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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
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Rotating electrical machines -- Qualification and type tests for Type Ⅰ electrical insulation systems used in rotating electrical machines fed from voltage converters
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GB/T 22720.1-2017: PDF in English (GBT 22720.1-2017) GB/T 22720.1-2017
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 29.160.01
K 20
GB/T 22720.1-2017 / IEC 60034-18-41:2014
Replacing GB/T 22720.1-2008
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, 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, IDT]
ISSUED ON: NOVEMBER 1, 2017
IMPLEMENTED ON: MAY 1, 2018
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3
Introduction ... 6
1 Scope ... 8
2 Normative References ... 8
3 Terms and Definitions ... 9
4 Motor Terminal Voltage Generated during Converter Operation ... 14
5 Electrical Stresses in the Insulation System of Motor Windings ... 18
6 Types of Motor Insulation ... 22
7 Stress Categories for Type I Insulation Systems Used in Motors Fed from
Converters ... 22
8 Qualification and Type Tests of Type I Insulation Systems ... 24
9 Test Equipment ... 25
10 Qualification of Type I Insulation Systems ... 27
11 Type Test Procedures of Type I Insulation Systems ... 32
12 Exit-factory Inspection ... 34
13 Analysis, Report and Classification ... 34
Appendix A (informative) Terminal Voltages of a Converter-fed Motor during
Operation ... 35
Appendix B (normative) Test Voltages of Type I Insulation Systems ... 38
Appendix C (normative) Derivation of Allowable Voltages in Operation ... 47
Appendix NA (informative) Derivation and Example of Conventional Withstand
Voltage Test of Motors with a Rated Voltage of 500 V ... 49
Bibliography ... 50
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
1 Scope
This Part specifies the assessment criteria for stator / rotor winding insulation systems
fed from voltage-source pulse-width-modulation (PWM). This Part is applicable to the
stator / rotor winding insulation systems of single-phase or multi-phase AC motors
powdered by converters.
This Part specifies the qualification and quality control (type and exit-factory) tests for
typical samples or complete motors, so as to verify the degree of fitness with voltage-
source converters.
This Part is inapplicable to:
---Rotating electrical machines only started by converters;
---Rotating electrical machines whose rated voltage has an effective value of ≤
300 V;
---Rotor windings of rotating electrical machines with an operating voltage (peak
value) ≤ 200 V.
2 Normative References
The following documents are indispensable to the application of this document. In
terms of references with a specified date, only versions with a specified date are
applicable to this document. In terms of references without a specified date, the latest
version (including all the modifications) is applicable to this document.
GB/T 17948.7-2016 Rotating Electrical Machines - Functional Evaluation of Insulation
Systems - General Guidelines (IEC 60034-18-1:2010, IDT)
IEC 60034-18-21 Rotating Electrical Machines - Part 18-21: Functional Evaluation of
Insulation Systems - Test Procedures for Wire-wound Windings - Thermal Evaluation
and Classification
IEC 60034-18-31 Rotating Electrical Machines - Part 18-31: Functional Evaluation of
voltage, PDIV is defined as peak to peak voltage.
3.3 Partial Discharge Extinction Voltage
PDEV
Partial discharge extinction voltage refers to the voltage when the voltage applied to
the sample gradually decreases from a certain relatively high value where partial
discharge is detected to the voltage where no partial discharge can be detected in the
test circuit.
NOTE: for sinusoidal voltage, PDEV is defined as the effective value of voltage; for impulse
voltage, PDEV is defined as peak to peak voltage.
3.4 Peak (impulse) Voltage
Up
Peak (impulse) voltage refers to the highest voltage value that a unipolar impulse can
reach (for example, Up in Figure 1).
NOTE 1: for bipolar impulse voltage, the peak (impulse) voltage is half of the peak to peak
voltage (see Figure 2);
NOTE 2: the definition of peak to peak voltage is described in Chapter 4.
3.5 Steady State Voltage Impulse Magnitude
Ua
Steady state voltage impulse magnitude refers to the final magnitude of the impulse
voltage (see Figure 1).
