generator Operating Modes
As the engine is controlled by its own controllers, the generator is controlled by
an AVR. The AVR has the control modes for the parallel and island operation depending if either the voltage or reactive power is controlled, as mentioned before.
The operation of the generator can be compared to the engine operation under different loading situations.
2.5.1
Voltage Droop
The principle of voltage droop control is similar to the speed droop control but the
parameters are different. Instead controlling the frequency by controlling the fuel
feed, in the voltage droop mode the system voltage is controlled with the generator field excitation. In the speed droop control the droop is related to active load
whereas in the voltage droop the corresponding variable is reactive load. Thus,
when the reactive load increases, the generator voltage decreases proportionally.
/21/
2.5.2
Voltage Droop Compensation And Cross Current Compensation
Voltage droop compensation (VDC) is a feature that can be used for generators
which are operating parallel in an island system and which are connected to the
same bus. According to its name VDC compensates the effect of the droop and
maintains the voltage level constantly at 100 %. VDC control shares the amount
of the reactive power digitally with the other parallel AVRs via RS-485 bus.
20
The VDC is a feature of the Unitrol 1020. The cross-current (or reactive differential) compensation is a feature used with Basler DECS 125 and like VDC it is a
feature that compensates the effect of the voltage droop. Instead of a digital communication it is an analog connection between different paralleling units, as the
secondary circuits of the measuring CTs (Current Transformers) are connected
together. It is also used in an island mode only. /1, 24/
2.5.3
Power Factor And var Control
Power factor (pf) control is a control method where the AVR is maintaining the
ratio of active and reactive power. The power factor mode can only be used when
the generator is operating parallel with the grid. The option for the constant power
factor is Var control, intended to keep a produced reactive power constant. /21/
21
4
BACKGROUND
Several Wärtsilä installations are still using an obsolete Basler DECS 125-15 type
AVR. This type AVR is not available as a spare part anymore. Wärtsilä is going
to contact the customers with the obsolete AVR to inform about the obsolescence
and to offer a replacement solution. The substitute for the Basler DECS 125-15 is
ABB Unitrol 1020 which Wärtsilä has taken into use in 2013.
For the customers it is more cost-effective to replace the obsolete AVR during the
pre-defined standstill than after the unexpected break down during operation. A
scheduled upgrade process requires less standstill time because the replacement
planning can be done during the generating set is operating. By updating the AVR
the customers will get the reliable excitation system with spare part availability
but also the new features, such as enhanced monitoring and control possibilities.
4.1 ABB Unitrol 1020
ABB Unitrol 1020 is an automatic voltage regulator which is intended for small
and medium sized synchronous machines (Figure 7). It uses IGBT (Insulated Gate
Bipolar Transistor) semiconductors to regulate the continuous excitation current
up to 20 ADC. Unitrol 1020 can be used in harsh conditions as it can operate in
the ambient temperature between -40 °C and 70 °C. It can also be mounted to the
generator as it withstands the vibrations. It is certified according the DNV (Det
Norske Veritas) and UL (Underwriters Laboratories) standards. /2/
22
Figure 7. ABB Unitrol 1020 /13/
4.2 Purpose of the Instructions
I
The instructions are meant to support the whole replacement project from the
saless to commissioning. For the sales the instructions are intended to represent the
replacement solution to get the information about the offered solution. To help the
designers the instructions are giving advice to get the information,
information such as required drawings
ngs and technical data of the generator to create the new drawings, as
well as the new parameters for the AVR. For commissioning the instructions
shows, for example, the measurement method for a certain parameter and connecconne
tions between the AVR and the generator.
The main objective of the instructions was the replacement of a Basler DECS
15 type AVR with an ABB Unitrol 1020. However, the instructions can be
125-15
easily adapted also for initial situations with different AVR, for example to ABB
GX300PR.
23
4.3 Making of the Instructions
This project was made in 2014, between the weeks 4. and 17. The project started
by getting acquainted with the subject by studying the material about the AVR
and engine controls. The studies included also participating in Wärtsilä internal
trainings concerning the subject. Because only a limited number of the AVR functions were able to be tested practically, very careful studying of the manuals was
required to be sure how the untested functions really works. Mainly the following
material was used during the project:
•
ABB Unitrol 1020 user manual and Modbus reference manual
•
Basler DECS instruction manual and commissioning manual
•
several different AVR training documents
•
several different manuals concerning operation modes and plant operation
The instructions were written with Microsoft Office Word. The body of the instructions was made in co-operation of the Plant automation personnel. The consultation of the personnel was used also during the project to develop the instructions to the right direction to meet the purpose of the instructions as well as possible.
