GB/T 1408 Insulating Materials - Test Methods for Electric Strength is classified into the following three parts:
——Part 1: Test at power frequencies;
——Part 2: Additional requirements for tests using direct voltage;
——Part 3: Additional requirements for 1.2/50μs impulse tests.
This part is Part 3 of GB/T 1408.
This part is developed according to the rules specified in GB/T 1.1-2009.
This part replaces GB/T 1408.3-2007 Insulating Materials - Test Methods for Electric Strength - Part 3: Additional Requirements for 1.2/50μs Impulse Tests; the following technical changes have been made with respect to GB/T 1408.3-2007 (the previous edition):
——"GB/T 1408.1-2006" is revised as "GB/T 1408.1-2006" in full text;
——The word “impulse” (脉冲) in full text is changed to “impulse” (冲击);
——The word "virtual" (虚) in Terms is changed to "virtual" (视在) (see 3.3~3.6, 3.3~3.6 of edition 2007);
——Terms "impulse breakdown voltage" and "withstand voltage" are added (see 3.7 and 3.8);
——"Report content" is modified.
The translation method used in this part is identical to IEC 60243-3: 2013 Electric Strength of Insulating Materials - Test Methods - Part 3: Additional Requirements for 1,2/50 μs Impulse Tests (edition 3).
This standard was proposed by the China Electrical Equipment Industrial Association.
This part is under the jurisdiction of SAC/TC 301 Technical Committee on National Electrical Insulating Material and Insulation System Evaluation of Standardization Administration of China.
The previous edition of the standard superseded by this part is:
——GB/T 1408.3-2007.
Insulating Materials - Test Methods for Electric Strength -
Part 3: Additional Requirements for 1.2/50μs Impulse Tests
1 Scope
This part of GB/T 1408 gives requirements additional to those in GB/T 1408.1 for the determination of the electric strength of solid insulating materials under 1,2/50 µs impulse voltage stress.
2 Normative References
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1408.1-2016 Insulating Materials - Test Methods for Electric Strength - Part 1: Test at Power Frequencies (IEC 60243-1: 2013, IDT)
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 1408.1-2016 apply.
3.1
full impulse-voltage wave
aperiodic transient voltage that rises rapidly to a maximum value, then falls less rapidly to zero (see Figure 1)
3.2
peak value of an impulse-voltage wave
Up
maximum value of voltage
3.3
virtual peak value of an impulse-voltage wave
U1
value derived from a recording of an impulse-voltage wave on which high-frequency oscillations, or overshoot of a limited magnitude, may be present
3.4
virtual origin of an impulse-voltage wave
O1
point of intersection O1 with the line of zero voltage of a line drawn through the points of 0,3 and 0,9 times the virtual peak value on the front of an impulse-voltage wave
3.5
virtual front time of an impulse-voltage wave
t1
equal to 1,67 times the interval tf between the instants when the voltage is 0,3 and 0,9 times the peak value (tf, Figure 1)
3.6
virtual front time to half-value
t2
time interval t2 between the virtual origin O1 and the instant on the tail when the voltage has decreased to half the peak value
3.7
impulse breakdown voltage
nominal peak voltage that the wave causing breakdown would have reached if breakdown had not occurred
3.8
withstand voltage
highest nominal peak voltage of a set of three impulses which did not cause breakdown
Figure 1 Full Impulse-voltage Wave
4 Significance of the Test
In addition to the information of Clause 4 of GB/T 1408.1-2016, the following points are of importance in connection with impulse-voltage tests.
High-voltage equipment may be subjected to transient voltage stresses resulting from such causes as nearby lightning strokes. This is particularly true of apparatus such as transformers and switchgears used in electrical power transmission and distribution systems. The ability of insulating materials to withstand these transient voltages is important in establishing the reliability of apparatus insulated with these materials.
Transient voltages caused by lightning may be of either positive or negative polarity. In a symmetrical field between identical electrodes, the polarity has no effect on the electric strength. However, with dissimilar electrodes, there may be a pronounced polarity effect. When asymmetrical electrodes are used for testing materials with which the tester has no previous experience or knowledge, it is recommended that comparative tests be made with both directions of polarity.
The standard wave shape is a 1,2/50 µs wave, reaching peak voltage in approximately 1,2 µs, and decaying to 50 % of peak value in approximately 50 µs after the beginning of the wave. This wave is intended to simulate a lightning stroke that may strike a system without breakdown.
