Today, we will start the explanation of Generator Sizing Calculations and as usual we start by the glossary of all terms and expressions that we will deal with through our explanation of Generator Sizing Calculations.
This glossary will help you to understand the technical meaning for any term or expression which will facilitate your understanding for the Generator Sizing Calculations.
Please read this glossary carefully because you will need to come back to it while our explanation for Generator Sizing Calculations.
Glossary of Generators – Part One |
Alternating Current (AC) |
Alternating
Current (AC) is electric current that alternates between a positive maximum
value and a negative maximum value at a characteristic frequency, usually 50
or 60 cycles per second (Hertz).
|
ANSI
|
American
National Standards Institute.
|
Acoustic
Material
|
Acoustic
material is any material considered in terms of its acoustic properties,
especially its 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 generator set's engine and is
limited by the horsepower of the engine. Active power does the work of
heating, turning motor shafts, etc.
|
Air Circuit Breaker |
An
air circuit breaker automatically interrupts the current flowing through it
when the current exceeds the trip rating of the breaker. Air is the medium of
electrical insulation between electrically live parts and grounded (earthed)
metal parts.
|
Alternator
|
Alternator
is another term for AC generator.
|
Amortisseur Windings |
The
amortisseur windings of a synchronous AC generator are the conductors
embedded in the pole faces of the rotor. They are connected together at both
ends of the poles by end rings or end plates. Their function is to dampen
waveform distortion during load changes.
|
Ampacity
|
Ampacity
is the safe current-carrying capacity of an electrical conductor in amperes
as defined by code.
|
Ampere
|
The
ampere is a unit of electric current flow. One ampere of current will flow
when a potential of one volt is applied across a resistance of one ohm.
|
Annunciator
|
An
annunciator is an accessory device used to give remote indication of the
status of an operating component in a system. Annunciators 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
|
Apparent
power is the product of current and voltage, expressed as kVA. It is real
power (kW) divided by the power factor (PF).
|
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.
|
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.
|
Automatic
(Exciter) Paralleling
|
Automatic
(Exciter) Paralleling describes a system where two or more generator sets can
be started and paralleled while coming up to rated frequency and voltage.
Because the generator excitation system is not turned on until the generator
set is started (thus the term "dead field"), the generator sets
automatically synchronize as they come to rated speed and voltage.
|
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.
|
Bandwidth
|
The
amount of data that can be transmitted in a fixed amount of time. For digital
devices, it is expressed as bits per second, or bytes per second. For analog
devices, it is usually expressed as cycles per second, or Hertz.
|
Base
Load
|
Base
load is that portion of a building load demand which is constant. It is the "base"
of the building demand curve.
|
Baud
Rate
|
The
speed of data transmission in serial data communications approximately equal
to the number of code elements (bits) per second (BPS). Bits per second are
also termed BPS, with the prefix (k) denoting thousands.
|
Binding
|
The
process of making the logical connections to the network (also called
connecting). This involves connecting network variable outputs to network
variable inputs using LonWorks software.
|
Bit
|
Binary
Digit.
|
Black
Start
|
Black
Start refers to the starting of a power system with its own power sources,
without the assistance from external power supplies.
|
Boolean
|
A
logical system used to express one of two states, such as on or off (yes or
no, 1 or 0, etc.)
|
Bound
|
A
network communication technique whereby a node automatically receives a
network variable from a sender node whenever the sender node sends it out.
Whenever this condition exists, the node is said to be "bound".
|
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 generators
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.
|
Bus
Bars
|
Bus
Bars are rectangular copper or aluminum bars that connect the output of the
generator set circuit breakers to the transfer switches, circuit breakers, or
fusible switches that transfer power to the load. The bus bars are sized and
assembled in multiples according to the current they must carry under load. A
typical sizing criteria for copper bus bars rated from 500-5,000 amps is to maintain
a current density of 1,000 amps per square inch of cross-sectional area. This
results in a bus temperature rise at full load that is within acceptable
limits.
|
Bus
Capacity
|
Bus
capacity is the maximum load that can be carried on a system without causing
degradation of the generator frequency to less than a prescribed level
(usually 59 Hz in a 60 Hz system).
|
CT
(Current Transformer)
|
Current
transformers are instrument transformers used in conjunction with ammeters,
control circuits and protective relaying. They usually have 5 ampere
secondaries.
|
Cellular
|
Refers
to a communication system that divides geographic regions into sections
called cells. The purpose of this division is to make the most use of the
limited number of transmission frequencies.
|
Channel
|
A
Channel is the physical communications media that connects the devices and
the properties of these media (such as transmission speed). Most PowerCommand
network installations will have only one channel (UTP cable and 78 KBPS
transmission speed). In a large network, there may be multiple channels and
each channel may or may not be of the same media type. Typically, channels
are linked together using routers.
|
Channel
Terminator
|
This
is used to terminate networks on devices that do not have terminate switches.
