Recommended Practice for Thermal Cycle Testing of Form-Wound Stator Bars and Coils for Large Rotating Machines
|Publication Date:||29 March 2012|
This procedure is intended for form-wound bars/coils for rotating machines rated 10 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. Examples of machine types that typically exhibit rapid load transitions include:
- Combustion turbine generators
- Pumped storage or peaking duty hydrogenerators
- Synchronous condensers
- Cyclic duty water pump motors
Various pass/fail criteria are presented, and the ones that apply in a specific circumstance must be agreed between the user and the manufacturer prior to commencement of testing. Whether a particular bar or coil has passed or failed is best determined by comparing the test results from a number of stator bars or coils.
A test method to determine the relative ability 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. The test procedure is primarily intended for machines where the stator windings are indirectly cooled by air or hydrogen. This procedure provides a recommended practice for performing thermal cycle testing of form-wound stator bars and coils without the use of a simulated core. To ensure the results of the thermal cycling test accurately represent the insulation deterioration expected in service, the bars or coils used in the test should represent in every way the characteristics of the production lot. Thermal cycle testing of bars and coils confined in a simulated core would require different parameters and therefore is not covered by this procedure.