A protective device for limiting surge voltages on equipment by discharging or bypassing surge current around the protected device, without any power frequency current flowing to ground, and is capable of repeating these functions as repeatedly. Sometimes spelled arrestor. Related terms: Surge arrester, SPD

arrester aging

There are two types of aging that can occur in arresters. Both are forms of long term degradation.

Disk Aging: This is a slow change in the electrical characteristic of the ZnO varistor due to electrical stress over time. If this does occur, the loss’s of the disk and arrester may increase to a point where the arrester could fail due to excess heating and thermal runaway of the disks.

Shed Aging: This is a slow change in the physical characteristics of the weather sheds that can lead to external flashover or puncture. If puncture occurs the arrester may fail internally due to ingress of moisture of contamination.

arrester body, EGLA SVU IEC

non-linear metal oxide resistor part, contained in a housing, which must be connected with an external series gap to construct a complete EGLA; the arrester body may include several units.

arrester classification IEC and IEEE

Arrester classification or arrester class is determined by prescribed test requirements of a standard. For arresters classified per IEEE standards, the classifications are station, intermediate, distribution heavy duty, distribution normal duty, distribution light duty.

arrester- deadfront type, dead-front arrester IEEE

An arrester assembled in a shielded housing providing system insulation and conductive ground shield, intended to be installed in an enclosure for the protection of underground and pad-mounted distribution equipment and circuits.

arrester - dead-break IEC

arrester which can be connected and disconnected from the circuit only when the circuit is de-energized.

arrester discharge current IEC and IEEE

The current that flows through an arrester resulting from an impinging surge.

arrester discharge voltage IEC and IEEE

The voltage that appears across the terminals of an arrester during the passage of discharge current.

arrester disconnector IEC and IEEE

A device that provides a means for disconnecting an arrester in anticipation of, or after, a overloaded in order to prevent a permanent fault on the circuit and to give indication of an overloaded arrester.

NOTE—Clearing of the fault current through the arrester during disconnection is generally done by the nearest source side overcurrent-protective device.

arrester - distribution, heavy duty class: IEEE

An arrester normally used to protect overhead distribution systems exposed to severe lightning currents. Related term: IEC Class 1 arrester

arrester - distribution, light duty class IEEE

An arrester normally installed on and used to protect underground distribution systems where the major portion of the lightning stroke current is discharged by an arrester located at the overhead line/cable junction.

arrester - distribution, normal duty class IEEE

An arrester normally used to protect overhead distribution systems exposed to normal lightning currents.

arrester duty cycle rating IEEE

The designated maximum permissible root-mean-square (rms) value of power-frequency voltage between its line and ground terminals at which it is designed to perform its duty cycle rating.

arrester – EGLA IEC

An externally gapped line arrester. The body of the arrester is referred to the SVU

arrester - gas-insulated metal enclosed surge arrester, GIS-arrester IEC

gas-insulated metal-enclosed metal-oxide surge arrester without any integrated series or parallel spark gaps, filled with gas other than air and used in gas-insulated switchgears.

NOTE The gas pressure is normally higher than 1 bar = 105 Pa.= 14.7psi

arrester – high voltage IEC

an arrester applied to transmission lines and generally tested to IEC standards. Related terms: station arrester, intermediate arrester, line discharge class 2.3.4.5 arresters.

arrester- line discharge class 2,3,4,5 IEC

Arresters tested per IEC 60099-4 and meet the test requirements of line discharge class 2,3,4,5 arresters

arrester - liquid-immersed type IEC and IEEE

An arrester designed for use immersed in an insulating liquid. Also referred to as under-oil arrester.

arrester - load-break arrester IEC

arrester which can be connected and disconnected when the circuit is energized.

arrester – medium voltage IEC

an arrester applied to distribution circuits and generally tested to IEC standards. Related terms; distribution arrester

arrester - MOV type IEC and IEEE

an arrester fabricated using nonlinear metal-oxide varistors for the valve elements.

arrester - polymer-housed IEC and IEEE

arrester using polymeric and composite materials for housing, with fittings.

NOTE Designs with an enclosed gas volume are possible. Sealing may be accomplished by use of the polymeric material itself or by a separate sealing system.

arrester - riser pole type IEEE

An arrester for pole mounting normally used to protect underground distribution cable and equipment.

arrester - separable type, separable arrester IEC

arrester assembled in an insulated or screened housing providing system insulation, intended

to be installed in an enclosure for the protection of distribution equipment and systems.

Electrical connection may be made by sliding contact or by bolted devices; however, all

separable arresters are dead-break arresters.

NOTE The use of separable arresters is common in Europe.

NOTE 1 Most dead-front arresters are load-break arresters.

