A current differential protection system for a multi-terminal power line comprising: a current sensor (52,54,56) for sensing a current at a local terminal (46,48,50); a controller (80,182) for time synchronizing the local terminal (46,48,50) and remote terminals, the controller (80,182) comprising: an analog to digital converter for sampling the current (I 1) at the local terminal (46,48,50); a receiver for receiving a time signal and an indexed current signal from remote terminals; a time measurement exchange module (94,186) for exchanging time stamp data including a message sent and a message received time at the local terminal (46, 48, 50) and a message sent and a message received time at remote terminals; an upper range clock for providing local time measurements to the time measurement exchange module (94, 186); a lower range clock for indexing the current at the local terminal (46,48,50) based on a sampling frequency of the analog to digital converter, wherein a first time period of the upper range clock is N times a second time period of the lower range clock where N is a number of terminals in the multi-terminal system; a clock offset calculation module for determining an average time offset based on time stamp data from remote terminals and the local terminal (46,48,50); a phase-frequency locked loop for determining phase and frequency signals for the upper range clock and the lower range clock based on the average time offset; a differential current calculator configured to determine a differential current (I diff) by a vector addition or subtraction of the current at local terminal (I 1) and a second current (I 2,I 3) of at least one of the remote terminals; and a fault detection module configured to detect a fault in the multi-terminal power line if the differential current exceeds (I diff) a threshold value (I t). a current sensor (52,54,56) for sensing a current at a local terminal (46,48,50); a controller (80,182) for time synchronizing the local terminal (46,48,50) and remote terminals, the controller (80,182) comprising: an analog to digital converter for sampling the current (I 1) at the local terminal (46,48,50); a receiver for receiving a time signal and an indexed current signal from remote terminals; a time measurement exchange module (94,186) for exchanging time stamp data including a message sent and a message received time at the local terminal (46, 48, 50) and a message sent and a message received time at remote terminals; an upper range clock for providing local time measurements to the time measurement exchange module (94, 186); a lower range clock for indexing the current at the local terminal (46,48,50) based on a sampling frequency of the analog to digital converter, wherein a first time period of the upper range clock is N times a second time period of the lower range clock where N is a number of terminals in the multi-terminal system; a clock offset calculation module for determining an average time offset based on time stamp data from remote terminals and the local terminal (46,48,50); a phase-frequency locked loop for determining phase and frequency signals for the upper range clock and the lower range clock based on the average time offset; a differential current calculator configured to determine a differential current (I diff) by a vector addition or subtraction of the current at local terminal (I 1) and a second current (I 2,I 3) of at least one of the remote terminals; and a fault detection module configured to detect a fault in the multi-terminal power line if the differential current exceeds (I diff) a threshold value (I t). an analog to digital converter for sampling the current (I 1) at the local terminal (46,48,50); a receiver for receiving a time signal and an indexed current signal from remote terminals; a time measurement exchange module (94,186) for exchanging time stamp data including a message sent and a message received time at the local terminal (46, 48, 50) and a message sent and a message received time at remote terminals; an upper range clock for providing local time measurements to the time measurement exchange module (94, 186); a lower range clock for indexing the current at the local terminal (46,48,50) based on a sampling frequency of the analog to digital converter, wherein a first time period of the upper range clock is N times a second time period of the lower range clock where N is a number of terminals in the multi-terminal system; a clock offset calculation module for determining an average time offset based on time stamp data from remote terminals and the local terminal (46,48,50); a phase-frequency locked loop for determining phase and frequency signals for the upper range clock and the lower range clock based on the average time offset; a differential current calculator configured to determine a differential current (I diff) by a vector addition or subtraction of the current at local terminal (I 1) and a second current (I 2,I 3) of at least one of the remote terminals; and a fault detection module configured to detect a fault in the multi-terminal power line if the differential current exceeds (I diff) a threshold value (I t).