Alternating Current (AC): An electric current that reverses its direction of flow periodically (see Frequency) as contrasted to Direct Current (DC) that constantly flows in one direction. In the US this direction change occurs 60 times a second (60 cycles or 60 hertz).
Ampere (Amp): The unit of measurement for the rate of flow of electric current. It is proportional to the quantity of Electrons flowing through a Conductor past a given point in one second. It is analogous to gallons per minute of water flowing in a water piping system. It is the unit current produced in a Circuit by one volt acting through a Resistance of one ohm.
Apparent Power: That power which is proportional to the mathematical product of the volts and amperes (volt-amps) measured in a Circuit divided by 1,000. It is designated in kilovolt-amperes (kVA) and is comprised of both "real" and "reactive" power.
Bus: An Electrical Conductor that serves as a common "connection" for two (or more) Electrical Circuits. Commonly used in Substations. It may be in the form of "rigid" Bars or Tubes, either circular or rectangular in cross-section, or in the form of Stranded-conductor Overhead Cables held under tension. Provides a quick, convenient means of rearranging Circuit "connections" to keep power flowing or to restore power in case of equipment damage.
Cable: A fully insulated package made of more than one Conductor that can be installed in place of individual Wires.
Capacitor: A device that maintains (or increases) the voltage of Transmission and Distribution Lines that is installed in Substations and on Poles.
Circuit: A Conductor or a system of Conductors providing the "path" through which an electric current flows-or is intended to-flow.
Circuit Breaker: A Switch that automatically disconnects power to a Circuit in the event of an "overloaded" condition caused by too many amps flowing on the Circuit.
Circuit Voltage: The voltage of a Circuit in an electric system is the electric pressure measured in volts. It is generally a "nominal rating" based on the normal difference of voltage between any two Conductors in the Circuit.
Conductor: A Wire, Cable, Busbar, Rod, or Tube that serves as a "path" for electrical flow.
Electric Cooperative (Co-op): A group of persons who have organized a joint venture for the purpose of supplying electric energy to a specified area. Such ventures are generally exempt from Federal Income Tax Laws. Most have been financed by the Rural Electrification Administration and are governed by an elected Board of Directors from the membership.
Cycle: During one Cycle of Alternating Electric Current, the current goes from "zero" potential (or voltage) to a maximum in one direction, back to "zero," then to a maximum in the other direction, and then back again to "zero." The number of such complete Cycles made each second determines the Frequency of the current.
Demand: The "rate" at which electric power is delivered to-or by-a system, part of a system, or a piece of equipment expressed in kilowatts, kilovolt-amperes or other suitable unit at a given instant-or averaged over any designated period of time. The primary source of an Electric Utility's "Demand" is the power-consuming equipment of its customers.
Demand Charge: The specified charge to be billed on the basis of the "demand" used by the customer under an applicable Rate Schedule or contract.
Demand Interval: The period of time during which the electric energy flow is averaged in determining electrical "demand" (i.e. 60-minute, 30-minute, 15-minute or instantaneous).
Design Voltage: The nominal voltage for which a Line or piece of equipment is designed. This is a reference level of voltage for identification-and not necessarily the precise level at which it operates.
Direct Current (DC): Electricity that flows continuously in one direction as contrasted with Alternating Current that flows in one direction than reverses. A Battery produces Direct Current.
Distribution: The act or process of distributing electric energy from convenient points on the transmission or bulk power system to the consumers. A functional classification relating to that portion of a Utility Plant used for the purpose of delivering electric energy from convenient points on the transmission system to the consumers or to expenses relating to the operation and maintenance of a Distribution Plant.
Distribution Feeder Line: An Electric Distribution Line supplying power to customers in a given area. Distribution Feeder Lines are commonly "tapped off" a Main Distribution Circuit to supply only a portion of the load in an area.
Distribution Line: One or more Circuits of an electrical distribution system that operates at less than 39,000 volts on the same line of Poles (or Supporting Structures).