NOTE 2 The use of dead-front arresters is common in the USA.

arrester - station class IEEE

An arrester tested per IEEE C62.11 that meets all station class test requirements. This arrester is generally of higher energy capability and better discharge characteristics than distribution and intermediate class arresters.

arrester unit IEC and IEEE

Any section of a multi-unit arrester.

arrester – 5kA arrester IEC and IEEE

An arrester that has a nominal discharge current of 5kA. Often times this is also called a normal duty arrester.

arrester – 10kA arrester IEC and IEEE

An arrester that has a nominal discharge current of 10kA . Often times this is a heavy duty distribution or line discharge class 1 arrester.

average sparkover voltage IEC and IEEE

power frequency sparkover voltage: The average of at least 5 successive power frequency sparkovers. lightning impulse sparkover voltage: The average of at least 5 successive lightning impulse sparkovers.

basic switching impulse insulation level (BSL) IEC and IEEE

a) The electrical strength of insulation expressed in terms of the crest value of a standard switching impulse. BSL may be expressed as either statistical or conventional.

b) A specific insulation level expressed as the crest value of a standard switching impulse.

See also: conventional basic switching impulse insulation level (BSL); statistical basic switching impulse insulation level (BSL).

backflash

An insulator flashover originating from the pole or tower ground across the insulator onto the phase conductor. This can occur during a lightning strike to the overhead shield wire and where the ground impedance is high. It is referred to as a back flashover since it is in the opposite direction of flashovers produced in laboratory tests. The backflash is usually followed by a standard flashover of the insulator with power frequency current that requires a breaker operation to terminate.

back flash overrate (BFOR) IEC and IEEE

characteristics of an overhead line or system with respect to the number of back flashovers typically given per 100 km and year.

bending moment IEC and IEEE

horizontal force acting on the arrester housing multiplied by the vertical distance between the mounting base (lower level of the flange) of the arrester housing and the point of application of the force. Related term cantilever strength

breaking load IEC

force perpendicular to the longitudinal axis of a porcelain-housed arrester leading to mechanical failure of the arrester housing

certification tests IEEE

Tests ran on a regular, periodic basis to verify that selected, key performance characteristics of a product or representative samples thereof have remained within performance specifications.

CFO

See critical flashover voltage IEC and IEEE

classifying current IEEE

The designated current used to perform the classification tests. The equivalent IEC term is nominal current, In

composite hollow core insulator IEC and IEEE

a hollow core insulator with and FRP tube covered with polymer sheds either molded on or slipped on.

conditioning tests

conditioning tests are test that take place in a standard test that is meant to represent stresses similar to long term service. They generally precede durability and withstand tests

conformance tests IEEE

Tests made, when required, to demonstrate selected performance characteristics of a product or representative samples thereof.

continuous current of an arrester IEEE and IEC

current flowing through the arrester when energized at the continuous operating voltage. Also referred to as leakage current or internal leakage current.

NOTE 1 The continuous current, which consists of a resistive and a capacitive component, may vary with temperature, stray capacitance and external pollution effects. The continuous current of a test sample may, therefore, not be the same as the continuous current of a complete arrester.

NOTE 2 The continuous current is, for comparison purposes, expressed either by its r.m.s. or peak value.

continuous operating voltage of an arrester, Uc IEC

designated permissible r.m.s. value of power-frequency voltage that may be applied continuously between the arrester terminals of an arrester. The equivalent IEEE term is maximum continuous operating voltage of an arrester (MCOV)

conventional basic lightning impulse insulation level (BIL) IEEE

Applicable specifically to non-selfrestoring insulations. The crest value of a standard lightning impulse for which the insulation does not exhibit disruptive discharge when subjected to a specific number of applications of this impulse under specified conditions. See also: statistical basic lightning impulse insulation level (BIL).

conventional basic switching impulse insulation level (BSL) IEEE

Applicable specifically to non-selfrestoring insulations. The crest value of a standard switching impulse for which the insulation does not exhibit disruptive discharge when subjected to a specific number of applications of this impulse under specified conditions. See also: statistical basic switching impulse insulation level (BSL).

coefficient of grounding (COG) IEEE

The ratio, ELG/ELL (expressed as a percentage), of the highest root-mean-square (rms) line-to-ground power-frequency voltage ELG on a sound phase, at a selected location, during a fault to ground affecting one or more phases to the line-to-line power-frequency voltage ELL that would be obtained at the selected location with the fault removed. ( ELL= line to line voltage ELG= Line to Ground Voltage)

conventional withstand voltage IEEE

The voltage that insulation is capable of withstanding with a 0% probability of failure. Related terms: critical flashover voltage

coordination of insulation IEC and IEEE

The selection of insulation strength consistent with expected overvoltages to obtain an acceptable risk of failure.