These are devices such as Gateways, RCI's, Routers, etc. that do not
terminate circuits built into their design.
|
Circuit
|
A
circuit is a path for an electric current across a potential (voltage).
|
Circuit
Breaker
|
A
circuit breaker is a protective device that automatically interrupts the
current flowing through it when that current exceeds a certain value for a
specified period of time. See Air Circuit Breaker, Main Breaker, Molded Case
Circuit Breaker and Power Circuit Breaker.
|
Circulating
Harmonic Currents
|
Circulating
Harmonic Currents are currents that flow because of differences in voltage
waveforms between paralleled power sources, or induced by operation of
non-linear loads.
|
Comma
Separated Value (CSV)
|
A
record layout that separates data fields with a comma and usually surrounds
character data with quotes. PowerCommand for windows uses the CSV record
format.
|
Connecting
Devices
|
Connecting
to refers to the process of assigning connections--linking an output variable
of one device to an input variable of another device. This process is also
called "binding".
|
Contactor
|
A
contactor is a device for opening and closing an electric power circuit.
|
Continuous
Load
|
A
continuous load is a load where the maximum current is expected to continue
for three hours or more (as defined by the NEC for design calculations).
|
Cross
Current
|
Cross
currents are currents that circulate between paralleled generator sets when
the internal (excitation) voltage of one genset is different from the other
genset(s). The genset with the higher internal voltage supplies reactive
power (kVAR) to the other genset(s). The amount of cross current that flows
is a measure of this reactive power. Cross currents are 90 degrees out of
phase (lagging) compared to the current that the generator would supply at
1.0 (unity) power factor.
|
Cross
Current Compensation
|
Cross
current compensation is a method of controlling the reactive power supplied
by AC generators in a paralleling system so that they share equally the total
reactive load on the bus without significant voltage droop.
|
Cross
Current Transformer (CCT)
|
Cross
Current Transformers are used to step down the higher line current to a lower
current that the control system was designed for.
|
Current
|
Current
is the flow of electric charge. Its unit of measure is the 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.
|
Cycle
|
A
cycle is one complete reversal of an alternating current or voltage from zero
to a positive maximum to zero again and then from zero to a negative maximum
to zero again. The number of cycles per second is the frequency.
|
Dead
Bus
|
Dead
Bus refers to the de-energized state of the power connections between outputs
of paralleled generator sets. The term bus in this usage can either be rigid
solid bus bars or insulated flexible cables.
|
Dead
Field Paralleling
|
Automatic
(Exciter) Paralleling
|
Delta
Connection
|
Delta
connection refers to a three phase connection in which the start of each
phase is connected to the end of the next phase, forming the triangle-shaped
Greek letter Delta. The load lines are connected to the corners of the
triangle.
|
Demand
Mode Standby Unit(s) (DMSU)
|
Demand
Mode Standby Units are generator sets that can be shut down by the system
when there is a low load level on the system.
|
Deviation
Factor
|
The
deviation factor is the maximum instantaneous deviation, in percent, of the
generator voltage from a true sine wave of the same RMS value and frequency.
|
Dielectric
Strength
|
Dielectric
strength is the ability of insulation to withstand voltage without breaking
down.
|
Differential
Relay
|
A
differential relay is a protective device that is fed by current transformers
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.
|
Digital
Master Control (DMC)
|
This
device is designed to control the power systems in a facility. It is offered
as an option on Cummins switchgear.
|
Direct
Current (DC)
|
Direct
current is current with no reversals in polarity.
|
Distributed
Control System
|
A
collection of nodes that interact to control a system whose components are
spread out over some distance. Each node has intelligence for operating its
own particular component of the system. Different parts of the system
communicate status and control information with one another to form a
distributed control system. Typically, they communicate on a peer-to-peer
level. This is different from a type of system where all control and
interaction between components is dictated by one central control. This is a
common master/slave arrangement.
|
Distribution
Circuit Breaker
|
A
distribution circuit breaker is a device used for overload and short current
protection of loads connected to a main distribution device.
