Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

horizontal polarization
a term used to identify the position of the electric field vector of a linearly polarized antenna or propagating EM wave relative to a local reference, usually the ground or horizon. A horizontally polarized EM wave is one with its electric field vector aligned parallel to the local horizontal.
horn gap
a V-shaped spark gap which provides a method of extinguishing a power-follow arc by allowing the arc to climb the sides of the V until it is too long to be maintained.
horsepower-rated switch
a manually operated switching device designed for motor circuit applications. It is designed to interrupt the rated overload current at rated voltage of a motor with a horsepower rating that is less than or equal to the horsepower rating of the switch.
hot tap
a clamp, applied with a hot stick that connects a branch circuit to an existing conductor and typically applied while the system is energized.
hybrid stepper motor
a stepper motor that combines the rotor design characteristics of variable-reluctance and permanent magnet stepper motors. Hybrid stepper motor rotors consist of an axially magnetized cylindrical permanent magnet capped on each pole by toothed, soft iron caps. Teeth on the caps are displaced with respect to each other to provide stepping control. Hybrid stepper motors combine the higher torque capability of permanent magnet motors with the higher step resolution of variable-reluctance motors.
hydropower
conversion of potential energy of water into electricity using generators coupled to impulse or reaction water turbines.
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.
imaginary power

See reactive power
impedance
(1) electrical property of a network that measures its ability to conduct electrical AC current for a given AC voltage. Impedance is defined as the ratio of the AC voltage divided by the AC current at a given point in the network. In general, impedance has two parts: a real (resistive) part and an imaginary (inductive or capacitive "reactive") part. Unless the circuit is purely resistive (made up of resistors only), the value of impedance will change with frequency.

(2) in an antenna, usually defined at the input to an antenna, the impedance is the ratio of the applied (or induced) voltage to the current flowing into (or out of) the antenna input. More generally, it is defined as the ratio of the electric field to the magnetic field.
impedance relay
a protective relay that senses the operational impedance at a location, i.e., the ratio of voltage to current at any given time. During fault conditions on the protected line, the impedance relay will sense the impedance (distance in ohms) between the location of the relay and the fault.

Typical impedance relay characteristics are mho and reactance. Impedance relays are widely used in sensing phase faults on transmission lines. Ground impedance relays are available that measure the distance to a single phase to ground fault using a modified technique.
See distance relay
impulse
a unit pulse.
See impulsive transient
impulse breakdown
a test of electrical insulation in which lightning or switching impulses are applied.
impulse generator
(1) an electronic device delivering single pulses of various shapes, preferably square.

(2) a high-voltage trigger generator.
impulsive transient
a rapid frequency variation of voltage or current during steady-state operation in which the polarity is mostly unidirectional.
incandescent lamp
a lamp made by heating a metal filament in vacuum; not a burning candle.
incident power
power in an electromagnetic wave that is traveling in an incident direction.
inductive coupling
a means of transferring electrical energy from one part (area) of a circuit to another part without requiring any ohmic (wire) connection. Instead, magnetic flux linkages couple two inductors (coils). The coils must be in close proximity in order to establish sufficient mutual inductance.
input impedance
(1) when a voltage is applied to a conducting material, a current will flow through the material. The ratio of the voltage to the current is known as the input impedance and is a complex number with magnitude measured in units of ohms. See also Ohm's Law.

(2) impedance seen when looking into the input terminals of an antenna. input layer a layer of neurons in a network
that receives inputs from outside the network. In feedforward networks, the set of weights connected directly to the input neurons is often also referred to as the input layer.
instantaneous power
power in an AC or modulated signal at a given instant in time.
instantaneous-trip circuit breaker
essentially an inverse-time circuit breaker with the thermal element removed. It will only trip magnetically in response to short-circuit currents. Thus, it is often referred to by other names, such as magnetic circuit breaker and magnetic-only circuit breaker.
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