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Rotating electrical machines - The winding insulation - Part 4: Measurement of insulation resistance and polarization index
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Basic data
| Standard ID | GB/T 20833.4-2021 (GB/T20833.4-2021) |
| Description (Translated English) | Rotating electrical machines - The winding insulation - Part 4: Measurement of insulation resistance and polarization index |
| Sector / Industry | National Standard (Recommended) |
| Classification of Chinese Standard | K20 |
| Word Count Estimation | 34,398 |
| Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration |
GB/T 20833.4-2021: Rotating electrical machines - The winding insulation - Part 4: Measurement of insulation resistance and polarization index
---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Rotating electrical machines - The winding insulation - Part 4.Measurement of insulation resistance and polarization index
ICS 29.160.01
K20
National Standards of People's Republic of China
Rotating motor winding insulation
Part 4.Insulation resistance and polarization index measurement
(IEC 60034-27-4.2018,Rotatingelectricalmachines-
Released on 2021-03-09
2021-10-01 implementation
State Administration of Market Supervision and Administration
Issued by the National Standardization Management Committee
Table of contents
Foreword Ⅲ
Introduction Ⅳ
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Insulation resistance components and influencing factors 2
5 Polarization index 3
6 Test of insulation resistance 3
7 Explanation of measurement results 8
8 Recommended limit values of insulation resistance and polarization index 9
9 Test report 10
Appendix A (informative appendix) Other DC tests 12
Appendix B (informative appendix) Current component of direct current 16
Appendix C (informative appendix) Example of test results of synthetic resin insulated high-voltage windings 20
Appendix D (informative appendix) Use test data to plot to estimate the slope parameter of temperature correction X 24
Appendix E (informative appendix) Test leakage current to evaluate phase-to-phase insulation resistance 25
Reference 27
Fig. 1 Equivalent circuit of winding insulation in DC voltage test Fig. 3
Figure 2 Connection mode of overall winding test 6
Figure 3 Connection mode for relative ground test 6
Figure A.1 Test of current and insulation resistance when the DAR calculation result is 1.09
Figure A.2 Charging and discharging currents after a 2.5kV step voltage is applied to the three-phase windings of a 50MVA hydraulic generator 13
Figure B.1 The relationship between different currents and time 16
Figure C.1 shows the relationship between the resultant current and time in clean and dry insulation on a logarithmic scale. 20
Figure C.2 The relationship between insulation resistance and time in clean and dry insulation 20
Figure C.3 Relationship between composite current and time in damp and polluted insulation 21
Figure C.4 Relationship between insulation resistance and time in damp and polluted insulation 21
Figure C.5 The relationship between the resultant current and time in the insulation of a dry and clean surface with a continuous end anti-corona layer 23
Figure C.6 The relationship between resistance and time in insulation with end anti-corona layer on a dry and clean surface 23
Figure D.1 Plot on logarithmic graph paper to estimate the slope parameter X 24
Figure E.1 The connection method of the phase-to-phase test, the test equipment is not connected to the ground, and other phase-to-phase combinations can also be used 25
Figure E.2 Measuring the phase-to-phase leakage current using a measuring instrument with a protective connection 26
Figure E.3 Measuring the phase-to-phase leakage current using a measuring instrument without a protective connection 26
Table 1 Value of parameter X used to correct temperature 4
Table 2 Guidelines for applied DC voltage range during insulation resistance measurement 7
Table 3 Minimum recommended value of insulation resistance at a reference temperature of 40°C 9
Table 4 The minimum recommended value of the polarization index of the high-voltage insulation structure 10
Table D.1 Example of insulation resistance test results under different winding temperatures 24
Rotating motor winding insulation
Part 4.Insulation resistance and polarization index measurement
1 Scope
This part of GB/T 20833 specifies the test procedures for the insulation resistance and polarization index of the stator and rotor windings of rotating electrical machines.
This section specifies the minimum recommended values for the insulation resistance and polarization index of the windings of rotating electrical machines with a rated power of 750W and above. This part
Suitable for low-voltage, high-voltage AC and DC rotating motors.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this article
Pieces. For undated reference documents, the latest version (including all amendments) is applicable to this document.
IEC 60050-411 International Electrotechnical Vocabulary Chapter 411.Rotating Electric Machine (Internationalelectrotechnicalvocabulary-
Chapter411.Rotatingmachinery)
3 Terms and definitions
The following terms and definitions defined by IEC 60050-411 apply to this document.