Electric Utilities: All enterprises engaged in the production and/or distribution of electricity for use by the public, including: Investor-owned Electric Utility Companies, Cooperatively-owned Electric Utilities, and Government/municipally-owned Electric Utilities.
Energized System: An operational system capable of supplying the Circuits rated voltage and Frequency. A system can be "energized" without actually supplying load.
Energy: The amount of power consumed over a given time period. As commonly used in the electric utility industry, electric energy is measured in units of kilowatt-hours.
Energy Charge: That portion of the billed charge for electric service based upon the electric energy (kilowatt-hours) used by the customer over some extended time period.
Extra High-Voltage (EHV): A term applied to voltage levels of Transmission Lines that are higher than the voltage levels commonly used. At present, the electric utility industry generally considers EHV to be any voltage greater than 345,000 volts (345 kW).
Fault: A failure (or interruption) in an Electrical Line, Cable, or an associated piece of equipment that create potentially hazardous conditions.
Frequency: The number of "cycles" through which an electric current passes per second. Frequency has been standardized in the North American electric industry at 60 cycles per second (60 hertz). Other areas around the world use either 60-or 50-cycles per second.
Generating Station, Generating Plant, or Power Plant: A facility (or operation) for converting mechanical, chemical, and/or nuclear energy into electric energy.
Ground: The practice of connecting one Wire of an Electrical Circuit to the earth electrically through a Wire and Ground Rod.
Insulation: The protective material covering the electric Wire that does not conduct electricity. Rubber, polyethylene, and thermoplastic materials are commonly used.
Insulator: The porcelain support used to insulate the Electrical Conductors from the Pole (or Tower) of a distribution of transmission system.
Investor-owned Electric Utilities: Those Electric Utilities organized as tax-paying businesses, usually financed by the sale of securities in the free market, and whose properties are managed by an appointed Board of Directors.
Kilovar (kVAR): 1000 "reactive" volt-amperes; the measure of the Reactive Power in an electrical system. (See Reactive Power.)
Kilovolt (kV): A kilovolt is equal to 1,000 volts. The common industry abbreviation is kV.
Kilovolt-amperes (kVA): 1,000 volt-amperes; the measure of the Apparent Power in an electrical system. (See Apparent Power.)
Kilowatt (kW): One (1) kilowatt is equal to 1000 watts; the measure of the Real Power in an electrical system. (See Watts, Real Power.)
Kilowatt-hour (kWH): The unit of electric energy used by most Electrical Utilities and measured by most Electrical Billing Meters. One kilowatt-hour is equal to one kilowatt of power supplied to-or taken from-an Electric Circuit steadily for one hour.
Load: The amount of electric power delivered (or required), at any specified point(s) on a system. Load originates primarily at the power-consuming equipment of the customers. (See Demand.)
Load Factor: The "ratio" of the average load in kilowatts applied during a designated period to the peak or maximum load in kilowatts occurring in that period. Multiplying the kilowatt-hours in the period by 100 and dividing by the product of the maximum demand in kilowatts and the number of hours in the period may also derive Load Factor in Percent.
Line Loss: Can refer to the amount of voltage, power, or energy lost when carrying-current over a "conductive path" due the Resistance of the "conductive path."
Nameplate Rating: The full-load continuous "rating" of a piece of electrical equipment under specified conditions as designated by the manufacturer; it is usually indicated on a Nameplate attached mechanically to the individual Machine or Device.
Ohm: The unit of measurement of electrical Resistance to the flow of current. It is that Resistance through which a difference of potential of one volt will produce a current of one ampere.
Peak Demand: The maximum amount of electrical power produced-or used by-a system during a specified time period.
Pole-Mounted Transformer: The Transformer mounted on a Pole for overhead electrical service which "steps down" primary distribution voltage for use by individual residential customers.
Power (Electric): the ability to do work; the "rate" of generating, transferring, or using electrical energy usually expressed in watts, kilowatts, or megawatts.
