Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

angular frequency
the rate of change of the phase of a wave in radians per second.
antenna Q
ratio of the energy stored to the energy dissipated (ohmically or via radiation) per cycle.
automatic frequency control (AFC)
(1) an automatic feedback control system that is used to maintain active power balance by means of the speed governor system. In an interconnected system, scheduled power interchanges are maintained by means of controlling area generations.
(2) electronic circuitry used to keep the received signal properly placed within the desired IF frequency range. In televisions, the AFC circuitry is also called the AFT or "automatic fine tuning" section. The AFC circuit will generate an error signal if the input frequency to the IF drifts above or below the IF frequency. The error signal is fed back to vary the local oscillator frequency in the tuner section. See also automatic fine tuning (AFT).
base quantity

See per-unit system
breakaway torque
minimum torque needed to begin rotating a stationary load. Breakaway torque represents the absolute
minimum starting torque specification for a motor used to drive the load.
breakdown torque
maximum torque that can be developed by a motor operating at rated voltage and frequency without experiencing a significant and abrupt change in speed. Sometimes also called the stall torque or pull-out torque.
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.
constant-torque drive
a variable-speed drive that is operating in a speed region where it is capable of maintaining rated torque. For DC machines, this region is below base speed and is achieved by reducing the applied armature voltage. For AC induction motors, this region is below rated speed and is achieved by reducing the frequency of the applied voltage.
torque developed in opposition to the rotation of a machine. It is produced as load current flows in the presence of and perpendicular to magnetic flux in a machine that is generating electric power.

diversity frequency
a method for increasing the reliability of digital communications in which multiple copies of the signal, or other types of redundant information, are transmitted. Frequency diversity implies that the received signal occupies a much wider bandwidth than the minimum bandwidth needed to carry the information.
electromagnetic torque
the torque produced in a machine by the interaction of the magnetic fields and/or by the varying reluctance principle where the field attempts to maximize its intensity in a machine during electromechanical energy conversion.
electron collision frequency
the average number of collisions per second an electron has with heavy particles in a medium such as plasma.
a method used in communication systems to compensate for the channel distortion introduced during signal transmission.
equivalence theorem
an electromagnetic theorem: If the tangential magnetic and electric fields are known everywhere on some closed surface S, then these fields may be replaced with equivalent electric and magnetic surface currents, respectively. These equivalent currents will produce the same field structure exterior to S as the original fields and the null field internal to S.
equivalent circuit
a combination of electric circuit elements chosen to represent the performance of a machine or device by establishing the same relationships for voltage, current, and power.
equivalent control
an algorithm used to determine a system's dynamics when restricted to a sliding surface. The method entails combining the solution to an algebraic equation involving the time derivative of the function describing the sliding surface and the dynamical system's model. See also variable structure system and sliding mode control.
equivalent current
a theoretical current used to obtain the scattered field from a surface or discontinuity. The equivalent current is formulated to represent the actual physical currents so as to result in an equivalent scattered field.
equivalent impedance
the impedance of the windings of an electromagnetic machine reflected to one side (component) of the machine. For example, in a transformer, the equivalent impedance consists of the combined leakage reactances and resistances of the primary and secondary.
equivalent noise voltage (ENV)
a noise voltage source that is effectively in series with either the inverting or noninverting input terminal of the op amp and represents the total noise contributed by the op amp if the inputs were shorted.
equivalent reactance
the reactance of the windings of an electromagnetic machine reflected to one side (component) of the machine.
See equivalent impedance