Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

voltage change
a deviation of the peak or RMS voltage between two levels that are of some fixed duration.
voltage dip

See sag
voltage distortion
a change from a nominal clean sinusoidal waveform
voltage drop
the difference in potential between the two ends of the resistor measured in the direction of flow current. The voltage drop is V = IR, where V is voltage across the resistor, I is the current through the resistor, and R is the resistance.
voltage fed inverter

See voltage source inverter
voltage instabilityproximity index
an index that gives an indication of the amount of real or reactive power margin available in the system before a voltage collapse occurs.
voltage interruption
the removal of the supply voltage from any phase, which is of momentary, sustained, of temporary duration.
voltage protection
the output voltage is limited to protect the load from an overvoltage condition. This can be accomplished by shunting the power-supply output or shutting down the drive circuit for the active switches in a switching supply if the output voltage exceeds a preset value.
voltage rating
the maximum voltage that may be applied to the resistor.
voltage regulating relay
a voltage regulating relay senses RMS voltage level and issues commands to devices such as load tap changers, which then adjust the tap position to bring the voltage back to the desired level.
voltage regulation
the change in delivered voltage from a generator or transformer from no-load to full-load. Voltage regulation is usually expressed as a percentage of the no-load voltage. For a DC generator, the voltage will always drop as the load increases and the voltage regulation will be a positive quantity. For AC generators and transformers, voltage regulation is the difference in the magnitude of the no-load and full-load voltages (ignoring phase angles). For capacitive (leading power factor) loads, the full-load voltage may have a higher magnitude than the no-load voltage, resulting in negative voltage regulation. Such a condition may lead to instability and is undesirable.
voltage regulator
similar to a voltage reference, but provides more output current at a less precisely controlled voltage. Primarily used to "clean up" (regulate) a varying input voltage to provide circuitry with a constant power supply voltage.
voltage source inverter
a power converter that takes a DC voltage from a battery or the output of a rectifier and supplies a voltage of controllable and variable frequency and magnitude to a single or multiphase load.
See current source inverter
voltage spread
the difference between a power system's specified maximum and minimum voltages.
voltage stability
a measure of power system stability which considers the system's capacity to support a given load.
voltage transformer
an instrument transformer specially designed and optimized for voltage measurement and power metering applications. The primary winding is rated to match the system voltage and the secondary is typically rated at a standard value to match common meters and display units.
See potential transformer
voltage unbalance
refers to the greatest change of the polyphase voltages from the average polyphase voltage divided by the average polyphase voltage.
voltage unit
a protective unit (in protective relaying) whose operation depends exclusively on the magnitude of voltage.
voltage variation
in short duration a change of the voltage RMS value from nominal for a time period from 0.5 cycles to 1 minute, and can be used with the words sag, swell, and interruption for magnitude changes, and the words instantaneous, momentary, of temporary for showing duration.
voltage-behind-reactance model
a representation of a machine in which the stator voltage equations are modeled as a voltage source in series with a reactance (and typically a resistance). The voltage source represents the back emf present on the stator windings due to the coupling between the stator and rotor circuits. In synchronous machine modeling, several different voltage-behindreactance models have historically been used, wherein approximations are used to represent the machine in various detail.
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