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SUMMARY Current differential protection is widely used in transmission line due to its inherent simplicity and good performance. In order to strive to increase sensitivity of protection without compromising stability on external faults, phase correlation current differential protection is presented in this paper. Current phase difference is introduced to the differential current principle so as to improve the sensitivity and reliability of differential protection simultaneously. Comprehensive analysis and comparisons of performance characteristics in Alpha Plane demonstrate that phase correlation current differential protection has preferable performance than that of conventional current differential protection. As far as CT saturation is concerned, the proposed protection scheme has flexible adaptability to ensure significant improvement in sensitivity and dependability for internal faults while still improving stability for external faults. The performance of the proposed protection is investigated for various faults of transmission line simulated by Electro-Magnetic Transients Program including DC and record fault data from real power system. The test results show that the proposed protection has satisfactory operation performance. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]