|
Distribution
Switchgear
|
Distribution
switchgear may include automatic transfer switches, drawout air frame circuit
breakers, fusible switches, or molded case breakers.
|
Domain
|
A
domain is a network concept that allows independently functioning networks to
share resources such as transmission media. A domain designation provides an
ID number to identify the devices that can communicate within that domain. A
network must have at least one domain. PowerCommand Network installations
will usually have only one specified domain.
|
Draw
Out Unit
|
A
draw out unit is a structure that holds a circuit breaker in an enclosure. It
has a movable carriage and contact structures that permit the breaker to be
removed from the enclosure without manually disconnecting power cables and
control wires.
|
Droop
Load Sharing
|
Droop
load sharing is a method of making two or more parallel generator sets share
a system kW load. This is accomplished by having each governor control
adjusted so that the sets have the same droop (reduction of speed). Typical
droop is two cycles in frequency from no load to full load.
|
Earth
Fault Protection
|
A
grounding bar is a copper bar that electrically joins all the metal sections
of the switchgear. This bar is connected to the earth or ground connection
when the system is installed. The grounding or earthing protects personnel
from stray currents that could leak to the metallic enclosures.
|
Efficiency
(EFF)
|
Efficiency
is the ratio of energy output to energy input, such as the ratio between the
electrical energy input to a motor and the mechanical energy output at the
shaft of the motor.
|
Electrical
Operator
|
An
electrical operator is the electric motor driven closing and tripping
(opening) devices that permit remote control of a circuit breaker.
|
Emergency
Bus
|
An
emergency bus is the silver-plated copper bus bars or flexible cable used to
connect the paralleling breakers to the emergency system feeder breakers, and
ultimately to automatic transfer switches or other distribution devices.
|
Emergency
System
|
An
emergency system is independent power generation equipment that is legally
required to feed equipment or systems whose failure may present a life safety
hazard to persons or property.
|
Energy
|
Energy
is manifest in forms such as electricity, heat, light and the capacity to do
work. It is convertible from one form to another, such as in a generator set,
which converts rotating mechanical energy into electrical energy. Typical
units of energy are kW/h, Btu (British thermal unit), Hp/h, ft/lbf, joule and
calorie.
|
Exciter
|
An
exciter is a device that supplies direct current (DC) to the field coils of a
synchronous generator, producing the magnetic flux required for inducing
output voltage in the armature coils (stator). See Field.
|
Exciter
Paralleling Control
|
An
exciter paralleling control initiates the start of generator excitation in
generator sets used in automatic paralleling systems.
|
Fault
|
A
fault is any unintended flow of current outside its intended circuit path in
an electrical system.
|
Feeder
Circuit Breaker
|
See
Distribution Circuit Breaker.
|
Fiber
Optic Cable
|
A
technology using glass or plastic threads (fibers) to transmit data. A fiber
optic cable is a bundle of either glass or plastic threads capable of
transmitting messages modulated into light waves. Typically, fiber optic
cable has greater bandwidth allowing them to carry more data than metal
wires. Fiber optic cable is lighter and less susceptible to interference than
metal wires. Also, data can be transmitted digitally rather being transformed
into analog data for transmission as is the case with metal wires when used
for computer data transmission. Fiber optics are becoming increasingly more
common for use with Local-Area Networks (LANs).
|
Field
|
The
generator field (rotor) consists of a multi-pole electromagnet which induces
output voltage in the armature coils (stator) of the generator when it is
rotated by the engine. The field is energized by DC supplied by the exciter.
|
Field
Breaker with Auxiliary Switch
|
This
is the circuit breaker (usually mounted in the generator control panel) that
monitors the alternating current input to the automatic voltage regulator. If
a malfunction occurs in the excitation system, the circuit breaker trips on
overcurrent-closing the auxiliary switch, shutting down the generator set,
and energizing the alarm circuit.
|
First
Start Sensor
|
A
first start sensor is an electronic device within some paralleling equipment
that senses generator set and bus voltage and frequency, and determines
whether or not a generator set is the first unit ready to close to the bus
following a call to start under "black start" conditions.
|
Free
Field (Noise Measurements)
|
In
noise measurements, a free field is a field in a homogeneous, isotropic
medium (a medium having the quality of transmitting sound equally in all
directions) which is free of boundaries. In practice, it is a field in which
the effects of the boundaries are negligible in the region of interest. In
the free field, the sound pressure level decreases 6 dB for each doubling of
the distance from a point source.
|
Frequency
|
Frequency
is the number of complete cycles per unit of time of any periodically varying
quantity, such as alternating voltage or current. It is usually expressed as
(Hz) Hertz or CPS (cycles per second).
|
Frequency
Adjust Potentiometer
|
A
frequency adjust potentiometer is used to manually bring the frequency
(speed) of the incoming set to that of the bus for synchronizing purposes.
