This part of GB/T 20833 which is a technical specification specifies a common basis for partial discharge off-line measurements on the stator winding insulation of rotating electrical machines when tested with alternating voltages up to 400 Hz, include:
— measuring techniques and instruments,
— the arrangement of test circuits,
— normalization and testing procedures,
— noise reduction,
— the documentation of test results,
— the interpretation of test results.
This part applies to rotating machines having bars or form wound coils with conductive slot coating. This is usually valid for machines with voltage rating of 6 kV and higher. The measurement methods described in this part may also be applied to machines without conductive slot coating. However, results may be different and are not covered by this part.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 7354-2003 Partial Discharge Measurements (IEC 60270:2000, IDT)
IEC 60060-1 High-voltage Test Techniques — Part 1: General Definitions and Test Requirements
IEC 60060-2 High-voltage Test Techniques — Part 2: Measuring Systems
3 Terms and Definitions
For the purposes of this document, the general terms and definitions for partial discharge measurements given in GB/T 7354-2003 apply, together with the following.
3.1
off-line measurement
measurement taken with the rotating machine at standstill, the machine being disconnected from the power system
Note: The necessary test voltage is applied to the winding from a separate voltage source.
3.2
on-line measurement
measurement taken with the rotating machine in normal operation
3.3
stress control coating
paint or tape on the surface of the groundwall insulation that extends beyond the conductive slot portion coating in high-voltage stator bars and coils
Note: The stress control coating reduces the electric field stress along the winding overhang to below a critical value that would initiate PD on the surface. The stress control coating overlaps the conductive slot portion coating to provide electrical contact between them.
