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In fighting a fire adjacent to this generator, fire extinguisher chemicals were discharged, contaminating this unit. The stator winding, rotor winding and core all were condemned.

Contamination

Problem: Contamination from dirty oil or other chemicals can initiate all sorts of problems for a turbine/generator. If the unit is hydrogen-cooled, maintaining gas purity is critical to the unit’s efficient operation and cooling. Oil leaking into the generator can compromise hydrogen purity enough to trip the machine offline. In air-cooled machines, dirt and dust are a common cause of electrical grounds. Generators operating outdoors or in “corrosive” environments face similar challenges with airborne contaminants. Even fire extinguisher chemicals can cause extensive damage, as shown in Fig. 3.

Prevention: Good maintenance practices can prevent much contamination and should include regular inspections of hydrogen dryers and leak detectors. Desiccant should be replaced regularly, leak detectors inspected for signs of oil or water leakage, and filters for air-cooled machines, cleaned regularly. While contamination from accidents may be unavoidable, work and emergency procedures should be reviewed to minimize risks. Polarization Index tests provide a good indication of a the overall cleanliness of stator or rotor winding.