A method of operation of a bipole voltage source converter apparatus , the bipole voltage source converter apparatus comprising: a plurality of converter units (202a-d) arranged to convert power between an alternating current and a direct current, wherein each converter unit (202a-d) has an AC side and a DC side, the DC side of each converter unit (202a-d) connected to a respective DC pole connection (204a-b) of a DC link; a plurality of neutral connections (218a-d), each neutral connection (218a-d) for connecting the DC side of a respective one of the converter units (202a-d) to a neutral bus (210a-b); a breaker switch (212a-d) arranged in at least one of the neutral connections (218a-d); and a plurality of AC breakers , each AC breaker (208a-b) connected to the AC side of a respective one of the converter units (202a-d), characterised in that the method comprises: i. monitoring a DC fault condition; ii. when the DC fault condition is met, opening the corresponding AC breaker (208a-d); iii. after opening the corresponding AC breaker (208a-d), determining if a breaker switch operation condition is met, by determining: if a current through the breaker switch (212a-d) is less than a threshold current; and/or if a current through the breaker switch (212a-d) is less than a threshold current and a current through the breaker switch (212a-d) is decreasing; and/or if a predetermined time has elapsed since the DC fault occurred; iv. when the breaker switch operation condition is met, opening the breaker switch (212a-d) associated with the pole of the DC link having the DC fault. a plurality of converter units (202a-d) arranged to convert power between an alternating current and a direct current, wherein each converter unit (202a-d) has an AC side and a DC side, the DC side of each converter unit (202a-d) connected to a respective DC pole connection (204a-b) of a DC link; a plurality of neutral connections (218a-d), each neutral connection (218a-d) for connecting the DC side of a respective one of the converter units (202a-d) to a neutral bus (210a-b); a breaker switch (212a-d) arranged in at least one of the neutral connections (218a-d); and a plurality of AC breakers , each AC breaker (208a-b) connected to the AC side of a respective one of the converter units (202a-d), characterised in that the method comprises: i. monitoring a DC fault condition; ii. when the DC fault condition is met, opening the corresponding AC breaker (208a-d); iii. after opening the corresponding AC breaker (208a-d), determining if a breaker switch operation condition is met, by determining: if a current through the breaker switch (212a-d) is less than a threshold current; and/or if a current through the breaker switch (212a-d) is less than a threshold current and a current through the breaker switch (212a-d) is decreasing; and/or if a predetermined time has elapsed since the DC fault occurred; iv. when the breaker switch operation condition is met, opening the breaker switch (212a-d) associated with the pole of the DC link having the DC fault. i. monitoring a DC fault condition; ii. when the DC fault condition is met, opening the corresponding AC breaker (208a-d); iii. after opening the corresponding AC breaker (208a-d), determining if a breaker switch operation condition is met, by determining: if a current through the breaker switch (212a-d) is less than a threshold current; and/or if a current through the breaker switch (212a-d) is less than a threshold current and a current through the breaker switch (212a-d) is decreasing; and/or if a predetermined time has elapsed since the DC fault occurred; iv. when the breaker switch operation condition is met, opening the breaker switch (212a-d) associated with the pole of the DC link having the DC fault. <EOS>