Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

rotational loss
one of several losses in a rotating electric machine that are primarily due to the rotation of the armature and include the friction and windage losses. Also called mechanical loss. They can be determined by running the machine as a motor at its rated speed at no load, assuming the armature resistance is negligible.
rotor
the rotating part of an electrical machine including the shaft, such as the rotating armature of a DC machine or the field of a synchronous machine.
rotor power developed
the amount of power developed by the rotor. In DC machines, the developed power, frequently denoted by Pd , is calculated as the product of the induced EMF Ea and the armature current Ia. In induction machines, the rotor power developed is obtained by subtracting the rotor copper losses from the air gap power.
rotor power loss
represents the portion of the power transferred across the air gap to the rotor of an induction motor that is lost either through ohmic heating of the rotor windings or due to friction and windage losses in the rotor. The mechanical power available at the motor shaft is the difference between rotor power input and rotor power losses.
rotor speed
quantification of the rotational operation of the moving part of a rotating electrical machine. The rotor speed is measured either in SI units in radians per second (rad/s) or in practical units in revolutions per minute (rev/min).
safety
the probability that a system will either perform its functions correctly or will discontinue its functions in a well-defined, safe manner.
safety-critical system
a system that is intended to handle rare unexpected, dangerous events.
sag
a decline ranging from 0.1 to 0.9 pu in RMS voltage or current at the supply frequency for a time period of 0.5 cycles to 1 minute.
sail switch
a device used in control systems that detects the flow of air, or other gas, and causes a relay to open or close as a result of the motion of the sail.
salient
feature a characteristic often local feature on an object which can be detected and used as part of the process of inferring the presence of an object from its features. Typical salient features include point features such as corners and small holes, or fiducial marks (e.g., on printed circuit boards), but may in addition include large-scale straightforwardly detected features such as large circular holes which can also aid the inference process.
salient-pole drive

See synchronous drive
salient-pole rotormachine
AC motor/generator design in which the rotor is constructed of outward-projecting pole pieces mounted on a shaft-mounted central spider assembly. Spider assemblies are typically spoked. Pole pieces are built up from laminated sheets, which are bolted together between a pole shoe on the outer end and dovetail fixture on the inner end. The dovetails are keyed into slots on the spider to mount the pole pieces to the rotor. Rotor windings are generally constructed from preformed, insulated coils that are fit over the pole pieces during assembly. Salient rotors are typically low-speed designs with short axial length and large diameter.
saturating control
a controller producing a bounded control signal. Finite limits on the magnitude of the control signals that are provided by the actuators are due to the fact that the actuators are physical devices and as such are subject to physical constraints.

Thus, the actuator saturates, that is, it has "limited authority."
saturation
(1) the failure of the output to increase as fast as the input. For example, often the current regulator used in variable-speed drives is unable to track the commanded current because of insufficient voltage difference between the motor back EMF and the supply.

In an amplifier, saturation results in a reduction of gain in an amplifier or loss in an absorber due the intensity of the signal being amplified or absorbed.

In ferromagnetic circuits, the magnetic flux initially increases linearly with the applied magnetomotive force (MMF), but eventually most of the domains in the ferromagnetic material become aligned, and the rate of increase in flux decreases as the MMF continues to increase. See figure below. See also saturation flux density. Saturation effect in a ferromagnetic circuit.

(2) with respect to color, the amount or purity of the color seen. A pure color is said to be fully saturated, and the saturation decreases as white is added to the mix. The color "pink," for example is a less saturated version of "red."
saturation angle the angular portion of the time-based output signal (in degrees) over which the device is saturated. It is always less than or equal to the conduction angle, since the device must conduct before it can saturate.
saturation flux density
the maximum value of intrinsic induction (Bi) beyond which an increase in magnetizing field yields no further improvement, indicating that all magnetic moments in the material have been aligned.
saturation magnetization
the magnetic moment per unit volume of a material when the magnetization in the sample is aligned (saturated) by a large magnetic field.
saturation parameter
reciprocal of the value of intensity for which the gain of an amplifying medium or the loss of an absorbing medium is reduced to one half of its unsaturated value.
saturation polarization
the value to which the externally measured electrical dipole moment of a ferroelectric body tends when subjected to an external electrical field greater than the coercive field.
SCADA
acronym for supervisory control and data acquisition. A system which measures critical power system parameters (e.g., voltage, power flow, circuit breaker status, and generator outputs) at remote points in an electric power system and transmits the data to a central control site where these conditions may be monitored.
scanner
(1) a device used for scanning written documents or printed pictures by tracing light along a series of many closely spaced parallel lines.

(2) any device that deflects a light beam through a range of angles, using mechanisms such as diffraction from electro-optic or acousto-optic gratings or mechanical deflectors.

(3) a type of projection printing tool whereby the mask and the wafer are scanned past the small field of the optical system that is projecting the image of the mask onto the wafer.
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