Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

sulfur hexaflouride
a heavy, highly-electronegative gas used as a high-voltage, self-healing insulation.
superfluorescence
usually refers to the enhanced spontaneous emission that occurs due to self-organization into a coherent state by a system of atoms or molecules.
superheater
a heat exchanger that increases the steam temperature to about 1000 degrees F. It is heated by the flue gases.
superparamagnetism
a form of magnetism in which the spins in small particles are exchange coupled by may be collectively switched by thermal energy.
surge
a short-duration (microsecond to millisecond) increase in power line voltage.
See spike
surge arrestor
a device that limits overvoltages by conducting large currents in response to an overvoltage. Surge arrestors are typically connected line to ground in transmission and primary distribution systems. They can be employed in a variety of connections in secondary distribution, and can be necessary in communications, sensing, and control circuits.
surge impedance
the ratio of voltage to current on that line for a high speed wave propagating down the line. The surge impedance of a line is a constant which depends on the line geometry and conductor characteristics. On power transmission lines, these waves are typically generated by lightning strokes, circuit breaker switching, etc.
See characteristic impedance
surge impedance loading (SIL)
of a transmission line, the characteristic impedance with resistance set to zero (resistance is assumed small compared to reactance). The power that flows in a lossless transmission line terminated in a resistive load equal to the line's surge impedance is denoted as the surge impedance loading of the line.
surge response voltage
the voltage that appears at the output terminals of surge protection equipment and is seen by loads connected to that device both during and after a surge condition.
surge tank
an empty vessel located at the top of the penstock. It is used to store water surge when the turbine valve is suddenly closed.
susceptibility
the part of the permittivity or permeability that is attributable to the electromagnetic behavior of the medium. In a linear, isotropic medium, the electric susceptibility is numerically equal to the relative permittivity minus one, and the magnetic susceptibility is equal to the relative permeability minus one. See also electric susceptibility.
sustained interruption
all interruptions that are not momentary. Generally used when referring to long duration voltage interruptions of greater than 1 minute.
Swan
Swan, Joseph (1828-1914) Born: Sunderland, England
is best known as the inventor of the incandescent lamp. During his life he acquired seventy patents in many areas. He was a devoted experimentalist with interests in photography, the development of miner's lamps, batteries, electroplating, and artificial silk. Swan teamed with Edison in 1883 to form the Edison and Swan United Electric Light Company after Edison's suit for patent infringement was dismissed. J. W. Starr and W. E. Staite were the early pioneers who inspired Swan to research that led to his knighthood in 1904.
swell
a voltage or current RMS value at supply frequency that increases for a time period from 0.5 cycles to 1 minute.
swing bus
in power-flow studies, a bus in the power system which is assigned unknown real and reactive power so as to compensate for losses in the system.
swing curve
a sinusoidal variation of a parameter, such as the critical dimension or the dose-to-clear, as a function of resist thickness caused by thin film interference effects.
swing equation
a nonlinear differential equation utilized in determining the dynamics of synchronous machines.
See electromechanical equation
switch
(1) a device that allows current flow when closed and provides isolation when open. The switch provides similar functions to the circuit breaker, but cannot interrupt fault currents. Some switches are capable of making and breaking load currents, while others are only able to break charging current. Switches can be either manually controlled or motor controlled. See also single-pole single-throw, single-pole double-throw, transmit/receive switch, all-optical switch.

(2) a device comprising a number of input and output ports and circuitry to switch packets from one input port to one or more output ports based on the addressing information contained in the packet header.
switchable shunt

See shunt capacitor
switchboard
literally, a large panel or board upon switches were mounted in early electrical systems.