Answer / karan

The thump rule is voltage rating +1 example for a 11KV
motor it should be 11+1=12 Mega ohm.
In addition to that the PI is the ratio between 1Mnts and
10 mnts.It should be above 1.5
For examle IR at 1mnts= 10M.ohm,
IR at 10 Mnts= 20 M.Ohm
Then the Polarisation index is 2 which is consdierd
good.When it is below 1.5 you can heat the tranformer or
motor then the value will come up.

Answer / priyan

see sundar
Meggering test is done for any electrical equipments to
find the insulation resistance value.
As per the standards for testing the machines 3 methods are
there
1)spot reading 2)time-resistance testing method 3)step
voltage test
the following is the second mehtod it is in use nowadays
PI=10 min/1 min value
Then the Polarisation index is 2 which is consdierd
good.When it is below 1.5 you can heat the tranformer or
motor then the value will come up.

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