Line differential protection is popular for its good selectivity and simplicity as long as there is a dependable communication system between the two ends of the line. However, the sensitivity needs to be compromised when the traditional line differential scheme is applied for ultra-high voltage (UHV)-alternating current lines because of the large charging current. A study of the impact of the UHV transmission line characteristics on line differential protection and a proposed solution based on the compensation of the phase shift that exists between the sending and receiving end currents are presented.