SPDC Terms beginning with T

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.
temperature coefficient of breakdown voltage

αV(BR), dV(BR)/dTJ
Ratio of the change in breakdown voltage, V(BR), to the change in temperature.
NOTE—Expressed as either millivolts per Kelvin (mV/K) or per cent per Kelvin (%/K) with reference to the 25 °C value of breakdown voltage. Alternatives to mV/K and %/K are mV/°C and %/°C.
[C62.35-2010]

temperature coefficient of breakdown voltage

αV(BR); dV(BR)/dTJ
The ratio of the change in breakdown voltage, V(BR), to changes in  temperature. Expressed as either millivolts  per degree Celsius (mV/°C), or percent per degree Celsius (%/°C) with reference to the 25 °C value of breakdown voltage (mV/°C or %/°C).
[62.37-1996]

temperature derating

Change of ratings with temperature above a specified base temperature.
NOTE 1—Expressed in percentage of the rating at the base temperature.
[C62.35-2010]

temperature derating

Derating with temperature above a specified base temperature, expressed as a percentage, such as may be applied to peak pulse current
[62.37-1996]

temporary overvoltage

An oscillatory phase-to-ground or phase-to-phase overvoltage that is at a given location of relatively long duration (seconds, even minutes) and that is undamped or only weakly damped. Temporary overvoltages usually originate from switching operations or faults (e.g., load rejection, single-phase fault, fault on a high-resistance grounded or ungrounded system) or from nonlinearities (ferroresonance effects, harmonics), or both. They are characterized by the amplitude, the oscillation frequencies, the total duration, or the decrement.
[C62.82.1-2010]

temporary overvoltage (TOV)

An oscillatory overvoltage, associated with switching or faults (for example, load rejection, single-phase faults) and/or nonlinearities (ferroresonance effects, harmonics), of relatively long duration, which is undamped or slightly damped.
[C62.22-2009]

terminals

The conducting parts provided for connecting the arrester across the insulation to be protected.
[C62.11-2005]

thermal resistance

RθJL, RθJC, RθJA
Effective temperature rise per unit power dissipation of a designated junction, above the temperature of a stated external reference point (lead, case or ambient) under conditions of thermal equilibrium.
[C62.35-2010]

thermal resistance

RθJL; RθJC; RθJA
The effective temperature rise per unit power dissipation of a designated junction, above the temperature of a stated external reference point (lead, case, or ambient) under conditions of thermal equilibrium.
[62.37-1996]

thyristor

A bistable semiconductor device comprising three or more junctions that can be switched from the off-state to the on-state or vise versa, such switching occurring within at least one quadrant of the principal voltage-current characteristic.
[62.37-1996]

time-to-crest value

Tr
The time that an impulse rises to crest value.
[C62.82.1-2010]

time-to-half value

Th
The time that an impulse drops to 0.5 crest value.
[C62.82.1-2010]

time-to-impulse sparkover

The time between virtual zero of the voltage impulse causing sparkover and the point on the voltage wave at which sparkover occurs.
[C62.11-2005]

tracking

Irreversible degradation of surface material from the formation of conductive carbonized paths.
[C62.11-2005]

transfer time

The time duration of the transverse voltage.
[C62.31-2006]

transient overvoltage

A short-duration highly damped, oscillatory or nonoscillatory overvoltage, having a duration of few milliseconds or less. Transient overvoltage is classified as one of the following types: lightning, switching and very fast front, short duration.
[C62.82.1-2010]

transient thermal impedance

ZθJL, ZθJC, ZθJA
change in the difference between the virtual junction temperature and the temperature of a specified reference point or region (lead, case, or ambient) at the end of a time interval divided by the step function change in power dissipation at the beginning of the same time interval which causes the change of temperature-difference.
NOTE—It is the thermal impedance of the junction under conditions of change and is generally given in the form of a curve as a function of the duration of an applied pulse.
[C62.35-2010]

transient thermal impedance

ZθJL(t); ZθJC(t); ZθJA(t)
The change in the difference between the virtual junction temperature and the temperature of a specified reference point or region (lead, case, or ambient) at the end of a time interval divided by the step function change in power dissipation at the beginning of the same time interval that causes the change of temperature-difference.
NOTE: It is the thermal impedance of the junction under conditions of change and is generally given in the form of a curve as a function of the duration of an applied pulse.
[62.37-1996]

transient voltage surge suppressor (TVSS)

A device that functions as a surge-protective device (SPD) or surge suppressor.
[C62.72-2007]

transition current

The current required at a given temperature and duration to cause a current-protective device to change state.
[C62.36-2000]

transition time

The time required for the voltage across a conducting gap to drop into the arc region after the gap initially begins to conduct.
[C62.31-2006]

transmission line arrester

A surge arrester installed on a transmission line, usually for the purpose of protecting transmission line insulation.
[C62.22-2009]

traveling wave

The resulting wave when an electrical variation in a circuit such as a transmission line takes the form of translation of energy along a conductor, such energy being always equally divided between current and potential forms.
[C62.22-2009]

turn insulation (rotating electric machinery)

The insulation applied to provide electrical separation between the turns of a coil.
NOTE: In the usual case, the insulation encircles each turn. It is sometimes referred to as turn-to-turn insulation.
[C62.21-2003]

two-port SPD

An SPD with two sets of terminals, input and output. A specific series impedance is inserted between these terminals.
[C62.34-1996]

Type 1 SPD

Permanently connected SPDs intended for installation between the secondary terminal of the supplying transformer and the line side of the service equipment overcurrent device, as well as the load side, including watt-hour meter socket enclosures and intended to be installed without an external overcurrent protective device.
[C62.62-2010]

Type 2 SPD

Permanently connected SPDs intended for installation on the load side of the service equipment overcurrent device; including SPDs located at the branch panel.
[C62.62-2010]

Type 3 SPD

Point of utilization SPDs, installed at a minimum conductor length of 10 meters (30 feet) from the service equipment to the point of utilization, for example cord connected, direct plug-in, receptacle type and SPDs installed at the utilization equipment being protected. The distance (10 meters) is exclusive of conductors provided with or used to attach SPDs. If the nominal discharge current test is performed on a Type 3 SPD, the minimum distance from the service equipment does not apply.
[C62.62-2010]

Type 4 SPD

Component SPDs, including discrete components as well as component assemblies.
[C62.62-2010]