Diagnostic Testing of Hydro and Turbo Generators and Large AC Motors in Service

Majority of the generating sets operating in our country are turbo generators contributing nearly 70 % of the total electrical power generated. Many of these generators are about 30–40 years old and have already come to the end of their notional design life. The important components that have direct bearing on the operational reliability and life of the machine are: (1) Stator winding, (2) Stator core, and (3) Rotor winding. The stator winding is the most important and expensive part of the generator, where full power is generated. The life of the stator is affected by one or more combinations of various stresses, like electrical, thermal, mechanical and environmental, at any point of time during operation of the machine. Since the mechanical stresses are relatively higher in turbo generators, many of the stator winding failures are mechanically induced electrical failures. Some of the degradation processes include loosening of wedges and coils, slot and end-winding discharges, erosion of stress grading and corona shielding coatings, de-lamination of insulation, de-bonding of copper from insulation, etc.