CA01082E_Catalog 30

Engineering Terminology

Maximum Design Cantilever Load-Static (MDCL-Static) : The maximum cantilever load the surge arrester is designed to continuously carry. 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. Q rs : Repetitive charge transfer rating given in Coulombs. Test performed on individual MOV blocks without thermal recovery. Q th : Thermal charge transfer rating given in Coulombs. Applicable for distribution arresters only. Reference Current (Iref) : 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. Reference Voltage (Vref) : 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. Routine Tests : Tests made by the manufacturer on every device to verify that the product meets the design specifications. Surge Arrester : A protective device for limiting surge voltages on equipment by diverting surge current and returning the device to its original status. It is capable of repeating these functions multiple times. TOV (Temporary Over Voltage) : A power frequency voltage in excess of normal line-to-ground voltage. A TOV is typically system generated. The magnitude and duration are a function of the power system parameters. Prior Duty TOV : The TOV of the arrester if it has been energized before an over voltage event. No Prior Duty TOV : The TOV of the arrester if it has not been energized prior to an over voltage event. W th : Thermal energy rating of a station or intermediate arrester given in kJ/kV of Ur (IEC) or kJ/kV of MCOV (IEEE)

dependability

Page 68 | October 2023