Note: if the object being tested has appreciable inductive characteristics, it may be difficult or impossible to attain the specified wave shape with less than 5 % oscillations, as prescribed in 8.2. However, the procedures given in this standard are for capacitive specimen only. Testing of more complex configurations, such as between coils of completed apparatus or models of such apparatus, should be performed in accordance with the specifications for that apparatus.
Because of the short time involved, dielectric heating, other thermal effects and the influence of injected space-charges may be reduced during impulse testing of most materials. Thus, impulse tests usually give higher values than the peak voltage of short-term ac tests. From comparisons of the impulse electric strength with the values drawn from longer time tests, inferences may be drawn as to the modes of failure under the various tests for a given material.
5 Electrodes and Test Specimens
Clause 5 of GB/T 1408.1-2016 is applicable.
6 Conditioning before Tests
Clause 6 of GB/T 1408.1-2016 is applicable.
7 Surrounding Medium
Clause 7 of GB/T 1408.1-2016 is applicable.
8 Electrical Apparatus
8.1 Voltage source
The test voltage applied to the electrodes shall be provided by an impulse generator having the following characteristics.
A choice of either positive or negative polarity shall be provided, one of the connections to the electrodes being earthed.
Controls within the generator shall be capable of adjusting the shape of the wave applied to the test specimen under test to have a virtual front time t1 of (1,2 ± 0,36) µs, and virtual time to half-value t2 of (50 ± 10) µs (see Figure 1).
The voltage capability and energy-storage capacity of the generator shall be sufficient to apply impulse waves of the proper shape to any test specimens to be tested, up to the breakdown voltage or specified proof voltage of the material.
The peak value of the voltage is taken as the virtual peak value, provided that the conditions of 8.2 are satisfied.
Foreword i 1 Scope 2 Normative References 3 Terms and Definitions 4 Significance of the Test 5 Electrodes and Test Specimens 6 Conditioning before Tests 7 Surrounding Medium 8 Electrical Apparatus 9 Procedure 10 Application of Voltage 11 Criterion of Breakdown 12 Number of Tests 13 Report
GB/T 1408 Insulating Materials - Test Methods for Electric Strength is classified into the following three parts:
——Part 1: Test at power frequencies;
——Part 2: Additional requirements for tests using direct voltage;
——Part 3: Additional requirements for 1.2/50μs impulse tests.
This part is Part 3 of GB/T 1408.
This part is developed according to the rules specified in GB/T 1.1-2009.
This part replaces GB/T 1408.3-2007 Insulating Materials - Test Methods for Electric Strength - Part 3: Additional Requirements for 1.2/50μs Impulse Tests; the following technical changes have been made with respect to GB/T 1408.3-2007 (the previous edition):
——"GB/T 1408.1-2006" is revised as "GB/T 1408.1-2006" in full text;
——The word “impulse” (脉冲) in full text is changed to “impulse” (冲击);
——The word "virtual" (虚) in Terms is changed to "virtual" (视在) (see 3.3~3.6, 3.3~3.6 of edition 2007);
——Terms "impulse breakdown voltage" and "withstand voltage" are added (see 3.7 and 3.8);
——"Report content" is modified.
The translation method used in this part is identical to IEC 60243-3: 2013 Electric Strength of Insulating Materials - Test Methods - Part 3: Additional Requirements for 1,2/50 μs Impulse Tests (edition 3).
This standard was proposed by the China Electrical Equipment Industrial Association.
This part is under the jurisdiction of SAC/TC 301 Technical Committee on National Electrical Insulating Material and Insulation System Evaluation of Standardization Administration of China.
The previous edition of the standard superseded by this part is:
——GB/T 1408.3-2007.
Insulating Materials - Test Methods for Electric Strength -
Part 3: Additional Requirements for 1.2/50μs Impulse Tests
1 Scope
This part of GB/T 1408 gives requirements additional to those in GB/T 1408.1 for the determination of the electric strength of solid insulating materials under 1,2/50 µs impulse voltage stress.
2 Normative References
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1408.1-2016 Insulating Materials - Test Methods for Electric Strength - Part 1: Test at Power Frequencies (IEC 60243-1: 2013, IDT)
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 1408.1-2016 apply.
