glossary of standard industry terminology and definitions

glossary of standard industry terminology and definitions
glossary of standard industry
terminology and definitions
AC
See ALTERNATING CURRENT
AC GENERATOR
AC generator is the preferred term for referring to a generator
that produces alternating current (AC). See ALTERNATOR and
GENERATOR.
ACCURACY
The comparison of an indicated value to an actual value. The
quality of accuracy is often expressed by stating the difference
between the two values as a percentage of the actual value.
ACOUSTIC MATERIAL
Acoustic material is any material considered in terms of its
acoustic properties, especially in properties of absorbing or
deadening sound.
ACTIVE POWER
Active power is the real power (kW) supplied by the generator
set to the electrical load. Active power creates a load on the
set’s engine and is limited by the power of the engine and
efficiency of the generator. Active power does the work of
heating, lighting, turning motor shafts, etc.
AIR CIRCUIT BREAKER
An Air circuit breaker automatically interrupts the current
flowing through it when that current exceeds the trip rating of
the breaker. Air is the medium of electrical insulation between
electricity love parts and grounded (earthed) metal parts. Also
see POWER CIRCUIT BREAKER.
AIR COOLED ENGINE
The engine of the generator is cooled only by air blown across it
by a fan.
AIR GAP
An interruption of a magnetic circuit through which space the
magnetic flux must pass. A typical representation of this space is
the clearance between the rotor and stator of a generator.
ALTERNATING CURRENT (AC)
Current which varies from zero to a positive maximum to zero to
a negative maximum to zero, a number of times per second, the
number being expressed in cycles per second or Hertz.
ALTERNATOR
A device for converting mechanical energy into electrical energy
in the form of alternating current. Alternator is another term for
AC generator.
ALTERNATOR STRIP HEATER
A small heater element mounted permanently in the generators
winding or control box to provide a warm, moisture free environment. These are popular in coastal areas or where extreme cold
may hamper controls from operating.
AMBIENT TEMPERATURE
The air temperature of the surroundings in which the generating
system operates.
AMMETER
An instrument designed to measure electric current flow.
AMORTISSEUR
A short-circuited winding consisting of conductors embedded in
the pole faces of the rotor of a synchronous generator. Its function is to damp out oscillations or hunting during load changes,
thereby improving transient stability.
AMPERE
The unit of electric current flow. One ampere will flow when one
volt is applied across a resistance of one ohm.
AMPACITY
Current carrying capacity of electric conductors expressed in
amperes.
AMPERE TURN
A unit of magnetizing force. The product of current flowing
multiplied by the number of turns in a coil.
ANNUNCIATOR
An annunciator is an accessory device used to give remote
indication of the status of an operating component in a system.
Annnunciators are typically used in applications where the
equipment monitored is not located in a portion of the facility
that is normally attended. The NFPA has specific requirements
for remote annunciators used in some applications, such as
hospitals.
APPARENT POWER
A term used to describe the product of current and voltage,
expressed in KVA. It is the real power in KW divided by the
power factor.
ARMATURE
The armature of an AC generator is the assembly of windings and metal core laminations in which the output voltage
is induced. It is the stationary part (stator) in a revolving field
generator.
AUTOMATIC TRANSFER SWITCH (ATS)
An automatic device for transferring an electrical load from one
power source to another.
AUTHORITY HAVING JURISDICTION
The authority having jurisdiction is the individual with the legal
responsibility for inspecting a facility and approving the equipment in the facility as meeting applicable codes and standards.
AUTO-TRANSFORMER
A transformer having a single continuous winding, portions of
which are used for the input and the output windings.
BThe negative polarity connection of a storage battery or any
other direct-current source.
B+
The positive polarity connection of a storage battery or any other
direct-current source.
BACKUP PROTECTION
Backup protection consists of protective devices which are intended to operate only after other protective devices have failed
to operate or detect a fault.
BASE LOAD
Base load is that portion of a building load demand which is
constant. It is the “base: of the building demand curve.
BLACK START
Black start refers to the starting of a power system with its own
power source, without assistance from external power supplies.
BLOCK HEATER
Used to keep the engine block warm during periods when the
engine is not running. Typically thermostatically controlled to only
operate during temperatures below 40 degrees and wired to a
Utility supply.
BRUSH
A conducting element, usually graphite and/or copper, which
maintains sliding electrical contact between a stationary and a
moving element.
BRUSHHOLDER
A device which supports the brush in the correct position but allows it to move in correct relationship to its spring.
BUMPLESS TRANSITION
Bumpless transition is make-before-break transfer of an electrical
load from one source to another where voltage and frequency
transients are kept to a minimum.
BUS
Bus can refer to the current-carrying copper bars that connect
the AC generator and loads in a paralleling system, to the paralleled output of the AC generators in a system or to a feeder in an
electrical distribution system.
CARB (CALIFORNIA AIR RESEARCH BOARD)
A state run board and regulatory agencies that now govern exhaust emissions from engines. The engines may be in cars, other
equipment or generators. The overall effect is to reduce pollution.
CAPACITANCE
The property of any system of dielectric and conductors to store
electrical energy. Expressed in micro-farads and its symbol is uf.
CAPACITOR
A device capable of storing electric energy consisting of two
conducting surfaces separated by an insulating material. It blocks
the flow of direct current while allowing alternating current to flow
proportional to its capacitance and the frequency and value of
applied voltage.