When the generator set is paralleled, operation of this potentiometer will
adjust the kW load assumed by the generator set.
|
Frequency
Regulation
|
Frequency
regulation is a measure that states the difference between no-load and
full-load frequency as a percentage of full-load frequency.
|
Fusible
Switch
|
A
fusible switch is an isolating switch and overcurrent protective device used
for feeder or transfer switch isolation and protection. It is typically a
manually operated, stored energy opening and closing, bolted compression
blade switch, with provisions for installing current limited fuses.
|
Gateway
|
A
device that acts as an interface between two different communication
protocols. The Network Gateway Module (NGM) provides a communication protocol
that a PC can understand. Other gateway devices may be used to interface
between our Lontalk protocol and other systems such as a SCADA or Building
Automation System. Typically, a gateway becomes necessary when a SCADA or BAS
does not have a driver developed for Lontalk.
|
Generator
|
A
generator is a machine which converts rotating mechanical energy into
electrical energy.
|
Genset
Communication Module (GCM)
|
The
GCM provides a communication gateway between the Model 3100 PowerCommand
Control (PCCI) and the network. The GCM communicates with the PCCI control
over a serial data link. The GCM gets data from the PCCI controls such as
voltage, current, engine speed, oil temperature, etc. and then sends it out
on the network if another network node is bound to it or requesting data.
|
Governor
|
A
governor is a device on the engine which controls fuel to maintain a constant
engine speed under various load conditions. The governor must have provision
for adjusting speed (generator frequency) and speed droop (no load to full
load).
|
Grid
|
The
utility-owned power distribution system.
|
Ground
|
A
ground is a connection, either intentional or accidental, between an
electrical circuit and the earth or some conducting body serving in place of
the earth.
|
Ground
Fault Protection
|
This
function trips (opens) a circuit breaker or sounds an alarm in the event that
there is an electrical fault between one or more of the phase conductors and
ground (earth). This ground fault protection function may be incorporated
into a circuit breaker.
|
Ground
Return
|
Ground
return is a method of ground fault detection that employs a single sensor
(CT) encircling the main bonding jumper between the power system neutral and
ground. This device in itself is not capable of locating the faulted circuit
but when used in conjunction with ground fault sensors on all feeders and
source connections, can provide bus fault protection when properly coordinated
(delayed).
|
Grounded
Neutral
|
A
grounded neutral is the intentionally grounded center point of a Y-connected,
four-wire generator, or the mid-winding point of a single phase generator.
|
Harmonic
Distortion (Total Harmonic Distortion)
|
Total
harmonic distortion is an expression of the total harmonic content of a
voltage waveform. The harmonic distortion (or harmonic content) of a waveform
is usually expressed as the square root of the sum of the squares of each of
the harmonic amplitudes (with amplitudes as a percent of the fundamental
voltage amplitude).
|
Harmonics
|
Harmonics
are voltage or current components which operate at integral multiples of the
fundamental frequency of a power system (50 or 60 Hertz). Harmonic currents
have the effect of distorting the shape of the voltage wave form from that of
a pure sine wave.
|
Hertz
(Hz)
|
The
term Hertz is the preferred designation for cycles per second (CPS) and is
used to describe frequency.
|
Hub
|
A
common connection point for devices or nodes in a network or sub-network.
Hubs are commonly used to connect segments of a LAN and contain multiple
ports.
|
Hunting
|
Hunting
is a phenomenon that can occur upon load changes in which the frequency or
the voltage continues to rise above and fall below the desired value without
reaching a steady-state value. It is caused by insufficient damping.
|
Incoming
Set
|
This
is the generator set that is about to be connected to (paralleled with) the
energized bus.
|
Insulated
Case Circuit Breaker
|
An
insulated case circuit breaker is a power circuit breaker that is provided in
a preformed case, similar to a molded case breaker.
|
Insulation
|
Insulation
is non-conductive material used to prevent leakage of electric current from a
conductor. There are several classes of insulation in use for generator
construction, each recognized for a maximum continuous-duty temperature.
