AC Alternating Current (AC) is electric current that alternates between a positive maximum value andanegative maximum value at a characteristic frequency, usually 50 or 60 cycles per second (Hertz).
American National Standards Institute.
Acoustic material is any material considered in terms of its acoustic properties,
especially its properties of absorbing or deadening sound.
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.
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 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.
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 is the product of current and voltage, expressed as kVA. It is real power (kW) divided by the power factor (PF).
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.
B 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.
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 is that portion of a building load demand which is constant. It is the "base" of the building demand curve.
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.
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.
Black Start refers to the starting of a power system with its own power sources, without the assistance from external power supplies.
A logical system used to express one of two states, such as on or off (yes or no, 1 or 0, etc.)
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).
C CT (Current Transformer)
Current transformers are instrument transformers used in conjunction with ammeters,
control circuits and protective relaying. They usually have 5 ampere secondaries.
circuit is a path for an electric current across a potential (voltage).
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.
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).
Current Current is the flow of electric charge. Its unit of measure is the ampere.
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.
D 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.
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.
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.
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.
E 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.
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 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.
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).
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.
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.
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.
H 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.
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.
L 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.
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.
Line-to-line voltage is the voltage between any two phases of an AC generator.
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 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.
The load factor is the ratio of the average load to the generator set power rating.
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-Area Network (LAN)
A computer network that spans a relatively small area.
Most LANs are confined to a single building or group of buildings.
AC system operating voltages from 120 to 600 VAC.
M 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.
Mains is a term used extensively outside of the United States to describe the normal power service (utility).
A control section in a typical paralleling system that provides total system metering and the interface point between the paralleling system and the facility.
AC system operating voltages from 601 to 15000 VAC.
An industrial networking system that uses RS-232 serial master-slave communications at data transfer rate of up to 19.2 KBPS.
An industrial networking system that uses token-passing peer-to-peer communications at data transfer rates of one megabit per second (MBPS).
The network media is shielded twisted-pair cable.
Modules are also called nodes or devices.
These are devices such as Genset Communication Modules (GCMs), Control Communication Modules (CCMs), and Digital Input/Output Modules (DIMs).
Molded Case Circuit Breaker
A molded case circuit breaker automatically interrupts the current flowing through it when the current exceeds the trip rating of the breaker.
case refers to the use of molded plastic as the medium of electrical insulation for enclosing the mechanisms,
for separating conducting surfaces from one another and from grounded (earthed) metal parts.
Molded case circuit breakers usually contain thermal-magnetic trip units, although larger sizes can be equipped with solid state trip sensors.
National Electrical Manufacturers Association
NFPA National Fire Protection Association
Network A collection of Nodes that communicate with one another over a common medium.
A signal that carries messages between nodes.
PowerCommand Networks use Manchester Encoding that makes the signal insensitive to polarity.
The signal is transformer-coupled to the network data wire at a rate of 78 KBPS.
Network Gateway Module A device acting as an interface between a modem or PC and the network wire.
The Gateway takes the UTP wire and then provides an RS-232 port for connection to either a modem or PC.
Neutral Current Neutral current is the current that flows in the neutral leg of a paralleling system.
Often, this term is used in reference to circulating currents or cross currents.
Node A module that can communicate over the network data to other modules.
A module contains a Neuron Chip. Certain devices are nodes such as Genset Communication Modules (GCMs) and Control Communication Modules (CCMs).
Other devices are not nodes, as they cannot communicate with other devices, but only receive messages. An example is the Network Annunciator Module (NAM).
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.
O Ohm The ohm is a unit of electrical resistance. One volt will cause a current of one ampere to flow through a resistance of one ohm.
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.
Overcrank is an alarm function provided with most generator sets that indicate that the generator set has failed to start.
Overshoot refers to the amount by which voltage or frequency exceeds the nominal value as the voltage regulator or governor responds to changes in load
P Paralleling Breaker
A paralleling breaker is the circuit breaker that connects the generator set to the emergency bus, and across which all the individual generator synchronizing functions occur.
A paralleling control contains the electrical equipment provided in a paralleling system for control of a single generator set.
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.
A network operating system where any device on the main network bus can initiate communication.
Phase angle refers to the relation between two sine waves which do not pass through zero at the same time.
