Measurement of insulation resistance of high-voltage equipment

For electrical equipment, especially high-voltage electrical equipment, insulation performance tests must be performed at the time of operation or after a period of operation. Check its electrical insulation performance. In accordance with the provisions of the International Preventive Test Regulations for Electric Power Equipment:

1. Fully-connected off-phase closed busbars with a rated voltage of 15kV and above are not less than 50MΩ at room temperature. The 6kV common box-type closed bus bar has a split phase insulation resistance value of not less than 6MΩ at normal temperature.

2. The insulation resistance of general busbars should not be lower than 1MΩ / kV. The insulation resistance of electrical equipment refers to the ratio of the DC voltage U applied to its electrical insulation material to the total electrical current flowing through it, that is, R = U / I. By measuring the insulation resistance of electrical equipment, you can check the insulation status of the equipment. Such as: whether it is wet or aging. Due to the influence of some unfavorable factors, the data measured by the test is inaccurate and cannot truly reflect the actual status of the equipment insulation, which affects the staff's correct judgment of the equipment condition. To this end, the author will share with you the problems encountered in the actual work process and improvement measures.

1. The effect of temperature on insulation The temperature rises, and the insulation resistance of many insulating materials will significantly decrease, because the temperature increases the atomic and molecular movements of the insulating material, and the original molecular structure becomes loose. Moving and transferring electrons, the insulating ability of the insulating material decreases. In view of this factor, the tester should convert the test results to the same temperature for vertical and horizontal comparison. If the test data is very different and does not comply with the test procedures, the insulation should be analyzed for aging or moisture based on the test results.

2. The effect of temperature on insulation (the insulation resistance can be measured with a high-voltage insulation resistance tester with temperature compensation). When the insulation is in a high humidity environment, its surface will absorb moisture to form a water film, which will increase its surface electrical conductivity. Significantly reduces the insulation resistance. In addition, some insulating materials have a capillary effect, which absorbs more moisture, increases electrical conductivity, and reduces overall insulation. In this case, equipotential shielding should be added.

3． The effect of test time on testing. When the measurement is repeated, the charging current and the absorption current obtained during the repeated measurement are smaller than the previous one due to the existence of the residual charge, resulting in a false increase in the insulation resistance. Therefore, after each measurement of the insulation resistance, the product under test should be fully discharged so that the discharge time is longer than the charging time to facilitate the exhaustion of residual charges.

4． Influence of oil pollution on insulation resistance. Contaminants such as dust or oil are easily attached to the surface of the test product. Most of these contaminated materials can conduct electricity and reduce the surface resistance of the insulator, but this does not represent the true situation of the insulator. In view of this situation, it is usually necessary to wipe the surface of the insulator clean with a cleaning method, so that the insulation resistance value of the test object will be greatly improved.

5. Operation method Improper use of the insulation resistance tester will make the data inaccurate. Therefore, you can choose an insulation resistance tester with a suitable voltage level. The pointer type insulation resistance tester should be connected correctly (measurement terminal "L", ground terminal "E", shield terminal "G"), and drive speed of 120 rpm. In this way, real data can be measured.