Power Factor: the "ratio" of Real Power (kW) to Apparent Power (kVA) for any given load and time generally expressed as a Percentage Ratio.
Primary Voltage: The voltage measured on the "supply side" of any piece of equipment in the electrical system; this is the "side" connected closest to the generation source. The voltage measured on the "output side" of the device connected away from the generation source is called the secondary voltage.
Re-closer: A Switch which functions like a Circuit Breaker, protecting Distribution Circuits from "fault" conditions. A Re-closer will automatically restore the Circuit in the event of a temporary "fault" after a short time period. Such things as Tree Branches brushing the Lines or Lightning can cause temporary "faults."
Reactive Power: The portion of Apparent Power that does no useful work in an Electrical Circuit. It is commonly measured in kilovars (kVARS) and must be supplied to most types of equipment with "Coils" of Wires using magnetic fields (i.e. Motors) to magnetize the Motor Windings. It is supplied by the Generator or by Capacitors.
Real Power: This is the work-producing part of Apparent Power. It is the "rate of supply" of the actual power doing the work and commonly measured in kilowatts (kW).
Relays: Electromechanical Devices that can be used in electrical systems to operate Switches and provide better control of Electrical Devices.
Secondary Distribution System: The lower-voltage system of Circuits and equipment that connects to the distribution system to provide service voltage to customers.
Secondary Circuit: The lower-voltage system of Circuits and equipment that connects to the Distribution Circuit on the low-voltage side of the Transformer between the Distribution Line and customer.
Secondary Voltage: The voltage measured on the "output side" of any piece of equipment in the electrical system. This is the side connected farthest away from the generation source. The voltage measured on the "input side" of the device connected closest to the generation source is called the primary voltage.
Service Drop: The Conductors between the Transformer connected to the Distribution Line and the customer's electrical service.
Step-Down: The process of lowering a Circuit's voltage from a higher-to-lower voltage.
Single-phase Line: A Circuit made up of Wires connected to only one "phase" of a multi-phase system; typically supplies much smaller loads than Three-phase Lines.
Substation: an assemblage of equipment for the purpose of switching and/or changing or regulating the voltage and flow of electricity. It consists of small buildings (or fenced-in yards) containing Switches, Transformers, other equipment, and structures. Adjustments of voltage, monitoring of Circuits, and other service functions take place in this installation.
Three-phase Line: An Electrical Circuit made up of three individual "phases" which collectively supply power at given voltage levels.
Transformer: An "electromagnetic" device for changing the voltage of Alternating- current electricity. A Step-up Transformer increases the voltage from primary-to-secondary, while a Step-down Transformer decreases it.
Transmission: The act or process of transporting electric energy in bulk from a source(s) of supply to other principal parts of the system or to other Utility Systems. Transmission Lines are Lines with voltages exceeding 39,000 volts (39 kV).
Trip: Refers to the action of disconnecting a Circuit to "de-energize" it. Usually refers to action taken while the Circuit was under load.
Turbine-Generator: A rotary-type unit consisting of a Turbine and an Electric Generator for making electricity.
Voltage: The unit of "electromotive force" or "electric pressure" analogous to water pressure in a water piping system that is a measure of the push or force which causes electricity to flow. It is the "electromotive force" of one (1) volt that, if steadily applied to a Circuit having a Resistance of one ohm, will produce a current of one (1) ampere.
Volt-ampere (VA): The basic unit of Apparent Power; the volt-amperes of an Electric Circuit are the mathematical product of the volts and amperes measured in the Circuit.
Voltage Regulator: A type of "adjustable" Transformer which helps maintain consistent voltage on Distribution Lines as the customer's "demand" for electricity changes.
Watt: The electrical unit of power or "rate" of doing work in the metric system; the "rate" of energy transfer equivalent to one (1) ampere flowing under a pressure of one (1) volt at unity power factor. It is analogous to horsepower of "mechanical power" in the English system of units. One horsepower equals 746 watts.