Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

arc resistance
period of time that the surface of an insulating material can be submitted to the action of an electrical arc without becoming conductive.
braking resistor
resistive elements which can be switched into the electrical system to create additional load in the event of a transient disturbance, thus limiting the generator rotor acceleration such that the system can more readily return to synchronism.
carbon resistor thermometer
a carbon resistor whose temperature sensitivity provides good temperature resolution.
computer-aided design (CAD)
field of electrical engineering concerned with producing new algorithms/programs which aid the designer in the complex tasks associated with designing and building an integrated circuit. There are many subfields of electrical CAD: simulation, synthesis, physical design, testing, packaging, and semiconductor process support.
corona resistance
capacity of a material to bear the action of the corona effect. This capacity is particularly important for polymeric materials, which have to withstand the chemical degrading effect promoted by ozone generated by the corona effect.

See corona effect
equivalent resistance
the resistance of the windings of an electromagnetic machine reflected to one side (component) of the machine.
See equivalent impedance
equivalent sphere illumination (ESI)
the level of sphere illumination that would produce task visibility equivalent to that produced by a specific lighting environment.
ESI

See equivalent sphere illumination
fault resistance
the resistance that occurs at the point of fault due to voltage drop across an arc or due to other resistance in the fault path.
field discharge resistor
a resistor used to dissipate the energy stored in the inductance of a field winding. It may be a standard power resistor that is connected across the winding just prior to opening the supply switch, or a permanent non-linear resistive device that has high resistance at normal voltage but low resistance when voltage rises at switching.
high-resistance grounded system
an electrical distribution system in which the neutral is intentionally grounded through a high resistance. The high-resistance grounded wye system is an alternative to solidly grounded and ungrounded systems.

High-resistance grounding will limit ground fault current to a few amperes, thus removing the potential for arcing damage inherent in solidly grounded systems.
hysteresis
(1) the phenomenon that the magnetic state of a substance is dependent upon its magnetic history, so that its magnetization for an increasing magnetizing force differs from that for a decreasing magnetizing force.

(2) the characteristic of magnetic materials that causes the trajectory of the flux density vs. field intensity curve as the intensity is increased to be different from that when the intensity is decreased, giving rise to a loss, which is proportional to the area enclosed by the two trajectories.
hysteresis brake
a braking device utilizing hysteresis to provide a constant braking torque irrespective of slip speed.
hysteresis control
a time-optimal feedback control method in which the control variable reaches a reference value in the shortest possible time and then stays within a prescribed hysteresis band around the set point through manipulation of the system state between two configurations. The actual variable is compared with the reference value, and if the error exceeds the hysteresis band, then the control input is changed such that the control variable is forced to decrease. On the other hand, if the actual variable falls below the hysteresis band then the control input is changed such that the control variable increases in magnitude.
hysteresis curve
a graph describing the relationship between the magnetic flux density and the magnetic field intensity in a (usually ferromagnetic) material.
hysteresis drive

See hysteresis torque coupling
hysteresis loss
the energy loss due to hysteresis in a magnetic material subjected to a varying magnetic field.
hysteresis motor
any of a variety of single-phase AC motors that use the hysteresis properties of hard magnetic materials to develop torque. Stator windings of a hysteresis motor can be of any design that produces a rotating flux within the machine. Motion of the rotating flux over the rotor magnetizes the hard magnetic material on the rotor; however, the hysteresis characteristics of the material cause the alignment of magnet flux to lag the rotating stator flux. This misalignment produces rotor torque. Because of the nature of the torque production, hysteresis motors operate at synchronous speed and have a constant torque characteristic, which permits them to synchronize any load that they
can accelerate.
hysteresis torque coupling
a magnetic drive in which the magnetizing stator magnet drives a rotor of hysteresis material through the complete hysteresis cycle once per rotation, resulting in a constant torque characteristic irrespective of relative speed.
insulation resistance
measured value of electrical resistance of the insulation of a product or device.
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