GB/T 6553-2024 Electrical insulating materials used under severe ambient conditions - Test methods for evaluating resistance to tracking and erosion
1 Scope
This document describes two test methods for the evaluation of electrical insulating materials for use under severe ambient conditions at power frequencies (45 Hz to 65 Hz) by the evaluation of the resistance to tracking and erosion, using a liquid contaminant and inclined plane specimens. The two methods are:
——Method 1: test at constant voltage,
——Method 2: test at stepwise increased voltage.
Method 1 is the most widely used method as there is less need for continual inspection.
The test conditions are designed to accelerate the production of the effects, but do not reproduce all the conditions encountered in service.
2 Normative references
There are no normative references in this document.
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
track
partially conducting path created by localized deterioration on the surface of an insulating
material
3.2
tracking
progressive formation of conductive paths, which are produced on the surface or within a solid insulating material, due to the combined effects of electric stress and electrolytic contamination
Note 1: Tracking usually occurs due to surface contamination.
Note 2: Remaining degraded materials need not necessarily remain conductive, especially after they have cooled.
[SOURCE: GB/T 2900.5-2013, 212-11-56, modified: Note 2 has been added.]
3.3
erosion
electrical loss of material by leakage current or electrical discharge
4 Test specimens
4.1 Dimensions
Flat specimens with a size of at least (50 × 1 20) mm2 shall be used. The preferred thickness should be 6 mm. Specimens with a different thickness may be used. Thickness shall be mentioned in the test report. The schematic diagram of the sample dimensions with fixed electrode holes is shown in Figure 1.
4.2 Preparation
The mechanical processing of the test specimens is as shown in Figure 1, to allow the attachment of electrodes.
The specimens shall be washed with a suitable solvent (e.g. isopropyl alcohol) to remove leftovers such as fatty residues from preparation and handling. The specimens shall then be rinsed with distilled water.
Specimens used for evaluation with criterion B (see Clause 6) shall be marked with reference marks on both long sides 25 mm above the upper edge of the lower electrode (Figure 1 and Figure 8). Unless otherwise specified, the test specimens shall be conditioned for a minimum of 24 h at (23 ± 2) °C, with (50 ± 10) % RH.
When mounting the cleaned and conditioned specimens, ensure they are not contaminated. Good wettability of the specimen surface with the contaminant (see 5.4) is a crucial prerequisite for this test method. The wettability shall be evaluated beforehand. If the contaminant does not wet the surface, the specimens can be slightly abraded. Grinding should be done with a fine (U.S. grade (CAMI): 400 mesh; European grade (FEPA): P800) aluminium-oxide- or zirconia-alumina-abrasive, under water, until the whole surface wets. Specimens shall be properly rinsed with distilled water after grinding. Grinding or any other type of changes of the surface shall be mentioned in the test report.
An alternative to grinding is to increase the flow rate, temporarily, until the specimen’s surface is properly wetted prior to switching on the test voltage.
The specimen preparation sequence is shown in Table 1.
