Abstract: In the measurement of 500 kV auto-transformer, it is difficult to connect and disconnect measuring lines to the transformer because of its large size and high placed bushings. However, the bushings at the ends of high- and medium-voltage and the neutral are connected by the same winding. If the low voltage winding is short-circuited and grounded, it is possible to achieve the values of bushings’ capacitance and dielectric loss by measuring neutral voltage and current from the bushing end without connecting or disconnect measuring lines. Through the computation of the simplified equivalent circuit model of 500 kV auto-transformer, the deviation of the capacitance and the dielectric loss of the testing bushing by using neutral voltage can be calculated. The proposed method is evaluated by using two 500 kV autotransformers in Xiangshan substation located in Zhongshan, Guangdong province, which demonstrates that the proposed method is effective and can be implemented in practice.

Key words: auto-transformer, bushing, indirect measurement, short-circuit impedance, capacitance deviation, dielectric loss deviation, induced electrical interference, 500 kV