NERC Reliability Coordinator Exam Vocabulary (Updated 2023 -2024) Questions and Answers with Complete Solutions Accelerating Power - Answer In a GENERATOR, the difference between the MECHANICAL INPUT POWER and the electrical output POWER (assuming no LOSSES). For a GENERATOR's TORQUE ANGLE to change, the GENERATOR must have accelerating POWER. Accumulated Inadvertent - Answer The accumulation over time of INADVERTENT ENERGY . The accumulated inadvertent account of a BALANCING AUTHORITY 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 - Answer 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 - Answer The metered INTERCHANGE over a specific INTERCONNECTION between two PHYSICALLY ADJACENT BALANCING AUTHORITIES. Actual Load - Answer 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 - Answer 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 Adequate Regulating Margin - Answer 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 - Answer A BALANCING AUTHORITY AREA that is interconnected to another BALANCING AUTHORITY AREA either directly or via a multi -party AGREEMENT or TRANSMISSION TARIFF. AGC Pulses - Answer 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 - Answer The air space between the ROTOR and STATOR of a motor or GENERATOR. Alternating Current (AC) - Answer In AC SYSTEM the CURRENT and VOLTAGE magnitudes constantly vary or alternate. CURRENT and VOLTAGE magnitudes do not alternate in a DC SYSTEM. Alternator - Answer A Rotating machine whose output is alternating VOLTAGE and CURRENT Aluminum Cable Steel Reinforced (ACSR) - Answer 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 - Answer A machine winding consisting of a number of conducting bars attached between the magnetic POLES of the machine's ROTOR. Amortisseur windings may be used as starter windings or to help dampen POWER OSCILLATIONS Ampere (amp) - Answer The unit of measurement for CURRENT flow, often stated as "amp". Amplitute - Answer The value or magnitude that a waveform has at a specific point in time. Analog Electronics - Answer 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) - Answer Those services that are necessary to support the TRANSMISSION 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 - Answer The opposite of ANGLE STABILITY . When a POWER 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 - Answer 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 - Answer 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 - Answer The discharge of CURRENT through the air or in a gas. Arcing Horns - Answer An enhancement to a DISCONNECT SWITCH to increase the switch's CURRENT interrupting capability. Area Control Area (ACE) - Answer The instantaneous difference between net actual and SCHEDULED INTERCHANGE, taking into account the effects of FREQUENCY bias including a correction for meter error. Armature - Answer The component of a machine in which the VOLTAGE is induced. In a SYNCHRONOUS GENERATOR the armature is usually the STATOR. The armature winding is wrapped about the armature. Asynchronous - Answer To be OUT -OF-STEP with a reference. An induction GENERATOR is an asynchronous GENERATOR as its ROTOR does not rotate in synchronism with the POWER SYSTEM. Auto -Load - Answer A feature on some GENERATORS that automatically moves the GENERATOR to a TARGET LOAD (MW) level. Automatic Generation Control (AGC) - Answer EQUIPMENT that automatically adjusts GENERATION in a BALANCING AUTHORITY AREA from a central location to maintain the BALANCING AUTHORITY's INTERCHANGE SCHEDULE plus FREQUENCY BIAS. AGC may also accommodate automatic INADVERTENT payback and TIME ERROR CORRECTION. Automatic Operations Systems - Answer SPECIAL PROTECTION SYSTEMS, REMEDIAL ACTION SCHEMEs, or other operating SYSTEMs installed on the electric SYSTEMs that require no intervention on the part of SYSTEM OPERATORS. Auto -Transformer - Answer A POWER TRANSFORMER with a single coil. The entire coil acts as the PRIMARY WINDING while a portion of the same coil acts as the SECONDARY WINDING. Auxiliary Relay - Answer A RELAY whose function is to supplement the actions of other types of RELAYS. For example, a LOCKOUT RELAY is an auxiliary relay with numerous contacts that each can perform an action. The IEEE has numbers assigned to two types of auxiliary relays; 86 (lock -out) and 94 (tripping). Availability - Answer A measure of time a generating unit, TRANSMISSION line, or other FACILITY is capable of providing service, whether or not it actually is in service. Typically, this measure is expressed as a percent available for the PERIOD under consideration.
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