CIRCUIT
A circuit is a path for an electric current across a potential (voltage).
CIRCUIT BREAKER
A protective switching device capable of interrupting current flow
at a pre-determined value.
COLLECTOR RINGS (SLIP RINGS)
The conducting rotating rings of a generator rotor which connects
the field winding through brushes to a source of direct current.
Also used on rotating armature AC generators to conduct the
output current to the brushes.
COMMERCIAL POWER
The term applied power furnished by an electric power company.
When available, it is usually the prime power source.
CONDUCTOR
A wire or cable designed for the passage of electrical current.
CONNECTOR
A device for electrically interconnecting two or more conductors.
CONTACTOR
An electro-mechanical device designed for repeatedly establishing
and interrupting an electrical power circuit when triggered by an
operating coil.
CONTINUOUS LOAD
Any load up to and including full rated load that the generator set
is capable of delivering for an indefinitely long period, except for
shutdown for normal preventive maintenance.
CONTINUOUS RATING
The load rating of an electric generating system which it is
capable of supplying without exceeding its specified maximum
temperature rise limits.
COPPER LOSS
That portion of the losses involved in generation caused by the
flow of current through the resistances of the coils and conductors within the generator. These losses are proportional to the
resistance and the “square” of the current and are referred to as
I2R losses.
CORE
The laminations in the generator constituting the magnetic
structure thereof.
CROSS-CURRENT COMPENSATION
One of two systems which permit generators in parallel to share
the reactive component of the power in proportion to their rating
while maintaining constant output voltage. See DROOP COMPENSATION.
CROSS-CURRENT COMPENSATION TRANSFORMER (CCCT)
A current transformer which controls the division of reactive KVA
in proportion to the ratings of generators operating in parallel.
CURRENT
The rate of flow of electricity. See AMPERE.
CURRENT LIMITING FUSE
A current limiting fuse is a fast-acting device that, when interrupting currents in its current-limiting range, will substantially reduce
the magnitude of current, typically within one-half cycle, that
would otherwise flow.
CURRENT TRANSFORMER (CT)
An instrument transformer used in conjunction with ammeters
and control circuits that produces an output proportional to
primary current.
CYCLE
One complete reversal of an alternating current or voltage, from
zero to a positive maximum to zero to a negative maximum back
to zero. The number of cycles per second is the frequency, expressed in Hertz (Hz).
CYCLE PER SECOND (CPS)
See FREQUENCY and HERTZ.
CYCLING
The variation in output either above or below the desired
operating point.
DC FIELD
The field poles and their winding, which when energized, produce
the magnetic flux in a generator.
DC GENERATOR
A generator which transforms mechanical energy into
unidirectional or d-c electric energy.
DAMPER WINDING
See AMORTISSEUR.
DAMPING
The process by which cycling is reduced to a minimum.
DECIBEL (DB)
Unit used to define noise level.
DELTA CONNECTION
A three-phase connection in which the start of each phase is
connected to the end of the next phase, forming the Greek letter
Delta (D). The load lines are connected to the corners of the delta.
In some cases a center tap is provided on each phase, but more
often only on one leg – thus supplying a four-wire output.
DEMAND FACTOR
The demand factor is the ratio of actual load to the potential total
connected load.
DEVIATION FACTOR
The deviation factor of a voltage wave is the ratio of the maximum difference between corresponding ordinates of the wave
and of a sine wave of the same root mean square and time
base to the peak value of this sine wave when this sine wave is
superimposed in such a way as to make this difference as small
as possible.
DIELECTRIC
Insulation.
DIELECTRIC STRENGTH
The ability of insulation to withstand voltage without rupturing,
usually expressed in volts per mil.
DIFFERENTIAL COMPENSATION
See CROSS CURRENT COMPENSATION.
DIFFERENTIAL RELAY
A differential relay is a protective device which is fed by current
transformer located at two different series points in the electrical
system. The differential relay compares the currents and picks up
when there is a difference in the two which signifies a fault in the
zone of protection. These devices are typically used to protect
windings in generators or transformers.
DIODE
A solid-state device which allows current to pass in one direction
only. Since it allows only one half cycle of an alternating current
pass, its output will be unidirectional and it may be considered a
rectifying element.
DIRECT CURRENT (DC)
An electric current which flows in one direction only.
DOUBLE-POLE SWITCH
A switch which opens or closes two isolated circuits at the same
time. It is actually two switches in one housing operated by a
common handle.
DOUBLE-THROW SWITCH
A switch which connects one circuit to either of two other
isolated circuits.
DRIFT
A gradual change in output at constant load sometimes caused
by a change in temperature.
DROOP COMPENSATION
A system which permits generators in parallel to share the reactive component of the power in proportion to their rating. This
system is so named because the voltage droops as the machines
become loaded. See also CROSS CURRENT COMPENSATION.
DROOP TYPE GOVERNOR
A governor that controls engine speed at a slightly higher point at
no load that at full load. Normally set for desired speed at full load.
EDDY CURRENT
Current circulating in conducting materials, caused by magnetic
fields. They represent losses in generators and are reduced by
the use of thin laminations of special steel.