3.1
Rated voltage
For three-phase AC motors, it refers to the rated line voltage between the two phases; for single-phase motors, it refers to the rated line voltage; for DC motors and excitation motors,
Refers to the rated DC voltage.
3.2
Insulation resistance
Rit
The electrical insulation capability of the winding against DC current. At a certain time (t) after the voltage is applied, the applied DC voltage is divided by the
The quotient of the total DC current of the insulation.
Note 1.The voltage application time is usually 1min (Ri1) and 10min (Ri10), but other values can also be used. The unit of time t is stipulated. the unit of 1 to 10 is
Minutes, the unit of 15 and above is seconds.
Note 2.Insulation resistance is sometimes abbreviated as IR.
3.3
Polarization index
PI
The quotient of the insulation resistance measured at two different times. Usually, after applying DC voltage, t2 and t1 are 10min and 1min respectively
This is an indicator of the insulation state.
Note. For other times, see Appendix A, A.2.
3.4
Polarization current
IP
5 Polarization index
The polarization index is the quotient of the insulation resistance at time t2 divided by the insulation resistance at time t1 after applying a DC voltage, see formula (1), where t2=
10min, t1=1min.
PI=
Ri10
Ri1
(1)
In special applications, the quotient calculated from the insulation resistance at other times can also be used as the polarization index.
Ming (see Appendix A). Reading more data within 10 minutes can provide more information.
The polarization index reflects the change in insulation resistance between two specific time points. Therefore, it is better than a single insulation resistance value.
It shows the contaminants and moisture deposits on the winding surface, and the moisture absorption of the windings. But it may not be able to judge due to unreasonable
Internal pores caused by impregnation process and thermal damage.
The polarization index can be used to evaluate whether the winding can be subjected to a withstand voltage test and whether it can be put into operation, and it can also provide an evaluation of the state of the insulation structure.
Set the required information.
Since the polarization current is negligible within 1 min to 10 min after the voltage is applied, the polarization index test may not be available
It is used in small motors with random winding, field windings of generator rotors, non-insulated excitation, squirrel cage rotor windings and DC motor armatures.
The polarization index depends on the type of insulation structure, especially the nature of the insulation material and the winding production process (for synthetic resins, insects, etc.)
For paint and asphalt, see 7.1). At the same time, it also depends on the type of end anti-corona layer (see Appendix C, C.3) and the size of the test voltage
(See 6.4.1). If the winding temperature is kept constant between 1min and 10min, then the temperature has little effect on the polarization index (see
6.1.2).
The polarization index should reach the minimum requirement (see 8.3 for the recommended value) before the withstand voltage test or put into operation.
6 Test of insulation resistance
6.1 Factors affecting insulation resistance test
6.1.1 Overview
Insulation resistance test results depend on environmental factors, mainly winding temperature and air humidity. The influence of winding temperature on insulation resistance can be
Evaluate with empirical data or test measurements, which can be used to modify the insulation resistance test results at different temperatures (see 6.1.2).
The relative humidity of the air affects the surface leakage current. This effect is usually difficult to evaluate because the relative humidity of the air mainly depends on the air.
Slightly disregarded.
6.2 Testing equipment
For the direct measurement method, the preferred device is an ohmmeter. When the reading of Ri1 is less than 5000MΩ, the digital high resistance meter should meet the following
condition.
---Display. three digits;
---Accuracy. Reading accuracy ±5%, range accuracy ±5.
If there is no insulation resistance meter, the insulation resistance can be obtained by measuring voltage and current (indirect method). This method may use regulated DC
Power supply, voltmeter, microammeter. In fact, the voltage output by the DC voltage source will fluctuate, causing the current to also change. ic(t)=C0dU0/
dt. Since the capacitance C0 of most high-voltage motors is very large, the DC power supply should have minimal stability and noise to ignore this effect.
According to the voltage and current readings, the insulation resistance is calculated according to formula (4).
Rit=U/It (4)
Where.
Rit---Insulation resistance value at time t, in megaohms (MΩ);
U ---The measured voltage of the DC voltage source (Voltmeter reading), in volts (V);
It --- the measured current (ammeter reading) at time t, in microamperes (μA).
When measuring large insulation resistance values, in order to avoid the influence of the leakage current and capacitance of the test cable, it is advisable to use a protective instrument.
The whole set of equipment should raise the voltage to the test value within 5s.
6.3 Test product and test circuit
6.3.1 Overview
According to the test target and its design, different test circuits are used. In order to check the minimum recommended value of insulation resistance, the entire winding should be checked
Test; In order to check the insulation problems between the windings of each phase and the windings, if the windings of each phase can be easily disconnected, it should be carried out phase by phase
measuring. In order to achieve the test purpose, the same connection method should be used.
