Appendix E
Glossary for Distribution System Terminology
Some of the most commonly used terms, both in this book and in general usage, are defined later. Most of the definitions given in this glossary are based on Refs. [1–8].
AAAC: Abbreviation for all-aluminum-alloy conductors. Aluminum-alloy conductors have higher strength than those of the ordinary electric-conductor grade of aluminum.
AA: Abbreviation for all-aluminum conductors.
ACAR: Abbreviation for aluminum conductor alloy reinforced. It has a central core of higher–strength aluminum surrounded by layers of electric-conductor grade aluminum.
ACL cable: A cable with a lead sheath over the cable insulation that is suitable for wet locations. It is used in buildings at low voltage.
ACSR: Abbreviation for aluminum conductor steel reinforced. It consists of a central core of steel strands surrounded by layers of aluminum strands.
Active filter: Any of a number of sophisticated power electronic devices for eliminating harmonic distortion.
Admittance: The ratio of the phasor equivalent of the steady-state sine-wave current to the phasor equivalent of the corresponding voltage.
Adverse weather: Weather conditions that cause an abnormally high rate of forced outages for exposed components during the periods such conditions persist, but which do not qualify as major storm disasters. Adverse weather conditions can be defined for a particular system by selecting the proper values and combinations of conditions reported by the Weather Bureau: thunderstorms, tornadoes, wind velocities, precipitation, temperature, etc.
Aerial cable: An assembly of insulated conductors installed on a pole line or similar overhead structures; it may be self-supporting or installed on a supporting messenger cable.
Air-blast transformer: A transformer cooled by forced circulation of air through its core and coils.
Air circuit breaker: A circuit breaker in which the interruption occurs in air.
Air switch: A switch in which the interruptions of the circuit occur in air. Al: Symbol for aluminum.
Ampacity: Current rating in amperes, as of a conductor.
ANSI: Abbreviation for American National Standards Institute.
Apparent sag (at any point): The departure of the wire at the particular point in the span from the straight line between the two points of the span, at 60°F, with no wind loading.
Arcing time of fuse: The time elapsing from the severance of the fuse link to the final interruption of the circuit under specified conditions.
Arc-over of insulator: A discharge of power current in the form of an arc following a surface discharge over an insulator.
Armored cable: A cable provided with a wrapping of metal, usually steel wires, primarily for the purpose of mechanical protection.
Askarel: A generic term for a group of nonflammable synthetic chlorinated hydrocarbons used as electrical insulating media. Askarels of various compositional types are used. Under arcing conditions, the gases produced, while consisting predominantly of noncombustible hydrogen chloride, can include varying amounts of combustible gases depending upon the askarel type. Because of environmental concerns, it is not used in new installations anymore.
Automatic substations: Those in which switching operations are so controlled by relays that transformers or converting equipment are brought into or taken out of service as variations in load may require, and feeder circuit breakers are closed and reclosed after being opened by overload relays.
Autotransformer: A transformer in which at least two windings have a common section.
AWG: Abbreviation for American Wire Gauge. It is also sometimes called the Brown and Sharpe Wire Gauge.
Base load: The minimum load over a given period of time.
Benchboard: A switchboard with a horizontal section for control switches, indicating lamps, and instrument switches; may also have a vertical instrument section.
BIL: Abbreviation for basic impulse insulation levels, which are reference levels expressed in impulse-crest voltage with a standard wave not longer than 1.5 × 50 μs. The impulse waves are defined by a combination of two numbers. The first number is the time from the start of the wave to the instant crest value; the second number is the time from the start to the instant of half-crest value on the tail of the wave.
Billing demand: The demand used to determine the demand charges in accordance with the provisions of a rate schedule or contract.
Branch circuit: A set of conductors that extend beyond the last overcurrent device in the low-voltage system of a given building. A branch circuit usually supplies a small portion of the total load.
Breakdown: Also termed puncture, denoting a disruptive discharge through insulation.
Breaker, primary-feeder: A breaker located at the supply end of a primary feeder that opens on a primary-feeder fault if the fault current is of sufficient magnitude.
Breaker-and-a-half scheme: A scheme that provides the facilities of a double main bus at a reduction in equipment cost by using three circuit breakers for each two circuits.
Bus: A conductor or group of conductors that serves as a common connection for two or more circuits in a switchgear assembly.
Bus, transfer: A bus to which one circuit at a time can be transferred from the main bus.
Bushing: An insulating structure including a through conductor, or providing a passageway for such a conductor, with provision for mounting on a barrier, conductor or otherwise, for the purpose of insulating the conductor from the barrier and conducting from one side of the barrier to the other.
BVR: Abbreviation for bus voltage regulator or regulation.
BW: Abbreviation for bandwidth.
BX cable: A cable with galvanized interlocked steel spiral armor. It is known as ac cable and used in a damp or wet location in buildings at low voltage.
Cable: Either a standard conductor (single-conductor cable) or a combination of conductors insulated from one another (multiple-conductor cable).
Cable fault: A partial or total load failure in the insulation or continuity of the conductor.
