ABSTRACT
Grade-skip trip incident is very common in coal mine high-voltage grid, but never be solved completely. It will not only expand the power off area, and also may cause gas accumulation because of the shutdown of fans. The main reason causing grade-skip trip is that both the fault feeder and the superior substation incoming line will receive fault signal when fault happens such as short circuit fault and single-phase earth fault, but fail to choose the right feeder switch to trip. Taking short circuit fault as example, optical fiber differential protection criterion can be used to solve grade-skip trip problem, but there are two requirements needed to be met. One is all the data should sampled synchronously, and the other is the trip decision should be made according to all the data in the whole power system. And WAMS (wide area measurement system) will just meet these two requirements.
