一种特高压3/2接线纵差保护抗电流互感器饱和措施

A Current Transformer Saturation Countermeasure for Differential Protection of UHV Transmission Line with Breaker-and-a-half Configuration

特高压长线路3/2接线侧母线附近区外故障时2个分电流互感器都有可能饱和,使引入2个电流互感器和电流的相量差动保护遇到了较大困难。提出了一种实用抗电流互感器饱和措施,采用低电压启动判据筛选出可能引起电流互感器饱和的3／2接线侧母线附近的区内和区外故障,然后根据短数据窗电流不饱和的特点,采用适当的定值区分3/2接线侧母线附近区内故障差流和区外故障分布电容电流,从而通过闭锁防止区外故障因饱和误动。该方法已在实验样机中得到应用, 并成功地通过保护动模试验。

When an external fault occurs near the breaker-and-a-half busbar of UHV transmission line, two current transformers may become saturated. This can bring about great difficulty to the current phasor differential protection, which adopts an input current to be the sum of current of two current transformers. This paper proposes a countermeasure to the problem of mentioned current transformer saturation. The proposed scheme can identify the internal and the external faults near the breaker-and-a-half busbar which cause the problem of current transformers saturation by low voltage start-up. Because usually there is no current transformers saturation in the first short data window, it is not difficult to use a threshold to separate the internal faults differential current from the external faults capacitive current near the breaker-and-aLhalf busbar. Then the external fault mal-operation can be blocked which is caused by current transformer saturation. The proposed scheme has been applied to WXH-803 digital transmission line protection tester and passed EPRI dynamic experiments for 750 kV transmission line protection successfully.