Research Of The New Protection Of Transformer In Order To Distinguish The Inrush And Fault Current Of That

The dissertation makes a deep analysis on the calculation of the equivalent instantaneous inductance of wye-delta connected transformer, two approaches are put forward. Based on this, aiming at the core problem of the power transformer, which is how to discriminate between inrush magnetizing current and internal faults, a new algorithm based on the principle of controlled closing and the relation of magnetism of transformer is put forward. The new algorithm can calculate the equivalent instantaneous inductance accurately. So it is able to distinguish the inrush and fault current even in the case of low percentage short circuit to ground and low percentage inter-turn fault. Furthermore the paper makes use of the keystone of correlation coefficients to analyze the sampling data. Eventually, considering the effect of residual flux to the new algorithm, the grounding resistor connected to the transformer neutral point is used to reduce the inrush current magnitude and restrain the inrush transient. Thereby, the veracity of new algorithm is farther enhanced.