EFFECTIVE VALUE
That value of a sinusoidally varying wave which produces steady
effects. For example, on a current wave it would be that portion
which produces heating or lighting. It is the R.M.S. (root mean
square) value of the wave and for sinusoidal variations its value
would be 0.707 times the maximum value. Most voltmeters and
ammeters indicate R.M.S. values.
EFFICIENCY
The efficiency of a generator set shall be defined as the ratio (expressed as a percentage) of its useful power outputs to its total
power input.
EGRESS LIGHTING
The illumination of means of egress (leaving) of a building or
structure.
ELECTRICAL DEGREE
One 360th part of a cycle of an alternating current or wave.
ELECTRICAL RADIAN
A part of an alternating current or voltage cycle; a cycle contains
2 radians.
ELECTRO-MAGNETIC FIELD
A magnetic field generated by the passage of current through a
coil surrounding a ferrous pole structure.
ELECTRO-MOTIVE FORCE (EMF)
The force which causes current to flow in a conductor; in other
words, the voltage or potential.
EMERGENCY POWER
An independent reserve source of electric energy which upon
failure or outage of the normal source, automatically provides reliable electric power within a specified time to critical devices and
equipment whose failure to operate satisfactorily would jeopardize
the health and safety of personnel or result in damage to property.
ENERGY
Capability of performing work. Expressed electrically in KW hours.
EXCITATION
The input of DC power into the field coils of a synchronous
generator, producing the magnetic flux required for inducing voltages.
EXCITER
A device for supplying excitation to generator fields. It may be
a rotating exciter, that is a DC generator of AC generator with
rectifiers, or it may be a static device using tubes or solid-state
components.
EXIT LIGHTING
The illumination of exit signs in buildings and structures.
FEEDBACK, NEGATIVE
Negative feedback is a feedback signal in a direction to reduce
the variable which the feedback represents.
FEEDBACK, POSITIVE
Positive feedback is a feedback signal in a direction to increase
the variable which the feedback represents.
FIELD
A region of space under magnetic influence resulting in a distribution of magnetic lines or flux in that space. The field may be
produced electrically or by means of permanent magnets.
FIELD COIL
The coils of the field structure being supplied with direct current
for excitation.
FIELD POLE
The part of the magnetic structure of a generator on which the
field coils are located.
FLUX
Magnetic lines of force.
FLUX DENSITY
Magnetic lines of force per unit of area.
FRAME
The mechanical portion of a generator consisting of all the nonrotating parts.
FREQUENCY
The number of complete cycles of an alternating voltage or current per unit of time, usually per second. So expressed in CPS,
cycle per second, or Hertz (Hz).
FREQUENCY BAND
The permissible variation from a mean value under steady state
conditions.
FREQUENCY DRIFT
Frequency drift is a gradual deviation of the mean governed
frequency above or below the desired frequency under a
constant load.
FREQUENCY DROOP
The change in frequency between steady state no load and
steady state full load which is a function of the engine and
governing systems.
FREQUENCY REGULATION
The percentage change in frequency from steady state no load
to steady state full load, which is a function of the engine and
governing system.
%R =
Fnl – Ffl x 100
Ffl
FREQUENCY RECOVERY TIME
The interval of time required for the frequency to return to
and remain with a prescribed frequency band following an
instantaneous load change.
FREQUENCY TRANSIENT
The maximum frequency deviation as a result of a sudden
change in load.
FULL LOAD CURRENT
The full load current of a machine or apparatus is the value of
current in RMS or DC amperes which it carries when delivering
its rated output under its rated conditions. Normally, the full load
current is the “rated” current.
FUNDAMENTAL FREQUENCY
Design frequency.
GENERATOR
A general name for a device for converting mechanical energy
into electrical energy. The electrical energy may be direct current (D.C.) or alternating current (A.C.). An A.C. generator may be
called an alternator.
GENERATOR CONSTANTS
Direct-Axis Synchronous Reactance (Xd). Used to determine
current flow at steady-state conditions.
Direct-Axis Transient Reactance (X’d). Used to calculate the
short circuit current produced by the generator after the first
few cycles following a fault (six cycles to five seconds). Also
used to determine voltage dips resulting from load applications.
Direct-Axis Subtransient Reactance (X”d). This is the
apparent reactance of the stator winding at the instant short
circuit occurs. It is used to calculate the current flow during the
first few cycles after a short circuit. The subtransient reactance
is important when determining the required capacity of a circuit
breaker to interrupt a fault within a system.
Negative Sequence Reactance (X2). Used to determine
line-to-line short circuit currents.
Zero Sequence Reactance (X0). Used to determine line-to neutral short circuit currents.
Potier Reactance (Xp). Used to calculate excitation of the
generator at different loads and power factors.
Direct-Axis Transient Short-Circuit Time Constant (T’d).
Time (seconds) for the slowly decreasing component of the
armature current to reach 36.8 percent of its initial value after
application of a short-circuit condition when the unit is running
at rated speed.
Direct-Axis Subtransient Short-Circuit Time Constant (T”d).
Time (seconds) for the rapidly decreasing component of the
armature current (present during the first few cycles after a
short circuit) to reach 36.8 percent of its initial value after
sudden application of a short-circuit condition when the unit is
running at rated speed.
Direct-Axis Transient Open-Circuit Time Constant (T’do).
