Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

short-circuit test
a transformer test conducted by placing a few percent of rated voltage on the voltage side while the low voltage winding is shorted. By measuring the voltage, current, and input power, it is possible to calculate the equivalent winding impedance for the transformer equivalent circuit.
shunt
(1) a device having appreciable impedance connected in parallel across other devices or apparatus and diverting some of the current from it. Appreciable voltage exists across the shunted device or apparatus, and an appreciable current may exist in it.

(2) an inductive element connected across a power line or bus. Those connected to buses are known as bus-connected reactors, while those connected across a power line are called line-connected reactors.
shunt capacitor
a capacitor or group of capacitors which are placed across an electric power line to provide a voltage increase or to improve the power factor of the circuit. A switchable shunt may be disconnected from the circuit when conditions warrant, while a fixed shunt is permanently connected to the power line.
shunt DC machine
a DC machine with the field winding connected in shunt with the armature. In shunt generators, residual magnetism must be present in the machine iron in order to initiate the generation process. These machines are also known as self-excited, since they supply their own excitation.
shunt field
a field winding of a DC machine consisting of many turns of fine wire, connected in parallel with the armature circuit. It may be connected to the same source as the armature or a separate source.
shunt peaking
use of a peaking coil in a parallel tuned circuit branch connecting the output load of one amplifier stage to the input load of the following stage, in order to compensate for high frequency loss due to the distributed capacitance of the two stages.
shunt reactor
a reactor intended for connection in shunt to an electric system to draw inductive current.
Siemens
Siemens, Ernst Werner von (1816-1892) Born: Lenthe, Hanover, Germany

is best known for the German and British companies that bear his name. Siemens was a strong believer in basic research, as well as an avid inventor. His early inventions included an improved guttapercha wrapped telegraph cable that allowed his companies to secure a number of lucrative cable contracts. His discovery of the dynamo principle, and his use of this in heavy-current applications, allowed his companies to become pioneers in devices to generate electricity and rail applications. Siemens' belief in basic research made him a champion of standards and research institutions that he helped
to establish.
signal-to-noise ratio (SNR)
the ratio of the average power of the information signal component to the average power of the noise component in a signal consisting of the sum of an information signal component and a corrupting noise component. It is a unitless quantity.
SIL

See surge impedance loading
simplex
term used to describe a method of winding the armature of a commutated electric machine in which consecutive coils are placed in adjacent coil slots around the periphery of the rotor. In a lap winding, this produces two parallel electrical path between brushes for each pole pair. In a wave winding, a simplex arrangement produces two parallel electrical paths between brushes regardless of the number of poles. See also duplex, multiplex.
sine transform
usually refers to the discrete sine transform. It also refers to a continuous time transform similar to the Fourier transform.
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.
sinewave brushless DC
a permanent magnet brushless motor with sinusoidally distributed stator phase windings. More
commonly known as permanent magnet synchronous machine.
single dwell detector
a detector in a communications receiver based on a decision on a transmitted symbol being made after a single correlation of the received signal with a reference signal. Compare with multiple dwell detector.
single electron transistor
solid state device that performs electronic functions using a single transistor's electron.
single line to ground fault
a fault on a three phase power line in which one conductor has become connected to ground.
single machine infinite bus system
a model of a power system consisting of a single generator working into an infinite bus which represents the remainder of the system.
single phase to ground fault

See single line to ground fault
single-element fuse
a fuse that is constructed with a single fusible element. It does not meet the standard definition of time-delay.
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