If possible, all external devices such as cables, switches, capacitors and current transformers should be disconnected from the windings. To record with
Winding connection equipment.
For the insulation resistance test of the direct water-cooled winding, it is advisable to completely drain the water to make the internal circuit completely dry. Maybe some water-cooled windings are manufactured
The supplier has provided a method for measuring insulation resistance without draining the cooling water. Generally, if the water is not excluded, the conductivity of the water should be less than the production plant
Recommended value of home. In this case, the conductivity of water will greatly affect the insulation resistance value, so it can be estimated that PI=1, Ri10=
1MΩ.
In any case, untested winding components should be grounded to avoid adverse effects, such as compensation current or induced AC in the test loop
Current.
6.3.2 Three-phase stator winding
6.3.2.1 Connection mode of integral winding to ground test
The windings of all phases are connected together, as shown in Figure 2.
Insulation test is an important part of motor calibration. It should be carried out before and after the test, and check with a high voltage resistance of about 100MΩ.
Operation of equipment. This is especially important for battery-powered equipment.
6.7.2 Special procedures
In order to obtain more information about the insulation status, other test procedures can also be used, see Appendix A for details.
7 Explanation of measurement results
7.1 Overview
Insulation resistance and polarization index can be used in the following aspects, but not limited to.
---Assess whether a motor is suitable for withstand voltage test or put into operation, it can be based on the minimum estimation of insulation resistance and polarization index.
Recommended value (see 7.2);
---As long as the test conditions of the controllable variables involved are the same, the historical data of the insulation resistance and polarization index of a given motor can be used
An effective method for judging the change trend of its insulation state after several years (see 7.3);
---As long as the test conditions of the controllable variables involved are the same, compare the windings of each phase by testing the insulation resistance and polarization index or the same
Insulation conditions of different motors designed.
Based on the above points, the factors that affect the test results should be fully considered when testing (see 7.4).
7.2 Feasibility of test and operation
Insulation resistance and polarization index can be used to evaluate the feasibility of the motor withstand voltage test and put into operation. Insulation resistance and poles of the motor
The chemical index should be greater than the minimum recommended value (see Table 3 and Table 4). If the test value is less than the minimum recommended value, it is not advisable to carry out a withstand voltage test on the motor
Or put into operation, unless there are design reasons or there are records of such lower values.
Insulation resistance can also be used to determine whether the winding is damaged in the withstand voltage test. If the insulation resistance value after the withstand voltage test is much smaller than the test
Before the test, it indicates that the insulation may be damaged during the withstand voltage test, even if the test voltage does not drop rapidly due to the presence of high fault current.
If the test value is lower than the minimum recommended value due to contamination or excessive moisture, after eliminating the possibility of insulation defects, it can be cleaned and
Dry measures improve the measurement results. The insulation resistance value can be used to monitor the effectiveness of the drying process.
If the insulation resistance Ri1 value at 40°C is greater than 5000MΩ, then the polarization index value may not be specified and may not be considered.
For shellac and asphalt-based insulation structures, an excessively high polarization index (such as greater than 8) indicates that the insulation may have been thermally aged and there is a risk of failure
It will be very high. If the physical inspection (such as knocking on the insulation) finds that the insulation is dry and brittle, it is best not to clean the winding or conduct a voltage test.
If the motor is put back into operation, it may malfunction at any time.
7.3 Trend analysis of insulation conditions
If you can get the historical data of the motor insulation resistance (Ri1), comparing the current test results with the previous ones will help you understand the insulation status.
However, comparative tests with similar conditions are very important, namely winding temperature, voltage range, test duration and relative humidity (see
6.1). At the same time, use the same test equipment as much as possible. To compare the test results at different winding temperatures, the results should be corrected to
The same reference temperature (see 6.1.2).
If Ri1 or PI drops sharply compared to the previous reading, it means that the surface is contaminated or damp. When the temperature increases (above 60℃), PI
The value is low. In order to check the actual insulation condition, the second measurement should be performed above the dew point and below 40℃.
7.4 Comparison between different motors or different phases
If the Ri1 of the entire winding is less than 5000MΩ, the significant difference in Ri1 or PI between the same motors may indicate surface contamination and moisture
Or the insulation is damaged. In this case, it is advisable to find out the cause of the discrepancy.
The characteristic polarization current IP in can cause significant changes in the insulation resistance values at 1 min and 10 min.
