Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

magnetoresistance
the change in electrical resistance in a conducting element experiencing a change in applied magnetic field. This is most pronounced when the magnetic field is perpendicular to current flow.
major hysteresis loop
for a magnetic material, the loop generated as intrinsic or magnetic induction (Bi or B) is plotted with respect to applied field (H) when the material is driven from positive saturation to negative saturation and back, showing the lag of induction with respect to applied field.
parasitic resistance
the generally undesirable and not-designed-for resistance associated with a conductor, or path of current on a conductor.
residual current circuit breaker
European term for ground fault interrupter.
residual magnetism
a form of permanent magnetism, referring to the flux remaining in a ferromagnetic material after the MMF that created the flux is removed. For example, if a bar of steel is surrounded by a coil and current is applied to the coil, the steel bar will create a magnetic field due to the rotation of the domains in the steel. After the current is removed, some of the domains will remain aligned, causing magnetic flux.
residual overcurrent relay
an overcurrent relay that is connected to sense residual current. Residual current is the sum of the three phase currents flowing in a current transformer secondary circuit, and is proportional to the zero sequence current flowing in the primary circuit at that point.
resistivity
(1) the product of the resistance of a given material sample times the ratio of its cross-sectional area to its length.

(2) an electrical material property described by a tensor constant indicating the impedance of free electron flow in the material. Resistivity relates the electric field strength to the conduction current, and can be expressed as the inverse of the conductivity.
resistance ratio
of the potential of an electrical current applied to a given conductor to the current intensity value.
resistance ground
a grounding scheme in which the neutral of Y-connected machines is connected to ground through a resistance such that ground-fault currents are limited.
resistance grounded
See low resistance grounded system, high-resistance grounded system
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.
robust controller design
a class of design procedures leading to control systems that are robust in the sense of required performance. Robust design is a feedback process involving robustness analysis. A specific technique used in robust controller design depends on the type of model describing a system and its uncertainty, control objective, and a set of admissible controllers. The first requirement is to ensure robust stability; this could be followed by guaranteed cost, disturbance rejection, robust poles localization, target sets or tubes reachability, or other demands.

Ackermann's three basic rules of robust controller design are as follows:

1. Require robustness of control system only for physically motivated parameter values and not with respect to arbitrarily assumed uncertainties of the model.

2. When you close a loop with actuator constraints, leave a slow system slow and leave a fast system fast.

3. Be pessimistic in analysis; then, you can afford to be optimistic in design.
secondary resistor
a resistor connected to the rotor of a wound-rotor induction machine to permit variation of the effective rotor resistance. By varying the resistance, machine characteristics may be optimized for starting or varying load conditions.
temperature coefficient of resistance
the change in electrical resistance of a resistor per unit change in temperature.
thermal resistance
a thermal characteristic of a heat flow path, establishing the temperature drop required to transport heat across the specified segment or surface; analogous to electrical resistance.
underground residential distribution
practices involved in the underground distribution of electric power to residential subdivisions through direct-buried cables and pad mound transformers.
voltage coefficient of resistance
the change in resistance per unit change in voltage, expressed as a percentage of the resistance at 10% of rated voltage.
water resistivity
a measure of the purity of cooling liquid for a power tube, typically measured in megohms per centimeter.
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