Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

momentary interruption
a loss of voltage of less than 0.1 pu for a time period of 0.5 cycles to 3 seconds.
momentary monitoring the duration at supply frequency from 30 cycles to 3 seconds.
MVA interrupting rating
the interrupting rating of a device expressed in terms of megavolt-amperes. The conversion between fault volt-amps and fault current in three-phase systems is VA = 1.73 x operating RMS line-line voltage x largest phase fault current expressed in RMS symmetrical amperes. Power circuit breakers can have separate MVA and maximum current interrupting ratings, with adjustments when the circuit breaker is operated below rated voltage.
optical fiber
a single optical transmission fiber usually comprised of a cylindrical core (5-100 mm diameter) in which the light is guided of higher index of refraction surrounded concentrically by a cladding (125-250 mm diameter) with a lower index of refraction. More properly defined as an optical waveguide. Some optical fibers may have multiple concentric cores and/or claddings.

Optical fibers made be of all glass, all plastic, or a combination of glass core and plastic cladding construction. Optical glass fibers may be silica-or fluoride-based glass.
optical fiber signal distortion
a change in the temporal shape of an optical signal transmitted through an optical fiber caused by a combination of wavelength effects (dispersion) and multimode and polarization effects. The wavelength effects include material dispersion, profile dispersion, and waveguide dispersion. The multi-mode effects cause distortion by the differential time delays between the various modes propagating in a multimode fiber. The polarization effect causes distortion by the differential time delay between the two polarizations of a single mode.
potential transformer (PT)
a device which measures the instantaneous voltage of an electric power line and transmits a signal proportional to this voltage to the system's instruments.
See voltage transformer
PT
potential transformer
See voltage transformer
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.
susceptibility
the part of the permittivity or permeability that is attributable to the electromagnetic behavior of the medium. In a linear, isotropic medium, the electric susceptibility is numerically equal to the relative permittivity minus one, and the magnetic susceptibility is equal to the relative permeability minus one. See also electric susceptibility.
sustained interruption
all interruptions that are not momentary. Generally used when referring to long duration voltage interruptions of greater than 1 minute.
temporary interruption
a loss of voltage of less than 0.1 pu for a duration of 3 seconds to 1 minute.
uninterrupted power supply (UPS)
(1) a power supply designed to charge an energy storage medium, while providing conditioned output power, during the presence of input power and to continue providing output power for a limited time when the input to the supply is removed. These power supplies are typically used in critical applications to prevent shut-down of these systems during power failures, power surges, or brownouts.

(2) a device that provides protection for critical loads against power outages, overvoltages, undervoltages, transients, and harmonic disturbances. A typical UPS is a rectifier supplied battery bank for energy storage, and a PWM inverter-filter system to convert a DC voltage to a sinusoidal AC output. UPS systems can be on-line, as shown in the figure, where the UPS inverter powers the load continuously, or off-line where the load is connected directly to the utility under normal
operation and emergency power is provided by the UPS.
voltage interruption
the removal of the supply voltage from any phase, which is of momentary, sustained, of temporary duration.
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