Abstract：Currently, high-voltage/ultra-high-voltage transmission lines mainly adopt unit protections as their main protection. However, considering communication failure, transmission time delay, and expensive construction cost for unit protections, non-unit protections, such as impedance relays, as complementary protection functions with the unit protections, play an indispensable role in the safe operation of the power grid. Due to protection selectivity and reliability, it is difficult for non-unit protections to cover the full length of the protected line. That is, there is a protection non-detection zone, usually the high-resistance zone within the protection scope, and all zones outside the protection scope of the protected line. In order to accelerate the fault clearing in the non-detection zone, non-unit protections must realize reliable identification of non-detection zone faults, namely, the fast sequential action principle. Therefore, many scholars have presented many achievements in early research. However, the performance of the existing fast sequential action principle is limited by operating conditions and system parameters, and they cannot withstand high fault resistance. Therefore, constructing a novel fast sequential action principle to overcome the above problems is urgent. This paper presents a novel fast sequential action principle based on the secondary oscillating traveling waves generated by remote circuit breaker operation. Firstly, the differences in the secondary oscillating traveling waves process under the internal non-detection zone and external faults are studied using the Bewley lattice diagram. The secondary oscillating traveling waves under different fault locations exhibit significant differences in oscillatory period and wave front polarity. Secondly, the local relay can always detect the secondary oscillating traveling waves generated by faults on the adjacent line. However, for the secondary oscillating traveling waves generated by internal fault, whether it can be effectively detected needs to analyze the reflection and refraction coefficient of the fault point. Therefore, the propagation processes of secondary oscillating traveling waves under different fault types are investigated based on the modulus equivalent circuit. And the special traveling waves processes under BC and ABC metallic faults are discussed. Afterward, the identification criterion of oscillating traveling waves' polarity based on the mathematical morphology gradient algorithm is proposed, which can deal with the most fault conditions in the non-detection zone. Otherwise, the additional criterion for BC metallic fault is constructed based on the Zone-2 impedance relay. For ABC metallic fault, an active scheme based on the signal injection and a passive scheme based on blocking fast sequential action principle are proposed, respectively. Finally, based on the PSCAD simulation platform, the proposed protection criterion's effectiveness, sensitivity, and reliability are verified through extensive simulation cases. The criterion adaptability to noises, the scope of the non-detection zone, the unloaded lines, and the tripping modes of the circuit breaker are analyzed. Compared with the existing schemes, the proposed approach is suitable for three-pole/single-pole tripping and all fault types, unaffected by operating conditions and system parameters, and can endure fault resistance up to 300 Ω. However, due to the sampling frequency having an upper limit, the oscillating frequency of secondary traveling waves processes is too high to be detected when the fault is extremely close to the opposite bus. In other words, there is a dead zone for the proposed fast sequential action principle. Although the preliminary solution is proposed based on the Zone-2 impedance relay, it can still not effectively cope with the high resistance fault in the dead zone, which is worth further studying.
吴宇奇, 肖澍昱, 黎钊, 李正天, 林湘宁. 基于二次振荡波过程的交流电网相继速动判据[J]. 电工技术学报, 2023, 38(24): 6695-6708.
Wu Yuqi, Xiao Shuyu, Li Zhao, Li Zhengtian, Lin Xiangning. The Fast Sequential Action Principle for AC Power Grid Based on the Secondary Travelling Waves Processes. Transactions of China Electrotechnical Society, 2023, 38(24): 6695-6708.
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2023, Vol. 38 
