Abstract: A protection circuit, for protecting a whole or part of a HVDC power transmission network, includes a number of sets of sensors, each of which set defines a respective protection zone. The protection circuit also includes a controller that is programmed to evaluate sensor information received from the sensors to determine whether a fault has occurred within a protection zone. The controller is further programmed, in the event of a sensor in a protection zone failing, to dynamically reconfigure the affected protection zone by including a sensor from another protection zone.