Researches On Several Problems Of Protection Relays On T-connection Lines

This paper proposes differential protective criterions used superimposed current components available for T-connection transmission lines. Under all kinds of conditions the paper makes theoretic deductions and analysis exhaustively, and discusses the cooperating relations of criterions, the reduction of calculating works and data transmission. The ATP simulation results show the correctness of the criterions. At the same time, this paper does research on fault location and fault phases selection, and puts forward fault location algorithm for EHV long lines. Based on distributed parameter line model, the algorithm makes use of the distributed regularity of positive sequence fault voltage to convert distributed parameter line location to lumped parameter line fault location. For the faults of two points on different phases existing in power system, this paper proposes a time domain fault location method, and deduces the common fault location formula under all kinds of conditions. For fault phases selection scalars concerning superimposed line voltage and current are constructed. The theory of fault phases selection is based on the relation of three scalars under all kinds of faults.