1. Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education(Shandong University), Jinan 250061, China; 2. Xuji Group Corporation, Xuchang 461000, China

The active power differential protection has unique advantages in dealing with distributed capacitance and high resistance faults. However, the defect of close metallic faults with small resistance limits its practical application. In order to overcome this shortcoming, a concept of virtual active power emanating from referring to the superposition principle is proposed, and the different characteristics for virtual active power under the internal fault and the external fault conditions are analyzed. On this basis, a split-phase action criterion for virtual active power differential protection is proposed and its operation characteristics are analyzed qualitatively. By using the model of 500 kV transmission lines on PSCAD, a number of simulations have been conducted for different fault locations, fault types, transition resistances, reactive elements operations and asynchronous data to evaluate the influences on the protection scheme performance comprehensively. Theoretical analysis and simulation results show that the proposed protection scheme is able to correctly identify the fault sections without dead zone for close metallic faults but a great capability against fault resistance, less data exchanges, a low requirement for synchronization and no need of capacitance compensation.