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- Alternating current (AC)
- That form of electric current that alternates or changes in magnitude and polarity (direction) in what is normally a regular pattern for a given time period called frequency.
- Ampere (AMP)
- The unit of current flow of electricity. It is to electricity as the number of gallons per minute is to the flow of water. One ampere flow of current is equal to one coulomb per second flow.
- Apparent power
- For single phase, the current in amperes multiplied by the volts equals the apparent power in volt-amperes. This term is used for alternating current circuits because the current flow is not always in phase with the voltage; hence, amperes multiplied by volts does not necessarily give the true power or watts. Apparent power for 3 phase equals the phase to neutral volts multiplied by ampere multiplied by 3.
- Automatic reclosing
- A circuit breaker has automatic reclosing when means are provided for closing without manual intervention after it has tripped under abnormal conditions.
- Automatic tripping (automatic opening; automatic disconnecting)
- The opening of a circuit breaker under predetermined conditions without the intervention of an operator.
- Avoided costs
- Avoided costs are the incremental costs to an electric utility of electric energy or capacity or both which, but for the purchase from the qualifying facility or qualifying facilities, the utility would generate itself or purchase from another source.
- Balanced load
- An equal distribution of current on all phases of an AC circuit.
- Bidirectional meter
- A meter that separately measures both the energy flowing from the utility to the customer and energy flowing from the customer’s generator to the utility.
- Capacity
- The number of amperes of electric current a wire will carry without becoming unduly heated; the capacity of a machine, apparatus or device, is the maximum of which it is capable under existing service conditions; the load for which a transformer, transmission circuit, apparatus, station or system is rated; for a generator, turbine, the URGE rating.
- Circuit
- A conducting path through which an electric current is intended to flow.
- Circuit breaker
- A device for interrupting a circuit between separable contacts under normal or fault conditions.
- Cogeneration
- The concurrent production of electricity and heat, steam or useful thermal energy from the same fuel source.
- Current
- A flow of electric charge measured in amperes.
- Delta-connected circuit
- A three phase circuit with three source windings connected in a closed delta (triangle). A closed delta is a connection in which each winding terminal is connected to the end (terminal) of another winding.
- Demand
- The rate at which electric power is delivered to or by a system; normally expressed in kilowatts, megawatts, or kilovolt-amperes.
- Direct current (DC)
- An electric current flowing in one direction only and substantially constant in value.
- Disconnect
- A device used to electrically isolate a piece of equipment. A disconnect may be gang operated (all poles switched simultaneously) or individually operated.
- Dispatchable
- Capable of having generator output (real and reactive power) adjusted ("dispatched") upon request of the power system operator. The adjustment includes capability to start-up and shut down generating units.
- Distributed generation
- A generating facility located near customer loads.
- Energy losses
- The general term applied to energy lost in the operation of an electrical system. Losses can be classified as transformation losses, transmission line losses or system losses.
- Federal Energy Regulatory Commission (FERC)
- Formerly the Federal Power Commission (FPC). FERC is an independent body within the Department of Energy regulating interstate transmission, prices of electricity and natural gas. It also licenses hydroelectric projects, interconnections, construction work in progress, rates for wholesale customers, utility accounting practices and procedures.
- Frequency
- The number of cycles occurring in a given interval of time (usually one second) in an electric current. Frequency is commonly expressed in hertz.
- Fuse
- A short piece of conducting material of low melting point which is inserted in a circuit for the purpose of opening the circuit when the current reaches a certain value.
- Generator
- Any device that converts one form of energy (mechanical, chemical or heat) into electrical energy and produces either direct or alternating current.
- Grid
- The transmission network (or “highway”) over which electricity moves from suppliers to customers.
- Ground
- A term used in electrical work in referring to the earth as a conductor or as the zero of potential. For safety purposes, circuits are grounded while any work is being done on or near a circuit or piece of equipment in the circuit; this is usually called protective or safety grounding.
- Hertz
- The term denoting frequency, equivalent to cycles per second.
- Interconnection
- The physical system of electrical transmission between the Customer's generation and the utility.
- Interruption
- A temporary discontinuance of the supply of electric power.
- Inverter
- A device that turns DC voltage into AC voltage.
- Independent Power Producer (IPP)
- A nonutility company engaged in the generation, transmission, and/or distribution of electric energy for sale in diverse markets.
- Island
- A part of an interconnected system may be isolated during a system disturbance and start operating as a subsystem with its own generation, transmission and distribution capability. Then the subsystem becomes an island of the main interconnected system without a tie. In such a case, the islanded system and the main interconnected system will operate at different frequencies and voltages.
- Kilovolt (kV)
- One thousand volts.
- Kilovolt-ampere (kVA)
- One thousand volt amperes. See the definition for “apparent power.”
- Kilowatt (kW)
- An electric unit of power which equals 1,000 watts.
- Kilowatt hour (kWh)
- One thousand watts of power supplied for one hour. A basic unit of electric energy equal to the use of 1 kilowatt for a period of one hour.
- Line losses
- Electrical energy converted to heat in the resistance of all transmission and/or distribution lines and other electrical equipment.
