Reconfiguring Leads to Extend Stator Life

摘要

The Unit 6 generator (original Cana-dian Westinghouse) at the 450-MW (420 MVa) Isle-Maligne powerhouse began operating in 1923 and still has the original stator core and frame. The stator winding was replaced at least twice, and the last winding installed in 1988 started to show signs of degradation. Rio Tinto's maintenance team assigned this stator winding the second lowest reliability rating of its entire fleet (52 hydro units). In January 2014, the unit failed. Returning the unit to service required taking three coils out of the circuit, for a total of 12 coils cut out on a 360-coil winding. This breakdown was the fourth in four years; all the defective coils were located in the first four electrical positions close to the main connections. All showed a voltage to ground of 6.6 kV or higher. Partial discharges (PD) were very high and growing since 2010.