Advanced generator protection and monitoring using transducer measurements

A number of generator issues are undetectable using the generator terminal voltage or current measurements. For example, a switching element failure in the exciter produces a characteristic harmonic signature in the field current. While some generator protective relays are capable of measuring the field current, the sampling rate may be insufficient to extract the relevant harmonics. Consider shaft current protection of hydroelectric generators. The measurement source is a shaft current transformer or Rogowski coil. The operating quantity is a fundamental or root mean square component, but the signal level will likely be too low for conventional current inputs to measure. This paper reviews a number of generator protection and monitoring applications that use transducer measurements to complement current protection. The paper describes the factors that govern the signal characteristics. It defines the operating principles of the protection functions and the resulting transducer measurement requirements.