Thumb rule to measure the IR value is add 1.5 to the
operating voltage (convert the voltage in KVolts) the
answer is the min. required safe IR value (Mega ohm).
For Example the Operating voltage is 22kV then 1.5 + 22 =
23.5. 23.5 Mega Ohm is the min. IR value required.
The IR value must alaways be on higher side.
insulation resistance 11kv to 33kv minimum IR value for new
cable ph to ph & ph to earth 400 megohms for 100 meter 1 minitue
cable after repair the resistance must not be less that
10 megohms ( megger size 1kv )