Considering one full cycle to be 360 degrees, the phase angle expresses how far apart the two waves are in relation to each other in degrees.
Phase rotation (or phase sequence) describes the order (A-B-C, R-S-T, or U-V-W) of the phase voltages at the output terminals of a three-phase generator.
The generator phase rotation must match the facility phase rotation. This must be checked prior to operation of the electrical loads in a facility with an on-site generator.
The external connector on a device at which the network cable or medium is attached.
Power factor is the cosine of the angle between the active power (kW) and apparent power (kVA) in a circuit.
Prime Power describes an application where the generator set(s) must supply power on a continuous basis and for long periods of time between shutdowns.
No utility service is present in typical prime power applications.
Priority control is the process by which the total loads on the bus is limited to the most critical loads in the system until adequate generation capacity is available to serve all loads.
A set of rules used mutually by two or more devices to communicate. Also, known as the "language" used in a network.
R Radio Interference
Radio interference refers to the interference with radio reception caused by a generator set.
Reactive power is power that flows back and forth between the inductive windings of the generator and the inductive windings of motors, transformers, etc.,
which are part of the electrical load. This power does no useful work in the electrical load nor does it present load to the engine. It does apply load to the generator and limits the capacity of the generator.
Reverse Power Relay
A reverse power relay is a relay with a wattmeter movement that senses the direction of power flow.
In paralleled sets, a flow of reverse power (i.e., power flow into set) will actuate the reverse power relay and disconnect the set from the system.
If one set stops and reverse power protection is not provided, the set still running will drive the set that has stopped. The generator on the set that has stopped will act as a motor.
A device for passing network messages over another media and sometimes protocol. Our network router is programmed as a "repeater" to create another channel on the main network bus.
Each channel can have a 4,600 ft. network bus and is capable of having 44 nodes. The PowerCommand Network can have up to twenty (20) channels.
Silicon Controlled Rectifier -- a three-electrode solid-state 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.
A short circuit is generally an unintended electrical connection between current carrying parts.
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.
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 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.
Sound Pressure Level (SPL)
Sound pressure level is a measurement of the pressure fluctuations of a sound wave as it propagates through the air.
Because of the wide range of pressures to which the ear responds,
a logarithmic scale is used and is expressed as a ratio of the measured pressure referenced to a pressure of 2x10-5 N/m2 (20 m Pa) which is the threshold of human hearing at 1000 Hz.
The measure is expressed in decibels (dB). The Bel unit is named after Alexander Graham Bell.
A standby system is an independent power system that allows operation of a facility in the event of normal power failure.
See Wye Connection.
The initial value of current drawn by a motor when it is started from standstill.
Surge is the sudden rise in voltage in a system, usually caused by load disconnect.
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.
Sync Check Relay
A sync check relay is an electrical device that monitors the phase relationship between two voltage sources and provides a signal
when the voltage sources are within specific preset parameters.
A synchronizer is an electronic device that monitors the phase relationship between two voltage sources and
provides a connection signal to an engine governor, to force the generator set to synchronize to the system bus.
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.
A resistive load placed at the end of a cable to prevent data signals from reflecting back into the data path.
A transfer switch is an electrical device for switching loads between alternate power sources.
An automatic transfer switch monitors the condition of the sources and connects the load to the alternate source if the preferred source fails.
Undershoot refers to the amount by which voltage or frequency drops below the nominal value as the voltage regulator or governor responds to changes in load.
The utility is a commercial power source that supplies electrical power to specific facilities from a large central power plant.
V Voltage Control
The voltage control is a rheostat that sets the operating point of the voltage regulator and therefore controls the output voltage of the generator set, within its design limits.
Voltage dip is the dip in voltage that results when a load is added, occurring before the regulator can correct it,
or resulting from the functioning of the voltage regulator to unload an overloaded engine-generator.
Voltage regulation is a measure that states the difference between maximum and minimum steady-state voltage as a percentage of nominal voltage.
w Watt-Hour Meter
A watt-hour meter records the total power output at a specific point in a system. Typical recording increment is in kW-hours.
A Wye connection is the same as a star connection. It is a method of interconnecting the phases of a three-phase system to form a configuration resembling the letter Y.
A fourth (neutral) wire can be connected at the center point.
Z 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 ground fault current in the circuit. This output is then measured by a relay to initiate circuit breaker tripping or ground fault alarm.