Measurement and Simulation of Hydro-Generator’s Asynchronous Operation

The extended testing of hydro-generator with Pelton turbine (rated 35 MVA) was performed on a generator whose lifespan expired and it was going to be replaced. This was the perfect opportunity to do some specific and uncommon testing. The complex testing plan was designed in order to enable recording of as much relevant data as possible (electrical, electromechanical, mechanical). Therefore, in some phases of testing, 29 to 44 quantities were measured simultaneously. Among the tests, there are short circuits with lowered voltage, bad synchronization at approximate angle of 15 degrees, asynchronous operation, generator overspeed and operation with short circuited field winding on one pole. The most interesting and the most critical operation during this testing is asynchronous operation of hydro-generator [1, 2, 3, 4, 5], which is also very dangerous for generator and drive equipment. During such operation synchronous generator operates at a speed unequal to rated speed. This slip causes increased damping winding currents, which increases the thermal stress of this winding beyond the designed level. This makes these tests very infrequent. Asynchronous operating was achieved by decreasing the excitation current. Complex mathematical model for computer simulation of hydro-generator’s asynchronous operation has been made, taking into consideration the magnetic saturation, damper winding and generator transformer’s influence. Results obtained by simulations have been compared to those obtained by measurements.