NERC Reliability Coordinator Exam Vocabulary Accelerating Power In a GENERATOR, the difference between the MECHANICAL INPUT POWER and the electrica l output POWER (assuming no LOSSES). For a GENERATOR's TORQUE ANGLE to change, the GENERATOR must have accelerating POWER. Accumulated Inadvertent The accumulation over time of INADVERTENT ENERGY. The accumulated inadvertent account of a BALANCING AUTHOR ITY represents the amount of excess ENERGY a BALANCING AUTHORITY has either supplied to the INTERCONNECTION or absorbed from the INTERCONNECTION. BALANCING AUTHORITIES monitor their accumulated inadvertent to ensure the accounts do not grow too large Active Power The component of the COMPLEX POWER that performs the work. The common unit of active power is the MW and the symbol is "P". Active power is sometimes called REAL POWER. Actual Interchange The metered INTERCHANGE over a specific INTERCONNECTI ON between two PHYSICALLY ADJACENT BALANCING AUTHORITIES. Actual Load The actual MW drawn by a LOAD from the POWER SYSTEM. The actual load will be different from the rated or NOMINAL LOAD if the LOAD's VOLTAGE or FREQUENCY vary from their NOMINAL values Adequacy The ability of the electric SYSTEM to supply the aggregate electrical DEMAND and ENERGY requirements of the end -use customers at all times, taking into account SCHEDULED and reasonably expected unSCHEDULEd OUTAGEs of SYSTEM ELEMENTS.ua Adequat e Regulating Margin The minimum on -line CAPACITY that can be increased or decreased to allow the SYSTEM to respond to all reasonable DEMAND changes in order to be incompliance with the CONTROL PERFORMANCE STANDARDS. Adjacent Balancing Authorities A BALAN CING AUTHORITY AREA that is interconnected to another BALANCING AUTHORITY AREA either directly or via a multi -party AGREEMENT or TRANSMISSION TARIFF. AGC Pulses The AGC SYSTEM sends signals to selected (regulating) GENERATORS to adjust their set -points. These signals are sent via telecommunication EQUIPMENT. The signals are often called AGC pulses. Air- Gap The air space between the ROTOR and STATOR of a motor or GENERATOR. Alternating Current (AC) In AC SYSTEM the CURRENT and VOLTAGE magnitudes constantly vary or alternate. CURRENT and VOLTAGE magnitudes do not alternate in a DC SYSTEM. Alternator A Rotating machine whose output is alternating VOLTAGE and CURRENT Aluminum Cable Steel Reinforced (ACSR) A common type of TRANSMISSION line CONDUCTOR that comes in many different sizes and designs. The aluminum is the CONDUCTOR and the steel provides strength. Amortisseur Winding A machine winding consisting of a number of conducting bars attached be tween the magnetic POLES of the machine's ROTOR. Amortisseur windings may be used as starter windings or to help dampen POWER OSCILLATIONS Ampere (amp) The unit of measurement for CURRENT flow, often stated as "amp". Amplitute The value or magnitude th at a waveform has at a specific point in time. Analog Electronics Electronic circuitry in which the magnitudes of quantities are used in a continuous manner to perform functions. For example, input CURRENT values may be amplified and used to perform work in an analog CIRCUIT. Analog is different than digital in the sense that analog CIRCUITS use VOLTAGE and CURRENT magnitudes continuously while digital CIRCUITS use VOLTAGE and CURRENT to determine the state (on or off) of ELEMENTS. Ancillary Services (FERC Definition) Those services that are necessary to support the TRA NSMISSION of CAPACITY and ENERGY from RESOURCES to LOADS while maintaining reliable operation of the TRANSMISSION SERVICE PROVIDER's TRANSMISSION SYSTEM in accordance with GOOD UTILITY PRACTICE. Angle Instability The opposite of ANGLE STABILITY. When a P OWER SYSTEM loses ANGLE STABILITY it enters a PERIOD of angle instability. An angle unstable SYSTEM has lost some portion of the magnetic bound that holds sections of the POWER SYSTEM in synchronism with one another. Angle Stability An angle stable POWER SYSTEM is one in which all ELEMENTS of the POWER SYSTEM are bound together via magnetic forces. For example, an angle stable GENERATOR's internal MAGNETIC FIELD rotates in synchronism (in -step) with the MAGNETIC FIELD of the 3Φ POWER SYSTEM to which it connects. Apparent Power The product of VOLTAGE and CURRENT PHASORS. Apparent power comprises both active and REACTIVE POWER, usually expressed in KILOVOLTAMPEREs (kVA) or megavoltamperes (MVA). Another term for apparent power is COMPLEX POWER. ARC The d ischarge of CURRENT through the air or in a gas. Arcing Horns An enhancement to a DISCONNECT SWITCH to increase the switch's CURRENT interrupting capability.
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