Evaluation Method of Oil-paper Insulation Bushing Damp Type Based on Polarity Reversal

Oil-paper insulation bushing has been widely used in power system due to its good electrical and mechanical properties. Moisture is the most important factor affecting the safe and stable operation of the bushing. The moisture in the bushing mainly comes from the internal capacitor core and the end screen. In order to determine the initial damp location of the oil-paper bushing, the simulation models of internal damp and external damp bushing were constructed, and the moisture content was determined. On this basis, the oil-paper insulation samples with internal and external dampness were prepared according to the simulation data, and the polarization and depolarization current (PDC) test curves under different voltages and the integral values in the time direction were obtained. The results show that the polarization current curves and the depolarization current curves of the bushing under the test voltage of 200V, 400V, 600V and 800V are higher than the corresponding curves under the external damp condition; The integral value of PDC curve is greater than 3.5×10−7 when the bushing is damp outside and less than 3.2 ×10−7 when the bushing is damp inside, which can be used as a criterion to distinguish the initial damp position of the bushing.