3.6 Voltage Overshoot
Ub
Voltage overshoot refers to the magnitude of the peak voltage value exceeding the
steady state voltage impulse magnitude (see Figure 1).
3.7 Peak to Peak Impulse Voltage
Upk/pk
Peak to peak impulse voltage refers to the peak to peak voltage at the impulse
repetition rate (see Figure 2).
3.8 Peak to Peak Voltage
3.15 Formette
Formette refers to a special test model used for the evaluation of the electrical
insulation systems for form-wound windings.
3.16 Motorette
Motorette refers to a special test model used for the evaluation of the electrical
insulation systems for wire-wound windings.
3.17 (electric) Stress
(electric) stress refers to electric field strength, which is expressed in V/mm.
3.18 Rated Voltage
UN
Rated voltage refers to the voltage value of the motor under the conditions of power
frequency operation. It is specified by the manufacturer and marked on the nameplate.
3.19 Impulse Voltage Insulation Class
IVIC
Impulse voltage insulation class refers to the safe peak to peak voltage specified by
the manufacturer and related to the rated voltage for the motor fed from a specific
converter. It is marked in the instruction manual and on the nameplate.
3.20 Fundamental Frequency
Fundamental frequency refers to the frequency in the spectrum obtained through the
Fourier transform of the periodic time function. All frequencies in the spectrum are
related to it.
NOTE: for this Part, the fundamental frequency of the motor terminal voltage determines
the speed of the variable frequency motor.
3.21 Impulse Duration / Width
Impulse duration / width refers to the time interval between the first instant and the last
instant when the transient impulse value reaches the specified value of the impulse
magnitude or the specified threshold.
3.22 Jump Voltage
Uj
Jump voltage refers to the change of the voltage at the motor terminal at the beginning
Key:
●---tr = 50 ns;
○---tr = 100 ns;
▼---tr = 200 ns;
▽---tr = 1,000 ns;
l---cable length;
Up /Ua---the ratio of peak voltages at the motor and at the converter terminals
Figure 4 -- Voltage Increment at Motor Terminal due to Reflection as a Function
of Cable Length for Different Impulse Rise Times
5 Electrical Stresses in the Insulation System of Motor
Windings
5.1 Overview
If the winding is subjected to short rise time impulse voltages with an extremely large
magnitude, then, high voltage stresses will be generated in the following locations
(Figure 5 and Figure 6):
---Between conductors in different phases;
---Between the conductor and the ground;
---Between adjacent turns in the line-end coil.
Due to the space and surface discharge generated in the insulation components, the
electrical stress depends on not only the transient voltage itself, but also the peak
voltage that the previous insulation withstands. Experience has shown that within a
certain effective limit of the various frequency power supply system, the stress
parameter is the peak to peak voltage. This is also the reason why the stresses
generated by unipolar impulse and bipolar impulse at the same peak to peak voltage
value are the same[1].
Key:
a---phase insulation / overhang insulation;
b---ground insulation;
c---turn insulation;
d---slot corona protection;
e---overhang corona protection (stress grading);
1---phase to phase;
2---phase to ground;
3---turn to turn.
Figure 6 -- An Example of Form-wound Winding Design
5.2 Voltage Stress on Phase to Phase Insulation
The maximum voltage stress on the phase to phase insulation is determined by the
winding design and the characteristics of the phase to phase voltage.
5.3 Voltage Stress on Phase to Ground Insulation
The maximum voltage stress on the phase to ground insulation is determined by the
winding design and the characteristics of the phase to ground voltage.
5.4 Voltage Stress on Turn and Strand Insulation
The electrical stress of the winding insulation is determined by the jump value of the
phase to ground voltage and the impulse rise time of this voltage at the motor terminal.
