What is the dielectric loss factor of the transformer and how is it tested?

The dielectric loss factor tgS is one of the basic indicators reflecting the insulation performance. The dielectric loss factor tgS reflects the characteristic parameter of the insulation loss, and it can be sensitively found that the overall insulation of the electrical equipment is damp, deteriorated, and the local defects of the small-volume equipment are penetrated and not penetrated.

The dielectric loss factor tgS has obvious advantages compared with the test of insulation resistance and leakage current. It has nothing to do with factors such as test voltage and sample size, and it is easier to judge the insulation variation of electrical equipment. Therefore, the dielectric loss factor tgS is one of the most basic tests for insulation testing of high voltage electrical equipment.

By measuring the dielectric loss factor tgS, it is used to check the overall deterioration of the transformer oil quality, the adhesion of sludge on the windings and serious local defects. Dielectric loss measurements are often subject to surface leakage and external conditions (such as interference with electric fields and atmospheric conditions) and measures are taken to reduce and eliminate the effects. At the site, we generally measure the tgS along with the casing, but in order to improve the accuracy of the measurement and the sensitivity of detecting the defect, a decomposition test is sometimes performed to determine the location of the defect. Measuring the leakage current is similar to measuring the insulation resistance, but its sensitivity is high, and it can effectively find some local defects of the transformer that cannot be found in other test items. The leakage current value is related to the insulation structure and temperature of the transformer. The judgment is emphasized with the factory test, compared with the same type transformer and empirical data; the effectiveness of the dielectric loss factor tgS and the leakage current test is increasing with the transformer voltage level. The capacity and volume increase and decrease, so the simple dielectric loss factor tgS and leakage current are less likely to correctly judge the winding insulation condition, but for capacitive devices, practice has proved such as capacitive bushings and capacitive voltage transformers. Measuring tantalum capacitors, etc. Measuring tgS and capacitance Cx is still an effective means of fault diagnosis.

The dielectric loss factor tgS can effectively find the following defects of insulation: moisture; (2) penetrating conductive channels; (3) free bubbles in the insulation, insulation delamination, shelling; (4) insulation is dirty, deterioration and aging.

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