A converter , for use in HVDC power transmission and distribution, comprising: first and second DC terminals for connection to a DC electrical network and between which extends a plurality of converter limbs , each converter limb including first and second limb portions separated by an AC terminal for connection to a respective phase (A,B,C) of a multi-phase AC electrical network , and each limb portion including a current sensor to measure current flowing in the corresponding limb portion (20A,22A,20B.22B,20C,22C); a plurality of further current sensors located elsewhere in the converter, the plurality of further current sensors includes a respective current sensor operatively associated with each of the first and second DC terminals to measure current flowing into or out of the converter via the corresponding said first or second DC terminal ; and a current sensor management unit programmed to: (a) receive a measured current value (i TA , i BA , i TB , i BB , i TC , i BC , i DCT , I DCB , i PhaseA , i PhaseB , i PhaseC ) from each current sensor ; characterised in that the current sensor management unit is further programmed to: (b) identify at least one faulty current sensor (28',28") from the received measured current values (i TA , i BA , i TB , i BB , i TC , i BC , I DCT , I DCB , i PhaseA , i PhaseB , i Phasec ); and (c) replace the measured current value of the or each identified faulty current sensor (28',28") with a calculated current value (ip haseA_Calc , i PhaseB_Calc ) derived from the measured current values from the other healthy current sensors . first and second DC terminals for connection to a DC electrical network and between which extends a plurality of converter limbs , each converter limb including first and second limb portions separated by an AC terminal for connection to a respective phase (A,B,C) of a multi-phase AC electrical network , and each limb portion including a current sensor to measure current flowing in the corresponding limb portion (20A,22A,20B.22B,20C,22C); a plurality of further current sensors located elsewhere in the converter, the plurality of further current sensors includes a respective current sensor operatively associated with each of the first and second DC terminals to measure current flowing into or out of the converter via the corresponding said first or second DC terminal ; and a current sensor management unit programmed to: (a) receive a measured current value (i TA , i BA , i TB , i BB , i TC , i BC , i DCT , I DCB , i PhaseA , i PhaseB , i PhaseC ) from each current sensor ; characterised in that the current sensor management unit is further programmed to: (b) identify at least one faulty current sensor (28',28") from the received measured current values (i TA , i BA , i TB , i BB , i TC , i BC , I DCT , I DCB , i PhaseA , i PhaseB , i Phasec ); and (c) replace the measured current value of the or each identified faulty current sensor (28',28") with a calculated current value (ip haseA_Calc , i PhaseB_Calc ) derived from the measured current values from the other healthy current sensors . (a) receive a measured current value (i TA , i BA , i TB , i BB , i TC , i BC , i DCT , I DCB , i PhaseA , i PhaseB , i PhaseC ) from each current sensor ; (b) identify at least one faulty current sensor (28',28") from the received measured current values (i TA , i BA , i TB , i BB , i TC , i BC , I DCT , I DCB , i PhaseA , i PhaseB , i Phasec ); and (c) replace the measured current value of the or each identified faulty current sensor (28',28") with a calculated current value (ip haseA_Calc , i PhaseB_Calc ) derived from the measured current values from the other healthy current sensors . <EOS>