Capability: The maximum load-carrying ability expressed in kilovoltamperes or kilowatts of generating equipment or other electric apparatus under specified conditions for a given time interval.
Capability, net: The maximum generation expressed in kilowatthours per hour that a generating unit, station, power source, or system can be expected to supply under optimum operating conditions.
Capacitor bank: An assembly at one location of capacitors and all necessary accessories (switching equipment, protective equipment, controls, etc.) required for a complete operating installation.
Capacity: The rated load-carrying ability expressed in kilovoltamperes or kilowatts of generating equipment or other electric apparatus.
Capacity factor: The ratio of the average load on a machine or equipment for the period of time considered to the capacity of the machine or equipment.
Charge: The amount paid for a service rendered or facilities used or made available for use.
Circuit, earth (ground) return: An electric circuit in which the earth serves to complete a path for current.
Circuit breaker: A device that interrupts a circuit without injury to itself so that it can be reset and reused over again.
Circuit-breaker mounting: Supporting structure for a circuit breaker.
Circular mil: A unit of area equal to 1/4 of a square mil (=0.7854 square mil). The cross-sectional area of a circle in circular mils is therefore equal to the square of its diameter in mils. A circular inch is equal to 1 million circular mils. A mil is one one-thousandth of an inch. There are 1974 circular mils in a square millimeter. Abbreviated cmil.
CL: Abbreviation for current limiting (fuse).
cmil: Abbreviation for circular mil.
Coincidence factor: The ratio of the maximum coincident total demand of a group of consumers to the sum of the maximum power demands of individual consumers comprising the group, both taken at the same point of supply at the same time.
Coincident demand: Any demand that occurs simultaneously with any other demands; also the sum of any set of coincident demands.
Component: A piece of equipment, a line, a section of a line, or a group of items that is viewed as an entity.
Condenser: Also termed capacitor; a device whose primary purpose is to introduce capacitance into an electric circuit. The term condenser is deprecated.
Conductor: A substance that has free electrons or other charge carriers that permit charge flow when an emf is applied across the substance.
Conductor tension, final unloaded: The longitudinal tension in a conductor after the conductor has been stretched by the application for an appreciable period, with subsequent release of the loadings of ice and wind, at the temperature decrease assumed for the loading district in which the conductor is strung (or equivalent loading).
Conduit: A structure containing one or more ducts; commonly formed from iron pipe or electrical metallic tubing, used in buildings at low voltage.
Connection charge: The amount paid by a customer for connecting the customer’s facilities to the supplier’s facilities.
Contactor: An electric power switch, not operated manually and designed for frequent operation.
Contract demand: The demand that the supplier of electric service agrees to have available for delivery.
Cress factor: A value that is displayed on many power quality monitoring instruments representing the ratio of the crest value of the measured waveform to the rms value of the waveform. For example, the cress factor of a sinusoidal wave is 1.414.
CT: Abbreviation for current transformers.
Cu: Symbol for copper.
Customer charge: The amount paid periodically by a customer without regard to demand or energy consumption.
Demand: The load at the receiving terminals averaged over a specified interval of time.
Demand charge: That portion of the charge for electric service based upon a customer’s demand.
Demand factor: The ratio of the maximum coincident demand of a system, or part of a system, to the total connected load of the system, or part of the system, under consideration.
Demand, instantaneous: The load at any instant.
Demand, integrated: The demand integrated over a specified period.
Demand interval: The period of time during which the electric energy flow is integrated in determining demand.
Depreciation: The component that represents an approximation of the value of the portion of plant consumed or “used up” in a given period by a utility.
Disconnecting or isolating switch: A mechanical switching device used for changing the connections in a circuit or for isolating a circuit or equipment from the source of power.
Disconnector: A switch that is intended to open a circuit only after the load has been thrown off by other means. Manual switches designed for opening loaded circuits are usually installed in a circuit with disconnectors to provide a safe means for opening the circuit under load.
Displacement factor (DPF): The ratio of active power (watts) to apparent power (voltamperes).
Distribution center: A point of installation for automatic overload protective devices connected to buses where an electric supply is subdivided into feeders and/or branch circuits.
Distribution switchboard: A power switchboard used for the distribution of electric energy at the voltages common for such distribution within a building.
Distribution system: That portion of an electric system that delivers electric energy from transformation points in the transmission, or bulk power system, to the consumers.
Distribution transformer: A transformer for transferring electric energy from a primary distribution circuit to a secondary distribution circuit or consumer’s service circuit; it is usually rated in the order of 5–500 kVA.
Diversity factor: The ratio of the sum of the individual maximum demands of the various subdivisions of a system to the maximum demand of the whole system.
Duplex cable: A cable composed of two insulated stranded conductors twisted together. They may or may not have a common insulating covering.
Effectively grounded: Grounded by means of a ground connection of sufficiently low impedance that fault grounds that may occur cannot build up voltages dangerous to connected equipment.
EHV: Abbreviation for extra high voltage.
Electric rate schedule: A statement of an electric rate and the terms and conditions governing its application.
Electric system loss: Total electric energy loss in the electric system. It consists of transmission, transformation, and distribution losses between sources of supply and points of delivery.
