GB/T 21707-2025 Insulation specification for frequency conversion machine
1 Scope
This document specifies the technical requirements, test methods, test equipment, and inspection rules for the insulation of frequency conversion machine.
This document is applicable to frequency conversion machine with a rated voltage of 1,140V or below. It may serve as a reference for high-voltage frequency conversion motors with rated voltages above 1,140 V.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions 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 4074.7-2024 Test methods of winding wires - Part 7: Test procedure for the determination of the temperature index of enamelled winding wires
GB/T 5591.3-2018 Combined flexible materials for electrical insulation - Part 3: Specifications for individual materials
GB/T 6109.1 Enamelled round winding wire - Part 1: General requirements
GB/T 7095.1 Enamelled rectangular copper winding wires - Part 1: General requirements
GB/T 17948.1-2018 Rotating electrical machines - Functional evaluation of insulation systems - Test procedures for wire-wound windings - Thermal evaluation and classification
GB/T 17948.3-2017 Rotating electrical machines - Functional evaluation of insulation systems - Test procedures for form-wound windings - Thermal evaluation and classification of insulation systems used in rotating machines
GB/T 20629.3-2019 Non-cellulosic papers for electrical purposes - Part 3: Unfilled aramid (aromatic polyamide) papers
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
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
JB/T 10508-2020 Slot wedges used in small and middle size electric machines - Specification
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 22720.1-2017 and the following apply.
3.1
type I insulation systems
insulation systems that do not bear partial discharge during its life for inverter-powered motors
3.2
type II insulation systems
insulation systems in which any part may bear partial discharge during its life for inverter-powered motors
Note: Generally, Type II insulation systems are used for motors with rated voltage greater than or equal to 700V.
3.3
impulse voltage insulation class; IVIC
safe peak to peak voltage specified by the manufacturer and related to the rated voltage for inverter-powered motors, as indicated in the manual and on the nameplate
[Source: GB/T 22720.1-2017, 3.19, modified]
3.4
partial discharge; PD
electrical discharge that only partially bridges the insulation between conductors
Note: PD may occur within the insulation or near conductors.
[Source: GB/T 22720.1-2017, 3.1]
3.5
partial discharge inception voltage; PDIV
minimum voltage at which partial discharge is first detected in the test circuit when the voltage applied to the test object is gradually increased from a lower value where no PD is observed
Note: For sinusoidal voltage, PDIV is defined as the RMS voltage. For impulse voltage, PDIV is defined as the peak to peak voltage.
[Source: GB/T 22720.1-2017, 3.2]
3.6
peak (impulse) voltage
Up
difference between the initial voltage level and the maximum voltage reached during a voltage impulse (as shown by Uₚ in Figure 1)
[Source: GB/T 22720.1-2017, 3.4, modified]
3.7
voltage overshoot
Ub
portion of peak voltage that exceeds the steady-state impulse voltage (see Figure 1)
[Source: GB/T 22720.1-2017, 3.6]
Key
U——voltage;
t——time;
Up——peak voltage;
Ub——voltage overshoot;
Ua——steady-state impulse voltage;
Upk/pk——peak to peak voltage
Figure 1 Schematic diagram of the bipolar symmetric square wave
3.8
peak to peak impulse voltage
U'pk/pk
peak to peak voltage under impulse repetition conditions (see Figure 2)
[Source: GB/T 22720.1-2017, 3.7]
Figure 2 Five-phase interphase voltage at motor terminal supplied by three-level inverter
3.9
peak to peak voltage
U'pk/pk
peak to peak voltage at the fundamental frequency (see Figure 2)
[Source: GB/T 22720.1-2017, 3.8]
3.10
impulse rise time
tr
time required for the peak voltage to rise from the negative level to 100% (see Figure 1)
Note: Unless otherwise specified, the impulse rise time is 1.25 times the duration from 10% to 90% of the peak voltage
[Source: GB/T 22720.1-2017, 3.13]
3.11
dc bus voltage
Udc
intermediate circuit voltage (dc link voltage) in a voltage-source inverter
[Source: GB/T 22720.1-2017, 3.23]
3.12
rated voltage
UN
voltage value of the motor under the power-frequency operating condition, which is specified by the manufacturer and marked on the nameplate
Note 1: The rated voltage refers to the line-to-line rated voltage (RMS value).
Note 2: For electric vehicle drive motors, the rated voltage is the nominal dc bus voltage declared by the manufacturer, where UN = Udc.
[Source: GB/T 22720.1-2017, 3.18]
3.13
overshoot factor; OF
ratio of the motor terminal voltage to the inverter output voltage
[Source: GB/T 22720.1-2017, 3.24]
Contents Foreword i 1 Scope 2 Normative references 3 Terms and definitions 4 Technical requirements 5 Test methods and test equipment 6 Inspection relus Annex A (Normative) Guidelines for measuring waveform parameters of high-frequency impulse test equipment Annex B (Informative) High-frequency impulse test system and influence factors Annex C (Informative) Measurement of volatile content in impregnating resins Annex D (Informative) Thermal endurance evaluation procedure for insulation systems under special operating conditions - Example of thermal endurance evaluation for insulation systems of new energy vehicle drive motors Annex E (Informative) Evaluation procedure for insulation systems of variable-frequency motors Bibliography Figure 1 Schematic diagram of the bipolar symmetric square wave Figure 2 Five-phase interphase voltage at motor terminal supplied by three-level inverter Figure A.1 Schematic diagram of comparison between "distorted" waveform and standard waveform Figure A.2 Wiring diagram Figure D.1 Temperature cycling curve in diagnostic test Figure E.1 Type I insulation system qualification test flow Figure E.2 Type II insulation system qualification test flow Table 1 General requirements for magnet wires Table 2 Life of enamelled round copper winding wires under high-frequency impulse power supply Table 3 Life of enamelled rectangular copper winding wires under high-frequency impulse power supply Table 4 Life of insulation systems under high-frequency impulse power supply Table 5 Waveform parameters for high-frequency impulse resistance test of magnet wires Table 6 Waveform parameters for high-frequency impulse resistance test of insulation systems Table D.1 Power frequency withstand voltage limits for drive motor windings to ground Table D.2 Turn-to-turn impulse test voltage limits Table D.3 Recommended aging temperatures and exposure times for aging sub-cycles Table D.4 Test voltages Table E.1 Test voltage for various parts of the insulation system of a motor powered by two-level converter (peak to peak value) Table E.2 Relationship between stress types and VC
