Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
speed of light
(1) a scalar constant in vacuum roughly equal to 3x108 meters per second.

(2) the phase velocity representing the rate of advance of the phase front of a monochromatic light wave.
speed range
the minimum and maximum speeds at which a motor must operate under constant or variable torque load conditions.

A 4:1 speed range for a motor with a top speed of 1800 rpm means that the motor must be able to operate as low as 450 rpm and still remain within regulation specifications. The controllable speed range of a motor is limited by the ability to deliver required torque below base speed without additional cooling.
speed regulation
the variation of the output speed of an electromechanical device as the load on the shaft is increased from zero to some specified fraction of the full load or rated load. Usually expressed as a percentage of the no-load speed. A large speed regulation is most often considered as a bad regulation from a control point of view.
speed sensor
a device used to detect the speed of the rotor of an electric machine. Optical (strobe) and electromagnetic tachometers are commonly used.
speed servo
a servo where the speed is the controlled parameter.
See servo
sphere gap
a spark gap whose electrodes are metal spheres. A sphere gap with carefully-calibrated electrode spacing is used as a measuring instrument for voltages in the kilovolt to megavolt range.
spike

See surge
spike suppressor
any of several devices e.g., metal-oxide varistors that clamp short-duration power line overvoltages to an acceptable level.
spiral inductor
an integrated circuit implementation of a common electrical element that stores magnetic energy. Two extreme behaviors of an inductor are that it will act as a short circuit to low frequency or DC energy, and as an open circuit to energy at a sufficiently high frequency (how high is determined by the inductor value).

In an MMIC, a spiral inductor is realized by a rectangular or circular spiral layout of a narrow strip of metal. The value of the inductance increases as the number of turns and total length of the spiral is increased. Large spiral inductors are very commonly used as "bias chokes" to isolate the DC input connection from the RF circuit. Since a large valued inductor essentially looks like an open circuit to high frequency RF/microwave energy, negligible RF/microwave energy will leak through and interact with the DC bias circuitry.
splice
a permanent connection between two fibers made by melting or fusing the two fibers together in an electric arc or gas flame. Or they may be held together in a variety of mechanical devices that align the two fiber cores. In fusion splicing, connections can be achieved with losses < 0.1 dB.
SPST

See single-pole single-throw
spur
a conductor which branches off of a main line.
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
stability
(1) the condition of a dynamic or closed-loop control system in which the output or controlled variable always corresponds, at least approximately, to the input or command within a limited range. In most devices, this is a measure of the inherent ability of the circuit to avoid internally generated oscillations.

In oscillators, stability denotes the ability of the circuit to maintain a stable internally generated amplitude and frequency. The circuit components, bias, loading, drive and environmental conditions, and possible variations therein, must be accounted for. See also Linville stability factor and Rollett stability factor.

(2) in electronic drives, the ability of a drive to operate a motor at constant speed (under varying load), without hunting (alternately speeding up and slowing down). It is related to both the characteristics of the load being driven and electrical time constants in the drive regulator circuits.
star connection

See Y connection
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