Time measured in seconds for the open circuit voltage of the
armature to drop to 36.8 percent of its initial value after the
field winding is shorted with the unit running at rated speed.
GOVERNOR
A device used to control prime mover speed.
GRID POWER
Same as COMMERCIAL POWER.
GROUND
A connection, either intentional or accidental, between an electric
circuit and the earth or some conducting body serving in place of
the earth.
GROUNDED NEUTRAL
A point of an electrical system which is intentionally connected to
ground. This current may or may not carry current.
HARMONIC
Deviations from the fundamental frequency sine wave can be
expressed as additional sine waves of frequencies which are a
multiple of the generated frequency. The additional frequencies
are called harmonics. They are expressed as third, fifth, etc.,
harmonics, denoting their frequency as a multiple of the main
frequency.
HARMONIC CONTENT
The harmonic content of a voltage waveform is a measure of the
presence of harmonics in the waveform expressed as a percentage of the fundamental frequency at each harmonic. The total
harmonic content is expressed as the square root of the sum of
the squares of each of the harmonic amplitudes (expressed as
percentage of the fundamental).
HEAT SINK
A device which conducts heat away from electronic devices.
HERTZ (Hz)
A term replacing cycles per second as an indication for frequency.
HUNTING
The oscillation of voltage or frequency above and below the
mean value. An unstable condition.
IMPEDANCE
The total opposition offered by a circuit to the flow of alternating
current. It is composed of resistance and reactance (inductive
and/or capacitive) and its symbol “Z” is expressed in OHMS.
INDUCED VOLTAGE
The voltage which is produced in a conductor which has motion
relative to a magnetic field, while under the influence of the field.
INDUCTANCE
The property of an electric circuit that opposes any change in
current flow. Expressed in henrys and its symbol is L.
INHERENT VOLTAGE DROOP
The decrease in voltage of an unregulated generator from no load
to full load with excitation fixed at 100% volts no load.
INRUSH CURRENT
The inrush current of a machine or apparatus is the maximum
value of RMS or DC amperes which it carries after being suddenly and fully energized and prior to reaching a stable operating
condition.
INHERENT VOLTAGE REGULATION
The inherent voltage droop expressed as a percentage.
INSULATION
Non-conductive material used to prevent leakage of electric
power from a conductor.
INSULATION RESISTANCE
The resistance that an insulating material has to the passage of
current to ground or to another conductor. It is usually measured
in megohms.
INTERMITTENT OVERLOAD
The power in excess of rated power which a generator is capable
of delivering, without damage, for a specified period of time.
IR DROP
Voltage drop across a resistance. Equal to the current in amperes
times the resistance in ohms.
IRON LOSS
That portion of generator losses involved in magnetic structures
caused by the magnetization of the iron. It depends of the flux
density, frequency, lamination thickness and chemical composition. These losses are composed of eddy current losses and
hysteresis losses.
ISOCHRONOUS GOVERNOR
A governor that maintains constant engine speed from no load to
full load. The isochronous governor is a zero droop governor.
KVA
1,000 Volt amperes (Apparent power). Equal to KW divided by the
P.F.
KW
1,000 Watts (Real power). Equal to KVA times P.F.
KVAR
1,000 Volt amp reactive (Reactive power).
KW HR
1 KW x 1 hr = 1KW HR. Unit of electric energy or work.
LAGGING POWER FACTOR
Caused by inductive loads, such as motors and transformers, in
which the current lags behind the voltage in an alternating current
network. See POWER FACTOR.
LAMINATED CORE
A ferromagnetic core consisting of a number of thin laminations
of steel, forming a magnetic path.
LEADING POWER FACTOR
Leading power factor in AC circuits (0.0 to 1.0) is caused by
capacitive loads or overexcited synchronous motors which cause
the current to lead the voltage. See POWER FACTOR.
LEG
A leg is a phase winding of a generator, or a phase conductor of
a distribution system.
MOLDED CASE CIRCUIT BREAKER
A molded case circuit breaker automatically interrupts the current
flowing through it when the current exceeds a certain level for a
specified time. Molded case refers to the use of a molded plastic
as the medium of electrical insulation for enclosing the mechanisms (earthed) metal parts.
LINE TO NEUTRAL VOLTAGE
The voltage existing between any phase conductor and the
neutral conductor.
MOTORING
In paralleling applications, unless a generator set is disconnected
from the bus when its engine fails (usually as a result of a fuel
system problem), the generator will drive (motor) the engine,
drawing power from the bus. Reverse power protection which
automatically disconnects a failed set from the bus is essential
from paralleling systems. Also, in certain applications such as
elevators, the load can motor the generator set if insufficient
additional load is present.
LOAD FACTOR
The load factor is the ratio of the average load to the generator
set power rating.
NEC
National Electrical Code. This document is the most commonly
referenced general electrical standard in the United States.
LOSSES
The difference between the input and the useful output of an
electric or mechanical device. See EFFICIENCY.
NEMA
National Electrical Manufactures Association
LINE TO LINE VOLTAGE
The voltage existing between any two conductors in polyphase
circuits, the voltage between phase conductors.
LOW VOLTAGE
In the context of this manual, low voltage refers to AC system
operating voltages from 120 to 600 VAC.
