PEC EPE Electrical key terms

The real component of AC power actually converted into useful work such as heat, light, or mechanical motion, measured in watts. It equals voltage times current times power factor in single-phase circuits.

Power that oscillates between source and reactive elements without doing net work, measured in volt-amperes reactive. It sustains magnetic fields in inductors and electric fields in capacitors and is needed for voltage support.

The product of RMS voltage and RMS current in an AC circuit, measured in volt-amperes. It is the vector sum of active and reactive power and determines the rating of transformers and generators.

The ratio of active power to apparent power in an AC circuit, equal to the cosine of the phase angle between voltage and current. A low value means more current is drawn for the same useful power.

Adding capacitors or other compensators in parallel with an inductive load to reduce the phase angle between voltage and current, raising power factor toward unity and cutting line current and losses.

A group of capacitors connected in parallel or series, switched in steps, used to supply reactive power locally for power factor correction or voltage support on distribution feeders.

A polyphase arrangement of three sinusoidal voltages equal in magnitude and displaced by 120 electrical degrees. It gives constant total power and is the standard for generation, transmission, and industrial motors.

A three-phase winding arrangement in which one end of each phase joins at a common neutral point. Line voltage equals phase voltage times root three, while line current equals phase current.

A three-phase winding arrangement in which the phases form a closed loop, with each phase connected between two lines. Line current equals phase current times root three, while line and phase voltages are equal.

The order in which the three phase voltages of a polyphase supply reach their positive maximum values. Reversing the sequence reverses rotation direction of three-phase induction motors.

Any linear two-terminal network can be replaced by a single voltage source in series with a single resistance. The source equals the open-circuit voltage and the resistance is found with sources deactivated.

Any linear two-terminal network can be replaced by a single current source in parallel with a single resistance. The current equals the short-circuit current and the resistance matches the Thevenin resistance.

In a linear circuit with multiple independent sources, the response in any branch equals the algebraic sum of the responses caused by each source acting alone while the others are deactivated appropriately.

A source delivers maximum power to a load when the load resistance equals the source's Thevenin resistance. Under this condition efficiency is only fifty percent, so it is not used for power systems.

A condition in an AC circuit containing inductance and capacitance where inductive and capacitive reactances cancel, making the circuit purely resistive and the current maximum or minimum depending on topology.

A dimensionless measure of the sharpness of a resonant circuit, equal to the ratio of stored energy to energy dissipated per cycle. Higher values give narrower bandwidth and greater selectivity.

Adjusting load impedance so it equals the complex conjugate of source impedance, maximizing power transfer and minimizing reflections in high-frequency and communication circuits.

A method that resolves an unbalanced three-phase set of voltages or currents into three balanced sets called positive, negative, and zero sequence, simplifying fault and unbalance analysis.

Calculation of fault currents and voltages at points in a power network for short-circuit, line-to-ground, or open-circuit conditions, used to select protective devices and rate equipment.

A normalization method in power systems where quantities are expressed as fractions of chosen base values of voltage, current, power, and impedance, simplifying transformer ratios and calculations across voltage levels.

A static electromagnetic device with two or more coupled windings that transfers electrical energy between circuits at different voltage levels through mutual induction while preserving frequency and approximately conserving power.

The ratio of the number of turns in a transformer's primary winding to the number in its secondary winding. It determines the ratio of voltages and the inverse ratio of currents.

Power dissipated as heat in the windings of a transformer or machine due to current flowing through their resistance. It varies with the square of the load current.

Power lost in the magnetic core of a transformer or machine from hysteresis and eddy currents. It is approximately constant at fixed voltage and frequency, independent of load.

The change in secondary terminal voltage of a transformer or generator from no load to full load, expressed as a percentage of rated voltage at a specified power factor.

An AC machine in which the rotating magnetic field of the stator induces currents in a rotor winding, producing torque without electrical connection to the rotor. It is the most common industrial drive.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a fraction or percentage of synchronous speed. It must be nonzero to induce rotor current.

The speed of the rotating magnetic field produced by a polyphase winding, equal to one hundred twenty times frequency divided by number of poles, in revolutions per minute.

An AC machine whose rotor turns at exactly synchronous speed and whose field excitation controls terminal voltage and reactive power output. It is the standard machine for bulk power generation.

The equipment that supplies and regulates direct current to a synchronous machine's field winding, controlling terminal voltage, reactive power, and stability of the generator.

A closed-loop controller that adjusts a generator's field excitation to hold terminal voltage at a setpoint despite changes in load, and to manage reactive power sharing.

The electrical angle by which the rotor of a synchronous machine leads the resultant air-gap magnetic field. It increases with load and determines the steady-state stability margin.

A device that continuously monitors currents, voltages, or other quantities and initiates tripping of circuit breakers when it detects a fault or abnormal condition within its protected zone.

A switching device capable of making, carrying, and interrupting normal and fault currents, with the arc extinguished in a controlled medium such as air, oil, vacuum, or sulphur hexafluoride.

A protective scheme that operates when current exceeds a preset threshold for a set time, using definite-time or inverse-time characteristics to isolate faults while allowing normal overloads.

A unit protection scheme that compares currents entering and leaving a protected zone and trips when their difference exceeds a threshold, giving fast and selective detection of internal faults.

Connecting exposed conductive parts or a neutral point to the general mass of earth, providing a low-impedance path for fault current and limiting touch and step voltages for safety.

A system of conductors, insulators, and towers that carries electrical energy at high voltage over long distances between generation and load centers, minimizing losses and voltage drop.

The load at which a lossless transmission line's reactive power generated by its capacitance equals that absorbed by its inductance, giving flat voltage profile and unity power factor.

Ionization of air around a high-voltage conductor when surface voltage gradient exceeds breakdown strength, causing power loss, audible noise, and radio interference, especially in humid conditions.

The ability of a power system to return to a steady operating point after a disturbance. Rotor angle, voltage, and frequency stability are the main categories studied in system planning.

The systematic application of Kirchhoff's laws, node or mesh equations, and network theorems to determine voltages and currents in an electrical network under given source conditions.

The principle that the algebraic sum of currents entering any node of a network is zero, expressing conservation of charge at a junction.

The principle that the algebraic sum of voltage drops and rises around any closed loop of a network is zero, expressing conservation of energy per unit charge.

A network containing resistance, inductance, and capacitance whose behavior is described by a second-order differential equation, exhibiting transient oscillation and resonance.