Hi all,
I am working as a field service engineer for the overhauling and testing of generators and exciters in power plants.
At my most recent project, I was measuring the resistance of the generator rotor winding using a Digital Low Resistance Micro Ohm Meter with the current set at 10mA. The winding resistance as per the manual is 98 m Ohm at 25 deg Celsius. But in my measurement it came to 120 m Ohm at 27 deg celsius. What does a drastic increase in the winding resistance mean! Please note that the thermal coefficient of the metal used for the winding is of the order of 10^-6 in SI units and so temperature increase has very little effect in this case.
From my experience, I understand that a lower resistance than the manufacturer's manual may mean an inter turn short in the winding. This rotor cleared the RSO check and the impedance of the winding was ok. I wish to know what this anomaly may mean.