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NERC-Transmission Exam | Actual Questions and Answers Latest Updated
2025 /202 6 (Graded A+)
Current Transformer - ✔✔Instrument Transformers design for transforming large current magnitudes to secondary current suitable for relaying and metering. The secondary current flow is proportional to the larger primary current flow. Cycle - ✔✔One full sine wave cycle that is divided into 360 Degrees. The waveform passes through zero, Rises to a maximum, drops back to zero, drops to a minimum, then rises again to zero. Both current and voltage in North America Power Systems have cycle wave forms that will a repeat 60 times a second. Fault - ✔✔An event occurring on an electric system such as a short circuit, a broken wire, or intermittent connection. Misoperation - ✔✔The failure of a Composite Protection System to operate as intended for protection purposes. Overlapping Zone - ✔✔Where two or more protective relay zones overlap at an electrical circuit of device. This ensures complete protection of the system. Pilot relaying - ✔✔Used to provide selective and high-speed tripping for any fault location on the protected line by establishing Communications between relays. Potential Transformer - ✔✔Also known as PT's transform primary voltage to a smaller secondary voltage suitable for metering relaying. The secondary voltage is usually around 120 volts and is proportional to the higher primary voltage. Power line carrier (PLC) - ✔✔This is a way of using power lines to carry Communications. It can be used to provide Communications between protective relays at either end of a transmission line. Protection system - ✔✔Protective relays, communication systems, voltage and current sensing devices, Station DC Supply associated with protective functions, and control circuitry associated with protective functions.
Wave trap - ✔✔A filter used to remove the power line carrier signal from the line and Route it to the line protective relays. Zones of protection - ✔✔The zones areas within which a protective Relay can sense abnormal conditions. Contingency - ✔✔The unexpected failure or outage of a system component, such as a generator, transmission line, circuit breaker, switch, or other electrical element. Emergency Rating - ✔✔The rating as defined by the equipment owner that specifies the level of electrical loading or output, usually expressed in megawatts (MW) or Mvar or other appropriate units, that a system, facility, or element can support, produce, or withstand for a finite period. The rating assumes acceptable loss of equipment life or other physical or safety limitations for the equipment involved. Facility rating - ✔✔The maximum or minimum voltage, current, frequency, or real or reactive power flow through a facility that does not violate the applicable equipment rating of any equipment comprising the facility. Operation Instructions - ✔✔A command by operating personnel responsible for the Real-time operation of the interconnected BES to change or preserve the state, status, output, or input of an Element of the BES. Operating Reserves - ✔✔That capability above firm system demand required to provide for regulation, load forecasting error, equipment forced and scheduled outages and local area protection. It consists of spinning and non-spinning reserve. Reactive Power - ✔✔The portion of electricity that establishes and sustains the electric and magnetic fields of AC equipment. It must be supplied to most types of magnetic equipment, such as motors and transformers. It must supply the reactive losses on transmission facilities. It is provided by generators, synchronous condensers, or electrostatic equipment such as cap0acitors and directly influences electric system voltage. It is usually expressed in kilovars (kvar) or megavars (Mvar).
System Operating Limits (SOL) - ✔✔The value (such as MW, Mvar, amperes, frequency, or volts that) that satisfies the most limiting of the prescribe operating criteria for a specific system configuration to ensure operation within acceptable reliability criteria. Transmission Congestion - ✔✔When a transmission path(s) does not have sufficient capacity to transfer power from source to demand. disturbance - ✔✔An unplanned event that produces an abnormal system condition. Interconnection reliability operating limit (IROL) - ✔✔A System Operating Limit that, if violated, could lead to instability, uncontrolled separation, or Cascading outages that adversely impact the reliability of the Bulk Electric System. Impedence - ✔✔A measure of the total opposition to current flow in an alternating current circuit. It has two components resistance and reactance. Phase angle - ✔✔The angular separation between the current and voltage Cycles. Power Angle - ✔✔Voltage angular difference between two locations in the power system. Voltage - ✔✔The force that causes current to flow in a conductor. Separation of charge between two points in a conductor gives rise to a potential difference or a voltage. Bulk Electric System - ✔✔All Transmission Elements operated at 100 KV or higher and Real Power and Reactive Power resources connected at 100 KV or higher N- 1 Contingency Planning - ✔✔The "Normal" [N] state minus the next contingency = N-1, planning the system to be reliable for the unexpected failure or outage of any single system component. Operational Planning Analysis - ✔✔An evaluation of projected system conditions to assess anticipated (pre-Contingency) and potential (post-Contingency) conditions for next-day operations. The evaluation
shall reflect applicable inputs including, but not limited to, load forecasts; generation output levels; Interchange; known Protection System and Special Protection System status or degradation; Transmission outages; generator outages; Facility Ratings; and identified phase angle and equipment limitations. (Operational Planning Analysis may be provided through internal systems or through third- party services.) Power Flow Study - ✔✔Also known as a load-flow study, it is a study that usually uses simplified notation such as a one-line diagram and a per-unit system, and focuses on various aspects of AC power parameters, such as voltages, voltage angles, real power, and reactive power. It analyzes the power system in steady state operation to obtain the magnitude and phase angle the voltage at each bus, and the real and reactive power flowing in each line. Reliability Operating Instructions - ✔✔A command by operating personnel responsible for the real-time operation of the interconnected BES to change or preserve the state, status, output, or input of an element of the BES or facility of the BES. Energy Emergency - ✔✔A condition when a Load-Serving Entity has exhausted all other options and can no longer provide its customers' expected energy requirements. Surge Impedance Load - ✔✔The MW loading on a TRANSMISSION line at which the line's natural REACTIVE POWER production equals its REACTIVE POWER usage. A line loaded above this level will be more inductive than capacitive and absorb MVARs causing voltage to drop.