|
Internal
Voltage
|
The
internal voltage is the voltage a generator would develop at no load if it
were not connected in a parallel operation. Excitation of the generator field
controls internal voltage.
|
Interoperability
|
Design
to allow one product to work with another product without modification.
|
Interruptible
|
This
refers to the practice of operating on-site power systems, at the request of
a utility, to reduce electrical demand on the utility grid during periods of
high consumption. Interruptible facilities may also be disconnected from all
electrical service in the event of high demand on the utility grid, even if
no on site power system is available.
|
Interrupting
Capacity
|
Interrupting
capacity is the magnitude of electrical current that a device can safely
interrupt (open against), without failure of the component.
|
kW
Load Sensor
|
The
kW load sensor is an electronic device provided to sense kW level at various
points in a system, for use in control functions within the system, such as
kW load alarms, or load demand.
|
kVA
(kilo-Volt-Amperes)
|
kVA
is a term for rating electrical devices. A device's kVA rating is equal to
its rated output in amperes multiplied by its rated operating voltage. In the
case of three-phase generator sets, kVA is the kW ouput rating divided by
0.8, the rated power factor. kVA is the vector sum of the active power (kW)
and the reactive power (kVAR) flowing in a circuit.
|
kVAR
|
kVAR
(kilo-Volt-Amperes Reactive) is the product of the voltage and the amperage
required to excite inductive circuits. It is associated with the reactive
power which flows between paralleled generator windings and between
generators and load windings that supply the magnetizing currents necessary
in the operation of transformers, motors and other electromagnetic loads.
Reactive power does not load the generator set's engine but does limit the
generator thermally.
|
kW
|
This
is an abbreviation for kilowatt, an alternate term for rating electrical
devices. Generator sets in the United States are usually rated in kW.
Sometimes called active power, kW loads the generator set engine.
|
kW-h(kilo-Watt-hour)
|
This
is a unit of electric energy. It is equivalent to one kW of electric power
supplied for one hour.
|
Lagging
Power Factor
|
Lagging
power factor in AC circuits (a power factor of less than 1.0) is caused by
inductive loads, such as motors and transformers, which cause the current to
lag behind the voltage. See Power Factor.
|
Lead
Unit
|
In
a paralleling system that has a load demand feature, the lead unit is the
last unit to be shut down in the event that load demand mode is in operation.
|
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.
|
Line-To-Line
Voltage
|
Line-to-line
voltage is the voltage between any two phases of an AC generator.
|
Line-To-Neutral
Voltage
|
In
a 3-phase, 4-wire, Y-connected generator, line-to-neutral voltage is the
voltage between a phase and the common neutral where the three phases are
tied together.
|
Load
Demand
|
Load
Demand is a paralleling system operating mode in which the system monitors
the total kW output of the generator sets, and controls the number of
operating sets as a function of the total load on the system. The purpose of
load demand controls is to reduce fuel consumption and limit problems caused
by light load operation of reciprocating diesel generator sets.
|
Load
Factor
|
The
load factor is the ratio of the average load to the generator set power
rating.
|
Load
Management
|
Load
management is the overall control of load connected to match available
generator capacity. Priority control and load shedding are the two features
required for load management.
|
Load
Shedding
|
Load
shedding is the process by which the total load on a paralleling system is
reduced, on overload of the system bus, so that the most critical loads
continue to be provided with reliable electrical service.
|
Local
Loop
|
A
method of branching out or creating a stub on the network. The maximum
distance this stub can be is 10ft. (3m) from the main network bus.
Effectively the node is "daisy-chained" into the network. This
involves two wires, one that goes to the node and another that returns to the
main network bus. The total local loop distance must be added to the total
network length. This becomes important when the main network bus nears the
4,600 ft. length and requires the use of Routers.
|
Local-Area
Network (LAN)
|
A
computer network that spans a relatively small area. Most LANs are confined
to a single building or group of buildings.
|
Locations
|
Locations
are subdivisions of a network that can be selected for easier organization.
Locations may designate physical places, but are not required to do so. For
example, network devices in one location may communicate with network devices
in another location when requested to do so.
|
Low
Voltage
|
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, that interrupts the genset's
power output. Main breakers provide overcurrent protection and a single
disconnect point for all power in a switchboard or device.
|
In the next article, we will continue explaining the Glossary of Generators – Part Two to start explaining Generators Sizing Calculations later. So, please keep following.
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