Application of an On-Line Air Gap Monitor for Hydroelectric Generator Protection and Problem Diagnosis

This paper presents the application of a new hydroelectric generator air gap measurement system. It is a continuous on-line system using optical triangulation, fiber-optics, a microprocessor-based monitor, specially developed instrumentation and power supplies. This system is non-invasive, insensitive to EMI and has 0.2% accuracy over a range of 2 to 40 mm. The paper presents air gap data obtained from B.C. Hydro´s Mica Creek Unit G2 (457 MVA) during March 1986. Readings were taken from stator-to-rotor and from rotor-to-stator to determine the unit´s characteristics prior to rotor rim shrink modifications. This data assisted in determining the individual contributions of the rotor and the stator to the generator´s behavior and provides a comparison for post-modification testing.