Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

loss-of-field relay
a protection relay used to trip a synchronous generator when the excitation system is lost. Loss of excitation causes the generator to run as an induction generator drawing reactive power from the system. This can cause severe system voltage reductions and damage to stator due to excessive heating.
low voltage holding coil
a holding coil that keeps the main-line contactor closed on low voltage conditions. Controllers that contain this feature are used in places where the motor is vital to the operation of a process, and it is necessary to maintain control of the motor under low voltage conditions.
low-level transmitter
a transmitter in which the modulation process takes place at a point where the power level is low compared to the output power.
low-pressure discharge
a discharge in which the pressure is less than a torr or a few torrs; low-pressure gases can be easily excited, giving spectra characteristic of their energy structure.
lower frequency band edge
the lower cutoff frequency where the amplitude is equal to the maximum attenuation loss across the band.
lumen
the SI unit of illumination measurement. Also, the hollow interior of a blood vessel or airway.
luminance
(1) formally, the amount of light being emitted or reflected by a surface of unit area in the direction of the observer and taking into account the spectral sensitivity of the human eye.
(2) the amount of light coming from a
scene.
See candela
luminosity
the ratio of luminous flux (total visible energy emitted) to the corresponding radiant flux (total energy emitted) usually in lumens per watt.
luminous efficiency
the measure of the display output light luminance for a given input power, usually measured in lumens per watt, which is equivalent to the nit.
maglev

See magnetic levitation
magnet
any object that can sustain an external magnetic field.
magnetic actuator
any device using a magnetic field to apply a force.
magnetic bearing
a component of a machine that uses magnetic force to provide non-contact support for another component moving relative to it.
magnetic bias
a constant magnetic field on which is superimposed a variable, often sinusoidal, perturbation magnetic field in devices like magnetic bearings.
magnetic brake
any device using a magnetic field to retard motion.
magnetic charge density
a fictitious source of the electromagnetic field that quantifies the average number of discrete magnetic charges (also fictitious) per unit volume. The magnetic charge density is often introduced in problems where duality and equivalence concepts are employed.
magnetic circuit
the possible flux paths within a system consisting of a source of flux (electromagnets, permanent magnets), permeable flux carrying materials (steel, nickel) and non-flux carrying materials (aluminum, air).
magnetic clamp
a device employing a magnetic field to deliver a clamping action.
magnetic current density
a fictitious source vector in electromagnetics that quantifies the amount of magnetic charge (also fictitious) crossing some cross-sectional area per unit time. The magnetic current density is often introduced in problems where duality and equivalence concepts are employed. The direction of the magnetic current density is in the direction of magnetic charge motion. SI units are volts per square meter.
magnetic damper
any device using a magnetic field to damp motion.
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