MAIN BREAKER
A main breaker is a circuit breaker at the input or output of the
bus, through which all of the bus power must flow. The generator
main breaker is the device, usually mounted on the generator set,
which can be used to interrupt generator set power output.
MAGNETIC LINES OF FORCE
Theoretical, invisible paths along which magnetic forces act in a
magnetic field.
MAGNETIC SATURATION
The point at which an increase in excitation current produces little
or no increase in flux density.
MANUAL TRANSFER SWITCH
A manually operated device for transferring an electrical load
from one power source to another.
MEAN GOVERNED SPEED
The average speed during a given period when an engine
generator set is operating under a sustained electrical load
with governing system in control. It is the arithmetic mean of all
instantaneous values of speed occurring during the period under
consideration.
MEDIUM VOLTAGE
In the context of this manual, medium voltage refers to AC
system operating voltages from 601 to 15,000 VAC.
MEGGER OR MEGOHMMETER
A high range ohmmeter utilizing a power source for measuring
insulation resistance.
NFPA
National Fire Protection Association
NEUTRAL
The point common to all phases of a polyphase circuit, a conductor connected to that point or the return conductor in a single
phase circuit.
NO BREAK POWER
Same as UNINTERRUPTED POWER.
NO LOAD POWER
No load power for a generator set is a state of operation at rated
speed wherein all control, monitoring and excitation circuits or
devices are energized and functioning and it is only necessary to
close the output switching device to provide power to the load.
In the event the generator set is equipped with more than one
power producing device, such as a battery charger, then these
devices shall be treated as separate power producing devices
whose no load state shall be as described above.
NONLINEAR LOAD
A nonlinear load is a load for which the relationship between voltage and current is not a linear function. Some common nonlinear loads are fluorescent lighting, SCR motor starters and UPS
systems. Nonlinear loads cause abnormal conductor heating and
voltage distortion.
OCTAVE BAND
In sound pressure measurements (using an octave band analyzer), octave bands are the eight divisions of the measured sound
frequency spectrum, where the highest frequency of each band is
twice that of its lowest frequency. The octave bands are specified
by their center frequencies, typically: 63, 125, 250, 500, 1,000,
2,000, 4,000 and 8,000 Hz (cycles per second).
OHM
Unit of electrical resistance. One volt will cause a current of one
ampere to flow through a resistance of one ohm.
OHMMETER
A device for measuring electrical resistance.
OIL HEATER
See BLOCK HEATER
ONE-LINE DIAGRAM
A one-line diagram is a schematic diagram of a three-phase
power distribution system which uses one line to show all three
phases. It is understood when using this easy to read drawing
that one line represents three.
OUT-OF-PHASE
The overload rating of a device is the load in excess of the
nominal rating the device can carry for a specified length of time
without being damaged.
OVERSHOOT
Overshoot refers to the amount by which voltage of frequency
exceeds the nominal value as the voltage regulator or governor
responds to change in load.
OPEN-CIRCUIT VOLTAGE
The voltage produced when no load is attached to the voltage
source, such as a generator.
OVERLOAD POWER
Overload power is that load in excess of rated load which the
generator set is capable of delivering for a specified period of
time. It should be recognized that the voltage, frequency and
operating temperature may differ from normal rated values.
OVERLOAD RELAY
A device which functions when a predetermined value of current
is reached or exceeded.
OVERSHOOT
The amount by which a quantity such as voltage or frequency
exceeds the nominal value after initial correction for a sudden
load change.
OUT-OF-PHASE
A condition in which the A.C. voltage waves of two generating
systems do not coincide.
PARALLEL CONNECTION
The procedure used to connect two or more generators in
parallel, that is, connect them to a common load.
PARALLEL OPERATION
Two or more generators of the same phase, voltage and
frequency characteristics supplying the same load.
PARALLELING
The procedure used to connect two or more generators in
parallel, that is, connect them to a common load.
PEAK LOAD
Peak load is the highest point in the kilowatt demand curve of a
facility. This is used as the basis for the utility company’s demand
charge.
PEAK SHAVING
Peak shaving is the process by which loads in a facility are
reduced for a short time to limit maximum electrical demand in
a facility and to avoid a portion of the demand charges from the
local utility.
PHASE
The number of complete voltage and/or current sine waves
generated per 360 electrical degrees. Each phase requires a
complete set of windings.
PHASE ANGLE
The relation between the sinusoidally varying quantities of voltage
and current at the same frequency which do not pass through
positive maximum at the same instant. One cycle is considered
to contain 360 degrees. The extent by which the zero points differ
is expressed as a part of the total of 360 degrees. See POWER
FACTOR.
PHASE ROTATION
The sequence in which the phases of a generator or network
pass through the positive maximum points of their waves. The
same sequence must exist when units are paralleled.
PITCH
Pitch is the ratio of the number of generator stator winding slots
enclosed by each coil to the number of winding slots per pole. It
is a mechanical design characteristic the generator designer may
use to optimize generator cost verse voltage wave form quality.
POLE
A part of a magnetic structure, there being two such parts, called
a North pole and a South pole. Since neither pole can exist
without the corresponding opposite, they always are present in
pairs. Hence a generator always has an even number of poles.
This term “pole” or “poles” may also be used to indicate the
number of circuits affected by a switch.
