On December 15

2012

a power level of 2 500 MW Island debugging was conducted in YunnanGuangdong Line ± 800 kV DC transmission project

in which the operation mode of the sending station converted from network to island. After the control mode of the high voltage converter transformer tap changer changed into Udi0 mode

the DC differential protection and the valve short circuit protection of pole 1 were activated

and the double-valve group of pole 1 locked. After inspection

an M-type surge arrester in low voltage valve hall of pole 1was found to be damaged. In this study

technical parameters comparison and disassembly test are carried out. It is concluded that because the surge arrester’s reference voltage under 10 mA reference current is too low and the current nonuniformity coefficient of each column is too big

in the condition of different tap changer control modes of high-and low-voltage ends of the converter transformer

the voltage of M-type surge arrester exceeds the reference voltage under 10 mA reference current with a long time of overvoltage

so that thermal breakdown happens due to slow energy release of the surge arrester to result in damage of the arrester. It is suggested that the reference voltage value under 10 mA reference current be raised

the current nonuniformity coefficient of each column be lowered

and the operation mode of different tap changer control of high-and low-voltage ends of converter transformer be avoided.