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Commonly used terms in the Electrical industry.
negative-sequence reactance
inductive reactance offered by a circuit for the flow of negative-sequence currents alone. Expressed in ohms, the inductive reactance is a function of frequency and the inductance of the circuit
to negative-sequence current flow.
See
negative-sequence impedance
normally closed contact
contact of a contactor that is closed when the coil of the contactor is deenergized and opened when the coil is energized.
normally open contact
a contact that is open under normal operating conditions and closes when an action is initiated in its controller. For a contact that is part of a relay, the contact remains open when the relay is deenergized and closes when the relay is energized.
nuclear reaction
a reaction which causes changes in the nucleus of an atom, thus changing elements to another element or isotope, usually with the release of energy.
nuclear reactor
(1) an apparatus designed to facilitate, contain, and control a nuclear chain reaction.
(2) any heat-producing array of fissile radioactive materials constructed so as to produce a controlled chain-reaction.
null a point on the radiation pattern that corresponds to zero or minimum values.
ohmic contact
a heavily doped and/or low barrier height metal to semiconductor interface or contact that has a very low resistance relative to the remainder of the device, such that the device performance is not significantly degraded. At lower doping levels, the ohmic contact is described by Ohm's Law, while at higher doping levels, tunneling dominates.
overcurrent protection
(1) the act of protecting electrical and electronic devices or circuits from a dangerous amount of input current.
(2) the effect of a device operative on excessive current.
overload protection
a protective device which opens the circuit to a piece of electrical equipment or power line in the event of current exceeding the upper design limit.
parasitic inductance
the generally undesirable and not-designed-for inductance associated with a conductor, or path of current on a conductor.
parasitic reactance
the generally undesirable and not-designed-for reactance associated with one or more conductors in a circuit.
phase detector gain
the ratio of the DC output voltage of the phase detector to the input phase difference. This is usually expressed in units of volts per radian.
photodetector
device capable of producing or modifying an electrical signal in proportion to the amount of light falling on the active area of the device.
photoelectric effect
the phenomenon whereby light of sufficiently short wavelength falls on the emitter electrode of a photocell and causes electrons to be emitted from the electrode.
photogalvanic effect
See
photovoltaic effect
pitch factor
in an electric machine, the ratio of the fractional pitch in electrical degrees to the full pitch, also in electrical degrees.
positive-sequence reactance
the inductive reactance offered by a circuit to the flow of positive-sequence currents alone. The positive-sequence reactance is a function of the operating frequency of the circuit and the inductance of the circuit to positive-sequence currents.
potential source rectifier exciter
a source of energy for the field winding of a synchronous machine obtained from a rectified stationary AC potential source. The AC potential can be obtained from the machine phase voltages, or from an auxiliary source. The components of the exciter are the potential source transformer and the rectifiers (including possible gate-circuitry).
Potier reactance
the leakage reactance obtained in a particular manner from a test on a synchronous machine at full load with a power factor of zero lagging. The test requires little power but supplies the excitation for short circuit and for normal rated voltage both at full-load current at zero power factor. The Potier reactance is determined
by a graphical manner from the open circuit characteristic and the short circuit point for full-load current.
power factor
in an AC system, the ratio of the (active component) real power P to the apparent power S; it is given by the cosine of the angle subtended by S on the real, P axis. See also apparent power, real power, reactive power.
power factor correction
the addition of reactive load to bring the combined power factor nearer unity. Since most industrial loads are inductive, capacitors are often employed as passive devices for power factor correction.