POLYPHASE
Separate complete voltage and/or current sine waves, each of
360 electrical degrees in length, occurring equally spaced within
360 electrical degrees. E.G. Three phase is three complete
separate sine waves spaced 120 electrical degrees apart. Two
phase is two complete separate sine waves spaced 180 electrical
degrees apart.
POWER
Rate of performing work, or energy per unit of time. Mechanical power can be measured in horsepower, electrical power in
kilowatts.
POWER CIRCUIT BREAKER
A power circuit breaker is a circuit breaker whose contacts are
forced closed via a spring-charged, over-center mechanism to
achieve a fast closing (5-cycle) and high withstand and interrupting ratings. A power circuit breaker can be an insulated case or
power air circuit breaker.
POWER FACTOR
(also cos 0) In a-c circuits, the inductances and capacitances
may cause the point at which the voltage wave passes through
zero to differ from the point at which the current wave passes
through zero. When the current wave precedes the voltage wave,
a leading power factor results. This is generally the case. The
power factor expresses the extent to which voltage zero differs from the current zero. Considering one full cycle to be 360
degrees, the difference between the zero points can then be expressed as an angle 0. Power factor is calculated as the cosine of
the 0 between zero points and is expressed as a decimal fraction
(.8) or as a percentage (80%). It can also be shown to be the ratio
of KW, divided by the KVA. In other words, KW = KVA x P.F.
PRECISE POWER
A descriptive term used to denote high quality power delivered by
a generator set. Definitions of precise power vary greatly.
PRIME POWER
That source of supply of electrical energy utilized by the user
which is normally available continuously day and night, usually
supplied by an electric utility company but sometimes by owner
generation.
PRIME POWER RATING
The prime power rating is applicable when supplying electrical
power in lieu of commercially purchased power. Prime power is
available for an unlimited number of annual operating hours in
variable load applications. Applications requiring any utility
parallel operation at constant load are subject to running time
limitations. In variable load applications, the average load factor
should not exceed 70% of the Prime Power Rating. A 10 percent
overload capability is available for a period of 1 hour within a 12
hour period of operation, but not to exceed 25 hours per year.
(Equivalent to Prime Power in accordance with ISO8528 and Over
Load Power in accordance with ISO3046, AS2789, DIN6271 and
BS5514.)
RADIO INTERFERENCE
Radio Interference refers to the interference with radio reception
caused by a generator set.
RADIO INTERFERECNE SUPPRESSION
Radio interference suppression refers to eh methods employed to
minimize radio interference.
RATED CURRENT
The rated continuous current of a machine or apparatus is
the value of current in RMS or DC amperes which it can carry
continuously in normal service without exceeding the allowable
temperature rises. Also see FULL LOAD CURRENT.
RATED POWER
The stated or guaranteed net electric output which is obtainable
continuously from a generator set when it is functioning at rated
conditions. If the set is equipped with additional power producing
devices, then the stated or guaranteed net electric power must
take into consideration that the auxiliaries are delivering their respective stated or guaranteed net output simultaneously, unless
otherwise agreed to. See EFFICIENCY.
RATED SPEED
Revolutions per minute at which the set is designed to operate.
RATED VOLTAGE
The rated voltage of an engine generator set is the voltage at
which it is designed to operate.
REACTIVE KVA (KVAR)
An a-c value consists of active and wattles components. The active component is expressed in KW, the wattles component in
Reactive KVA. The resultant KVA is calculated from KVA = KW2 +
KVAR2.
REAL POWER
A term used to describe the product of current, voltage and
power factor, expressed in KW.
RECTIFIER
A device that converts AC to DC. See DIODE.
RELAY
An electrically operated switch usually used in control circuits
and whose contacts are considered low amperage, compared to
a contactor.
RESIDUAL MAGNETISM
The magnet induction which remains after the magneto-motive
force is removed.
RESISTANCE
Opposition to the flow of current. See OHM
RESPONSE TIME
The ability to quickly recover to the steady state operating value
after a sudden change in load.
RIPPLE VOLTAGE
The varying component of the unidirectional voltage from a
source of direct current power.
ROOT MEAN SQUARE (RMS)
The conventional measurement of alternating current and voltage
and represents a proportional value of the true sine wave.
ROTOR
The rotating element of a motor or generator.
REVOLUTIONS PER MINUTE
RPM
SCR
(Silicon Controlled Rectifier) A SCR is a three-electrode solidstate device which permits current to flow in one direction only,
and does this only when a suitable potential is applied to the third
electrode, called the gate.
SATURATION
A core is said to have reached saturation when an increase in
excitation produces little or no increase in flux density.
REACTANCE
The out-of-phase component of impedance that occurs in circuits containing inductance and/or capacitance.
SECONDARY
That part of a transformer to which the load is connected; it receives energy from the primary or input side through
electromagnetic induction.
REACTIVE POWER
Reactive power is the product of current, voltage and the sine of
the angle by which current leads or lags voltage and
is expressed as VAR (volts-amperes-reactive).
SELECTIVE COORDINATION
Selective coordination is the selective application of over-current
devices such that short circuit faults are cleared by the device
immediately on the line side of the fault, and only by that device.
SELECT SWITCH
A manually operated multi-position switch for selecting an
alternative control circuit.
SERIES CONNECTION
An electrical connection in which the output terminal of one
element is connected to the input terminal of another element,
thereby providing one path for current flow.
