Answer Posted / elangovan t

Lightning arrester is to protect the system from any high
voltages such as lightning.
If the system voltage is 11kv, then the phase voltage will
be 11/sqrt(3)=6.35kv. It means the RMS voltage of the phase.
The maximum voltage or the peak voltage across the arrester
and earth will be 6.35*sqrt(2)=8.98kv.i.e 9kv.
Therefore, for 11kv line it is rated for 9kv.

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