SPDC Terms beginning with O

Terms and definitions extracted from current SPDC published documents
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off-state capacitance

The capacitance in the off-state measured at specified frequency, f, amplitude, Vd, and dc bias, VD.

off-state current

The dc value of current that results from the application of the off-state voltage.

off-state of a thyristor surge protection device (SPD)

The state of a thyristor SPD, in a quadrant in which switching can occur, that corresponds to the high dynamic-resistance portion of the characteristic between the origin and the beginning of the breakdown region.

off-state voltage

The dc voltage when the device is in the off-state.

on-state (region)

The condition of the thyristor corresponding to the low-resistance low-voltage portion of the principal voltage-current characteristic in the switching quadrant(s).

on-state current

The current through the device in the on-state condition.

on-state voltage

The voltage across the device in the on-state condition at a specified current.

one-port SPD

A SPD with protective components connected in shunt with the circuit to be protected. A one-port SPD may have separate input and output terminals without a specified series impedance between these terminals.

open-circuit voltage (OCV)

The voltage available from the complete test set-up as configured (surge generator, coupling circuit, back filter, connecting leads), prior to connecting the equipment under test (EUT), at the terminals where the surge protective device (SPD) under test will be connected.

operating duty cycle

One or more unit operations, as specified.

oscillatory surge

A surge that includes both positive and negative polarity values.

oscillatory surge

A surge that includes both positive and negative polarity values.

outdoor arrester

An arrester that is designed for outdoor use.

overhead groundwire (lightning protection)

Grounded wire or wires placed above phase conductors for the purpose of intercepting direct strokes in order to protect the phase conductors from the direct strokes. They may be grounded directly or indirectly through short gaps.

overshoot duration (Varistor)

The time between the point at which the wave exceeds the clamping voltage level (VC) and the point at which the voltage overshoot has decayed to 50% of its peak. For the purpose of this definition, clamping voltage is defined with an 8/20 µs current waveform of the same peak current amplitude as the waveform used for this over-shoot duration.


Abnormal voltage between two points of a system that is greater than the highest value appearing between the same two points under normal service conditions. Overvoltages may be low-frequency, temporary, and transient (surge).


Voltage, between one phase and ground or between two phases, having a crest value exceeding the corresponding crest of the maximum system voltage. Overvoltage may be classified by shape and duration as either temporary or transient.
NOTE 1 — Unless otherwise indicated, such as for surge arresters, overvoltages are expressed in per unit with reference to maximum rms system voltage, Vm*(2/3)0.5.
NOTE 2 — A general distinction may be made between highly damped overvoltages of relatively short duration (transient overvoltages) and undamped or only slightly damped overvoltages of relatively long duration (temporary overvoltages). The transition between these two groups cannot be clearly defined.