If there is a significant change in the winding temperature between the insulation resistance at 1 min and 10 min, the value should be corrected
Calculate the polarization index after reaching the reference temperature of 40°C.
Table 4 Minimum recommended value of polarization index for high-voltage insulation structure
The minimum recommended values in Table 4 do not apply to.
---Small motors with scattered windings, motors with uninsulated field windings, squirrel cage rotor windings and DC motor armatures (see section 5
chapter);
--- The winding is connected to a motor with an end anti-corona layer that is in contact with the current (see Appendix B, B.6 and Appendix C, C.3);
---Ri1 value >5000MΩ winding (see 7.5).
9 Test report
9.1 Winding in operation
The test report should provide at least test data and test conclusions. If it is used for trend analysis and comparison of insulation conditions,
Result to be explained. The test report should include the following.
a) Identification information.
---Factory Name;
---Motor number.
b) Date of measurement.
c) Environmental conditions.
---Ambient temperature;
---Winding temperature;
---Calculate relative temperature and ambient temperature of absolute humidity and dew point.
d) Test equipment.
---Name, model;
---Manufacturer;
---serial number;
---The effective date of measurement.
e) Test circuit, instrument settings and test conditions.
---Test voltage and polarity;
---Test duration (if required).
f) Test the insulation characteristics under the measurement conditions and correct to the reference temperature.
--Insulation resistance at -1min;
--Insulation resistance at -10min (if applicable);
---Polarization index (if applicable);
---Temperature correction (if applicable).
g) Draw measurement curve (if applicable).
---The relationship between the measured current and time, the logarithmic coordinate is better;
---The relationship between the measured insulation resistance and time, the logarithmic coordinate is better.
h) Name of test personnel.
i) Record specific information.
j) Notes (such as differences from the standard test procedure, phenomena observed during the test, etc.).
It is advisable to save all test results in the form of original data for future reference.
According to the document type, independent testing and certification, or as part of the status assessment report, the report content can include corresponding additional information, such as
Working mode, motor life, etc.
9.2 New winding
For brand new windings, the insulation resistance test can be used as a supplement to the withstand voltage test, and the insulation resistance is carried out for 1 min before and after the withstand voltage test.
test.
Therefore, most of the information required by a complete test report will become part of the withstand voltage test protocol. Defined in 9.1
The required information may be sufficient.
Appendix A
(Informative appendix)
Other DC tests
A.1 Overview
In the insulation resistance test and polarization index calculation described in this section, the winding is understood through DC voltage and DC current in actual operation.
State is not the only way. In addition to measuring insulation resistance and polarization index, the new insulation tester provides other methods.
This appendix summarizes the current better methods for evaluating the winding condition of rotating electrical machines, including changing the test time, DC test voltage, and environmental conditions.
Pieces etc.
A.2 Dielectric Absorption Ratio (DAR)
The polarization index (PI) is generally defined as the ratio of the insulation resistance (Ri10) at 10 min to the insulation resistance (Ri1) at 1 min. In the old
For insulating structures (such as pitch-mica), it takes 10 minutes or even longer for the polarization current to decay to close to zero.
However, in low-voltage motors with scattered windings and field windings, the polarization current may decay to close to zero within 1 min. So some tests
Candidates will calculate a derivative polarization index that is different from the traditional polarization index PI. The derived polarization index includes but is not limited to the calculation of formula (A.1)
method.
DAR=Ri1/Ri30 (A.1)
Where.
DAR---dielectric absorption ratio;
Ri1 ---Insulation resistance reading when voltage is applied for 60s;
Ri30 ---Insulation resistance reading when voltage is applied for 30s.
Figure A.1 illustrates the insulation resistance value of the random-wound stator winding measured within 1 min after the voltage is applied, and Ri1 is 4083MΩ.
Ri30 is 3745MΩ, and the obtained DAR is 1.09.Some insulation resistance testers have automatic test settings to perform DAR measurements. versus
The difference between the traditional method is that the time for applying a DC voltage is shorter, so the time for the winding to ground is also shorter (see 6.6). Due to the use of
With the insulation structure of mica, the polarization current will drop to 0 within 1 min. Therefore, the insulation resistance of a shorter time is selected for calculation, which can be greatly shortened.
Test time, and almost no loss of information on the degree of contamination or moisture of the winding. When testing Ri30, the test object should rise to the test within 1s
Voltage.
The limitations of using these derived polarization indices are.
--- There is no standard for the time interval for recording Ri values, and different institutions use different ratios (see 3.3);
---Different from the traditional polarization index, there is no consistent judgment standard for the derived polarization index.
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