Before assembly of a machine that contains a three phase generator I check the resistance between the 3 phases of the generator with an ohmmeter. The generator is kept stationary and the temperature is somewhere around 20 degrees centigrade.
The measurement ensures that the generator has no internal wiring fault.
The success criterion is that the resistance between the different poles is equal and matches the resistance specified by the manufacturer (58 Ohm).
Now I have a generator that has a correct measurement between phase 1-2, but any measurement involving the 3rd phase shows me a varying resistance value.
The value jumps around (from 20 to 140 Ohm), converges to the correct resistance value after 20-30 seconds and then starts diverging again.
What could cause this odd behaviour?