Answer / shane e.

It is the ratios of of insulation resitance on a DC hi-pot test over 10 minutes. If less than 1 insulation is surely breaking down.

Answer / lovy

Polarization index is an indirect method of testing which may mislead about healthiness of transformer insulation
so instead of pi , capacitance and tan delta should be measured for keeping a correct check on insulation

Answer / josephat murusura

PI is the ratio of the 10minutes megger value to that of
the 1 minute.The minimum acceptable value is 2.Any value
below 2 is not good enough for the operation of the
electrical machine[motor or transformer]& it indicates that
the winding insulation has detoriated.

Answer / karthik

It's minimum acceptabce value depends on the class of
insulation also. Minimum recommended value IR(60 sec)/IR(15
sec) should be 1.3 for all classes of insulation.

Answer / sandipan sarkar

it is ratio of insulation resistance (IR)for 10 minutes to
insulation resistance for 1 minute.

it should be 2.5

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