cracking IEEE

The rupture of the weathershed material to depths greater than 0.1 mm.

creepage distance IEC and IEEE

the shortest distance between the high and low voltage points along the external insulating surface of an arresters weathersheds. Creepage distance is also referred to as the leakage or creep distance. The creepage distance and surface characteristics determine the power-frequency withstand of an insulator. Related term is strike distance.

crest value (of a wave, surge, or impulse) IEC and IEEE

The maximum value that a wave, surge, or impulse attains. Synonym: peak value

critical flashover voltage (CFO) IEEE

The amplitude of voltage of a given waveshape that, under specified conditions, causes flashover through the surrounding medium on 50% of the voltage applications.

damage limit IEC

lowest value of a force perpendicular to the longitudinal axis of a polymer-housed arrester leading to mechanical failure of the arrester housing

deadfront type arrester IEEE

see arrester – deadfront type

deflector IEEE

A means for directing the flow of the gas discharge from the vent of the arrester.

degradation IEEE and IEC

any negative or undesirable change in an arresters characteristics resulting from service or testing. Degradation can occur during a surge or from the environment over a long period of time. Degradation can be electrical or physical in nature.

design tests IEEE

Tests made on each design to establish the performance characteristics and to demonstrate compliance with the appropriate standards of the industry. Once made, they need not be repeated unless the design is changed so as to modify performance. Related terms: conformance test, acceptance tests, routine tests, type tests certification tests

designation of an impulse shape IEC and IEEE

combination of two numbers, the first representing the virtual front time (T1) and the second the virtual time to half-value on the tail (T2)

NOTE It is written as T1/T2, both in microseconds, the sign "/ " having no mathematical meaning.

discharge counter IEEE and IEC

A means for recording the number of arrester discharge operations.

discharge current IEEE and IEC

The surge current that flows through an arrester.

discharge indicator IEEE

A means for indicating that the arrester has discharged.

discharge voltage IEEE

The voltage that appears across the terminals of an arrester during passage of discharge current. Also referred to as IR drop, residual voltage, clamping voltage

discharge voltage-current characteristic IEEE

The variation of the crest values of discharge voltage with respect to discharge current.

NOTE—This characteristic is normally shown as a graph based on three or more current-surge measurements of the same wave shape but of different crest values. The IEC equivalent is residual voltage U-I characteristic.

discharge withstand current IEEE

The specified magnitude and wave shape of a discharge current that can be applied to an arrester a specified number of times without causing damage to it.

disconnector

See ground lead disconnector. Also known as GLD, isolator more - ArresterFacts 005 Arrester Disconnector

disruptive discharge IEEE and IEC

The sudden and large increase in current through an insulating medium due to

the complete failure of the medium under electrical stress.

NOTE 1 The term applies to electrical breakdowns in solid, liquid and gaseous dielectric, and combinations of these.

NOTE 2 A disruptive discharge in a solid dielectric produces permanent loss of electric strength. In a liquid or gaseous dielectric the loss may be only temporary.

distribution arrester IEEE

see arrester- distribution. Related terms: medium voltage arrester, line arrester, line discharge class 1 arrester, arrester - 10kA, arrester - 5kA

duty-cycle voltage rating IEEE

The maximum voltage between the terminals of an arrester at which the arrester is designed to perform its duty cycle test as designated in IEEE C62.11. Related term: MCOV, Ur, Uc

earth fault factor (also ground fault factor) IEC and IEEE

the ratio of the rms value of the highest line to ground voltage during an earth fault and the line to ground voltage of the same line when not faulted. Typical fault factors are 1.4 for a solidly grounded 4 wire system and 1.73 for impedance and ungrounded systems. Related terms Coefficient of Grounding (note these are not synonyms)

electrical unit IEEE and IEC

Portion of an arrester in which each end of the unit is terminated with an electrode which is exposed to the external environment.

NOTE An electrical unit is identical to a "unit of an arrester"

electrical aging

See: arrester aging

electrical unit of SVU IEC

portion of an SVU in which each end is terminated with an electrode which is exposed to the external environment

NOTE An electrical unit of SVU is identical to a "unit of SVU"

energy absorption capability

the maximum amount of energy an arrester can absorb due to

a) Thermal energy absorption capability: maximum amount of energy that can be absorbed by an arrester in the form of several subsequent discharges within a short time interval without leading to thermal instability. The thermal energy absorption capability is greater than the impulse energy absorption capability. A multiple impulse switching surge type test measures the thermal absorption capability. This capability is limited by the maximum operating temperature of the ZnO material.

b) Single impulse energy absorption capability: the maximum amount of energy that can be absorbed during a single discharge operation. This capability is limited by the thermo-mechanical strength of the ceramic.

