Analysis of complex electromagnetic transient leading to the mal-operation of power transformer differential protection

作者：Weng Han Li^*; Lin Xiang Ning

来源：Proceedings of the CSEE, 2009, 29(13): 65-71.

• 2nd harmonic restraint criterion
• Electromagnetic transient
• Inrush
• Nonlinear load switching in
• Transformer differential protection

When a nonlinear load with high capability, such as a furnace, is switched in a transformer-involved power system, the interactions among various electric quantities make the analyses complex because the transformer is located in a network with two nonlinear components. In this case, the mal-operation of transformer differential protection is difficult to analyze and usually attributed to a category of uncertain reasons. In order to illustrate the mechanism of differential protection mal-operation, a novel model including transformer and nonlinear load was proposed and the analytic and numerical analyses were done. Based on this model, a system of non-linear differential equations was formed. The waveform and harmonic characteristic of the differential current during nonlinear load switching in were analyzed. It is pointed out that when the nonlinear load is switched in, the interaction between two nonlinear components makes the transformer core to enter and stay within the area around the saturation point. Therefore, the differential current may exceed the threshold and the percentage of second order harmonic is low, which leads to the mal-operation of the differential protection. The conclusions were verified by simulation tests. ? 2009 Chin.Soc.for Elec.Eng.

• 出版日期2009
• 单位华中科技大学