Insulation Testing for Motor & Alternators

Few people knows this formula for Insulation testing for a motor or alternator/ Transformer. I am saying this because i got this formula after long discussion with colleges. so you are lucky
  

Formula of LT Motor/Alternator  Insulation resistance  


Insulation resistance for LT motor = 1+ (Motor Ratted Voltage in KV) In Mega Ohm 

LT Motor (415volt) internal resistance should be 90~100 Mega Ohm.


Acceptable Internal Resistance for Motor = 2 ~ 10 Mega Ohm 

Note:- For LT equipment we used 500 V (500 Volt) Meggar.

Formula of HT Motor/Alternator Insulation resistance

Insulation resistance for HT motor = (Voltage in KV *2)+3  In Mega Ohm

For example : 11 kv HT Motor IR   = (11*2)+3 =25 Mega Ohm

Note:- For HT equipment we used 5 KV (5000 Volt) Meggar.

For Alternator or Transformer winding testing we withstand the 5KV voltage for around 2 minutes.