Electrical reserve: The capability in excess of that required to carry the system load.
Emergency rating: Capability of installed equipment for a short time interval.
EMT: Abbreviation for electrical metallic tubing. A raceway that has a thin wall that does not permit threading. Connectors and couplings are secured by either compression rings or setscrews. It is used in buildings at low voltage.
Energy: That which does work or is capable of doing work. As used by electric utilities, it is generally a reference to electric energy and is measured in kilowatthours.
Energy charge: That portion of the charge for electric service based upon the electric energy consumed or billed.
Energy loss: The difference between energy input and output as a result of transfer of energy between two points.
Express feeder: A feeder that serves the most distant networks and must traverse the systems closest to the bulk power source.
Extra high voltage: A term applied to voltage levels higher than 230 kV. Abbreviated EHV.
Facilities charge: The amount paid by the customer as a lump sum or, periodically, as reimbursement for facilities furnished. The charge may include operation and maintenance as well as fixed costs.
FCN: Abbreviation for full-capacity neutral.
Feeder: A set of conductors originating at a main distribution center and supplying one or more secondary distribution centers, one or more branch-circuit distribution centers, or any combination of these two types of load.
Feeder, multiple: Two or more feeders connected in parallel.
Feeder, tie: A feeder that connects two or more independent sources of power and has no tapped load between the terminals. The source of power may be a generating system, substation, or feeding point.
First-contingency outage: The outage of one primary feeder.
Fixed-capacitor bank: A capacitor bank with fixed, not switchable, capacitors.
Flicker: Impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time.
Flicker factor: A factor used to quantify the load impact of electric arc furnaces on the power system.
Forced interruption: An interruption caused by a forced outage.
Forced outage: An outage that results from emergency conditions directly associated with a component, requiring that it be taken out of service immediately, either automatically or as soon as switching operations can be performed; or an outage caused by improper operation of equipment or by human error.
Frequency deviation: An increase or decrease in the power frequency. Its duration varies from few cycles to several hours.
Fuel adjustment clause: A clause in a rate schedule that provides for adjustment of the amount of the bill as the cost of fuel varies from a specified base amount per unit.
Fuse: An overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcurrent through it.
Fuse cutout: An assembly consisting of a fuse support and holder; it may also include a fuse link.
Ground: Also termed earth; a conductor connected between a circuit and the soil; an accidental ground occurs due to cable insulation faults, an insulator defect, etc.
Ground wire: A conductor having grounding connections at intervals that is suspended usually above but not necessarily over the line conductor to provide a degree of protection against lightning discharges.
Harmonics: Sinusoidal voltages or currents having frequencies that are an integer multiple of the fundamental frequency at which the supply system is designed to operate.
Harmonic distortion: Periodic distortion of the sign wave.
Harmonic resonance: A condition in which the power system is resonating near one of the major harmonics being produced by nonlinear elements in the system, hence increasing the harmonic distortion.
HMWPE: Abbreviation for high-molecular-weight polyethylene (cable insulation).
HV: Abbreviation for high voltage.
Impedance: The ratio of the phasor equivalent of a steady-state sine-wave voltage to the phasor equivalent of a steady-state sine-wave current.
Impulsive transient: A sudden (nonpower) frequency change in the steady-state condition of the voltage or current that is unidirectional in polarity.
Incremental energy costs: The additional cost of producing or transmitting electric energy above some base cost.
Index of reliability: A ratio of cumulative customer minutes that service was available during a year to total customer minutes demanded; can be used by the utility for feeder reliability comparisons.
Indoor transformer: A transformer that must be protected from the weather.
Installed reserve: The reserve capability installed on a system.
Interruptible load: A load that can be interrupted as defined by contract.
Interruption: The loss of service to one or more consumers. An interruption is the result of one or more component outages.
Interruption duration: The period from the initiation of an interruption to a consumer until service has been restored to that consumer.
Investment-related charges: Those certain charges incurred by a utility that are directly related to the capital investment of the utility. kcmil: Abbreviation for a thousand circular mils.
Isolated ground: It originates at an isolated ground-type receptacle or equipment input terminal block and terminates at the point where neutral and ground are bonded at the power source. Its conductor is insulated from the metallic raceway and all ground points throughout its length.
K-factor: A factor used to quantify the load impact of electric arc furnaces on the power system.
Lag: Denotes that a given sine wave passes through its peak at a later time than a reference time wave.
Lambda: The incremental operating cost at the load center, commonly expressed in mils per kilowatthour.
Lateral conductor: A wire or cable extending in a general horizontal direction or at an angle to the general direction of the line; service wires either overhead or underground are considered laterals from the street mains.
LDC: Abbreviation for line-drop compensator.
Lightning arrestor: A device that reduces the voltage of a surge applied to its terminals and restores itself to its original operating condition.
L-L: Abbreviation for line to line.
Limit switch: A switch that is operated by a moving part at the end of its travel typically to stop or reverse the motion.
Limiter: A device in which some characteristic of the output is automatically prevented from exceeding a predetermined value.
