Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

single-pole single-throw (SPST)
a switch that has a pair of input-output ports. By changing its status, the switch works as short or open circuit.
skew
(1) an arrangement of slots or conductors in squirrel cage rotors so that they are not parallel to the rotor axis.

(2) in computer buses, a condition where values on certain bus lines have slightly different transmission times than values on other lines of the same bus. See also tape skew.
skewed symmetry
the nonperpendicular appearance of a symmetry-axes system for an object, when the plane of the object is not perpendicular to the line of sight from the viewpoint.
skewing
(1) the bending of a curve away from it's original shape.

(2) In a differential amplifier, the offset between two signals.
skin effect
the tendency of an alternating current to concentrate in the areas of lowest impedance.
slip
in an induction motor, slip is defined as the ratio of the slip speed to the synchronous speed. The slip speed is the difference between the synchronous speed and the speed of the rotor.
See synchronous speed
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.
slip power recovery control
a method of controlling the speed of a wound rotor induction machine by recovering the slip frequency power from the rotor to an AC power source or mechanical shaft through the converter connected to the rotor windings of the motor. Slip power recovery control reduces the losses that occur with rotor resistance control.
slip-ring contact
a rotating, brush-contacted ring electrode connected to one end of a coil in an AC generator.
slot
a space between the teeth used to place windings in electrical machines.
slot pitch
the angular distance (normally in electrical degrees) between the axes of two slots.
slotless motor
permanent magnet brush-less DC motor in which stator teeth are removed and the resulting space is partially filled with copper. The slotless construction permits an increase in rotor diameter within the same frame size, or alternatively an increase in electric loading without a corresponding increase in current density.
soil electrode
an electrical connection to the soil, often in the form of a metal stake driven into the earth.
solenoid
a wound cylindrical and magnetic material assembly used typically for producing linear motions.
solidly grounded
an electrical distribution system in which one of the normal current-carrying conductors, often the neutral, is intentionally connected to ground with no impedance other than that of the conductor comprising the connection.
solidly grounded system
a grounding scheme in which the neutral wire of a power system is connected to ground at frequent intervals so as to minimize the impedance between neutral and ground.
spark gap
a pressurized high-current switch using a principle of electric field disruption to start the electron flow.
spectrometer
optical instrument that disperses broadband light into its component wavelengths, allowing the measurement of light intensity at each individual wavelength. Spectrometers may use prisms or gratings for wavelength dispersion and any of a variety of light detectors including photomultiplier tubes or charge-coupled devices.
spectrum
(1) a range of electromagnetic energy ordered in accordance with their relative periodicity.

(2) the magnitude of the Fourier transform of a (deterministic) signal. The word spectrum is also used to refer to the power spectrum of a random process. spectrum analyzer a test system that measures RF or microwave devices in terms
of signal frequency and signal power.
speed droop
a linear characteristic that is provided to governors of two or more units operating in parallel for stable load division in case of load increase.
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