Duty cycle of lightening arrestor

I gotta tell you that I used to build arresters - even had a couple of patents - and I have no idea what a duty cycle means for an arrester. Theoretically it would mean how often it can fire in some given time, but how do you define the lightning stroke? One of the IEEE waveforms? How often are you getting hit?

Surge arrester duty cycle defines the ability of an arrester to discharge impulse current (while energized at duty cycle voltage) and thermally recover at MCOV (in the case of gapless metal-oxide surge arresters). For older gap or valve type surge arresters with silicon-carbide blocks, it defines the voltage at which the arrester can discharge surge current and reseal. If the gaps are not current-limiting, reseal typically occurs at the next system voltage zero.

In the U.S. the standard duty cycle test is defined in IEEE Std C62.11, "IEEE Standard for Metal-Oxide Surge Arresters for Alternating Current Power Circuits".

Well, duh! I wasn't even thinking about MOVs, just big honking gap arresters. A GA to you.

Our arrestors ratings are: discharge current 10 ka , rating 60 kv, type : zno wat should be its duty cycle ?

The 10 kA discharge current is simply the impulse classifying current at which the discharge voltage is measured and represents only one point on the discharge voltage current curve. If 60 kV is truly the rated voltage, that is the duty cycle rating which corresponds to an MCOV (maximum continuous operating voltage) of 48 kV.

The voltage and impulse current indicates a station class surge arrester which means the impulse current used for the duty cycle test is 10 kA crest with an 8/20 microsecond waveshape.

The duty cycle test itself involves energizing the arrester or a pro-rated section of the arrester at the power frequency duty cycle voltage times an overvoltage factor (based on watts loss) and initiating 20 discharges of an 8/20 impulse current with a time interval between operations of 50 - 60 seconds. The current discharges are timed to occur approximately 60° before the crest of the power frequency voltages having the same polarity as the impulse.