The Study On Improved Scheme Of EHV Shunt Reactor Differential Protection

With increasing demand about large capacity and long distance for EHV(Extra High Voltage)and UHV(Ultra-High Voltage),the importance of EHV shunt reactor is becoming more and more significant in recent years.The EHV shunt reactor can compensate circuit distributed capacitive,balance reactive power,optimize the voltage on the transmission line,prevent overvoltage resonance issue and then speed up power flow automatically extinguished.So the EHV shunt reactor is very important to ensure power grid operate safely.This paper analyses the principle and research status on shunt reactor in the EHV transmission lines,and at the same time find out the problem of shunt reactor protection in Mongolia power grid.When the head end and last end variable ratio of shunt reactor has big difference,there may be differential protection mis-operation issue.For this issue this paper analyzes the impact on current transformer differential protection about selection variable ratio between head and last end,studies the error reasons of current transformer and relevant factors.Based on this,puts forward the EHV shunt reactor differential protection improvement methods: change the head end winding to reduce its variable ratio,thus narrowing the variable ratio difference between head and last end of current transformer;Increase zero-sequence differential protection lock criterion to reduce the impact of current distortion which is due to excitation power.The improved methods has good performance in dynamic simulation and actual running.The improvement methods make sure the EHV transmission lines with parallel reactor operate safely and 500 kV power grid operate stable.At the end of the paper,the reasonable variable ratio range between head and last end is given when selecting the EHV shunt reactor.