Insulating materials - Test methods for electric strength - Part 1: Test at power frequencies
1 Scope
This part of GB/T 1408 provides test methods for the determination of short-time electric strength of solid insulating materials at power frequencies between 48 Hz and 62 Hz.
This standard does not cover the testing of liquids and gases, although these are specified and used as impregnates or surrounding media for the solid insulating materials being tested.
Note: Methods for the determination of breakdown voltages along the surfaces of solid insulating materials are included.
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.
ISO 293 Plastics - Compression moulding of test specimens of thermoplastic materials
ISO 294-1 Plastics - Injection moulding of test specimens of thermoplastic materials - Part 1: General principles, and moulding of multipurpose and bar test specimens
ISO 294-3 Plastics - Injection moulding of test specimens of thermoplastic materials - Part 3: Small plates
ISO 295 Plastics - Compression moulding of test specimens of thermosetting materials
ISO 10724 Plastics - Injection moulding of test specimens of thermosetting powder moulding compounds
IEC 60212 Standard conditions for use prior to and during the testing of solid electrical insulating materials
IEC 60296 Fluids for electrotechnical applications - Unused mineral insulating oils for transformers and switchgear
IEC 60455-2 Specification for solvent-less polymerizable resinous compounds used for electrical insulation - Part 2: Methods of lest
IEC 60464-2 Varnishes used for electrical insulation - Part 2: Methods of test
IEC 60684-2 Flexible insulating sleeving - Part 2: Methods of test
IEC 60836 Specifications for unused silicone insulating liquids for electrotechnical purposes
IEC 61099 Insulating liquids - Specifications for unused synthetic organic esters for electrical purposes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
electric breakdown
severe loss of the insulating properties of test specimens while exposed to electric stress, which causes the current in the test circuit to operate an appropriate circuit-breaker
Note: Breakdown is often caused by partial discharges in the gas or liquid medium surrounding the test specimen and the electrodes which puncture the specimen beyond the periphery of the smaller electrode (or of both electrodes, if of equal diameter).
3.2
flashover
loss of the insulating properties of the gas or liquid medium surrounding a test specimen and electrodes while exposed to electric stress, which causes the current in the test circuit to operate an appropriate circuit-breaker
Note: The presence of carbonized channels or punctures through the specimen distinguishes tests where breakdown occurred, from others where flashover occurred.
3.3
breakdown voltage
3.3.1
(tests with continuously rising voltage) voltage at which a specimen suffers breakdown under the prescribed test conditions
3.3.2
(step-by-step tests) highest voltage which a specimen withstands without breakdown for the duration of the time at that voltage level
3.4
electirc strength
quotient of the breakdown voltage and the distance between the electrodes between which the voltage is applied under the prescribed test conditions
Note: The distance between the test electrodes is determined as specified in Sub-clause 5.5, unless otherwise specified.
4 Significance of the test
Electric strength test results obtained in accordance with this standard are useful for detecting changes or deviations from normal characteristics resulting from processing variables, ageing conditions or other manufacturing or environmental situations. However, they are not intended for use in evaluating the behavior of insulating materials in an actual application.
Measured values of the electric strength of a material may be affected by many factors, including:
a) Condition of test specimens:
1) the thickness and homogeneity of the specimen and the presence of mechanical strain;
2) previous conditioning of the specimens, in particular drying and impregnation procedures;
3) the presence of gaseous inclusions, moisture or other contamination.
b) Test conditions:
1) the frequency, waveform and rate of rise or time of application of the voltage;
2) the ambient temperature, pressure and humidity;
3) the configuration, the dimensions, and thermal conductivity of the test electrodes;
4) the electrical and thermal characteristics of the surrounding medium.
The effects of all these factors shall be considered when investigating materials for which no experience exists. This standard defines particular conditions which give rapid discrimination between materials and which can be used for quality control and similar purposes.
The results given by different methods are not directly comparable but each may provide information on relative electric strengths of materials. The electric strength of most materials decreases as the thickness of the specimen between the electrodes increases and as the time of voltage application increases.
