Some critical aspects of generator capability under unbalanced operating conditions

The transient negative sequence rating of a generator is discussed and I2²t is concluded to be inadequate for rating the generator imbalance capability. The possible fault asymmetry, the excitation system and the duration of the fault should also be considered when rating a generator. Measurements of rotor heating during controlled tests on a large generator are discussed, and a method of calculating the loss and temperature in the main body of the rotor is examined. The calculated temperatures were in good agreement with the measurements.