Optimization of Differential Protection for Converter Transformers Based on Lateral Differential Current Identification

In response to the problem of slow differential protection action caused by the continuous blocking of the second harmonic braking criterion during the actual inter turn short circuit fault of ultra-high voltage converter transformers, this article analyzes the characteristics of inrush current and developmental inter turn short circuit faults in converter transformers through theoretical analysis. It is found that by comparing the corresponding differential current of two parallel operating converter transformers horizontally, the inrush current and inter turn fault of converter transformers can be identified. Based on this, Propose an optimization method for differential protection of converter transformers based on lateral differential current identification. Through on-site waveform recording and real-time digital simulation system (RTDS) simulation verification, the proposed protection method has high speed in the event of inter turn short circuit fault and second harmonic braking criterion mislocking. For actual faults that expose problems, the protection action time is shortened from 56 ms to 23.6 ms. At the same time, it ensures reliable and reliable operation under various inrush current conditions.