A protection scheme based on dual criterion of active injection and virtual voltage for distribution network line with T-connected distributed photovoltaic and load

This paper firstly analyses the fault equivalent circuit of DG( Distributed Generation) as a high-frequency harmonic source, and then deduces the fault characteristics of the electrical quantities at both ends on the basis of high-frequency harmonic injection, pointing out the weaknesses: easily affected by the load capacity of the T-connected load. Afterwards, this paper draws the equivalent circuit diagram of the positive sequence component after the fault and derives the difference expression of the virtual electrical quantity at the opposite end under internal or external faults at different locations, and then analyses the fault characteristics of positive sequence under the industrial frequency. On this basis, this paper proposes a double-terminal protection scheme based on the combination of high-frequency harmonic injection and virtual positive sequence differential principle. Finally, the protection scheme is verified on the MATLAB/SIMULINK platform that it is not affected by the type of fault, transition resistance, location of the fault and capacity of T-connected load.