4.4 Testing
A part of the project was testing out the Modbus communication. The tests were
done by using Ananas which is the software that can act as a Modbus TCP client
and server. Thus, it can be used for reading and writing values to holding registers
of the Unitrol 1020. Ananas was used for testing and figuring out how the communication alarm works but also for reading the measurement values and writing
parameters.
Unitrol 1020 has a function which is for monitoring the status of Modbus communication. In Unitrol 1020 there is a bit for the communication alarm that must
be toggled on and off within the defined keep alive time. If the keep alive time
24
expires and the keep alive bit is not toggled, the AVR will give a communication
alarm. When the state of the alarm is on, it turns loss of Modbus communication
alarm on. When the alarm is on, also the state of the communication alarm bit is
on which causes that no alarm is received in a broken bus situation as the alarm
signal is not received.
25
5
CONTENTS OF THE INSTRUCTIONS
The instructions are based on the material and tests carried out as well as on the
expected needs of the update projects. The instructions are meant to be clear with
no unnecessary information.
5.1 Initial Information
The first section of the instructions is called Initial information. The initial information needed to handle the upgrade process is represented in this section and that
information consists of:
•
drawings
•
generator specifications
•
manuals
Drawings are mainly needed from the excitation circuit but also the drawings of
which has been referenced in the excitation circuit diagram are needed. The excitation circuit diagram shows the connections between the generator and the AVR
but also the references where the control signals from the PLC (Programmable
Logic Controller) as well as the power supply for the AVR is coming from. The
measured and calculated data from the generator which is needed for setting the
new parameters for the new AVR can be found from the technical specifications
of the generator.
If the technical specifications for the generator cannot be found, the generator rating plate includes the most important values and the serial number of the generator. The manufacturer of the generator might have the stored data available against
the serial number. In addition to the previous, the initial information also includes
the list of the needed manuals. The only required manuals are Unitrol 1020 user
manual and Modbus reference manual. Other manuals, such as manual for DECS
125-15 are not mandatory. This kind of unnecessary manuals and other documents
are listed separately to avoid the possible confusions.
26
5.2 Basic Setup And the New Setup
The next chapter of the instructions handles the operation modes and the required
connections to enable each of the modes. This chapter starts by representing the
simple basic connections which is needed to enable the voltage droop mode and
the measurement functions. The required connections are:
•
power supply for the AVR (Unitrol 1020 requires an auxiliary supply
unlike DECS 125)
•
excitation power from the potential transformer (input)
•
excitation current (regulated output current from the AVR)
•
voltage and current measurement
•
excitation on/off command and status
•
increase and decrease signals for the manual control of the excitation
current
•
boost current transformers for short circuit excitation (if the excitation
power is supplied from the PTs)
•
status of the generator circuit breaker (required for enabling the PF and
VDC modes)
•
parallel with grid status (required for enabling the PF mode)
Special attention needs to be paid to the current and voltage measurements. The
polarity of the current measurement connection needs to be correct to sense the
reactive current correctly. If the polarity is connected wrong, the AVR senses the
positive reactive current as negative and vice versa. That causes no problems in
no-load operation, but when the generator is loaded, the generator voltage is increasing when the load is increasing.
The engine direction of the rotation is clockwise. When the generator is connected
to the engine, the generator is rotating counterclockwise. Due to that, the phase
order of the generator is reversed. The phase L1 of the generator is connected to
the L3 of the bus and correspondingly the L3 of the generator to L1 of the bus.
27
Phase L2 is the same. Because of that phases L1 and L3 must be crossed between
the PTs and the AVR. Otherwise, the AVR senses the power incorrectly. To
measure the current and the voltage of the generator correctly, Unitrol 1020 also
requires that the secondary circuits of the CTs and PTs are grounded.
Basler DECS 125-15 includes the PF control mode, but it does not have an input
to give a power factor setpoint. Instead giving the setpoint to the AVR, the required level for the power factor is controlled by giving increase and decrease
pulses with PLC (Programmable Logic Controller). The PLC compares the measured power factor to the setpoint value and gives the increase and decrease pulses
to the AVR which again increases or decreases the excitation voltage to reach the
required power factor set point. ABB Unitrol 1020 has the input for the power
factor setpoint. Only the PF setpoint is given by the PLC and the Unitrol 1020
measures and calculates the actual value internally and controls the field excitation to reach the setpoint.
If cross current compensation (CCC) have been used with DECS 125-15, the voltage droop compensation (VDC) can be taken into use with the Unitrol 1020. The
cross current loop is an analog connection between the current transformers of the
parallel operating generators, whereas the VDC communicates over RS-485 bus
between the AVRs. Digital RS-485 based VDC line is not dependent from the line
resistance as the analog CCC is. The connections required for each control mode
are represented more precisely in the instructions.
