3P Capacitor Bank

What is the voltage of the capacitor bank?

Threshold gap is admissible for L.V. when glass encapsulated arrestor is tested with a 1 kv high voltage tester.

If you are trying to choose arrester ratings based on your voltage and phase configuration, most arrester manufacturers have guidelines in their catalogs. There are different MCOV ratings recommended depending on whether it is solidly grounded wye, impedance grounded, or ungrounded (delta). However, you will also need to consider also the limits of the equipment you are protecting (your capacitors) - things like BIL rating, etc. - and how quickly your protection system operates (relay / breaker clearing times) when you finally choose your arresters. You need qualified help for this.