GB/T 4207-2022 Method for the determination of the proof and the comparative tracking indices of solid insulating materials
1 Scope
This document specifies the method of test to the determination of the proof and comparative tracking indices of solid insulating materials on pieces taken from parts of equipment and on plaques of material using alternating voltage.
This document provides a procedure for the determination of erosion when required.
Note 1: The proof tracking index is used as an acceptance criterion as well as a means for the quality control of materials and fabricated parts. The comparative tracking index is mainly used for the basic characterization and comparison of the properties of materials.
This test method evaluates the composition of the material as well as the surface of the material being evaluated. Both the composition and surface condition directly influence the results of the evaluation and are considered when using the results in material selection process.
Test results are not directly suitable for the evaluation of safe creepage distances when designing electrical apparatus.
Note 2: This is in compliance with IEC 60664-1, Insulation coordination for equipment within low-voltage systems - Part 1: Principle, requirements and tests.
Note 3: This test discriminates between materials with relatively poor resistance to tracking, and those with moderate or good resistance, for use in equipment which can be used under moist conditions. More severe tests of longer duration are available for the assessment of performance of materials for outdoor use, utilizing higher voltages and larger test specimens (see the inclined plane test of IEC 60587). Other test methods such as the inclined method can rank materials in a different order from the drop test given in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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 4287 Geometrical Product Specification (GPS) - Surface texture: Profile method - Terms, definition and surface texture parameters
Note: GB/T 3505-2009 Geometrical product specifications (GPS) - Surface texture: Profile method - Terms definitions and surface texture parameters (ISO 4287:1997, IDT).
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
——ISO Online browsing platform: available at http://www.iso.org/obp;
——IEC Electropedia: available at http://www.electropedia.org/.
3.1
tracking
progressive formation of conducting paths, which are produced on the surface and/or within a solid insulating material, due to the combined effects of electric stress and electrolytic contamination
3.2
tracking failure
failure of insulation due to tracking between conductive parts
Note: In the present test, tracking is indicated by operation of an over-current device due to the passage of a current across the test surface and/or within the specimen.
3.3
electrical erosion
wearing away of insulating material by the action of electrical discharges
3.4
air arc
arc between the electrodes above the surface of the specimen
3.5
comparative tracking index
CTI
numerical value of the maximum voltage (in V) at which five test specimens withstand the test period for 50 drops without tracking failure and without a persistent flame occurring and including also a statement relating to the behaviour of the material when tested using 100 drops.
Note 1: No tracking failure and no persistent flame are allowed at any lower test voltage.
Note 2: The criteria for CTI may also require a statement concerning the degree of erosion.
Note 3: Although a non-persistent flame is allowed in the test without constituting failure, materials which generate no flame at all are preferred unless other factors are considered to be more important. See also Annex A.
Note 4: Some materials can withstand high test voltages, but fail at lower test voltages. See also 11.2.
3.6
persistent flame
flame which burns for more than 2 s
3.7
proof tracking index
PTI
numerical value of the proof voltage (in V) at which five test specimens withstand the test period for 50 drops without tracking failure and without a persistent flame occurring
Note: Although a non-persistent flame is allowed in the test without constituting failure, materials which generate no flame at all are preferred unless other factors are considered to be more important. See also Annex A.
3.8
de-ionized water
water for analytical laboratory use in accordance with ISO 3696, grade 3, or equivalent quality
4 Principle
The upper surface of the test specimen is supported in a horizontal plane and subjected to an electrical stress via two electrodes. The surface between the electrodes is subjected to a succession of drops of electrolyte either until the over-current device operates, or until a persistent flame occurs, or until the test period has elapsed.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Test specimen
6 Test specimen conditioning
6.1 Environmental conditioning
6.2 Test specimen surface state
7 Test apparatus
7.1 Electrodes
7.2 Test circuit
7.3 Test solutions
7.4 Dropping device
7.5 Test specimen support platform
7.6 Electrode assembly installation
7.7 Conditioning chamber
8 Basic test procedure
8.1 General
8.2 Preparation
8.3 Test procedure
9 Determination of erosion
10 Determination of proof tracking index (PTI)
10.1 Procedure
10.2 Report
11 Determination of comparative tracking index (CTI)
11.1 General
11.2 Screening test
11.3 Determination of the maximum 50 drop withstand voltage
11.4 Determination of the 100 drop point
11.5 Report
Annex A (Informative) List of factors that should be considered
Annex B (Informative) Solution B
Annex C (Informative) Electrode material selection
C.1 Platinum electrodes
C.2 Alternatives
Bibliography
