Control circuit

A control circuit (30) comprises: first and second primary terminals (32,34) for respective connection to first and second power transmission lines (36,38); a current transmission path extending between the first and second primary terminals (32,34) and having first and second current transmission path portions (40,42) separated by a third primary terminal (44), the first current transmission path portion (40) including at least one primary switching element (46) connected in series between the first and third primary terminals (32,44), the second current transmission path portion (42) including an energy conversion block connected between the second and third primary terminals (34,44), the energy conversion block including at least one primary energy conversion element (48) for removing energy from the power transmission lines (36,38); a converter limb (50) connected across the second and third primary terminals (34,44), the converter limb (50) including an auxiliary converter (52); and a control unit (62) which controls the auxiliary converter (52) to selectively provide a voltage source to minimise a voltage across the or each primary switching element (46) prior to switching of the or each primary switching element (46).