A novel accelerated trip scheme for AC grids based on open-switching traveling waves

Abstract

The delayed operation of a zone-2 impedance relay for handling faults on the end-section of a protected line can exacerbate power system instability. To accelerate the trip of a zone-2 circuit breaker (CB), many accelerated trip (AT) schemes have been proposed for AC power grids. However, these schemes remain by their pre-fault operating conditions, tripping modes, fault resistance, and fault types. Considering these limitations, this paper presents a novel AT scheme based on open-switching traveling waves (TWs) generated by CB operation. First, characteristic differences in the oscillation period and wavefront polarity of the open-switching TWs generated by remote CB operation under internal, remote busbar, and external faults are analyzed. Then, an identification criterion for open-switching TWs utilizing the order and number of wavefront polarities is proposed, thereby forming a new AT scheme. Finally, based on the PSCAD/EMTDC software, the effectiveness, sensitivity, and reliability of the proposed AT scheme are verified. The proposed AT scheme can operate at high speed without being affected by pre-fault operating conditions, tripping modes, or fault types, and its ability to endure fault resistance reaches 300 Ω.

Keywords

• Accelerated trip
• Open-switching traveling waves
• Circuit breaker operation
• Oscillation period
• Wavefront polarity