Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

sine-squared pulse
pulse string made from a standard sinewave with an added DC component equal to one-half of the peak-topeak value of the sine wave. The pulse string is, therefore, always positive in value.
slip frequency
the frequency of the rotor induced currents in an induction machine. Denoted by fsl, the slip frequency is given by slip - stator frequency (fs) and is the prime frequency used in slip frequency control of induction machines.
squirrel-cage induction motor
an induction motor in which the secondary circuit (on the rotor) consists of bars, short-circuited by end rings. This forms a squirrel cage conductor structure, which is disposed in slots in the rotor core.
See cage-rotor induction motor
starting torque
the torque at zero speed obtained at the very beginning of the starting process of an electrical machine. The condition to obtain the rotation of the rotor is that the starting torque has to be greater than the load torque at zero speed.
swing equation
a nonlinear differential equation utilized in determining the dynamics of synchronous machines.
See electromechanical equation
torque
the product of a force acting at a total harmonic distortion (THD) an in-distance. The output of an electric motor. dex that quantifies the amount of distortion in the voltage or current waveform with respect torque angle the displacement angle be-to the fundamental component.
torque pulsation
oscillating torque produced by the interaction between the air gap flux, consisting mainly of the fundamental component, and the fluxes produced by harmonics in the rotor. Torque pulsations can stimulate complex mechanical vibrations that can flex and damage rotor and turbine elements.
torque ripple
in variable speed motor drives, refers to the torque not being smooth as the rotor moves from one position to another. Torque ripple may be produced from space harmonics within the machine or time harmonics generated by the supply.
torque servo
a servo where the output torque is the controlled variable and the operating speed depends on the load torque.
See servo
ultra-high frequency (UHF)
electromagnetic spectrum with frequencies between 300 MHz and 3000 MHz or wavelengths between 10 cm and 100 cm. Also called as decimetric waves.
underfrequency relay
a protection device that curtails loads in an area that is deficient in generation. Lower generation compared to load demands give rise to lower frequency and a frequency threshold can be used by the relay to initiate load shedding in order to balance generation and demand.
variable frequency drive
electric drive system in which the speed of the motor can be varied by varying the frequency of the input power.
zero-sequence reactance
the reactive component of the zero sequence impedance.
See symmetrical component