For wire-wound windings, the transient voltage distribution depends on the relative
position of individual turns in the slot. The impulse of short rise time causes the voltage
distribution throughout the coils to be uneven, and high stress is distributed in the first
turn or inter-turn (depending on the winding design) of split-phase winding. In fact, the
first turn and the last turn may be adjacent to each other, and the inter-turn voltage is
almost equal to the voltage that the coil withstands. Take the impulse rise time as a
function; the volage applied to the inter-turn insulation in a variety of stators under the
most severe circumstance is shown in Figure 7. The shown voltage is a part of the
phase to ground jump voltage, and the data can be obtained through the graphs
provided in Bibliography [2], [3] and [4]. For specially designed rotating electrical
machines, if the manufacturer is aware of the voltage distribution in the coil with a
function of the rise time, then, the data can be used to replace Figure 7 to calculate the
jump voltage applied to the inter-turn insulation in the most severe circumstance (see
Table B.6 of Appendix B). The jump voltage appears at both the rising and falling edges
resistant composite insulating materials, the designer can allow the existence of partial
discharges.
Another factor that may affect the insulation life is the high-frequency dielectric heating
caused by the converter waveform. If the coils have slot corona protection and stress
grading, then, the high-frequency current caused by the power supply in these
materials may cause overheating and degradation. The repetition frequency and the
frequencies related to the rise time of the rising edge will cause the insulating materials
to overheat due to dielectric loss. The most severe areas are the main wall insulation,
the inter-turn insulation and phase to phase insulation.
6 Types of Motor Insulation
This Part and IEC/TS 60034-18-42 divide winding insulations into two types. Type I
winding insulation (Figure 5) is not expected to withstand PD at any part of the
insulation during its life. Type II winding insulation (Figure 6) may have to withstand PD
in certain parts of the insulation during its life, so PD-resistant materials shall be used.
Motors with a rated voltage of 700 V and below may have both Type I and Type II
winding insulations. Motors with a rated voltage of above 700 V usually have Type II
winding insulation. The manufacturer specifies a rated voltage for each motor at a
power frequency, which assumes that the voltage from the power supply is 50 Hz or
60 Hz sinusoidal voltage. When the motor is fed from a converter, although the
manufacturer indicates a rated voltage of 50 Hz / 60 Hz and marks it on the nameplate
of the motor, the conventional definition of rated voltage is no longer applicable to the
winding insulation system. In order to solve this problem, the definition of impulse
voltage insulation class is introduced, which is to be separately indicated on the
instruction manual and nameplate as described in Appendix C. The classification of
Type I insulation can be determined by the absence of partial discharges during
operation or when subjected to the test procedures described in this Part.
7 Stress Categories for Type I Insulation Systems Used
in Motors Fed from Converters
In order to obtain sufficient reliability of the electric drive system, the strength of the
motor winding insulation system shall be coordinated with the electrical stress that it
bears. In other words,
---If the system supplier provides a complete electric drive system, it is responsible
for coordinating the strength of the motor winding insulation system and the
electrical stress, and ensuring the compatibility of the components, or;
---The drive system integrator shall explain to the motor designer the voltages that
appear at the motor terminal, so as to ensure that its design satisfies the
motorette or form-wound formette to conduct thermal cycling and treatment procedure
tests. The treatment procedure tests include mechanical vibration, moisture exposure
and high voltage test. The sample or the complete winding is used for diagnostic test,
the purpose of which is the evaluate the existence of PD. The second stage is the type
test of the complete winding or motor.
Based on the results of the qualification test and type test, determine the impulse
voltage insulation class of the motor, which specifies the maximum allowable voltage
applied to the insulation system under the power supply by the converter, expressed
in UN (see Appendix C).
8.2 Qualification Test
For this Part, the qualification test is used to study the capability of the insulation
systems to withstand various stresses. The qualification test of Type I insulation
systems is based on the voltage stress obtained through the thermal cycle and PDIV
test before and after other tests specified in IEC 60034-18-21 and IEC 60034-18-31,
and one of the stress categories specified in Chapter 7, multiplied by the increase
factor described in B.3. In accordance with IEC 60034-18-21 and IEC 60034-18-31, if
the thermal class of the insulation systems has been determined, the thermal ageing
test only needs to be conducted at any of the three ageing temperatures specified in
IEC 60034-18-21 or IEC 60034-18-31.
