When measuring the Insulation resistance of a motor winding (winding to earth)

When measuring the Insulation resistance of a motor winding
(winding to earth) using a megger meter, Applied
voltage(1000V) was automatically reduced to 500V. and the
measured insulation resistance values are also very low (in
Kohm range) Can anyone give me a reason???

Question Posted / dum

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When measuring the Insulation resistance of a motor winding (winding to earth) using a megger mete..

Answer / sridhar

there are two reasons of getting the value low.
1. due to moisture in the motor
2. winding has become weak

to overcome these problems the methods can be adopted
1. heater or halogen lamp to be provided near to the
winding of the motor to bring the resistance value as per
std.
2. by this above method, the insulation resistance is not
upto the mark, the same winding can be overhauled to
achieve the required insulation resistance value.

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When measuring the Insulation resistance of a motor winding (winding to earth) using a megger mete..

Answer / raghavendran.r

The reason for the fall in supply voltage could be because of the fact Insulation has started conducting heavily as mentioned that insulation resistance is also poor.

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When measuring the Insulation resistance of a motor winding (winding to earth) using a megger mete..

Answer / dum

Thanx Sridhar.. ur answer is clear. But i want to know why the applied voltage is automatically reduced as i have mentioned in my question?? is there any theoretical explanation for that??

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