externally gapped line arresters, EGLA IEC

a line surge arrester designed with an external spark gap in series with a SVU part to protect the insulator assembly from lightning caused fast front overvoltages only; this is accomplished by raising the spark over level of the external series gap to a level that isolates the arrester from power frequency overvoltages and from the worst case slow front overvoltages due to switching and fault events expected on the line to which it is applied.

fail-open current rating for liquid-immersed arrester IEC and IEEE

fault current level above which the arrester is claimed to evolve into an open circuit upon overload

fail-short current rating for liquid-immersed arrester IEC and IEEE

fault current level below which the arrester is claimed to evolve into a short-circuit upon overload

fast-front overvoltage, FFO IEC and IEEE

transient overvoltage usually unidirectional, with time to peak between 0,1 µs to 20 µs, and tail duration < 300 µs.

fault indicator IEEE and IEC

device intended to provide an indication that the arrester is faulty and which does not disconnect the arrester from the system.

ferroresonance IEEE and IEC

An resonant overvoltage phenomena that can occur on system under very specific circumstances. Can occur between the capacitance to ground of an ungrounded circuit and voltage transformers with primary windings that are grounded. This phenomenon is also possible in gas insulated systems. Arresters are not designed to protect from this type of temporary overvoltage event.

flashover IEEE and IEC

A disruptive discharge around or over the surface of a solid insulator

flashover rate, FOR

characteristics of an overhead line or system with respect to total number of flashovers typically given per 100 km and year.

follow current (i-follow) IEC

the current immediately following an impulse through an EGLA with the power frequency voltage as the source; the external series gap shall be able to interrupt follow current due to external leakage current on a polluted arrester body (SVU) as well as due to internal resistive current through the non-linear metal oxide resistor blocks; that is, the performance of the EGLA under polluted conditions is introduced by the gap resealing performance under wet and polluted condition, and it is verified by the follow current interruption test.

follow current of an arrester IEC and IEEE

the current from the connected power source which flows through an arrester following the passage of discharge current.

front of an impulse IEEE and IEC

part of an impulse which occurs prior to the peak

front-of-wave impulse sparkover voltage IEEE and IEC

The impulse sparkover voltage with a wave front that rises at a uniform rate and causes sparkover on the wave front.

gapless IEEE

Not possessing gaps, series, or parallel as in gapless arrester.

grading current IEEE and IEC

the peak value of current flowing through the arrester while a voltage is applied.

grading or control ring IEEE and IEC

A metal part, usually circular or oval in shape, mounted to modify electrostatically the voltage gradient or distribution.

ground lead disconnector (GLD)

a device attached to the ground end of an arrester to disconnect it from the ground in the event of a faulted arrester. Sometimes attached to the line side of the arrester however still referred to as a GLD. (more info in ArresterFacts 005 Arrester Disconnector)

ground terminal IEEE

The conducting part provided for connecting the arrester to ground.

high current impulse IEC and IEEE

peak value of discharge current having a 4/10 or 2/20 impulse shape, which is used to test the withstand capability of arresters on extreme lightning occasions.

highest voltage of a system, Us IEC

highest value of the phase-to-phase operating voltage (r.m.s. value) which occurs under normal operating conditions at any time and at any point in the system.

highest voltage for equipment, Um IEC

highest value of the phase-to-phase voltage (r.m.s. value) for which the equipment is designed in respect of its insulation as well as other characteristics which relate to this voltage in the relevant equipment Standards. Under normal service conditions specified by the relevant apparatus committee this voltage can be applied continuously to the equipment.

housing IEC and IEEE

external insulating part of an arrester, which provides the necessary creepage distance and protects the internal parts from the environment.

NOTE Housing may consist of several parts providing mechanical strength and protection against the environment.

hydrophobic IEC and IEEE

the physical characteristic of a surface to repel water in such a way to form droplets on the surface instead of a thin film of water that is considered a hydrophilic characteristic. A surface that is hydrophobic is considered to demonstrate hydrophobicity.

hydrophilic IEC and IEEE

the physical characteristic of a surface to not repel water when the surface is wetted. A hydrophilic surface forms a thin sheet of water on the surface as opposed to droplets on a hydrophobic surface.

IEC

the abbreviation for the International Electrotechnical Commission. The IEC is the world's leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies .

IEEE

A non-profit organization, IEEE is the world's leading professional association for the advancement of technology.

The IEEE name was originally an acronym for the Institute of Electrical and Electronics Engineers, Inc. Today, the organization's scope of interest has expanded into so many related fields, that it is simply referred to by the letters I-E-E-E (pronounced Eye-triple-E).

impulse IEEE and IEC

unidirectional wave of voltage or current which, without appreciable oscillations, rises rapidly to a maximum value and falls, usually less rapidly, to zero with small, if any, excursions of opposite polarity.

