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Technical Dictionaries
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.
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