The measured electric strength of most materials is significantly affected by the intensity and the duration of surface discharges prior to breakdown. For designs which are free from partial discharges up to the test voltage, it is very important to know the electric strength without discharges prior to breakdown. However, the methods in this standard are generally not suitable for providing this information.
Materials with high electric strength will not necessarily resist long-term degradation processes such as heat, erosion or chemical deterioration by partial discharges, or electrochemical deterioration in the presence of moisture, all of which may cause failure in service at much lower stress.
5 Electrodes and specimens
5.1 General
The metal electrodes shall be maintained smooth, clean and free from defects at all times. Electrode arrangements for tests on boards and sheets perpendicular to the surface are shown in Figure 1.
Note: This maintenance becomes more important when thin specimens are being tested. Stainless steel electrodes e.g. minimize electrode damage at breakdown.
The leads to the electrodes shall not tilt or otherwise move the electrodes, nor affect the pressure on the specimen, nor appreciably affect the electric field configuration in the neighborhood of the specimen.
When very thin films (for example < 5 µm thick) are to be tested, the standards for those materials shall specify the electrodes and special procedures for handling and specimen preparation.
5.2 Tests perpendicular to the surface of non-laminated materials and normal to laminate of laminated materials
5.2.1 Boards and sheet materials, including pressboards, papers, fabrics and films
5.2.1.1 Unequal electrodes
The electrodes shall consist of two metal cylinders with the edges rounded to give a radius of (3 ± 0.2) mm. One electrode shall be (25 ± 1) mm in diameter and approximately 25 mm high. The other electrode shall be (75 ± 1) mm in diameter and approximately 15 mm high. These two electrodes shall be arranged coaxially within 2 mm as in Figure 1a).
Note: Radii for surface not in contact with the electrode are not critical with respect to test results but should avoid partial discharges in the surrounding medium.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Significance of the test
5 Electrodes and specimens
6 Conditioning before tests
7 Surrounding medium
8 Electrical apparatus
9 Test procedures
10 Mode of increase of voltage
11 Criterion of breakdown
12 Number of tests
13 Test report
Annex A (Informative) Treatment of experimental data
Bibliography
Insulating materials - Test methods for electric strength - Part 1: Test at power frequencies
1 Scope
This part of GB/T 1408 provides test methods for the determination of short-time electric strength of solid insulating materials at power frequencies between 48 Hz and 62 Hz.
This standard does not cover the testing of liquids and gases, although these are specified and used as impregnates or surrounding media for the solid insulating materials being tested.
Note: Methods for the determination of breakdown voltages along the surfaces of solid insulating materials are included.
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.
ISO 293 Plastics - Compression moulding of test specimens of thermoplastic materials
ISO 294-1 Plastics - Injection moulding of test specimens of thermoplastic materials - Part 1: General principles, and moulding of multipurpose and bar test specimens
ISO 294-3 Plastics - Injection moulding of test specimens of thermoplastic materials - Part 3: Small plates
ISO 295 Plastics - Compression moulding of test specimens of thermosetting materials
ISO 10724 Plastics - Injection moulding of test specimens of thermosetting powder moulding compounds
IEC 60212 Standard conditions for use prior to and during the testing of solid electrical insulating materials
IEC 60296 Fluids for electrotechnical applications - Unused mineral insulating oils for transformers and switchgear
IEC 60455-2 Specification for solvent-less polymerizable resinous compounds used for electrical insulation - Part 2: Methods of lest
IEC 60464-2 Varnishes used for electrical insulation - Part 2: Methods of test
IEC 60684-2 Flexible insulating sleeving - Part 2: Methods of test
IEC 60836 Specifications for unused silicone insulating liquids for electrotechnical purposes
IEC 61099 Insulating liquids - Specifications for unused synthetic organic esters for electrical purposes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
electric breakdown
severe loss of the insulating properties of test specimens while exposed to electric stress, which causes the current in the test circuit to operate an appropriate circuit-breaker
Note: Breakdown is often caused by partial discharges in the gas or liquid medium surrounding the test specimen and the electrodes which puncture the specimen beyond the periphery of the smaller electrode (or of both electrodes, if of equal diameter).
