Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

air core transformer
two or more coils placed so that they are linked by the same flux with an air core. With an air core the flux is not confined.
air terminal
a lightning rod; any device which extends upward into the air from a structure for purposes of lightning protection.
air-blast circuit breaker
a circuit breaker in which the arc which forms between the contacts on opening is extinguished with a blast of high-pressure air.
air-gap line
the line that is obtained by continuing the linear portion of the saturation curve of a synchronous machine or a DC machine. The figure shows a plot of generated voltage vs. field current at constant machine speed. Initially, an increase in field current yields a linear increase in the generated voltage, but as the iron becomes saturated, the voltage rolls off. The air-gap line gives the voltage that would be obtained without saturation.
air-gap voltage
the internal voltage of a synchronous machine that is generated by the air gap flux. Also referred to as the voltage behind leakage reactance.
alley arm
a crossarm meant for use in an alleyway or other confined area in which poles must be placed close to buildings.

See crossarm
alternating current (AC)
a periodic current the average value of which over a period is zero.

alternating current machine
an electromechanical system that either converts alternating current electrical power into mechanical power (AC motor), or converts mechanical power into alternating current electrical power (AC generator, or alternator). Some AC machines are designed to perform either of these functions, depending on the energy source to the dynamo.

alternator-rectifier exciter
a source of field current of a synchronous machine derived from the rectified output voltage of an alternator. The components of the exciter consist of the alternator and the power rectifier (including possible gate circuitry), exclusive of all input control elements. The rectifier circuits may be stationary, or rotate with the alternator, which may be driven by a motor, prime mover, or by the shaft of the synchronous machine.

ambient field
the background magnetic field level existing in the environment, without contribution from specific magnetic field sources.

ambient temperature
the temperature of the air or liquid surrounding any electrical part or device. Usually refers to the effect of such temperature in aiding or retarding removal of heat by radiation and convection from the part or device in question.

American National Standards Institute (ANSI)
The U.S. organization that recommends standards for metrology, drawing
symbology and numerous other facets for products and industries.

an instrument for measuring electric current in amperes.

amortisseur winding
See damper winding
the maximum current which can be safely carried by a conductor under specified conditions.

ampere interrupting rating
the interrupting rating of a device expressed in amps (often rms symmetrical amps).
See MVA interrupting rating
a special generator that acts like a DC power amplifier by using compensation coils and a short circuit across its brushes to precisely and fastly control high powers with low level control signals.

analog-to-digital (A/D)
conversion a method by which a continuously varying signal (voltage) is sampled at regularly occurring intervals. Each sample is quantized to a discrete value by comparisons to preestablished reference levels. These quantized samples are then formatted to the required digital output (e.g., binary pulse code words).
The A/D converter is “clocked” to provide updated outputs at regular intervals. In order not to lose any baseband information, sampling must occur at a rate higher than twice the highest incoming signal frequency component.

analog-to-digital (A/D)
converter a device that changes an analog signal to a digital signal of corresponding magnitude. This device is also called an encoder, ADC, or A/C converter.
angular frequency
the rate of change of the phase of a wave in radians per second.