In this paper

the cause of higher secondary voltage of one capacitor voltage transformer is analyzed in detail.It is shown that since medium-voltage capacitor C 22 terminal outlet wire without using terminal block

but using copper wire winding and soldering treatment

the manufacturer is not strict in the process control in the connection

wiring end of outlet wire has defects.The defects is developed gradually and finally formed into discharge during long term operation

which damages sealing structure between oil compartments

causes breakdown of C 12 upper capacitor element due to lack of oil and then causes secondary voltage rise.Moreover

corresponding preventive measure is proposed based on system operation.