Rotating electrical machines—Functional evaluation of insulation systems (Type II)—Procedures for form-wound windings—Electrical endurance qualification
GB/T 17948.4-2024 Rotating electrical machines - Functional evaluation of insulation systems (Type II) - Procedures for form - wound windings - Electrical endurance qualification
1 Scope
This document describes qualification procedures for the evaluation of electrical endurance of insulation systems for use in rotating electrical machines using form-wound windings energized with sinusoidal power frequency voltage. The test procedures for the main wall insulation are comparative in nature, such that the performance of a candidate insulation procedure of inverter duty insulation system for form-wound windings can be found in GB/T 22720.2-2019 or IEC 60034-18-41. A new and informative test procedure for the stress control system is introduced and defined in Annex B.
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 17948.5-2016 Rotating electrical machines - Functional evaluation of insulation systems - Test procedures for form-wound windings - Multifactor evaluation by endurance under simultaneous thermal and electrical stresses (IEC/TS 60034-18 -33: 2010, IDT)
GB/T 22715-2016 Impulse voltage withstand levels of form-wound stator coils for rotating a.c. machines (IEC 60034-15: 2009, 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)
IEC 60034-1 Rotating electrical machines- Part 1: Rating and performance
Note: GB/T 755- 2019 Rotating electrical machines - Rating and performance (IEC 60034-1: 2017，IDT )
IEC 60034-18-1 Rotating electrical machines- Part 18-1: Functional evaluation of insulation systems- General guidelines
Note: GB/T 17948.7-2016 Rotating electrical machines - Functional evaluation of insulation systems - General guidelines (IEC 60034-18-1: 2010, IDT)
IEC 60034-18-41 Rotating electrical machines - Part 18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters - Qualification and quality control tests
Note: GB/T 22720.1-2017 Rotating electrical machines - Qualification and quality control tests of partial discharge free electrical insulation systems(Type I) used in rotating electrical machines fed from voltage converters (IEC 60034- 18-41: 2014, IDT)
IEC 60034-27-1 Rotating electrical machines - Part 27-1: Off- line partial discharge measurements on the winding insulation
Note: GB/T 20833.1-2021 Rotating electrical machines - The winding insulation - Part 1:Off-line partial discharge measurements (IEC 60034-27-1: 2017, IDT)
IEC 60034-27-3 Rotating electrical machines - Part 27-3: Dielectric dissipation factor measurement on stator winding insulation of rotating electrical machines
Note: GB/T 20833.3-2018 Rotating electrical machines - Stator winding insulation of rotating electrical machines - Part 3 : Dielectric dissipation factor measurement (IEC 60034 -27-3: 2015, IDT)
IEC 62539 Guide for the statistical analysis of electrical insulation breakdown data
Note: GB/T 29310-2012 Guide for the statistical analysis of electrical insulation breakdown data (IEC 62539: 2007, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
mainwall insulation
main electrical insulation that separates the conductors from the earthed stator/rotor core in motor and generator windings
3.2
strand insulation
electrical insulation that covers each conductor in coils/bars
3.3
turn insulation
electrical insulation that separates the conductor turns from each other in coils/bars
3.4
conductive slot coating
conductive paint or tape layer in intimate contact with the mainwall insulation in the slot portion of the coil side, often called semi-conductive coating
Note : The purpose is to prevent partial discharge from occurring between the coil/bar and the stator core.
3.5
stress control coating
paint or tape on the surface of the mainwall insulation that extends beyond the conductive slot coating in high-voltage stator bars and coils
Note: The purpose of the coating is to prevent surface discharges near the slot exit or in the end winding area.
3.6
stress control system
generic name for the combination of the conductive slot coating and stress control coating in high-voltage stator bars and coils
3.7
confidence interval
range of values so defined that there is a specified probability that the value of a parameter (voltage, stress or time) lies within it
3.8
test temperature
temperature of the outer surface of the bar/coil at the straight part of the bar/coil measured with an appropriate selected and placed sensor
4 General considerations
4.1 Relationship to IEC 60034-18-1
The principles of IEC 60034-18-1 should be followed, unless otherwise indicated in this document.
4.2 Selection and designation of test procedures
One or more of the procedures in this document should be suitable for the majority of evaluations. Evaluation is usually performed by the manufacturer of the machine/coils or by a third-party laboratory. It is the manufacturer's responsibility to justify the most suitable procedure on the basis of past experience and knowledge of the insulation systems to be compared.
Following test procedures are described:
- Mainwall insulation
- Turn insulation only with the main insulation test
- Conductive slot coating (Annex B)
- Stress control coating (Annex B)
- Mainwall insulation, where voltage level and/or life time differs from the reference system
4.3 Reference insulation system
A reference insulation system should be tested using a test procedure equivalent to that used for the candidate system (see IEC 60034-18-1). The reference insulation system should have service experience at not less than 75 % of the intended maximum rated voltage of the candidate system. When extrapolation of the insulation thickness is used, information such as “different insulation thickness at same electrical field stress levels by obtaining equal or similar breakdown time "should be provided showing the correlation between electrical lifetime and electrical stress for the different insulation thicknesses. If no reference insulation system is available the diagram in Annex A shall be used as criterion.
4.4 Test procedures
4.4.1 General
Electrical ageing tests are usually performed at fixed voltage levels until failure (mainwall insulation) or in combination with elevated temperature until signs of deterioration occur (conductive slot coating system). Statistical evaluation of the results of testing should be performed according to IEC 62539.
4.4.2 Electrical ageing of the mainwall insulation
From such tests, characteristic times to failure at each voltage level are obtained. The results for both the candidate system and the reference system should be reported on a graph, as shown by the example in Figure 1, and compared. There is no proven physical basis for extrapolation of this characteristic to the service voltage level UN/√3, where UN is the r. m. s. rated phase to phase voltage.
In service, electrical ageing of the mainwall insulation is primarily caused by continuous electrical stress at power frequency. In addition, the insulation is required to withstand transient overvoltage arising from switching surges or inverter supply. The ability of the mainwall insulation to withstand transient overvoltage from converter supplies may be demonstrated by the system's performance using GB/T 22720.2-2019.
This document specifies electrical ageing of the mainwall insulation, carried out at power frequency or higher. In order to keep acceleration of ageing in a linear progression, a maximum of 10 times of the power frequencies is appropriate. Latest experiences with the application of GB/T 22720.2-2019 show that a frequency of up to 1000 Hz can be used as well. Care shall be taken that the dielectric losses do not increase the temperature of the insulation beyond the service temperature to avoid additional thermal ageing effects. (GB/T 17948.5-2016, Table 1)
4.4.3 Electrical ageing of the stress control system
In order to allow a full qualification of the entire insulation system Annex B describes methods to qualify the conductive slot coating and stress control coating.
4.4.4 Electrical ageing of the turn insulation
In normal direct-on-line operation of rotating machines the turn insulation is subjected to a stress significantly below the partial discharge inception voltage. Continuous electrical ageing is then not taking place and turn insulation qualification is therefore excluded from this document. Withstand against transient overvoltage should be tested according to GB/T 22715-2016.
In converter fed or other types of special operation the turn insulation may continuously be subjected to a stress above the partial discharge inception voltage. Electrical ageing should then be performed according to GB/T 22720.2-2019.