8.3 Type Test
For Type I insulation systems, partial discharge test needs to be conducted to prove
that there is no partial discharge[5][6]. The complete winding or motor is subjected to a
voltage suitable for the selected stress category (Table 4), multiplied by the safety
factor (Table B.2). For example, for a motor driven by a voltage-source converter, the
stress factor of its terminal voltage is 1.3 (benign); the overshoot factor used to
calculate the test voltage is 1.5 (overshoot) and 0.3 μs (see the rise time in B.1).
9 Test Equipment
9.1 PD Measurement at Power Frequency
When a 50 Hz or 60 Hz sinusoidal waveform voltage is applied to the sample, the
conventional partial discharge measuring instrument in the laboratory uses a high-
voltage coupling capacitor or a radio frequency current transformer. See IEC/TS
60034-27 for the details of the test equipment and methods. The 50 Hz or 60 Hz test
voltage and the partial discharge test method described in IEC/TS 60034-27 shall be
exclusively used for capacitive samples of single coil, wire-wound motorette and form-
wound formette.
9.2 PD Measurement at Impulse Voltage
Generally speaking, the sensitivity of the partial discharge detector decreases with the
decrease of the load impedance (or the increase of the capacitance). For reference,
the expected sensitivity of the qualification and type tests involved in this Part, at 50
Hz/ 60 Hz, should be 1 pC per nF capacitive load, and the lowest sensitivity is 1 pC.
The measurement system that can achieve this sensitivity is considered to be
sufficiently sensitive to perform PD test on inductive loads with equal impedance.
9.5 PD Test
9.5.1 Power frequency voltage
When measurements are conducted at 50 Hz / 60 Hz, for the inter-turn samples, wire-
wound motorette and form-wound formette samples, this Part specifies that the partial
discharge shall be less than 5 pC. These values are also the highest noise level
allowed during the measurements. In accordance with the procedures in IEC/TS
60034-27, conduct the partial discharge test.
9.5.2 Impulse voltage
In accordance with IEC/TS 61934, use impulse voltage for PD test; the background
noise level is expressed in mV. In accordance with IEC/TS 61934, record the
background noise level and the sensitivity.
10 Qualification of Type I Insulation Systems
10.1 Overview
For Type I insulation systems, electrical breakdown test is not used in the qualification
of the failure. The samples are subjected to thermal, mechanical cycles and various
electrical tests in accordance with IEC 60034-18-21 and IEC 60034-18-31. After each
sub-period, perform a partial discharge diagnostic test on the samples. When the
partial discharge inception voltage is lower than the test voltage specified by the
selected stress category, the end of the test appears.
The qualification test is to compare the performance of a reference system specified
in 4.3 of GB/T 17948.7-2016. This reference system has been qualified under the
conditions of 10.4. The system to be tested shall withstand the same or a longer ageing
cycle as the reference system, and there shall be no partial discharge under the
specified test value; the inception voltage is the lowest voltage when the partial
discharge can be detected. At the power frequency, in accordance with IEC/TS 60034-
27, within the sensitivity limit stated in 9.4, conduct the measurement. Under the
impulse voltage, in accordance with IEC/TS 61934, conduct the partial discharge
measurement, which describes the sensitivity checks and reporting requirements.
Successful operating experience allows the manufacturer to specify the stress
category for the motor with a specially designed insulation system. Under this
The partial discharge test performed on the impregnated twisted pair samples cannot
be used to evaluate the impregnation resin and manufacturing processes used in the
wire-wound motorette, form-wound formette or complete winding. It is allowed to use
the wire-wound motorette, form-wound formette or complete winding for this evaluation.
