Insulator Laboratory Tests

Insulator Laboratory Tests include Visual inspection, Wet tests, and Step impulse test. The insulators sent to the laboratory were submitted to these tests as per the Brazilian National Standard NBR 5049.

Insulator Laboratory Tests

Insulator Laboratory Tests:
The insulators sent to the laboratory were submitted to the following tests, as per the Brazilian National Standard NBR 5049:
1. Visual inspection
2. Wet tests – Power frequency withstanding
3. Step impulse test – 20 discharges
The step impulse tests were applied only during the first part of the present research [1]. The application of these tests was discontinued due to two factors: the first was the complete absence of insulator failure that could be associated to improved performance. Insulator failures in these tests were common in the past. However, to solve this, much research work has been done in the last decades.

The second factor is associated to a lower impulse rate rise of 1.000 kV/μs; however this is a test-equipment limitation impossible to be solved with the present laboratory facilities. The visual inspection considers the bulk analysis of the insulator, checking for imperfections. Non approved insulators were not submitted to the wet tests and were discarded.

The aim of the wet test is to determine the leakage current levels and insulation failure – disruptive discharges that can be attributed to poor insulator field performance. During this test partial disruptive discharges can occur, where the test sample is bridged by a low energy power arc, and the voltage between the sample terminals is reduced to zero or close to zero. Depending on the characteristic of the test circuit and of the test sample, dielectric strength recovery is possible. For this research that was not considered as being a failure. The insulators were tested without considering the removal of the any existing pollutants.

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