Question

The armature of a 600 kW, 0.24 k, 1000 rpm DC generator has an indicated IR to ground of 2 MΩ at a temp. of 30°C. what is the recommended value of insulation? Is it advisable to put the machine in service? Give reason. Correction factor for 30°C is 0.5.

Answer 1

Data given are

kV – 0.24

Indicated IR – 2MΩ

Temp. - 30°C

Correction factor – 0.5

Recommended value (Rm) = kV + 1 MΩ

= 0.24 + 1

= 1.24 MΩ

Indicated IR at 30°C = 2MΩ

Correction factor – 0.5

So value corrected to 40°C = Rm = kt * Rt

= 0.5 * 2

= 1MΩ

The generator cannot be put in service because the corrected value is lesser than recommended value. It should be sent for IR re-conditioning .