Power Engineering Glossary

The component of power that performs useful work in an AC circuit, measured in watts (W). Also called real power: $P = VI\cos\phi$.

The product of RMS voltage and RMS current: $S = VI$ (measured in VA). It relates to active and reactive power by $S = \sqrt{P^2 + Q^2}$.

A system that continuously adjusts generator outputs to maintain system frequency and scheduled interchange between control areas.

The minimum level of demand on an electrical grid over a period of time, and by extension, the power plants that run continuously to meet that demand at lowest cost.

A metallic strip or bar in a switchgear, substation, or panel board that serves as a common connection point for multiple circuits.

A group of capacitors connected together to supply reactive power and improve power factor at a specific point in the electrical network.

A switching device capable of making, carrying, and breaking currents under normal conditions and interrupting fault currents to protect equipment and personnel.

The simultaneous production of electricity and useful heat from the same fuel source, also known as combined heat and power (CHP). Achieves overall efficiencies of 70-90%.

A power generation configuration using both a gas turbine and a steam turbine in tandem. Exhaust heat from the gas turbine generates steam to drive the steam turbine, achieving efficiencies above 60%.

Ionization of air surrounding a high-voltage conductor that produces power losses, audible noise, and radio frequency interference.

Changes in electric usage by end-use customers from their normal consumption patterns in response to changes in price or incentive payments.

The portion of the electric power system that delivers electricity from distribution substations to end-use customers, typically at voltages from 4 kV to 35 kV.

An optimization process that allocates total system load among available generating units to minimize total fuel cost while respecting operational constraints.

Flexible AC Transmission Systems — power electronics-based devices that enhance controllability and increase power transfer capability of AC transmission systems.

The abnormally high current ($I_f = \frac{V}{Z_f}$) that flows through a circuit during a short circuit. Its magnitude determines equipment ratings and protective relay settings.

The process of maintaining power system frequency at its nominal value (50 or 60 Hz) by balancing generation and load in real time.

A measure of power plant efficiency expressed as the amount of thermal energy input (in BTU or kJ) required to produce one unit of electrical energy output (kWh). Lower heat rate means higher efficiency.

The total opposition to current flow in an AC circuit: $Z = R + jX$, comprising resistance $R$ (real part) and reactance $X$ (imaginary part), measured in ohms.

The ratio of the average load over a given period to the peak load during that period. A high load factor indicates efficient utilization of generation and transmission assets.

A localized electrical network with defined boundaries that includes distributed generation, storage, and loads, capable of operating independently from the main grid.

The ratio of real power to apparent power: $PF = \frac{P}{S} = \cos\phi$. Indicates how effectively electrical power is being used. Unity power factor ($PF = 1.0$) means no reactive power.

The component of AC power that oscillates between source and load: $Q = VI\sin\phi$ (measured in VAR). Necessary for maintaining voltage and supporting magnetic fields.

The extra generating capacity available from units already connected to and synchronized with the grid, able to respond within seconds to compensate for generation or transmission outages.

A facility where voltage is transformed from high to low or vice versa using transformers, and where switching, protection, and metering equipment are located.

The high-voltage network (typically 69 kV to 765 kV) that carries bulk electrical power from generation plants to distribution substations over long distances.