Phase comparison protection possesses the superior performance of distinguishing between power system oscillation and fault, but the sensitivity of conventional phase comparison protection during internal faults is susceptible to the influence of load current and the fault resistance, and its performance is significantly influenced by the distributed capacitance of ultra high voltage (UHV) transmission lines, which leads to the maloperation of phase comparison relay. A novel distributed parameters model based positive sequence superimposed components phase comparison protection principle is proposed. The protection performance of the novel principle is not affected by load current and the fault resistance theoretically. On the other hand, the novel principle completely overcomes the effects of distributed capacitance to protection, greatly improves the security of protection. The protection maloperation problem as the external fault of long distance UHV line occurs as well as the maloperation of non-faulty circuit as fault occurs in one of the double-circuit line on the same tower can be solved. Extensive simulations are performed to evaluate the performance of the proposed algorithm. The results show that the algorithm is reliable for UHV power transmission line protections. Also it is immune to fault resistances and system condition.