High-speed reclosing, switching surges, and bus differential protection security - A case study

During an ice storm with high winds, a dual-circuit 345 kV transmission line owned and operated by American Electric Power (AEP) tripped correctly for galloping conductors. On the subsequent high-speed reclose, a high-impedance bus differential relay located over 50 miles from the reclosing breaker operated. Analysis of time-aligned and high-resolution event data from multiple locations on the system helped determine that the reason for the differential operation was a transformer surge arrester operation. In this case, there was a trapped charge on the line that operated and the high-speed reclose occurred at just the right moment to lead to a large transient overvoltage on the system. In this paper, we use high-resolution event data to discuss switching surges caused by high-speed reclosing on high-voltage lines and their impact on bus differential relays. We show that without high-resolution data, the root cause of this event would have been very difficult to determine. In fact, higher sampling rates would have aided in the analysis of the event and helped show the propagation of the switching surge in the adjacent line. We discuss enhancements to maintain security during a surge arrester operation for both low-impedance and high-impedance differential relays. Some of the enhancements discussed are internal to the relay designs, while others require the relay user to implement custom logic. An overview of line capacitance and its effects on switching surges is covered. AEP is a pioneer in detailing switching surges in high-voltage systems and has published a wealth of information on the topic. This paper provides a brief history of AEP's work in this field and applies previous research to this event.