10.3.3 Wire-wound motorette / form-wound formette or complete winding
Use the same materials and processes as the actual coil for sample preparation. When
two coils of different phases are located in the same slot, phase to phase insulation
will be used, and the model or complete winding shall replicate this design
characteristic. When the motor uses impregnated windings, the impregnated sample
shall be tested. The phase to phase insulation and the main wall insulation shall
replicate all creepage distances and electrical clearances (phase to phase) in the
finished windings. For each type of insulation being tested, the sample shall replicate
the insulating materials and the thickness used in the product. Under the circumstance
of testing the complete winding, in accordance with the procedures provided in 11.2
and 11.3, conduct the test.
10.4 Qualification Test
10.4.1 Overview
The purpose of the qualification test is to conduct a thermal ageing test on the
insulation system components and related parts in accordance with IEC 60034-18-21
or IEC 60034-18-31, so as to determine at what point partial discharge inception occurs
below the specified test voltage. In the test conclusion, the stress category (Chapter 7)
of the system under the qualification test, the ageing procedures and diagnostic data
shall be reported. If compared with the reference system that has been proven to have
operating experience, the system to be evaluated can withstand the same or a longer
ageing cycle (no partial discharge occurs below the specified test value), then, the
insulation system to be evaluated is qualified. In order to obtain effective statistical test
results, at least 5 samples shall be used for the partial discharge test. For a complete
winding, 1 sample is sufficient.
10.4.2 Pre-diagnostic test
The pre-diagnostic electrical ageing test shall be carried out at room temperature for
24 h; the applied voltage should be multiplied by the selected stress category by the
factor in Table B.2, and the frequency shall be elevated. The purpose of this test is to
detect the existence of high-dielectric loss dielectric materials in the early stage, even
though satisfactory performance can be obtained at power frequency. During the
operation of the converter, it may cause overheating at a relatively high frequency. The
selection of frequency depends on the expected maximum impulse voltage repetition
rate during operation.
10.4.3 Diagnostic test
Appearance inspection shall be conducted on the sample to observe the condition of
the insulating materials, which shall be included in the report. However, this is not an
end-point criterion for evaluation.
10.5 Pass Criterion for Qualification Test
The pass criterion for the qualification of Type I samples is that the partial discharge
inception voltage is greater than the selected stress category voltage (Table B.3 and
Table B.4) multiplied by the enhancement factor (Table B.2); the test is performed on
the samples that have been thermally aged. The system to be evaluated shall
withstand the same or a longer thermal ageing cycle as the reference system, and with
the absence of partial discharge below the specified value. B.6 describes an example
of how to calculate the test voltage.
In terms of the partial discharge test performed under the impulse conditions, the
impulse voltage shall comply with the requirements in B.2.
11 Type Test Procedures of Type I Insulation Systems
11.1 Overview
The type tests are carried out on a complete winding or motor. After passing a series
of tests, and during the tests, the partial discharge inception voltage is higher than the
specified value, then, it is qualified. In accordance with Table 5, conduct the test under
the impulse conditions or power frequency. If the qualification test has been
successfully performed on a complete winding, then, the insulation system has actually
passed the type test, and no additional type test is required.
For the power frequency voltage test, when all phases can be separated, it is easier to
carry out the test, leading to conservative test results. The impulse test is more
realistically reflected in the expected stress under the operating conditions of the
converter. In addition, for the test, the impulse voltage waveform shall be as close as
possible to the actual waveform provided by the converter. Under any circumstance,
the waveform shall comply with Figure B.1 and Figure B.2. Due to the different test
voltage distributions in the winding during the test, the test results may be different[2].
For the sine-wave test, when at least 1 pulse is detected in each cycle, then, the partial
discharge inception appears. For the impulse test, if at least 1 pulse is detected during
all impulses within a fundamental frequency operating cycle, then, partial discharge
inception appears.
Under the maximum peak to peak operating voltage multiplied by the enhancement
factor, the partial discharge test is performed. An example of how to calculate the test
voltage is described in B.6; the winding temperature shall be 20 °C ± 10 °C. This test
shall be carried out by agreement between the purchaser and the manufacturer.
...... Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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