Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

polarity
the notation used in the assignment of voltages. In DC generators, the polarity of the armature voltage can be reversed by either reversing its field current or by rotating the generator in reverse direction.
polarization
(1) the shape traced out by the tip of the electric field vector as a function of time and the sense in which it is shaped.

(2) a description of the form of the temporal variation of the electric field vector of a light field. In general, the polarization state can be described by the ellipse that tip of the electric field vector traces each optical cycle.
Commonly encountered limiting forms are linear polarization and circular polarization.

(3) the response of material systems, an applied light field by developing a time varying dipole moment. The response is described quantitatively in terms of the dipole moment per unit volume, which is known as the polarization vector.

(4) description of the direction and motion of the electric field vector of a wave. Plane waves may be linearly or elliptically (including circularly) polarized. polarization controller a device that alters only the polarization state of the incident light.
pole
one end of a magnet or electromagnet in electrical machines, created by the flux of the machine.
pole line
any power line which is carried overhead on utility poles.
pole pitch
the angular distance (normally in electrical degrees) between the axes of two poles in an electrical machine.
pole top pin
a steel pin onto which a pin insulator is screwed.
pole-top transformer
generally a distribution transformer which is mounted atop a utility pole near the customer.
polyphase system
electrical system that has more than one phase, which are separated by angles of 360=n, where n is the number of phases. For example, three phase systems are polyphase systems where the three phases are separated by 120 electrical degrees from each other. A six-phase system is a polyphase system where each successive phase is separated by 60 electrical degrees from the other.
position sensor
a device used to detect the position of the rotor with respect to the stator. The most commonly used position sensors for electric motors are Hall effect devices, encoders, and resolvers with resolver-to-digital converters.
position servo
a servo where mechanical shaft position is the controlled parameter.
See servo
positioner
a mechanical device used to move an antenna or target to a desired position for measurement purposes. Positioners can be single or multi-axis and are usually controlled by computers and automated measurement equipment.
positive sequence the set of balanced normal (abc) sequence components used in symmetrical components. Balanced load currents, for example, are strictly positive sequence.
positive transition angle
the angular portion of the time-based output signal (in degrees) that has a positive slope. This quantity could be loosely interpreted as the "leading edge" angle.
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.
post insulator
an electrical insulator which is supported by its firmly-bolted base, either in an upright position or cantilevered out horizontally from a utility tower.
pot head
a fork-shaped transition between a three-phase buried cable and an overhead three-phase electric power line.
potential
an auxiliary scalar or vector field that mathematically simplifies the solution process associated with vector boundary value problems. See also Hertzian potential.
potential coil
a long, finely wound, straight coil, similar in operation to a Chat-tuck coil, that is used with a fluxmeter to measure magnetic potential difference between a point in a magnetic field and a flux-free point in space.
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).
potential transformer (PT)
a device which measures the instantaneous voltage of an electric power line and transmits a signal proportional to this voltage to the system's instruments.
See voltage transformer
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.
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