Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

lockout relay
an auxiliary relay which is operated by protective relay(s) that in turn opens the appropriate circuit breakers or other fault clearing devices. The lockout relay will remain in the trip position until manually reset, and is used in protective zones where temporary faults are unusual and the potential for equipment damage is high.
loss
(1) decrease of intensity of an electromagnetic wave due to any of several physical mechanisms. See also attenuation.
(2) a term for electric power which does not register on the consumer's electric meter, e.g., through ohmic losses in transmission lines, iron losses in transformers, or theft.
loss coefficient
a factor used in economic dispatch calculations that relates power line losses to the power output of generating plants.
loss factor
the product of the dielectric constant and the power factor.
loss of service
the complete loss of electric power exclusive of sags, swells, and impulses.
loss tangent

See dissipation factor
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 resistance grounded system
an electrical distribution system in which the neutral is intentionally grounded through a low resistance.

Low resistance grounding will limit ground fault current to a value that significantly reduces arcing damage but still permits automatic detection and interruption of the fault current.
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.
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