Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

subtransient current
the fault current that flows during the subtransient period when the generator and motor apparent impedances are their respective subtransient impedances.
subtransient impedance
the series impedance that a generator or motor exhibits during the subtransient period, typically the first few cycles of a fault. Subtransient impedances are generally used in calculating fault currents for determining instantaneous relay settings.
subtransient open-circuit time constant
See quadrature-axis transient open-circuit time constant and direct-axis subtransient open-circuit time constant.
subtransmission
the circuits which connect bulk power substations to distribution substations.
subway transformer
another name for a submersible transformer.
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 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.
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