Research On New Fast Algorithm Of Extra-high Voltage Transformer Protection

Transformer is one of major electric apparatuses in power system. It plays an importantrole in the transmission of power supply. The transformer run in safety, especially inextra-high voltage transformer, influenced to all power system. Therefore, the research fornew algorithm of extra-high voltage transformer protection with high performance, such asfast, reliable and sensible capabilities, is in highly demand.A new area-ratio algorithm of fast distinguishing the inrush and fault current of powertransformer (in 10 sec) based on the concavo-convex character of differential current is firstput forward in this paper. This paper firstly analyzed variant regularity of equivalentinstantaneous inductance from point of voltage-current wave, and use voltage-currentphase-shifting instantaneous sampling ratio to replace traditional measuringexciting-resistance. It also use the regularity to distinguish the inrush and inner fault current oftransformer, and according to this method constitute fast criterion in half cycle and a cycle.For sake of hard selection of the threshold value of second harmonics principle and waveformsymmetry principle, the paper adopted a method of calculation ratio which can meet differentthreshold value in mathematical expectation of probability distribution, and synthesizedthree phase calculation value to constitute criterion for distinguishing inrush and inner faultcurrent of transformer.