SOUND PRESSURE LEVEL (SPL)
Sound pressure level refers to the magnitude of the pressure differential caused by a sound wave. It is expressed on a dB scale
(A, B, C) referenced to some standard (usually 10-12 microbars).
SERVICE ENTRANCE
The service entrance is the point where the utility service enters
the facility. In low voltage systems the neutral is grounded at the
service entrance.
SPEED DRIFT
A gradual deviation of the mean governed speed above or below
the desired speed. See FREQUENCY DRIFT.
SHORT CIRCUIT
Generally an unintentional electrical contact between current
carrying parts resulting in the passage of current through an
undesirable path.
SHORT-OUT
To by-pass or remove a device from the circuit by connecting a
jumper across its terminals.
SHUNT CONNECTION
Parallel connection in which the terminals of two or more devices
are connected together.
SHUNT TRIP
Shunt trip is a feature added to a circuit breaker or fusible switch
to permit the remote opening of the breaker or switch by an
electrical signal.
SIGNAL
A signal is information which can be transmitted in a system.
SILICON-CONTROLLED RECTIFIER (SCR)
Solid state device, similar to diode, which permits current to
flow in one direction only when triggered by a suitable potential
applied to the control lead or terminal, called the gate.
SINE WAVE
A wave which represents the sine of angles on the vertical scale
and the corresponding angles on the horizontal scale. A-C
voltage and current waves approximate such a curve.
SINGLE PHASE
An A.C. load or source of power normally having only two input
terminals if a load or two output terminals if a source.
SLIP RINGS
See COLLECTOR RINGS.
SOFT LOADING
Soft loading refers to the ramping of load onto or off of a generator in a gradual fashion for the purpose of minimizing voltage and
frequency transients on the system.
SOUND
Sound is considered both in terms of the sound pressure waves
traveling in air (pressures superimposed on the atmospheric
pressure) and the corresponding aural sensation. Sound can be
“structure-borne”, that is, transmitted through any solid elastic
medium, but is audible only at points where the solid medium
“radiates” the pressure waves into the air.
SOUND LEVEL METER
A sound level meter measures sound pressure level. It has
several frequency weighted decibel (dB) scales (A,B,C) to cover
different portions of the range of measured loudness. Sound level
meters indicate RMS sound, unless the measurements are qualified as instantaneous or peak sound level.
SPEED DROOP
The change in speed between steady state no load and steady
state full load. See FREQUENCY DROOP.
SPEED REGULATION
The percentage change in speed at constant loads between
steady state no load and steady state full load.
STABILITY
See RESPONSE TIME.
STANDBY POWER
An independent reserve source of electrical energy which upon
failure or outage of the normal source, provides electric power of
acceptable quality and quantity so that the user’s facilities may
continue in satisfactory operation.
STANDBY POWER RATING
The standby power rating is applicable to emergency power
applications where power is supplied for the duration of normal
power interruption. No sustained overload capability is available
for this rating. (Equivalent to Fuel Stop Power in accordance with
ISO3046, AS2789, DIN6271 and BS5514).This rating is applicable
to installations served by a reliable normal utility source. This
rating is only applicable to variable loads with an average load
factor of 80 percent of the standby rating for a maximum of 200
hours of operation per year. In installations served by unreliable utility sources (where outages last longer and occur more
frequently), where operation will likely exceed 200 hours per year,
the prime power rating should be applied. The standby rating is
only applicable to emergency and standby applications where the
generator set serves as the back-up to the normal utility source.
No sustained utility parallel operation is permitted with this rating.
For applications requiring sustained utility parallel operation, the
prime power or base load rating must be utilized.
STANDBY SYSTEM
A standby system is an independent power system that allows
operation of a facility in the event of normal power failure.
STAR CONNECTION
See WYE CONNECTION.
STARTING CURRENT
The initial value of current drawn by a motor when it is started
from standstill and voltage is applied across its terminals.
Commonly referred to as locked-rotor current. See INRUSH
CURRENT.
STATIC EXCITER
A solid state, non-rotating device for finishing direct current to
the generator field.
STATOR
The stationary part of a generator or motor.
STATOR WINDING
The winding in which the output voltage is induced, in revolvingfield type generators.
STEADY STATE
The operating point under constant load when all fluctuations due
to transients have been eliminated.
STEADY STATE FREQUENCY
The mean governed frequency occurring when engine generator
is functioning with a steady state electrical load.
STEADY STATE SPEED
The mean governed speed occurring when the engine generator
is functioning with a steady state electrical load.
STEADY STATE VOLTAGE
The steady state voltage of an engine generator set is the value
of output voltage when the set is operating at a steady state
condition; that is, at constant load, under stabilized conditions
and with all fluctuations due to a transient or transients having
been eliminated.
SURGE
A sudden transient variation in current, voltage or frequency.
SURGE SUPPRESSOR
Surge suppressors are devices capable of conducting high
transient voltages. They are used for protecting other devices
that could be destroyed by the transient voltages.
SYNCHRONISM
The state of being of the same frequency and in-phase.
SYNCHRONIZING
To match one wave to another by adjusting ones’ frequency and
phase angle until the two coincide.
SYNCHRONOUS
Applied to a type of motor or generator in which the relation
between frequency in cycles per second and the speed in RPM is
fixed and invariable.