3.1
full impulse-voltage wave
aperiodic transient voltage that rises rapidly to a maximum value, then falls less rapidly to zero (see Figure 1)
3.2
peak value of an impulse-voltage wave
Up
maximum value of voltage
3.3
virtual peak value of an impulse-voltage wave
U1
value derived from a recording of an impulse-voltage wave on which high-frequency oscillations, or overshoot of a limited magnitude, may be present
3.4
virtual origin of an impulse-voltage wave
O1
point of intersection O1 with the line of zero voltage of a line drawn through the points of 0,3 and 0,9 times the virtual peak value on the front of an impulse-voltage wave
3.5
virtual front time of an impulse-voltage wave
t1
equal to 1,67 times the interval tf between the instants when the voltage is 0,3 and 0,9 times the peak value (tf, Figure 1)
3.6
virtual front time to half-value
t2
time interval t2 between the virtual origin O1 and the instant on the tail when the voltage has decreased to half the peak value
3.7
impulse breakdown voltage
nominal peak voltage that the wave causing breakdown would have reached if breakdown had not occurred
3.8
withstand voltage
highest nominal peak voltage of a set of three impulses which did not cause breakdown
Figure 1 Full Impulse-voltage Wave
4 Significance of the Test
In addition to the information of Clause 4 of GB/T 1408.1-2016, the following points are of importance in connection with impulse-voltage tests.
High-voltage equipment may be subjected to transient voltage stresses resulting from such causes as nearby lightning strokes. This is particularly true of apparatus such as transformers and switchgears used in electrical power transmission and distribution systems. The ability of insulating materials to withstand these transient voltages is important in establishing the reliability of apparatus insulated with these materials.
Transient voltages caused by lightning may be of either positive or negative polarity. In a symmetrical field between identical electrodes, the polarity has no effect on the electric strength. However, with dissimilar electrodes, there may be a pronounced polarity effect. When asymmetrical electrodes are used for testing materials with which the tester has no previous experience or knowledge, it is recommended that comparative tests be made with both directions of polarity.
The standard wave shape is a 1,2/50 µs wave, reaching peak voltage in approximately 1,2 µs, and decaying to 50 % of peak value in approximately 50 µs after the beginning of the wave. This wave is intended to simulate a lightning stroke that may strike a system without breakdown.
Note: if the object being tested has appreciable inductive characteristics, it may be difficult or impossible to attain the specified wave shape with less than 5 % oscillations, as prescribed in 8.2. However, the procedures given in this standard are for capacitive specimen only. Testing of more complex configurations, such as between coils of completed apparatus or models of such apparatus, should be performed in accordance with the specifications for that apparatus.
Because of the short time involved, dielectric heating, other thermal effects and the influence of injected space-charges may be reduced during impulse testing of most materials. Thus, impulse tests usually give higher values than the peak voltage of short-term ac tests. From comparisons of the impulse electric strength with the values drawn from longer time tests, inferences may be drawn as to the modes of failure under the various tests for a given material.
5 Electrodes and Test Specimens
Clause 5 of GB/T 1408.1-2016 is applicable.
6 Conditioning before Tests
Clause 6 of GB/T 1408.1-2016 is applicable.
7 Surrounding Medium
Clause 7 of GB/T 1408.1-2016 is applicable.
8 Electrical Apparatus
8.1 Voltage source
The test voltage applied to the electrodes shall be provided by an impulse generator having the following characteristics.
A choice of either positive or negative polarity shall be provided, one of the connections to the electrodes being earthed.
Controls within the generator shall be capable of adjusting the shape of the wave applied to the test specimen under test to have a virtual front time t1 of (1,2 ± 0,36) µs, and virtual time to half-value t2 of (50 ± 10) µs (see Figure 1).
The voltage capability and energy-storage capacity of the generator shall be sufficient to apply impulse waves of the proper shape to any test specimens to be tested, up to the breakdown voltage or specified proof voltage of the material.
The peak value of the voltage is taken as the virtual peak value, provided that the conditions of 8.2 are satisfied.
Contents of GB/T 1408.3-2016
Foreword i
1 Scope
2 Normative References
3 Terms and Definitions
4 Significance of the Test
5 Electrodes and Test Specimens
6 Conditioning before Tests
7 Surrounding Medium
8 Electrical Apparatus
9 Procedure
10 Application of Voltage
11 Criterion of Breakdown
12 Number of Tests
13 Report
