CA01065E_Catalog 70

ARRESTERS

Technical Terms

BIL (Basic Lightning Impulse Insulation Level): The electrical strength of insulation in terms of the crest value of a standard lightning impulse under standard atmospheric conditions. Equipment BIL is compared against the arrester residual voltage to determine the margin of protection. Creepage Distance: The distance between the line and ground terminals of an arrester drawn along the outside of the housing. Also referred to as leakage distance.

Crest Value: The maximum value that a wave, surge or impulse attains.

Design (Type) Tests: Tests made on each arrester family or design to establish performance characteristics and to demonstrate compliance with the appropriate industry standards. Once made, they need not be repeated unless the design is changed, so as to modify performance. Discharge Voltage: The voltage that appears across the terminals of an arrester during passage of discharge current. Also referred to as residual voltage.

Fault Current: The current from the connected power system that flows in a short circuit. Ground Terminal: The conducting part provided for connecting the arrester to ground.

Line Terminal: The conducting part of an arrester provided for connecting the arrester to the circuit conductor. MOV (Metal Oxide Varistor): The power semi-conductor that limits the surge voltage allowing the arrester to perform its protection function. This is the electrically active component of the surge arrester. MCOV (Maximum Continuous Operating Voltage): The maximum designated root-mean-square (rms) value of power-frequency voltage that may be applied continuously between the terminals of the arrester. Partial Discharge (PD): A localized electric discharge resulting from ionization in an insulation system when the voltage stress exceeds critical value. The discharge partially bridges the insulation between electrodes. Phase-to-Ground clearance: The phase to ground spacing required between metal parts at 1800m in order to prevent flashover.

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