3.2
flashover
loss of the insulating properties of the gas or liquid medium surrounding a test specimen and electrodes while exposed to electric stress, which causes the current in the test circuit to operate an appropriate circuit-breaker
Note: The presence of carbonized channels or punctures through the specimen distinguishes tests where breakdown occurred, from others where flashover occurred.
3.3
breakdown voltage
3.3.1
(tests with continuously rising voltage) voltage at which a specimen suffers breakdown under the prescribed test conditions
3.3.2
(step-by-step tests) highest voltage which a specimen withstands without breakdown for the duration of the time at that voltage level
3.4
electirc strength
quotient of the breakdown voltage and the distance between the electrodes between which the voltage is applied under the prescribed test conditions
Note: The distance between the test electrodes is determined as specified in Sub-clause 5.5, unless otherwise specified.
4 Significance of the test
Electric strength test results obtained in accordance with this standard are useful for detecting changes or deviations from normal characteristics resulting from processing variables, ageing conditions or other manufacturing or environmental situations. However, they are not intended for use in evaluating the behavior of insulating materials in an actual application.
Measured values of the electric strength of a material may be affected by many factors, including:
a) Condition of test specimens:
1) the thickness and homogeneity of the specimen and the presence of mechanical strain;
2) previous conditioning of the specimens, in particular drying and impregnation procedures;
3) the presence of gaseous inclusions, moisture or other contamination.
b) Test conditions:
1) the frequency, waveform and rate of rise or time of application of the voltage;
2) the ambient temperature, pressure and humidity;
3) the configuration, the dimensions, and thermal conductivity of the test electrodes;
4) the electrical and thermal characteristics of the surrounding medium.
The effects of all these factors shall be considered when investigating materials for which no experience exists. This standard defines particular conditions which give rapid discrimination between materials and which can be used for quality control and similar purposes.
The results given by different methods are not directly comparable but each may provide information on relative electric strengths of materials. The electric strength of most materials decreases as the thickness of the specimen between the electrodes increases and as the time of voltage application increases.
The measured electric strength of most materials is significantly affected by the intensity and the duration of surface discharges prior to breakdown. For designs which are free from partial discharges up to the test voltage, it is very important to know the electric strength without discharges prior to breakdown. However, the methods in this standard are generally not suitable for providing this information.
Materials with high electric strength will not necessarily resist long-term degradation processes such as heat, erosion or chemical deterioration by partial discharges, or electrochemical deterioration in the presence of moisture, all of which may cause failure in service at much lower stress.
5 Electrodes and specimens
5.1 General
The metal electrodes shall be maintained smooth, clean and free from defects at all times. Electrode arrangements for tests on boards and sheets perpendicular to the surface are shown in Figure 1.
Note: This maintenance becomes more important when thin specimens are being tested. Stainless steel electrodes e.g. minimize electrode damage at breakdown.
The leads to the electrodes shall not tilt or otherwise move the electrodes, nor affect the pressure on the specimen, nor appreciably affect the electric field configuration in the neighborhood of the specimen.
When very thin films (for example < 5 µm thick) are to be tested, the standards for those materials shall specify the electrodes and special procedures for handling and specimen preparation.
5.2 Tests perpendicular to the surface of non-laminated materials and normal to laminate of laminated materials
5.2.1 Boards and sheet materials, including pressboards, papers, fabrics and films
5.2.1.1 Unequal electrodes
The electrodes shall consist of two metal cylinders with the edges rounded to give a radius of (3 ± 0.2) mm. One electrode shall be (25 ± 1) mm in diameter and approximately 25 mm high. The other electrode shall be (75 ± 1) mm in diameter and approximately 15 mm high. These two electrodes shall be arranged coaxially within 2 mm as in Figure 1a).
Note: Radii for surface not in contact with the electrode are not critical with respect to test results but should avoid partial discharges in the surrounding medium.
Contents of GB/T 1408.1-2016
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Significance of the test
5 Electrodes and specimens
6 Conditioning before tests
7 Surrounding medium
8 Electrical apparatus
9 Test procedures
10 Mode of increase of voltage
11 Criterion of breakdown
12 Number of tests
13 Test report
Annex A (Informative) Treatment of experimental data
Bibliography