SPDC Terms beginning with P

Terms and definitions extracted from current SPDC published documents
Click one of the capital letters above to advance the page to terms beginning with that letter.
p-gate thyristor

A three-terminal thyristor in which the gate terminal is connected to the p-region adjacent to the region to which the cathode is connected and that is normally switched to the on state by applying a positive signal between the gate and cathode terminals.


A device descriptor that is measurable or quantifiable, such as a characteristic or rating.

partial discharge (PD)

A localized electric discharge resulting from ionization in an insulation system when the voltage stress exceeds the critical value. This discharge partially bridges the insulation between electrodes.

peak forward recovery voltage

The maximum value of forward conduction voltage across the device upon the application of a specified voltage rate of rise and current rate of rise following a zero or specified reverse-voltage condition.

peak gate switching current

The maximum value of current through the gate terminal during the transition from the off-state to the switching point, when a specified gate bias voltage, VG, is applied.

peak impulse current

The peak current for a series of essentially identical impulse waveforms.

peak nominal Varistor voltage

Voltage across the varistor measured at a specified peak ac current, IN(ac), of specific duration. IN(ac) is specified by the varistor manufacturer.

peak off-state gate current

The maximum gate current that results from the application of the peak off-state gate voltage, VGDM.

peak pulse impulse current

Rated maximum value of peak impulse pulse current (IPP) applied for 10 pulses with 10/1000 µs waveform and maximum duty factor of 0.01% without causing failure.

peak value

See: crest value.

per unit (pu)

The ratio of the actual value of a quantity to the base value of the same quantity.

per unit surge voltage (rotating electric machinery)

The ratio of a surge voltage crest magnitude to the crest value of the machine rated voltage. For a three-phase machine, the divisor (1pu) is the crest value of the rated phase-to-neutral voltage and equals phase-to-phase rated voltage V times the square-root of two divided by the square-root of three, V(2/3)0.5.

performance criterion

The criterion upon which the insulation strength or withstand voltages and clearances are selected. The performance criterion is based on an acceptable probability of insulation failure and is determined by the consequence of failure, required level of reliability, expected life of equipment, economics, and operational requirements. The criterion is usually expressed in terms of an acceptable failure rate (number of failures per year, years between failures, risk of failure, etc.) of the insulation configuration.

phase-to-ground insulation configuration

An insulation configuration between a terminal and the neutral or ground.

phase-to-phase insulation configuration

An insulation configuration between two-phase terminals.

positive-breakdown-resistance thyristor surge protection device (SPD)

A thyristor SPD, whose static breakdown characteristic has a net positive-resistance slope prior to switching.

power cross

An event in an electrical distribution system where a higher voltage conductor, such as from a transmission line, falls on a lower voltage conductor, such as a distribution or secondary line.

power-frequency sparkover voltage

The root-mean-square (rms) value of the lowest powerfrequency sinusoidal voltage that will cause sparkover when applied across the terminals of an arrester.

power-frequency withstand voltage

A specified root-mean-square (rms) test voltage at a power frequency that will not cause a disruptive discharge.

preferred values

The parameters listed for various tests are preferred in the sense that their use promotes uniformity. However, specific applications may require values other than the listed preferred values.

principal current

A generic term for the current through the device excluding any gate current.
NOTE: It is the current through both main terminals.

principal voltage

The voltage between the main terminals.
NOTE 1 - In the case of reverse blocking and reverse conducting thyristors, the principal voltage is called positive when the anode potential is higher than the cathode potential, and called negative when the anode potential is lower than the cathode potential.
NOTE 2 - For bidirectional thyristors, the principal voltage is called positive when the potential of main terminal 2 is higher than the potential of main terminal 1.a
NOTE 3 - For forward-conducting thyristors the principal voltage is called positive when the cathode potential is higher than the anode potential, and called negative when the cathode potential is lower than the anode potential.

principal voltage-current characteristic

The function, usually represented graphically, relating the principal voltage to the principal current.

production tests

See: routine tests.

prorated section

A complete, suitably housed part of an arrester, comprising all necessary components, including gaseous medium, in such a proportion as to accurately represent, for a particular test, the characteristics of a complete arrester.

prospective (available) short-circuit current (at a given point in a circuit)

The maximum current that the power system can deliver through a given circuit point to any negligible impedance, short circuit applied at the given point or at any other point that will cause the highest current to flow through the given point
NOTE 1?This value can be in terms of either symmetrical or asymmetrical, peak or root-mean-square (rms) current, as specified.
NOTE 2?In some resonant circuits, the maximum available short-circuit current may occur when the short circuit is placed at some other point than the given one where the available current is measured.

prospective overvoltage

The theoretical voltage that a lightning event might couple or induce into a power system if it were not truncated by flashover of insulation or action of an surge protective device (SPD).

protective margin (PM)

The value of the protective ratio (PR), minus one, expressed in percent. PM = (PR-1)*100.

protective ratio (PR)

The ratio of the insulation strength of the protected equipment to the overvoltages appearing across the insulation.


See surge protector.

pulse life

The number of surges of specified voltage, current amplitudes, and wave shapes that may be applied to a device without causing degradation beyond specified limits. The pulse life applies to a device connected to an ac line of specified characteristics and for pulses sufficiently spaced in time to preclude the effects of cumulative heating.


(A) A disruptive discharge through a solid dielectric.
(B) A disruptive discharge through solid insulation.
(C) Term used to denote when a disruptive discharge occurs through a solid dielectric and produces permanent loss of dielectric strength; in a liquid or gaseous dielectric, the loss may be only temporary.