GB/T 20833.1-2021Rotating electrical machines - The winding insulation - Part 1: Off-line partial discharge measurements (English PDF)

6.2 of the 2016 Edition);

--- Add calibration pulse level and tolerance (see 7.1 of this Edition);

---Modify the standard measurement (see 7.3.2 and 7.3.3 of this Edition; 7.3.2 of the 2016

Edition);

--- Add the use of integrated test equipment (see 7.3.4 of this Edition);

--- Modify the partial discharge measurement of windings and winding components (see 9.1

of this Edition; 9.1 of the 2016 Edition);

--- Delete the electromagnetic probe (see 9.2.2 of the 2016 Edition);

--- Modified the evaluation of test results (see 10.1, 10.2.1 and 10.3.1 of this Edition; 10.1,

10.2.1 and 10.3.1 of the 2016 Edition);

--- Delete the annex of on-line partial discharge measurement (see Annex A of the 2016

Edition);

--- Add the influence of the test frequency parameter on the test process (see Annex A of this

Edition);

--- Add other methods for determining the amplitude of partial discharge (see Annex B of

this Edition);

--- Modify the method of off-line partial discharge detection and off-line location (see Annex

C of this Edition, Annex B of the 2016 Edition);

--- Add interpretation of partial discharge measurement and induction discharge/vibration

spark from terminal and star-connected neutral point (see Annex D of this Edition);

--- Add the complete winding measurement connection circuit (see Annex G of this Edition);

--- Modify the broadband and narrowband systems (see Annex H, 5.4 of the 2016 Edition).

This Part used translation method to equivalently adopt IEC 60034-27-1:2017 Rotating

Electrical Machines - Part 27-1: Off-Line Partial Discharge Measurements on the Winding

Insulation.

The Chinese documents that have consistent correspondence with the international documents

cited in this part are as follows:

--- GB/T 7354-2018 High-voltage test techniques - Partial discharge measurements (IEC

60270-2000, MOD);

--- GB/T 16927.1-2011 High-voltage test techniques—Part 1: General definitions and test

requirements (IEC 60060-1:2010, MOD);

--- GB/T 16927.2-2013 High-voltage test techniques - Part 2: Measuring systems (IEC

60060-2:2010, MOD);

--- GB/T 17948.4-2016 Rotating electrical machines - Functional evaluation of insulation

systems - Test procedures for form-wound windings - Evaluation by electrical endurance

(IEC 60034-18-32:2010, IDT);

--- GB/T 22720.2-2019 Rotating electrical machines - Qualification tests for the partial

discharge resistant electrical insulation systems (Type II) used in rotating electrical

machines fed from voltage converters (IEC 60034-18-42:2017, IDT);

--- GB/T 20833.2-2016 Rotating electrical machines - The stator winding insulation of

Rotating Electrical Machines - The Winding Insulation -

Part 1: Off-Line Partial Discharge Measurements

3.1 Partial discharge; PD

Localized electrical discharge that only partially bridges the insulation between conductors and

which can or cannot occur adjacent to a conductor.

3.2 Off-line measurement

at phase terminal side of stator winding. The PD activity results in increased ageing through

erosion of the main insulation. Coil loosening can also lead to mechanical abrasion in a severe

case.

As insulation erosion is caused by high voltage induced slot discharges, it will occur more

severely at bars/coils near HV terminals. Therefore, off-line PD measurements will provide

different PD intensity and, sometimes, patterns at terminal and neutral side, in the presence of

slot discharges.

Bar or coil vibration within the slots during operation, caused e.g., by forces due to the

electromagnetic field and in the condition that the bars and coils are not tight anymore, may be

the initial state of slot portion coating damage. Under certain conditions vibration sparking may

occur during machine operation. This is caused by intermitted interruption of driven currents

which are caused by electromagnetically induced voltages. Although it is not a PD phenomenon

it may occur similarly during measurements.

When the conductive slot coating is deteriorated by the vibration sparking, in standstill these

can be measured as slot discharges. Since vibration sparking is driven by the magnetic field this

phenomenon can occur mainly in the slot section of each bar or coil, from terminal side to

neutral side, the effect may be measured on both sides of the winding. Comparative

measurements including pattern analysis on terminal and neutral side may give an indication

for vibration sparking. F.1.4 provides more background information.

4.2.4 End-winding gap and surface discharges

Partial discharges in the end-winding area may occur at several locations with high local electric

field strengths. Such discharges usually occur at interfaces between different elements of the

stator winding overhang. If the stress control coating of the end-winding becomes ineffective

because of poorly designed interfaces, contamination, porosity, thermal effects, etc., reliable

field grading is no longer ensured and surface discharges will develop, which may gradually

erode the insulation and surface materials. This is normally a slow ageing mechanism. The PD

behavior might be subjected to relatively fast changes due to surface effects.

In addition, PD may occur between phases, for example due to inadequate interface clearance,

at elements of the overhang support system, or as phase to ground discharges on the end-

winding surface.

4.2.5 Foreign conductive materials discharges

Conductive contamination of the winding may result in a strong local concentration of partial

discharges. These may result in a localized damage in the insulation. More dangerous may be

larger metal pieces such as broken bolts or screws, as well as unintentionally forgotten tools.

Beside the local concentration of PD and its potentially damaging effect it may lead to

secondary impact such as immediate mechanical damage or abrasion driven by the impact of

the magnetic field to such metal pieces.

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