SYNCHRONOUS GENERATOR
A synchronous generator is an AC generator having a DC exciter.
Synchronous generators are used as stand-alone generators for
emergency power and can also be paralleled with other synchronous generators and the utility system.
TACHOMETER
A device for measuring rotative speed usually expressed in RPM.
TAP
A connection point in the body of a coil or resistor.
TELEPHONE INFLUENCE FACTOR (TIF)
The telephone influence factor of a synchronous generator is a
measure of the possible effect of harmonics in the generator voltage wave on telephone circuits. TIF is measured at the generator
terminals on open circuit at rated voltage and frequency.
TEMPERATURE DRIFT
A condition in which temperature changes cause a regulated
value to deviate from the nominal value. See DRIFT.
TERMINAL
A fitting for convenience in making electrical connections.
THERMOCOUPLE
A device for measuring temperature. It consists of a connection
between two wires of dissimilar material which generates a small
voltage proportional to the temperature of the ambient.
THREE-PHASE
See POLYPHASE.
TIME CONSTANT
The time required to change from one condition to another,
usually a decay or build-up rate.
TRANSFORMER
A component consisting of two or more coils that are coupled
together by magnetic induction and used to transfer electric
energy from one circuit to another without change in frequency
but usually with changed values of voltage and
current.
TRANSIENT
That part of the variation in a variable during transition from one
steady-state operating condition to another and which ultimately
disappears.
TRANSIENT VOLTAGE
The transient voltage is the absolute value of voltage appearing
during the transition from one operating condition to another.
Performance requirements covering an engine generator set may
specify the limiting band width for transient voltages occurring at
defined load changes.
UNINTERRUPTIBLE POWER SUPPLY (UPS)
A system designed to provide power without delay or transients,
during any period when the normal power supply is incapable of
performing acceptably.
UNDERSHOOT
The amount by which quantity such as voltage or frequency
drops below the nominal value after initial correction for a sudden
load change.
UNIDIRECTIONAL CURRENT
A current which flows in one direction only. It is also called direct
current.
UNITY POWER FACTOR
A load whose power factor is 1.0 has no reactances causing the
voltage wave to lag or lead the current wave.
UTILITY POWER
The same as COMMERCIAL POWER.
VOLT
The volt is a unit of electrical potential. A potential of one volt will
cause a current of one ampere to flow through a resistance of
one ohm.
VOLTAGE BALANCE
The voltage balance of an engine generator set is a measure of
the line to line, or line to neutral voltages with equal loads. It is
expressed as a percentage of the maximum difference divided by
the rated voltage, unless otherwise specified.
VOLTAGE DIP
The maximum reduction in voltage resulting from an increase in load.
VOLTAGE DRIFT
A gradual deviation of the mean regulated voltage above or
below the desired voltage under a constant load.
VOLTAGE DROOP
The change in voltage between steady state no load and steady
state full load which is a function of the regulator and paralleling
components.
VOLTAGE DROP
The reduction in voltage, caused by the current which flows
through a resistance. Equal to the product of current and
resistance.
VOLTAGE RANGE
The voltage range of an engine generator set is a performance
requirement which states the band width of voltage through
which the set should be capable of adjustment and operation
at any load from no load through full load and at specified design
conditions.
WIRING HARNESS
A pre-assembled group of wires of the correct length and
arrangement to facilitate interconnection.
WYE CONNECTION
Same as STAR CONNECTION. A method of interconnecting the
phases of a three phase system to form a configuration resembling the letter Y. A fourth or neutral wire can be connected to the
center point.
ZERO SEQUENCE
Zero sequence is a method of ground fault detection that utilizes
a sensor (CT) that encircles all the phase conductors as well as
the neutral conductors. The sensor will produce an output proportional to the imbalance of current ground fault in the circuit.
This output is then measured by a relay to initiate circuit breaker
tripping or ground fault alarm.
ZONES OF PROTECTION
Zones of protection are defined areas within a distribution system
that are protected by specific groups of protective sensing and
interrupting devices.
VOLTAGE RECOVERY TIME
The time required for the voltage to return to and remain within
the permissible voltage steady state band after a transient.
VOLTAGE REGULATION
The voltage regulation of an engine generator set is the difference
between the mean regulated no load and the mean regulated
full load output voltage expressed as a percentage of the mean
regulated full load voltage.
VOLTAGE REGULATOR
A device which maintains the voltage output of a generator nears
its nominal value.
VOLTAGE UNBALANCE
See VOLTAGE BALANCE.
VOLTMETER
An instrument for measuring voltage.
WATT
Unit of electric power. In direct current equals volts times
amperes. In alternating current equals effective volts times
effective amps times power factor times a constant dependent
on the number of phases. 1,000 watts equals 1 kilowatt.
WATT-HOUR
Unit of electrical energy equal to one watt of power consumed
during an hour.
WAVEFORM
The shape of a wave, graphically represented.
WINDING
All the coils of a generator. Stator winding consists of a number
of stator coils and their interconnections. Rotor windings consist
of all windings and connections on the rotor poles.
www.clarkegen.com
8015 Piedmont Triad Parkway, Greensboro, NC 27409, USA
Tel +1-336-292-9240 Toll Free: 1-866-334-4367
G131369 Rev A
13 APRIL 2012
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