Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

load center
the geographic point within a load area, used in system calculations, at which the entire load could be concentrated without affecting the performance of the power system.
load flow study

See power flow study
load frequency control
the purpose of load frequency control is to maintain the power system frequency at its nominal value while maintaining the correct outputs on individual generators to satisfy the loading on the system. As the load varies, the inputs to the generator prime movers must be controlled to keep the generation in balance with the loads.
load line
with a slope, also known as the permeance coefficient, determined solely by the geometry of the magnetic circuit, this line intersects with the normal demagnetization curve to indicate a magnet's operating point.
load mismatch
the load impedance does not match the device output impedance, resulting in power reflection. A perfect match occurs when the real parts of the load and device output impedance are equal and the reactive parts cancel or resonate, resulting in maximum power transfer. The magnitude of the load mismatch is usually expressed in terms VSWR, reflection coefficient or return loss.
load tap changer (LTC)
a tapped transformer winding combined with mechanically or electronically switched taps that can be changed under load conditions. The load tap changer is used to automatically regulate the output of a transformer secondary as load and source conditions vary.
load torque
the resisting torque applied at the motor shaft by the mechanical load that counterbalances the shaft torque generated by the motor and available at the shaft.
load-break device
any switch which can be opened while the circuit is loaded
load-commutated inverter (LCI)
an inverter in which the commutating voltages are supplied by the load circuit.
load-pull
the systematic variance of the magnitude and phase of the load termination of a device under test.
loaded Q
dimensionless ratio of the average over any period of time (T = 1/frequency) of the ratio of the maximum energy stored (Umax) to the power absorbed or dissipated (Pabsorbed = Pin - Pout) in a passive component or circuit, including external loading effects, expressed as a dimensionless ratio. For most applications, the higher the Q, the better the part.
locked-rotor current
the current drawn by an induction motor when the shaft is not moving and rated voltage is applied. The starting current is essentially equal to the locked rotor current and may be as much as eight times the rated current of the machine.
locked-rotor torque
the torque produced in an induction motor when the rotor is locked and rated AC voltage is applied to the stator.
lockout
the condition following fault clearing when the circuit will not attempt a reclose. Transformers, generators, and buses typically trip once and lockout immediately. Transmission lines and distribution lines will generally attempt one or more recloses, and will lockout if the fault remains following the last reclose in the sequence.
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
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