Trial Use Recommended Practice for Thermal Cycle Testing of Form-Wound Stator Bars and Coils for Large Generators
|Publication Date:||3 July 1996|
A test method to determine the relative ablility of high-voltage, form-wound stator bars and coils of large rotating machines to resist deterioration due to rapid heating and cooling resulting from machine load cycling is described.
Peaking duty and pump storage hydrogenerators, synchronous condensers, and gas turbine generators are generally subject to load cycling. This load cycling creates shear stress between copper and the groundwall insulation of the stator winding that can result in the delamination of the groundwall, and under certain circumstances, into the puncture of the insulation.
This standard provides a test procedure that can be performed within a reasonable amount of time for accelerated thermal aging of production, prototype, or similar design bars/coils under laboratory conditions. The effects of this accelerated thermal aging on the bars/coils would provide some indication of the thermal aging of the stator winding of generators subject to cyclic duty.
This procedure is intended for bars/coils for rotating machines rated 11 kV or more at 50 Hz or 60 Hz that are subjected to many transitions from no-load to full-load current during normal operations, and where rapid load variations are typical. Only the thermal cyclic degradation within the groundwall insulation and/or the conductor package and delamination of the groundwall insulation from the conductor are addressed by this test.
The procedure is applicable to the following machines:
- Indirectly cooled combustion turbine generators
- Indirectly cooled pumped storage or peaking load hydrogenerators
- Indirectly cooled synchronous condensers
No pass/fail criteria are presented; rather, the test results on a variety of stator bars and coils are compared. Pass/fail criteria may be established by users of this recommended practice.