Line: A component part of a system extending between adjacent stations or from a station to an adjacent interconnection point. A line may consist of one or more circuits.
Line-drop compensator: A device that causes the voltage-regulating relay to increase the output voltage by an amount that compensates for the impedance drop in the circuit between the regulator and a predetermined location at the circuit.
Line loss: Energy loss on a transmission or distribution line.
L-N: Abbreviation for line to neutral.
Load center: A point at which the load of a given area is assumed to be concentrated.
Load diversity: The difference between the sum of the maxima of two or more individual loads and the coincident or combined maximum load, usually measured in kilowatts over a specified period of time.
Load duration curve: A curve of loads, plotted in descending order of magnitude, against time intervals for a specified period.
Load factor: The ratio of the average load over a designated period of time to the peak load occurring in that period.
Load-interrupter switch: An interrupter switch designed to interrupt currents not in excess of the continuous-current rating of the switch.
Load, interruptible: A load that can be interrupted as defined by contract.
Load losses, transformer: Those losses that are incident to the carrying of a specified load. They include I2R loss in the winding due to load and eddy currents, stray loss due to leakage fluxes in the windings, etc., and the loss due to circulating currents in parallel windings.
Load tap changer: A selector switch device applied to power transformers to maintain a constant low-side or secondary voltage with a variable primary voltage supply, or to hold a constant voltage out along the feeders on the low-voltage side for varying load conditions on the low-voltage side. Abbreviated LTC.
Load-tap-changing transformer: A transformer used to vary the voltage, or phase angle, or both, of a regulated circuit in steps by means of a device that connects different taps of tapped winding(s) without interrupting the load.
Loop feeder: A number of tie feeders in series, forming a closed loop. There are two routes by which any point on a loop feeder can receive electric energy, so that the flow can be in either direction.
Loop service: Two services of substantially the same capacity and characteristics, supplied from adjacent sections of a loop feeder. The two sections of the loop feeder are normally tied together on the consumer’s bus through switching devices.
Loss factor: The ratio of the average power loss to the peak-load power loss during a specified period of time.
Low-side surges: The current surge that appears to be injected into the transformer secondary terminals upon a lighting strike to grounded conductors in the vicinity.
LTC: Abbreviation for load tap changer.
LV: Abbreviation for low voltage.
Main distribution center: A distribution center supplied directly by mains.
Maintenance expenses: The expense required to keep the system or plant in proper operating repair.
Maximum demand: The largest of a particular type of demand occurring within a specified period.
MC: Abbreviation for metal clad (cable).
Messenger cable: A galvanized steel or Copperweld cable used in construction to support a suspended current-carrying cable.
Metal-clad switchgear, outdoor: A switchgear that can be mounted in suitable weatherproof enclosures for outdoor installations. The base units are the same for both indoor and outdoor applications. The weatherproof housing is constructed integrally with the basic structure and is not merely a steel enclosure. The basic structure, including the mounting details and withdrawal mechanisms for the circuit breakers, bus compartments, transformer compartments, etc., is the same as that of indoor metal-clad switchgear.
Metal-enclosed switchgear: Primarily indoor-type switchgear. It can, however, be furnished in weatherproof houses suitable for outdoor operation. The switchgear is suitable for 600 V maximum service.
Minimum demand: The smallest of a particular type of demand occurring within a specified period.
Momentary interruption: An interruption of duration limited to the period required to restore service by automatic or supervisory-controlled switching operations or by manual switching at locations where an operator is immediately available.
Monthly peak duration curve: A curve showing the total number of days within the month during which the net 60 min clock-hour integrated peak demand equals or exceeds the percent of monthly peak values shown.
NC: Abbreviation for normally closed.
NEC: Abbreviation for National Electric Code.
NESC: Abbreviation for National Electrical Safety Code.
Net system energy: Energy requirements of a system, including losses, defined as (1) net generation of the system, plus (2) energy received from others, less, and (3) energy delivered to other systems.
Network distribution system: A distribution system that has more than one simultaneous path of power flow to the load.
Network protector: An electrically operated low-voltage air circuit breaker with self-contained relays for controlling its operation. It provides automatic isolation of faults in the primary feeders or network transformers. Abbreviated NP.
NO: Abbreviation for normally open.
Noise: An unwanted electrical signal with a less than 200 kHz superimposed upon the power-system voltage or current in-phase conductors, or found on neutral conductors or signal lines. It is not a harmonic distortion or transient. It disturbs microcomputers and programmable controllers.
No-load current: The current demand of a transformer primary when no current demand is made on the secondary.
No-load loss: Energy losses in an electric facility when energized at rated voltage and frequency but not carrying load.
Noncoincident demand: The sum of the individual maximum demands regardless of time of occurrence within a specified period.
Nonlinear load: An electrical load that draws current discontinuously or whose impedances vary throughout the cycle of the input ac voltage waveform.
Normal rating: Capacity of installed equipment.
Normal weather: All weather not designated as adverse or major storm disaster.
Normally closed: Denotes the automatic closure of contacts in a relay when deenergized. Abbreviated NC.
Normally open: Denotes the automatic opening of contacts in a relay when deenergized. Abbreviated NO.
