Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

Typical symbol for load resistance.
commonly used symbol for source impedance.
commonly used symbol for transformation ratio.
a channel within a building which holds bare or insulated conductors.
radial intensity histogram
a histogram of average intensities for a round object in circular bands centered at the center of the object, with radial distance as the running index. Such histograms are easily constructed, and, suitably normalised, form the basis for scrutinizing round objects for defects, and for measuring radius and radial distances of cylindrically symmetrical features.
radial system
a network of straight wires or other conductors radiating from the base of a vertical monopole antenna that simulates the presence of a highly conducting ground plane beneath the antenna. Typically, radial wires are approximately a quarter wavelength long and are arranged to have equiangular spacing between them. The radial wire ends at the base of the monopole are electrically bonded together and to one conductor of the feedline.
rare-earth magnet
a magnet that has any of the rare-earth elements in its composition. Typically stronger than other magnet materials, these include neodymium iron boron and samarium cobalt.
rare-earth permanent magnet
magnet made of compounds of iron, nickel, and cobalt with one or more of the rare-earth elements such as samarium. These materials combine the high residual flux density of the alnico-type materials with greater coercivity than ferrites.
rated voltage
the voltage at which a power line or electrical equipment is designed to operate.
reactance grounded
an electrical system in which the neutral is intentionally grounded through a reactance. Frequently used in the neutral of generators and transformers to limit the magnitude of line to ground fault currents.
reactive compensation
process of counteracting the reactive component of a device by means of capacitors and inductors. Both series and shunt compensation are prevalent.
reactive load
a load that is purely capacitive or inductive.
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.
reactive power Q
The region of allowable operation is determined by factors such as rotor thermal limit, stator thermal limit, rated power of prime mover (alternator operation), and stability torque limit.
a container where the nuclear reaction takes place. The reactor converts the nuclear energy to heat.
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.
(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.
a self-contained device placed on distribution lines that senses line currents and opens on overcurrent. Reclosing is employed to reenergize the protected line segment in the case of temporary faults. Reclosers have the capability for fast tripping for fuse saving, and slow tripping to allow sectionalizing fuse operation for faults on laterals. The recloser will retrip on permanent faults and go on to lockout. Reclosers are suitable for pole mounting on overhead lines.
reclosing relay
an auxiliary relay that initiates circuit breaker closing in a set sequence following fault clearing. Reclosing relays are typically employed on overhead lines where a high proportion of the faults are temporary.