Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

reactive power
(1) electrical energy per unit time that is alternately stored, then released. For example, reactive power is associated with a capacitor charging and discharging as it operates on an AC system. Symbolized by Q, with units of volt-amperes reactive (VAR), it is the imaginary part of the complex power.

(2) the power consumed by the reactive part of the load impedance, calculated by multiplying the line current by the voltage across the reactive portion of the load. The units are vars (volt-ampere reactive) or kilovars.
real power
consider an AC source connected at a pair of terminals to an otherwise isolated network. The real power, equal to the average power, is the power dissipated by the source in the network.
reciprocity
(1) a consequence of Maxwell's equations, stipulating the phenomenon that the reaction of the sources of each of two different source distributions with the fields generated by the other are equal, provided the media involved have certain permeability and permittivity properties (reciprocal media). Referring to reciprocal circuits, reciprocity
states that the positions of an ideal voltage source (zero internal impedance) and an ideal ammeter (infinite internal impedance) can be interchanged without affecting their readings.

(2) in antenna theory, the principal that the receive and transmit patterns of an antenna are the same.

reciprocity in scattering law according to which the source and detector points can be exchanged, providing the source amplitude and phase are preserved.
reciprocity theorem
in a network consisting of linear, passive impedances, the ratio of the voltage introduced into any branch to the current in any other branch is equal in magnitude and phase to the ratio that results if the positions of the voltage and current are interchanged.
recoil permeability
the average slope of the minor hysteresis loop, which is roughly the slope of the major hysteresis loop at zero applied field (H ), and is most often used to determine the effect of applying and removing a demagnetizing field to and from a magnetic material.
repulsion-induction motor
a single-phase motor designed to start as a repulsion motor, then run as an induction motor. The rotor has a DC-type winding with brushes shorted together, in addition to the normal squirrel cage winding. Although it is an expensive design, it provides excellent starting torque with low starting current (similar to a universal motor) and relatively constant speed under load.
right hand circular polarization
the state of an electromagnetic wave in which the electric field vector rotates clockwise when viewed in the direction of propagation of the wave.
RMS power
root-mean-squared power
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).
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.
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.
schematic capture
a design entry method wherein the designer draws the schematic of the desired circuit using a library of standard cells. The program outputs a netlist of the schematic.
second harmonic component
the signal component of a periodic signal whose frequency is twice the fundamental frequency.
set point
(1) a specified constant value of the controlled variable of a dynamical process that a controller is required to maintain. The controller must generate a control signal that drives the controlled variable to the set point and keeps it there, once it is reached. The set point is often referred to as reference point or operating point. In aircraft flight control, the set point is also called the trim condition.

(2) the intersection of the load line and the normal B-H curve, indicating the flux density and energy a permanent magnet is delivering to a given magnetic circuit geometry.
shaded-pole motor
a single-phase induction type motor that uses shaded poles on the stator to create a weak quasi-rotating magnetic field. Shaded-pole motors are only built in small fractional horsepower sizes and produce a very low starting torque that is suitable only for fan-type loads. See also shaded pole.
shell-type transformer
a power transformer in which the magnetic circuit surrounds and normally encloses a greater portion of the electrical winding.
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