Earth Fault Protection

[bob]

Hi,

 

I am looking for the ideal setting for the earth fault protection on a 6000 HP 11 k V wound motor. I am using a protection relay which uses the vector sum of the three CTs to calculate the fault current to earth.My problem is that the maximum earth fault current on my network is limited to 20 Amps and the motor is tripping at a setting 20 amps IDMT. The previous setting for earth fault on this motor was 40 Amps and the motor has been operating like this unnoticed fo years .

Is there any convenient way to measure the leak current during stating ?

 

Bob