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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

I-line
a line of the mercury spectrum corresponding to a wavelength of about 365 nm.
IAEA
International Atomic Energy Agency, an organization which monitors nuclear materials and energy.
IDC
DC current in amperes.
ideal transformer
a transformer with zero winding resistance and a lossless, infinite permeability core resulting in a transformer efficiency of 100 percent. Infinite permeability would result in zero exciting current and no leakage flux. For an ideal transformer, the ratio of the voltages on the primary and secondary sides would be exactly the same as the ratio of turns in the windings, while the ratio of currents would be the inverse of the turns ratio.
IEC

See International Electro-technical Commission
IEEE

See Institute of Electrical and Electronics Engineers
IEEE Color Books
a series of seven books related to industrial and commercial power systems containing recommended
IEEE/ANSI standards and practices. The books are color-coded as to subject as follows:

Gray: Power systems in commercial buildings

Green: Grounding industrial and commercial power systems

Brown: Power system analysis

Gold: Design of reliable industrial and commercial power systems

Orange: Emergency and standby power for industrial and commercial power systems

Red: Electric distribution practice in industrial plants

Buff: Protection and coordination of industrial and commercial power systems.
ignitron
a high-voltage mercury switch. The device is found in modulators used to dump the capacitor bank voltage in the event of a PA crowbar. An ignitron passes electrical current to a pool of liquid mercury at ground potential.
illumination
(1) in vision science, the amount of light per unit area delivered to a surface and accounting for the spectral sensitivity of the human eye.

(2) informally, the amount of light falling on an object. Also called illuminance. See also luminance.

(3) the effect of a visible radiation flux received on a given surface. Illumination is measured by the illuminance, which is the luminous flux received by surface unit, usually expressed in lux. One lux equals 1 lumen/m2.
illumination system
the light source and optical system designed to illuminate the mask for the purpose of forming an image on the wafer.
imaginary power

See reactive power
immittance
a response function for which one variable is a voltage and the other a current. Immittance is a general term for both impedance and admittance and is generally used where the distinction is irrelevant.
immunity to a disturbance
an equipment or systems capability to operate if an electromagnetic disturbance occurs.
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.