5.3 Settings And Parameters
In the instructions this chapter represents the most relevant parameters that the
AVR needs to regulate the field current properly. These parameters concerns the
rated values of the generator or measuring transformers. The data required for the
system data parameters is available from the technical specifications. For the system data, the most important values from the generator are:
28
•
nominal excitation current
•
no-load excitation current
•
nominal voltage
•
nominal frequency
•
nominal current
•
machine reactance
•
the ratings of the current and voltage transformers
In addition to the previous list, the AVR requires also the ceiling factor, which is
the relation between the maximum output voltage of the AVR and the nominal
voltage of the generator in no-load operation. This ceiling factor can be defined
either by using the oscilloscope function of the AVR or by calculating. Both
methods are represented in the instructions.
Besides the system data parameters the other important parameters, depending on
the generator features, are the values for the PID (Proportional, Integral, Derivative) controller. The proportional part of the controller is defining how strongly
the controller reacts to the change in the measured value. The proportional controller itself is not very accurate and it causes some offset to the controlled value.
However, the integral action is eliminating that offset. The control is depending
on how large the deviation is and how long it lasts. The output of the derivative
action depends on the rate of change and it is typically used to reduce the overshoots. With the Unitrol 1020, the time constant of the exciter machine is approximately eliminated with the derivative action. /1, 9, 16/
Tuning the PID controller of the Unitrol 1020 requires the following parameters:
-
proportional gain
-
integration time
-
derivation time
29
The PID parameters can be calculated with the software tool intended for that and
the values required for calculations can be mostly found from the technical specifications of the generator.
5.4 New Functions And Features of the ABB Unitrol 1020
ABB Unitrol 1020 includes lots of the new and improved functions from the operation modes to the control and monitoring. Among the most important improvements are monitoring functions such as CMT1000 and the features it provides. The former model of the Unitrol 1020 is Unitrol 1000-15 which has lots of
the same functions than Unitrol 1020. However, the instructions are concentrating
on comparing the Unitrol 1020 to Basler DECS 125-15. Because of great number
of the new features and functions, only the most relevant ones are represented
here.
5.4.1
CMT 1000
CMT1000 is a PC software tool for configuration and monitoring the AVR. It enables that the parameters and settings can easily be modified with the graphical
interface of the software or by modifying the parameter file which can be therefore downloaded to the device with CMT1000. It also enables that the parameters
from the AVR can be exported to the text file. That enables creating backup files
which are valuable in the situations where the currently used AVR breaks down.
The stored backup file can be downloaded easily to the device without calculating
and setting the parameters again which makes the spare part delivery easier and
faster.
If there are several AVRs connected to the same network, each one can be connected with only one PC with CMT1000 installed on. It only requires that the IP
addresses of the AVR and the PC are in the same area. AVRs can be identified
also from the individual ID (identifier) number.
30
One of the functions the CMT1000 has to offer is the data logger. It can record up
to 12 signals 5 of which are configurable and the recording can be triggered from
the configurable events. AVR can store up to 10 event logs which can be loaded
to the PC and monitored later with the CMT1000.
The event logger provides a time stamped events based on the activity of AVR.
Events are created for example from active generator operation modes, such as
from the limiter and alarm status changes. The time stamped events can be read
out by using the AVR configuration and monitoring software CMT1000 or by using PLC to read the events from the Modbus registers. To get the most out of the
event logger, it is important that the time of the AVR is synchronized.
5.4.2
Ethernet Interface / Modbus Communication
Modbus is an open communications protocol developed by Modicon and it is
widely used in industrial applications. Modbus serial is a master-slave protocol
and it has two modes for serial communications: RTU and ASCII. In master-slave
communication there is one device, for example PLC, configured as a master. The
master sends a request to the slave device, for example ABB Unitrol 1020 in order
to read or write data from the slave device. The slave device performs the action
requested by the master and sends a response to the master. Modbus has also TCP
(Transmission control protocol) implementation which enables communication
over the Ethernet. In Modbus TCP the master is considered as a client and slave as
a server. /17/
ABB Unitrol 1020 has a standard RJ-45 Ethernet connector and it uses Modbus
TCP for communication. Modbus communication provides a wide range of monitoring and control possibilities. For example the setpoints can be given and parameters can be changed by utilizing Modbus. However, it is not so useful a function as the parameters must rarely be changed and setpoints can be given to an analog input of Unitrol 1020. The more valuable benefit from the Modbus communication is the monitoring. For example, the current operation mode of the AVR
31
can be indicated as well as the measurements of the AVR. For example, the AVR
is measuring an excitation current which can be monitored and trended on WOIS
(Wärtsilä Operators Interface System) computer. WOIS is a PC based graphical
interface for operators to monitor and control the system. /25/
5.4.3
Time Synchronization
The internal clock of the Unitrol 1020 can be updated by using SNTP (Simple
Network Time Protocol). SNTP is a simplified version of NTP (Network Time
Protocol) and as the SNTP is using the same packet format as NTP, they are compatible together. NTP is a very commonly used protocol for maintaining accurate
time over the network. The basic idea of NTP is to keep the times of the networkconnected devices as close to UTC (Coordinated Universal Time) as possible.
