Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
ammeter
an instrument for measuring electric current in amperes.
amortisseur winding

See damper winding
ampacity
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
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.
antenna
a device used to couple energy from a guiding structure (transmission line, waveguide, etc.) into a propagation medium, such as free space, and vice versa. It provides directivity and gain for the transmission and reception of electromagnetic waves.
antenna beamwidth
the effective angular extent of the antenna radiation pattern usually specified between points of fixed amplitude relative to the main lobe gain (e.g., -3 dB points).
antenna gain
the maximum ratio of an antenna's ability to focus or receive power in a given direction relative to a standard; the standard is usually an isotropic radiator or a dipole. The gain includes the efficiency of the antenna.
antenna Q
ratio of the energy stored to the energy dissipated (ohmically or via radiation) per cycle.
antifuse
a fuse-like device that when activated becomes low-impedance.
antiparticle
a particle having the same mass as a given fundamental particle, but whose other properties, while having the same magnitude, may be of opposite sign. Each particle has a partner called an antiparticle. For example, electrical charge in the case of the electron and positron, magnetic moment in the case of the neutron and antineutron. On collision a particle and its antiparticle may mutually annihilate with the emission of radiation. Some properties of the antiparticle will be identical in magnitude but opposite in sign to the particle it is paired with.
antipodal
symmetry created by simultaneously mirroring an object in both the X and Y axes.
antireflection coating

See antireflective coating
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