NP: Abbreviation for network protector.
NSW: Abbreviation for nonswitched.
Notch: A switching (or other) disturbance of the normal power voltage waveform, lasting less than a half cycle, which is initially of opposite polarity than the waveform. It includes complete loss of voltage for up to a 0.5 cycle.
Notching: A periodic disturbance caused by normal operation of a power electronic device, when its current is commutated from one phase to another.
NX: Abbreviation for nonexpulsion (fuse).
Off-peak energy: Energy supplied during designated periods of relatively low system demands.
On-peak energy: Energy supplied during designated periods of relatively high system demands.
OH: Abbreviation for overhead.
Operating expenses: The labor and material costs for operating the plant involved.
Outage: The state of a component when it is not available to perform its intended function due to some event directly associated with that component. An outage may or may not cause an interruption of service to consumers depending upon the system configuration.
Outage duration: The period from the initiation of an outage until the affected component or its replacement once again becomes available to perform its intended function.
Outage rate: For a particular classification of outage and type of component, the mean number of outages per unit exposure time per component.
Oscillatory transient: A sudden and nonpower frequency change in the steady-state condition of voltage or current that includes both positive and negative polarity values.
Overhead expenses: The costs that in addition to direct labor and material are incurred by all utilities.
Overload: Loading in excess of normal rating of equipment.
Overload protection: Interruption or reduction of current under conditions of excessive demand, provided by a protective device.
Overvoltage: A voltage that has a value at least 10% above the nominal voltage for a period of time greater than 1 min.
Pad-mounted: A general term describing equipment positioned on a surface mounted pad located outdoors. The equipment is usually enclosed with all exposed surfaces at ground potential.
Pad-mounted transformer: A transformer utilized as part of an underground distribution system, with enclosed compartment(s) for high-voltage and low-voltage cables entering from below, and mounted on a foundation pad.
Panelboard: A distribution point where an incoming set of wires branches into various other circuits.
Passive filter: A combination of inductors, capacitors, and resistors designed to eliminate one or more harmonics. The most common variety is simply an inductor in series with a shunt capacitor, which short-circuits the major distorting harmonic component from the system.
PE: Abbreviation used for polyethylene (cable insulation).
Peak current: The maximum value (crest value) of an alternating current.
Peak voltage: The maximum value (crest value) of an alternating voltage.
Peaking station: A generating station that is normally operated to provide power only during maximum load periods.
Peak-to-peak value: The value of an ac waveform from its positive peak to its negative peak. In the case of a sine wave, the peak-to-peak value is double the peak value.
Pedestal: A bottom support or base of a pillar, statue, etc.
Percent regulation: See Percent voltage drop.
Percent voltage drop: The ratio of voltage drop in a circuit to voltage delivered by the circuit, multiplied by 100 to convert to percent.
Permanent forced outage: An outage whose cause is not immediately self-clearing but must be corrected by eliminating the hazard or by repairing or replacing the component before it can be returned to service. An example of a permanent forced outage is a lightning flashover that shatters an insulator, thereby disabling the component until repair or replacement can be made.
Permanent forced outage duration: The period from the initiation of the outage until the component is replaced or repaired.
Phase: The time of occurrence of the peak value of an ac waveform with respect to the time of occurrence of the peak value of a reference waveform.
Phase angle: An angular expression of phase difference.
Phase shift: The displacement in time of one voltage waveform relative to other voltage waveform(s).
Pole: A column of wood or steel, or some other material, supporting overhead conductors, usually by means of arms or brackets.
Pole fixture: A structure installed in lieu of a single pole to increase the strength of a pole line or to provide better support for attachments than would be provided by a single pole. Examples are A fixtures, H fixtures.
Primary disconnecting devices: Self-coupling separable contacts provided to connect and disconnect the main circuits between the removable element and the housing.
Primary distribution feeder: A feeder operating at primary voltage supplying a distribution circuit.
Primary distribution mains: The conductors that feed from the center of distribution to direct primary loads or to transformers that feed secondary circuits.
Primary distribution network: A network consisting of primary distribution mains.
Primary distribution system: A system of ac distribution for supplying the primaries of distribution transformers from the generating station or substation distribution buses.
Primary distribution trunk line: A line acting as a main source of supply to a distribution system.
Primary feeder: That portion of the primary conductors between the substation or point of supply and the center of distribution.
Primary lateral: That portion of a primary distribution feeder that is supplied by a main feeder or other laterals and extends through the load area with connections to distribution transformers or primary loads.
Primary main feeder: The higher-capacity portion of a primary distribution feeder that acts as a main source of supply to primary laterals or direct connected distribution transformers and primary loads.
Primary network: A network supplying the primaries of transformers whose secondaries may be independent or connected to a secondary network.
Primary open-loop service: A service that consists of a single distribution transformer with dual primary switching, supplied from a single primary circuit that is arranged in an open-loop configuration.
Primary selective service: A service that consists of a single distribution transformer with primary throw-over switching, supplied by two independent primary circuits.
Primary transmission feeder: A feeder connected to a primary transmission circuit.