The WISE (Wärtsilä Information System Environment) computer acts as an NTP
client when it is synchronizing its time from NTP server equipped with a GPS
(Global Positioning System) receiver. WISE is acting also as an NTP server while
it is transmitting the time further to the AVR. Thus, the WISE computer is both,
server and client, whereas the AVR is only a client. Time stamped events and data
logs can be valuable when analyzing the collected data either the use of data is
failure analysis or improvement of the performance. /8, 10, 25/
5.4.4
Rotating Diode Monitoring (RDM)
Unitrol 1020 has a function called diode monitoring which observes the condition
of the rectifier diodes in the rotor. It detects if the diode breaks down causing an
open circuit or if the diode is short circuited. With this function, a diode failure
causing an open circuit can be set to trig an alarm function and a diode short circuit can be set to trig a trip function. If the diode monitoring function does not exist in the AVR, it must be carried out with a diode monitoring relay which is sensing the field circuit of the AVR. /1/
32
Because the diodes are in the rotor, they can only be monitored in indirectly. The
broken diode results in an unbalanced load in the AC exciter. The unbalanced situation causes an appreciable ripple current to the exciter field. Monitoring is carried out by detecting the AC or ripple induced to the field circuit. Because the excitation current is rectified from the AC, there is always some ripple in the field
current. Nevertheless, a ripple caused by broken diode is significantly greater than
a ripple caused by the rectifier itself. /1, 14/
5.4.5
Limiters
Unitrol 1020 includes configurable limiter functions which are meant to prevent
the undesirable operation of the generator. The AVR limiters are not meant as a
protection but to prevent the generator operating in such a manner that the protection relays would act. For example, the PQ limiter of the AVR can be configured
to be more sensitive than a trig function of the generator protection relay which is
preventing the under-excitation of the generator. The AVR PQ limiter is determined by defining the minimum Q at the 5 different P values from 0 % to 100 %.
The Ie minimum current limiter prevents the generator from the loss of synchronism and operating beyond the generator under-excitation limit which could cause
over heating in the stator. The Ie maximum current limiter monitors the field current and limits too high field currents to prevent the field windings from overheating. It limits the output current after a predefined time. V/Hz (Volts per Hertz)
limiter prevents the generator and the connected transformer core lamination insulation from breaking down due to overheating. The overheating is caused if the
flux density grows too high. The name Volts-per-Hertz limiter comes from “the
fact that the generator flux density is proportional to the ratio of terminal voltage
to frequency” /7/. The other limiters in the Unitrol 1020 are:
•
UM limiter to limit the minimum and maximum machine voltage
•
IM limiter which limits the maximum current of the machine
•
Temperature influenced limiters for IM and Ie /7/
33
6
CONCLUSION
The output of the project is the work instructions for the AVR upgrade projects.
This document describes just the basic theory behind the AVR and devices closely
related to it, functions of the AVR, how the instructions were made and what are
the contents of the instructions. All the details, for example the connections and
calculations for parameters, are represented in the instructions.
Time used for studying could have been used more efficiently, for example better
notes could have been made to ease the studying and understanding the subject
faster. There was a large amount of the source material for the instructions and the
relevant knowledge was dispersed into those which caused the challenges to handle all the material. All of the studying material was written in English which of
course slowed down the studying process a little because there were lots of new
terms to assimilate. However, because all the material was written in English as
were the instructions too, it was logical to write the thesis in the same language to
avoid incorrect translations. Also the minor initial knowledge and lack of a practical experience about the subject was slowing down, but on the other hand it offered good challenges.
It is hard to assess the instructions before any update process has been completed
and any feedback received. If necessary, the instructions can easily be modified
after the feedback is received. However, there are some improvements that could
be done for further development, for example modifications for the different
AVRs. The instructions can be easily modified as the parts of the instructions
concerning the new AVR, can be used without modifications.
This thesis taught lot about the power plant operation and controls and gave a
wide picture of the control systems and how those are related to each other. Working with the subject was a great learning opportunity and gave valuable
knowledge for the future. During the thesis a lots of new things came up which
34
would have been interesting to learn more about, but with a limited amount of
time it was necessary to focus on the main subject.
35
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/17/
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/18/
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/21/
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/22/
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/23/
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/24/
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/25/
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http://www.wartsila.com/en/engines/gensets/generating-sets
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