NOTE The parameters which define a voltage or current impulse are polarity, peak value, front time and time to half-value on the tail.

impulse protective level IEEE

For a defined wave shape, the higher of the maximum sparkover value or the corresponding discharge-voltage value.

impulse protective levels of an arrester IEC

a) Fast front protective level: The highest of either the steep current residual voltage or the front-of-wave impulse spark over voltage

b) Standard lightning impulse protective level: The highest of the residual voltage at nominal current or 1,2/50 lighting impulse spark over voltage.

c) Switching impulse protective level: The highest of either the maximum residual voltage for the specified switching current or the specified switching impulse spark over voltage.

impulse protective volt-time characteristic IEEE

The discharge-voltage time response of the device to impulses of a designated wave shape and polarity, but of varying magnitudes.

impulse sparkover voltage IEEE and IEC

The highest value of voltage attained by an impulse of a designated wave shape and polarity applied across the terminals of an arrester that will cause gap sparkover prior to the flow of discharge current.

impulse sparkover volt-time characteristic IEEE and IEC

The gap sparkover response of the device to impulses of a designated wave shape and polarity, but of varying magnitudes.

NOTE—For an arrester, this characteristic is shown by a graph of crest voltage values plotted against time to sparkover.

impulse withstand voltage IEEE

The crest value of an impulse that, under specified conditions, can be applied without causing a disruptive discharge.

indoor arrester IEEE

An arrester that, because of its construction, must be protected from the weather.

insulation coordination IEC and IEEE

selection of the dielectric strength of equipment in relation to the operating voltages and overvoltages which can appear on the system for which the equipment is intended and taking into account the service environment and the characteristics of the available preventing and protective devices.

insulation level IEEE

A combination of voltage values (both power frequency and impulse) that characterize

the insulation of an equipment with regard to its capability of withstanding dielectric stresses.

internal grading system of an arrester IEC and IEEE

Grading impedance, in particular linear/non-linear resistors and/or grading capacitors connected in parallel to one or to a group of non-linear metal-oxide resistors and/or series gap , to control the voltage distribution along the arrester and/or between the metal oxide resistors and gaps.

ionization current IEEE

The electric current resulting from the movement of electric charges in an ionized

medium, under the influence of an applied electric field.

ionization voltage IEEE

A high-frequency voltage appearing at the terminals of an arrester, generated by all sources, but particularly by ionization current within the arrester, when a power-frequency voltage is applied across the terminals.

lead length

the section of conductor leading to and from an arrester that carry surge current and are in parallel with the protected insulation.

lightning IEEE

An electric discharge that occurs in the atmosphere between clouds or between clouds and ground.

lightning current impulse IEEE and IEC

8/20 current impulse with limits on the adjustment of equipment such that the measured values are from 7 μs to 9 μs for the virtual front time and from 18 μs to 22 μs for the time to half-value on the tail

NOTE The time to half-value on the tail is not critical and may have any tolerance during the residual voltage type tests

lightning impulse protective level, LIPL IEC

maximum permissible peak voltage on the terminals of a surge arrester subjected to lightning impulses under specific conditions.

lightning impulse withstand voltage, LIWV IEC

Standard rated lightning impulse withstand voltage of an equipment or insulation configuration.

lightning overvoltage IEEE and IEC

The crest voltage appearing across an arrester or insulation caused by a lightning surge.

lightning surge IEEE and IEC

A transient electric disturbance on an electric circuit caused by lightning.

line arrester IEEE and IEC

a type of arrester that is commonly applied to power systems to reduce the risk of insulator flashover during a lightning transient. It may or may not be used to protect the insulator from other types of transients such as switching surges. A line arrester is not generally used to protect any equipment other than line insulators.

line discharge class IEC

in IEC arrester standard 60099-4 there are 5 line discharge classes of arresters, 1-5. It is the present means of characterizing the energy handling capability of an arrester subjected to switching type surges in during the line discharge test.

line terminal IEEE

The conducting part of the arrester provided for connecting the arrester to the circuit conductor.

liquid-immersed type arrester IEEE and IEC

An arrester designed for use immersed in an insulating liquid. Also referred to as under oil arrester

long-duration current impulse IEC and IEEE

rectangular impulse which rises rapidly to maximum value, remains substantially constant for a specified period and then falls rapidly to zero

Note: The parameters which define a rectangular impulse are polarity, peak value, virtual duration of the peak and virtual total duration.

margin of protection

the ratio of arrester protective level and the equipment withstand level. A 1.15 or 15% margin of protection is generally considered a minimum level for a safety margin for aged insulation.

