Increase in Rotor Resistance

You need to give more information please. What problem(s) did you exsperience from the generators, low output voltage, regulation or what? What tempt you to look at the resistance of the poles??

You are talking about generators.. The same scenario on all of them?? How many?

Thanks..

The problem wsa a tripping due to excitation lost, we found a cable blowed fron the exciter to the poles..we have 27 generators but only tis one with this problem..we aldready change a pole in this 10 pole generator due to low isolation resistance

If there are no loose connections in the circuit, I'm afraid that since you've already changed one pole, the insulation on the rest are also deteriating rapidly. I assume these are fairly old units and has to be refurbished eventually.

The increase in resistance is as a result of the deteriation of the insulation between the wires. You need to put a maintenance program in place and start replacing the poles..

Were these two resistance measurements made at the same temperature? Due to the temperature coefficient of resistance in copper, you'd get this change in resistance for a rise of about 200°C.

Yes, the measuremets was made almost at the same temperature and our tester has an internal coeficient corrector, do you have some file or table for the impact of tmeprature in cooper resistance?

Hyperphysics is a very useful resource.

Check cold resitance valuesie at ambient and when machine is stopped and cooled down.Then take hot resitance and compare the values.