Primary unit substation: A unit substation in which the low-voltage section is rated above 1000 V.
Protective relay: A device whose function is to detect defective lines or apparatus or other power-system conditions of an abnormal or dangerous nature and to initiate appropriate control circuit action.
Power: The rate (in kilowatts) of generating, transferring, or using energy.
Power, active: The product of the rms value of the voltage and the rms value of the in-phase component of the current.
Power, apparent: The product of the rms value of the voltage and the rms value of the current.
Power, instantaneous: The product of the instantaneous voltage multiplied by the instantaneous current.
Power, reactive: The product of the rms value of the voltage and the rms value of the quadrature component of the current.
Power factor: The ratio of active power to apparent power.
Power-factor adjustment clause: A clause in a rate schedule that provides for an adjustment in the billing if the customer’s power factor varies from a specified reference.
Power pool: A group of power systems operating as an interconnected system and pooling their resources.
Power transformer: A transformer that transfers electric energy in any part of the circuit between the generator and the distribution primary circuits.
PT: Abbreviation for potential transformers.
pu: Abbreviation for per unit.
Raceway: A channel for holding wires, cables, or busbars. The channel may be in the form of a conduit, electrical metallic tubing, or a square sheet-metal duct. It is used in buildings at low voltage.
Radial distribution system: A distribution system that has a single simultaneous path of power flow to the load.
Radial service: A service that consists of a single distribution transformer supplied by a single primary circuit.
Radial system, complete: A radial system that consists of a radial subtransmission circuit, a single substation, and a radial primary feeder with several distribution transformers each supplying radial secondaries; has the lowest degrees of service continuity.
Ratchet demand: The maximum past or present demands that are taken into account to establish billings for previous or subsequent periods.
Ratchet demand clause: A clause in a rate schedule that provides that maximum past or present demands be taken into account to establish billings for previous or subsequent periods.
Rate base: The net plant investment or valuation base specified by a regulatory authority upon which a utility is permitted to earn a specified rate of return.
RCN: Abbreviation for reduced-capacity neutral.
Recloser: A dual-timing device that can be set to operate quickly to prevent downline fuses from blowing.
Reclosing device: A control device that initiates the reclosing of a circuit after it has been opened by a protective relay.
Reclosing fuse: A combination of two or more fuse holders, fuse units, or fuse links mounted on a fuse support(s), mechanically or electrically interlocked, so that one fuse can be connected into the circuit at a time and the functioning of that fuse automatically connects the next fuse into the circuit, thereby permitting one or more service restorations without replacement of fuse links, refill units, or fuse units.
Reclosing relay: A programming relay whose function is to initiate the automatic reclosing of a circuit breaker.
Reclosure: The automatic closing of a circuit-interrupting device following automatic tripping. Reclosing may be programmed for any combination of instantaneous, time-delay, singleshot, multiple-shot, synchronism-check, dead-line-live-bus, or dead-bus-live-line operation.
Recovery voltage: The voltage that occurs across the terminals of a pole of a circuit-interrupting device upon interruption of the current.
Required reserve: The system planned reserve capability needed to ensure a specified standard of service.
Resistance: The real part of impedance.
Return on capital: The requirement that is necessary to pay for the cost of investment funds used by the utility.
RP: Abbreviation for regulating point.
Sag: The distance measured vertically from a conductor to the straight line joining its two points of support. Unless otherwise stated, the sag referred to is the sag at the midpoint of the span.
Sag: A decrease to between 0.1 and 0.9 pu in rms voltage and current at the power frequency for a duration of 0.5 cycles to 1 min.
Sag, final unloaded: The sag of a conductor after it has been subjected for an appreciable period to the loading prescribed for the loading district in which it is situated, or equivalent loading, and the loading removed. Final unloaded sag includes the effect of inelastic deformation.
Sag, initial unloaded: The sag of a conductor prior to the application of any external load.
Sag of a conductor (at any point in a span): The distance measured vertically from the particular point in the conductor to a straight line between its two points of support.
Sag section: The section of line between snub structures. More than one sag section may be required to properly sag the actual length of conductor that has been strung.
Sag span: A span selected within a sag section and used as a control to determine the proper sag of the conductor, thus establishing the proper conductor level and tension. A minimum of two, but normally three, sag spans are required within a sag section to sag properly. In mountainous terrain or where span lengths vary radically, more than three sag spans could be required within a sag section.
Scheduled interruption: An interruption caused by a scheduled outage.
Scheduled outage: An outage that results when a component is deliberately taken out of service at a selected time, usually for purposes of construction, preventive maintenance, or repair.
Scheduled outage duration: The period from the initiation of the outage until construction, preventive maintenance, or repair work is completed.
Scheduled maintenance (generation): Capability that has been scheduled to be out of service for maintenance.
SCV: Abbreviation for steam cured (cable insulation).
Seasonal diversity: Load diversity between two (or more) electric systems that occurs when their peak loads are in different seasons of the year.
Secondary, radial: A secondary supplied from either a conventional or completely self-protected (type CSP) distribution transformer.