maximum continuous operating voltage rating (MCOV) IEEE

The maximum designated root-mean square (rms) value of power frequency voltage that may be applied continuously between the terminals of the arrester.

maximum design cantilever load-static (MDCL-static) IEEE

The maximum cantilever load the surge arrester is designed to continuously carry. Related IEC term is Mean Breaking Load MBL

maximum system voltage IEEE

The highest voltage at which a system is operated.

mean breaking load, MBL IEC

the average breaking load for porcelain or cast resin-housed arresters determined from tests.

mechanical unit IEEE

Portion of an arrester in which the valve elements within the unit are mechanically restrained from moving in an axial direction.

metal-oxide surge arrester (MOSA) IEEE

A surge arrester utilizing valve elements fabricated from nonlinear resistance metal-oxide materials.

metal-oxide surge arrester without gaps IEC and IEEE

arrester having non-linear metal-oxide resistors connected in series and/or in parallel without any integrated series or parallel spark gaps.

metal-oxide surge arrester with gapped structures IEC and IEEE

an arrester having non-linear metal-oxide resistors connected in series and/or in parallel with any internal series or shunt spark gaps

metal-oxide surge arrester with external series gap (EGLA) IEC

arrester designed to protect the insulator assembly from lightning caused fast front overvoltages only; this is accomplished by raising the spark over level of the external series gap to a level that isolates the arrester from power frequency overvoltages and from the worst case slow front overvoltages due to switching and fault events expected on the line to which it is applied

metal-oxide varistor (MOV) IEEE

A surge arrester utilizing valve elements fabricated from nonlinear resistance metal-oxide materials.

MOSA IEEE and IEC

See metal metal-oxide surge arrester

MOV arrester IEEE and IEC

See metal-oxide varistor

neutral earthing or grounding of a system IEEE and IEC

See system neutral

nominal discharge current of an arrester, In IEEE and IEC

peak value of lightning current impulse which is used to classify an arrester in IEC standards 60099-4, 60099-6, and 60099-8.

nominal rate of rise (of an impulse) IEEE and IEC

For a wave front, the slope of the line that determines the virtual zero. It is usually expressed in volts or amperes per microsecond.

nominal system voltage IEEE and IEC

A nominal value assigned to designate a system of a given voltage class, referred to as Un in IEC market.

non gapped line arresters, NGLA

a line surge arrester designed without any external gapped structures to protect the line insulator assembly from lightning caused fast front overvoltages. It may also protect the line insulators against switching surges if so selected.

NOTE NGLA are generally equipped with a disconnector device that facilitates fast reclosing in case of an arrester overloading.

non-linear metal-oxide resistor IEC and IEEE

part of the surge arrester which, by its non-linear voltage versus current characteristics, acts as a low resistance to overvoltages, thus limiting the voltage across the arrester terminals, and as a high resistance at normal power-frequency voltage.

nonself-restoring insulation IEEE

An insulation that loses its insulating properties or does not recover them completely after a disruptive discharge caused by the application of a test voltage; insulation of this kind is generally, but not necessarily, internal insulation.

normal lightning current IEEE

Lightning currents of 65 kA or less. See also: severe lightning current.

overvoltage IEEE and IEC

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).

operating duty cycle IEEE

One or more unit operations, as specified.

oscillatory surge IEEE

A surge that includes both positive and negative polarity values.

outdoor arrester IEEE

An arrester that is designed for outdoor use.

partial discharge (PD) IEEE and IEC

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

peak value IEEE and IEC

maximum value of a voltage or current impulse. Related term is crest value

NOTE: Superimposed oscillations may be disregarded

peak (crest) value of opposite polarity of an impulse IEC and IEEE

maximum amplitude of opposite polarity reached by a voltage or current impulse when it oscillates about zero before attaining a permanent zero value

polymer-housed arrester IEEE and IEC

arrester using polymeric and composite materials for housing, with fittings.

NOTE Designs with an enclosed gas volume are possible. Sealing may be accomplished by use of the polymeric material itself or by a separate sealing system.

porcelain-housed arrester IEEE and IEC

arrester using porcelain as housing material, with fittings and sealing systems

power-frequency sparkover voltage IEEE and IEC

The root-mean-square (rms) value of the lowest power frequency 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.

power-frequency withstand voltage versus time characteristic of an arrester IEEE and IEC

power-frequency withstand voltage versus time characteristic shows the maximum time durations for which corresponding power-frequency voltages may be applied to arresters without causing damage or thermal instability also known as TOV curve

pressure-relief device of an arrester IEEE and IEC

means for relieving internal pressure in an arrester and preventing violent shattering of the housing following prolonged passage of fault current or internal flashover of the arrester

pressure relief rating IEEE and IEC

the pressure relief rating of an arrester refers to the magnitude of fault current an arrester can withstand without significant fragmentation during an end-of-life-event. The rating is determined by subjecting the arrester to internal fault currents during the short circuit tests.