- Merchant plant
- A merchant plant is a power generation facility whose energy is sold on the open market. The generation facility will interconnect to the local utility's transmission or distribution system but the energy will be sold to a third party.
- NAERO — North American Electric Reliability Organization.
- Formerly NERC. A national organization responsible for establishing the operating and planning standards to assure the reliability of the electric grid.
- NERC — North American Electric Reliability Council
- In the process of reorganizing as NAERO (North American Electric Reliability Organization). A national organization responsible for establishing the operating and planning standards to assure the reliability of the electric grid.
- Net metering
- The process that allows generation to be made available to the company from a consumer who owns and operates a solar, wind, fuel cell or hydroelectric facility with a generating-installed capacity of 25 kW or less. The facility must operate in parallel with the company’s existing facilities and be primarily intended to offset part or all of the consumer’s own electrical requirements. The consumer-generator shall be credited/charged for the net energy supplied.
- Nonspinning reserve
- All unloaded generating capability not meeting the Spinning Reserve criteria that can be made fully effective in 10 minutes. This may include generation that shall be made available within 10 minutes by interrupting or curtailing loads or changing schedules.
- OASIS — Open Access Same-time Information System
- An Internet-based system designed to allow all participants in the power market to obtain information concerning the capability and use of the transmission system in a nondiscriminatory manner.
- Ohm
- The practical unit of electrical impedance equal to the resistance of a circuit in which a potential difference of 1 volt produces a current of 1 ampere.
- One-line diagram
- A diagram in which several conductors are represented by a single line and in which various devices or pieces of equipment are denoted by simplified symbols. The purpose of such a diagram is to present an electrical circuit or circuits in a simple way so that their function can be readily grasped.
- Operating reserve
- The sum of spinning and nonspinning reserve.
- Parallel operation
- The operation of a customer-owned generator while connected to the utility’s grid. Parallel operation may be required solely for the customer’s operating convenience or for the purpose of delivering power to the utility’s grid.
- Peak load
- The maximum electric load consumed or produced in a stated period of time.
- Peak shaving
- Generator operation which results in reducing customer’s peak load or demand.
- Photovoltaic (PV)
- Solar cells that convert light to electrical energy.
- Point of interconnection
- The point where the customer’s conductors meet the company’s conductors.
- Power
- Actual, active or real power. The time rate of transferring or transforming energy or the power that accomplishes work. Measured in watts.
- Power factor
- The ratio of actual power (kW) to apparent power (kVA).
- Protection
- All of the relays and other equipment which are used to open the necessary circuit breakers to clear lines or equipment when trouble develops.
- Qualifying facility (QF)
- A power generating facility that has met criteria as defined in the Code of Federal Regulations, 18CFR292.203 to be certified by FERC as a “qualifying facility” and that has rights established by the PURPA of 1978.
- Reactive power (VAR)
- The power that oscillates back and forth between inductive and capacitive circuit elements without ever being used. The function of reactive power is to establish and sustain the electric and magnetic fields required to perform useful work.
- Reclose
- To return a circuit breaker to its closed position after it has opened by relay action.
- Relay
- A device that is operative by a variation in the condition of one electric circuit to affect the operation of another device in the same or in another electric circuit.
- Small power production facility
- A small power production facility produces electricity using as a primary energy source biomass, waste, renewable resources, or any combination thereof as defined in the Code of Federal Regulations, 18CFR292.203.
- Spinning reserve
- The amount of unloaded generating capability of a participant connected to and synchronized with the interconnected system of the participants and ready to take load. Spinning reserve allocation to any generator shall not exceed the amount of generation increase that can be realized in 10 minutes.
- Switch
- A device for making, breaking or changing the connections in an electric circuit.
- Synchronism
- Expresses the condition across an open circuit wherein the voltage sine wave on one side matches the voltage sine wave on the other side in frequency and amplitude without phase angle difference.
- System
- The entire generating, transmitting and distributing facilities of an electric company.
- Transformer
- An electric device, without continuously moving parts, in which electromagnetic induction transforms electric energy from one or more other circuits at the same frequency, usually with changes of value of voltage and current.
- Voltage
- Electric potential or potential difference expressed in volts.
- Volt-ampere
- A unit of apparent power in an alternating-current circuit.
- VAR
- Volt ampere reactive; see “reactive power.”
- Watt-hour
- A unit of work or energy equivalent to the power of one watt operating for one hour.
- WECC — Western Electric Coordinating Council
- Responsible for coordinating and promoting electric system reliability, supporting efficient competitive power markets, and assuring open and nondiscriminatory transmission access among members.
- Wheeling
- The use of transmission facilities of one utility system to transmit power to another utility system, or between customer facilities within a single utility system or between systems.
- WSCC — Western Systems Coordinating Council
- Merged with Southwest Region Transmission Association in 2002 forming the WECC.
- Wye or “Y” connected circuit (star connected)
- A three-phase circuit in which windings of all three phases have one common connection.
- Time Of Use (TOU)
- Energy use is charged different rates depending on the time that it is used. Usually differentiated into on-peak, mid-peak, and off-peak time and price ranges.
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