Secondary current rating: The secondary current existing when the transformer is delivering rated kilovoltamperes at rated secondary voltage.
Secondary disconnecting devices: Self-coupling separable contacts provided to connect and disconnect the auxiliary and control circuits between the removable element and the housing.
Secondary distributed network: A service consisting of a number of network-transformer units at a number of locations in an urban load area connected to an extensive secondary cable grid system.
Secondary distribution feeder: A feeder operating at secondary voltage supplying a distribution circuit.
Secondary distribution mains: The conductors connected to the secondaries of distribution transformers from which consumers’ services are supplied.
Secondary distribution network: A network consisting of secondary distribution mains.
Secondary distribution system: A low-voltage ac system that connects the secondaries of distribution transformers to the consumers’ services.
Secondary distribution trunk line: A line acting as a main source of supply to a secondary distribution system.
Secondary fuse: A fuse used on the secondary-side circuits, restricted for use on a low-voltage secondary distribution system that connects the secondaries of distribution transformers to consumers’ services.
Secondary mains: Those that operate at utilization voltage and serve as the local distribution main. In radial systems, secondary mains that supply general lighting and small power are usually separate from mains that supply three-phase power because of the dip in voltage caused by starting motors. This dip in voltage, if sufficiently large, causes an objectionable lamp flicker.
Secondary network: It consists of two or more network-transformer units connected to a common secondary system and operating continuously in parallel.
Secondary network service: A service that consists of two or more network transformer units connected to a common secondary system and operating continuously in parallel.
Secondary selective service: A service that consists of two distribution transformers, each supplied by an independent primary circuit, and with secondary main and tie breakers.
Secondary spot network: A network that consists of at least two and as many as six networktransformer units located in the same vault and connected to a common secondary service bus. Each transformer is supplied by an independent primary circuit.
Secondary system, banked: A system that consists of several transformers supplied from a single primary feeder, with the low-voltage terminals connected together through the secondary mains.
Secondary unit substation: A unit substation whose low-voltage section is rated 1000 V and below.
Secondary voltage regulation: A voltage drop caused by the secondary system, it includes the drop in the transformer and in the secondary and service cables.
Second-contingency outage: The outage of a secondary primary feeder in addition to the first one.
Sectionalizer: A device that resembles an oil circuit recloser but lacks the interrupting capability.
Service area: Territory in which a utility system is required or has the right to supply or make available electric service to ultimate consumers.
Service availability index: See Index of reliability.
Service drop: The overhead conductors, through which electric service is supplied, between the last utility company pole and the point of their connection to the service facilities located at the building or other support used for the purpose.
Service entrance: All components between the point of termination of the overhead service drop or underground service lateral and the building main disconnecting device, with the exception of the utility company’s metering equipment.
Service entrance conductors: The conductors between the point of termination of the overhead service drop or underground service lateral and the main disconnecting device in the building.
Service entrance equipment: Equipment located at the service entrance of a given building that provides overcurrent protection to the feeder and service conductors, provides a means of disconnecting the feeders from energized service conductors, and provides a means of measuring the energy used by the use of metering equipment.
Service lateral: The underground conductors, through which electric service is supplied, between the utility company’s distribution facilities and the first point of their connection to the building or area service facilities located at the building or other support used for the purpose.
SF6: Formula for sulfur hexafluoride (gas).
St: Abbreviation for steel.
Strand: One of the wires, or groups of wires, of any stranded conductor.
Stranded conductor: A conductor composed of a group of wires, or of any combination of groups of wires. Usually, the wires are twisted together.
Submarine cable: A cable designed for service under water. It is usually a lead-covered cable with a steel armor applied between layers of jute.
Submersible transformer: A transformer so constructed as to be successfully operable when submerged in water under predetermined conditions of pressure and time.
Substation: An assemblage of equipment for purposes other than generation or utilization, through which electric energy in bulk is passed for the purpose of switching or modifying its characteristics.
Substation voltage regulation: The regulation of the substation voltage by means of the voltage regulation equipment that can be load-tap-changing (LTC) mechanisms in the substation transformer, a separate regulator between the transformer and low-voltage bus, switched capacitors at the low-voltage bus, or separate regulators located in each individual feeder in the substation.
Subtransmission: That part of the distribution system between bulk power source(s) (generating stations or power substations) and the distribution substation.
Susceptance: The imaginary part of admittance.
Swell: An increase to between 1.1 and 1.8 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.
Sustained interruption: The complete loss of voltage (<0.1 pu) on one or more phase conductors for a time greater than 1 min.
Switch: A device for opening and closing or for changing connections in a circuit.
Switch, isolating: An auxiliary switch for isolating an electric circuit from its source of power; it is operated only after the circuit has been opened by other means.
Switch, limi: A switch that is operated by some part or motion of a power-driven machine or equipment to alter the electric circuit associated with the machine or equipment.
Switchboard: A large single panel, frame, or assembly of panels on which are mounted (on the face, or back, or both) switches, fuses, buses, and usually instruments.
Switched-capacitor bank: A capacitor bank with switchable capacitors.