production tests IEEE

See: routine tests.

prorated section IEEE

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) IEEE and IEC

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.

protective characteristics of an arrester IEC and IEEE

the combination of the following:

a) residual voltage for steep current impulse

b) residual voltage versus discharge current characteristic for lightning impulses

NOTE 1 The lightning impulse protection level of the arrester is the maximum residual voltage for the nominal discharge current.

c) residual voltage for switching impulse

NOTE 2 The switching impulse protection level of the arrester is the maximum residual voltage at the specified switching impulse currents.

protective zone IEC

the distance on either side of an arrester in which the margin of protection remains above the desired level for a give surge. The rate of rise of the surge and the system configuration are the major factors in determining the zone of protection. IEC 60099-5 Section 4.1 offers the formulae to determine the protective zone. Related IEEE term is separation distance.

puncture IEEE and IEC

(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.

radio-influence voltage (RIV) IEEE

A high-frequency voltage, generated by any source of ionization current that appears at the terminals of electric-power apparatus or on power circuits.

rating IEEE

The designation of an operating limit for a device.

rated frequency of an arrester IEC and IEEE

frequency of the power system on which the arrester is designed to be used.

rated voltage of an arrester Ur IEC

maximum permissible r.m.s. value of power-frequency voltage between its terminals at which it is designed to operate correctly under temporary overvoltage conditions as established in the operating duty tests

NOTE 1 The rated voltage is used as a reference parameter for the specification of operating characteristics.

NOTE 2 The rated voltage as defined in this standard is the 10 s power-frequency voltage used in the operating duty test after high-current or long-duration impulses.

reference current (Iref) IEEE and IEC

The peak value of the resistive component of a power-frequency current high

enough to make the effects of stray capacitance of the arrester negligible. This current level shall be

specified by the manufacturer.

NOTE—Depending on the arrester design, the reference current will typically be in the range of 0.05 mA to 1.0 mA per square centimeter of disk area.

reference current of an SVU (Iref) IEC

peak value (the higher peak value of the two polarities if the current is asymmetrical) of the resistive component of a power frequency current used to determine the reference voltage of the MOR

NOTE 1 The reference current shall be high enough to make the effects of stray capacitances at the measured reference voltage of the MOR units negligible and is to be specified by the manufacturer.

NOTE 2 Depending on the nominal discharge current of the arrester, the reference current will be typically in the range of 0,05 mA to 1,0 mA per square centimeter of disc area for single column arresters.

reference voltage (Vref) (Uref) IEEE and IEC

The lowest peak value independent of polarity of power-frequency voltage divided by the square root of 2, required to produce a resistive component of current equal to the reference current of the arrester or arrester element. The reference voltage of a multi-unit arrester is the sum of the reference voltages of the series units. The voltage level shall be specified by the manufacturer.

reference voltage of an SVU (Uref) IEC

peak value of power-frequency voltage divided by √2, which shall be applied to the SVU to obtain the reference current

NOTE The reference voltage of a multi-unit arrester body is the sum of the reference voltages of the individual units.

residual voltage of an arrester, Ures IEC

peak value of voltage that appears between the terminals of an arrester during the passage of discharge current.

NOTE The term "discharge voltage" is used in some countries.

riser pole type arrester IEEE

An arrester for pole mounting most often used to protect underground distribution cable and equipment.

routine tests IEEE and IEC

Tests made by the manufacturer on every device or representative samples, on parts or on materials, as required to verify that the product meets the design specifications.

salt deposit density (SDD) IEC

the amount of salt in the deposit on a given surface of the arrester housing, divided by the area of this surface; it is generally expressed in mg/cm².

section of an arrester IEC and IEEE

complete, suitably assembled part of an arrester necessary to represent the behaviour of a complete arrester with respect to a particular test

NOTE A section of an arrester is not necessarily a unit of an arrester.

self-restoring insulation IEEE and IEC

Insulation that completely recovers its insulating properties after a disruptive discharge caused by the application of an overvoltage; insulation of this kind is generally external insulation.

separation distance

the distance from the arrester where the margin of protection remains above 1.15 related term is protective zone

series gap IEEE and IEC

An intentional gap(s) between spaced electrodes in series with the valve elements across which all or part of the impressed arrester terminal voltage appears.

severe lightning current IEEE

Lightning currents greater than 65 kA but not greater than 100 kA. See also: normal lightning current.

shed IEC and IEEE

insulating part projecting from the housing, intended to increase the creepage distance. Also known as a weathershed

shielding failure flashover rate, SFFOR IEC and IEEE

characteristics of an overhead line with respect to the number of shielding failures leading to flashover typically given per 100 km and year.

shielding failure rate, SFR IEC and IEEE

characteristics of an overhead line with respect to the number of shielding failures typically given per 100 km and year.

shunt gap IEEE and IEC

Intentional gap(s) between spaced electrodes that is electrically in parallel with one or more valve elements.

slow-front overvoltage, SFO IEC

transient overvoltage usually unidirectional, with time to peak between 20 µs to 5 000 µs, and tail duration < 20 µs.

sparkover IEEE and IEC

A disruptive discharge between electrodes of a measuring gap, voltage-control gap, or

gap-type protective device.

