This paper presents a methodology of fault current unbalance analysis with the objective of supplying transmission lines unit protection. The presented solution is based on the phase comparison protection principle (PC protection) and uses as input signals the direct axis components Id obtained at both line terminals by applying the Park’s transformation (TDQ). By doing so, since the Id signals contain current directionality information and present a second harmonic component due to the occurrence of fault current unbalance, the protection operation time is speeded up by two times, without loss of security and reliability. The Alternative Transients Program (ATP) was used to simulate a wide variety of fault scenarios on a 230 kV/60 Hz transmission line 200 km long. Based on simulations, the results obtained by using the traditional and the proposed PC protection were compared, demonstrating that the presented approach is reliable and faster than the classical function.