Switchgear: A general term covering switching or interrupting devices and their combination with associated control, instrumentation, metering, protective, and regulating devices; also assemblies of these devices with associated interconnections, accessories, and supporting structures.
Switching time: The period from the time a switching operation is required due to a forced outage until that switching operation is performed.
System: A group of components connected together in some fashion to provide flow of power from one point or points to another point or points.
System interruption duration index: The ratio of the sum of all customer interruption durations per year to the number of customers served. It gives the number of minutes out per customer per year.
Total demand distortion (TDD): The ratio of the root-mean-square (rms) of the harmonic current to the rms value of the rated or maximum demand fundamental current, expressed as a percent.
Total harmonic distortion (THD): The ratio of the root-mean-square of the harmonic content to the root-mean-square value of the fundamental quantity, expressed as a percent of the fundamental.
Triplen harmonics: A term frequently used to refer to the odd multiples of the third harmonic, which deserve special attention because of their natural tendency to be zero sequence.
True power factor (TPF): The ratio of the active power of the fundamental wave, in watts, to the apparent power of the fundamental wave, in root-mean-square voltamperes (including the harmonic components).
Underground distribution system: That portion of a primary or secondary distribution system that is constructed below the earth’s surface. Transformers and equipment enclosures for such a system may be located either above or below the surface as long as the served and serving conductors are located underground.
Unit substation: A substation consisting primarily of one or more transformers that are mechanically and electrically connected to and coordinated in design with one or more switchgear or motor control assemblies or combinations thereof.
Undervoltage: A voltage that has a value at least 10% below the nominal voltage for a period of time greater than 1 min.
URD: Abbreviation for underground residential distribution.
Utilization factor: The ratio of the maximum demand of a system to the rated capacity of the system.
VD: Abbreviation for voltage drop.
VDIP: Abbreviation for voltage dip.
Voltage, base: A reference value that is a common denominator to the nominal voltage ratings of transmission and distribution lines, transmission and distribution equipment, and utilization equipment.
Voltage, maximum: The greatest 5 min average or mean voltage.
Voltage imbalance (or unbalance): The maximum deviation from the average of the three-phase voltages or currents, divided by the average of the three-phase voltages or currents, expressed in percent.
Voltage, minimum: The least 5 min average or mean voltage.
Voltage, nominal: A nominal value assigned to a circuit or system of a given voltage class for the purpose of convenient designation.
Voltage, rated: The voltage at which operating and performance characteristics of equipment are referred.
Voltage, service: Voltage measured at the terminals of the service entrance equipment.
Voltage, utilization: Voltage measured at the terminals of the machine or device.
Voltage dip: A voltage change resulting from a motor starting.
Voltage drop: The difference between the voltage at the transmitting and receiving ends of a feeder, main or service.
Voltage flicker: Voltage fluctuation caused by utilization equipment resulting in lamp flicker, that is, in a lamp illumination change.
Voltage fluctuation: A series of voltage changes or a cyclical variation of the voltage envelope.
Voltage interruption: Disappearance of the supply voltage on one or more phases. It can be momentary, temporary, or sustained.
Voltage magnification: The magnification of capacitor switching oscillatory transient voltage on the primary side by capacitors on the secondary side of a transformer.
Voltage regulation: The percent voltage drop of a line with reference to the receiving-end voltage.
% regulation=|ˉEs|−|ˉEr||ˉEr|×100
where
|ˉEs|
|ˉEr| is the magnitude of the receiving-end voltage
Voltage regulator: An induction device having one or more windings in shunt with, and excited from, the primary circuit, and having one or more windings in series between the primary circuit and the regulated circuit, all suitably adapted and arranged for the control of the voltage, or of the phase angle, or of both, of the regulated circuit.
Voltage spread: The difference between maximum and minimum voltages.
VRR: Abbreviation for voltage-regulating relay.
Waveform distortion: A steady-state deviation from an ideal sine wave of power frequency principally characterized by the special content of the deviation.
XLPE: Abbreviation for cross-linked polyethylene (cable insulation).
References
1 IEEE Committee Report: Proposed definitions of terms for reporting and analyzing outages of electrical transmission and distribution facilities and interruptions, IEEE Trans. Power Appar. Syst., PAS-87(5), May 1968, 1318–1323.
2. IEEE Committee Report: Guidelines for use in developing a specific underground distribution system design standard, IEEE Trans. Power Appar. Syst., PAS-97(3), May/June 1978, 810–827.
3. IEEE Standard Definitions in Power Operations Terminology, IEEE Standard 346-1973, November 2, 1973.
4. Proposed standard definitions of general electrical and electronics terms, IEEE Standard 270, 1966.
5. Pender, H. and W. A. Del Mar: Electrical Engineers’ Handbook-Electrical Power, 4th edn., Wiley, New York, 1962.
6. National Electrical Safety Code, 1977 edn., ANSI C2, IEEE, New York, November 1977.
7. Fink, D. G. and J. M. Carroll (eds.): Standard Handbook for Electrical Engineers, 10th edn., McGraw-Hill, New York, 1969.
8. IEEE Standard Dictionary of Electrical and Electronics Terms, IEEE, New York, 1972.