SPD IEEE

Surge protective device. Generally used when describing low voltage protectors.

specified continuous load (SCL) IEC

force perpendicular to the longitudinal axis of an arrester, allowed to be continuously applied during service without causing any mechanical damage to the arrester.

specified short-term load (SSL) IEC

greatest force perpendicular to the longitudinal axis of an arrester, allowed to be applied during service for short periods and for relatively rare events (for example, short-circuit current loads, very high wind loads or seismic loads) without causing any mechanical damage to the arrester.

NOTE For seismic load an even higher load than the SSL may be considered.

standard lightning impulse IEEE

The wave shape of the standard impulse used is 1.2/50µs (when not in conflict with products standards).

standard lightning impulse sparkover voltage of an arrester IEC and IEEE

the lowest prospective peak value of a standard lightning voltage impulse which, when applied to an arrester causes sparkover on every application.

standard switching impulses IEEE

The wave shapes of standard impulse tests depend on equipment being tested:

a) For air insulation and switchgear: 250/2500µs

b) For transformer products: 100/1000µs

c) For arrester sparkover tests:

1) 30-60/90-180µs

2) 50-300/400-900µs

3) 1000-2000/3000-6000µs (The tail duration is not critical)

statistical basic lightning impulse insulation level (BIL) IEEE

Applicable specifically to self-restoring insulations. The crest value of a standard lightning impulse for which the insulation exhibits a 90% probability of withstand (or a 10% probability of failure) under specified conditions. See also: conventional basic lightning impulse insulation level (BIL).

statistical basic switching impulse insulation level (BSL) IEEE

Applicable specifically to self-restoring insulations. The crest value of a standard switching impulse for which the insulation exhibits a 90% probability of withstand (or a 10% probability of failure) under specified conditions. See also: conventional basic switching impulse insulation level (BSL).

statistical withstand voltage IEEE

The voltage that an insulation is capable of withstanding with a given

probability of failure, corresponding to a specified probability of failure (e.g., 10%, 0.1%).

steep current impulse IEC

current impulse with a virtual front time of 1 µs with limits in the adjustment of equipment such that the measured values are from 0,9 µs to 1,1 µs and the virtual time to half-value on the tail is not longer than 20 µs.

strike distance IEC and IEEE

the shortest straight line distance between the high voltage and low voltage ends points on an arrester. This distance is the major factor influencing the impulse withstand capability of an insulator.

surface current of SVU IEC

current that flows on the surface of the SVU.

surge IEEE and IEC

A transient wave of current, potential, or power in an electric circuit.

surge arrester IEEE and IEC

switching overvoltage IEEE

Any combination of switching surge(s) and temporary overvoltage(s) associated with a single switching episode.

switching surge IEEE

A heavily damped transient electrical disturbance associated with switching. System

insulation flashover may precede or follow the switching in some cases but not all.

switching current impulse of an arrester IEC and IEEE

peak value of discharge current having a virtual front time greater than 30 µs but less than

100 µs and a virtual time to half-value on the tail of roughly twice the virtual front time

switching impulse protective level SIPL IEC

maximum permissible peak voltage on the terminals of a surge arrester subjected to switching impulses under specific conditions.

switching impulse withstand voltage, SIWV IEC and IEEE

Standard rated switching impulse withstand voltage of an equipment or insulation configuration.

switching surge flashover rate, SSFOR IEC and IEEE

characteristics of an overhead line with respect to the number of switching surges leading to flashover typically given per 100 km and year.

system voltage IEEE and IEC

The root-mean-square (rms) phase-to-phase power frequency voltage on a three phase alternating current electric system. Designated as Um in IEC market.

system neutral grounding or system ground

with respect to surge arresters, the type of earthing or grounding of the system neutral determines the maximum voltage reached during a fault on the system. There are several types of neutral grounding scenarios:

a) Solidly grounded: where the neutral is tied to earth or ground in many places along the power system. Sometimes referred to as effectively grounded.

b) Impedance grounded: where the neutral of the system is connected to earth through a low or high impedance at the source transformer. Sometimes referred to as non-effectively grounded

c) &