Study on Loss of Excitation Fault Analysis and Protection of Variable Speed Pumped Storage Units
Lu Qinghui1, Yin Xianggen1, Qiao Jian1, Wang Yikai1, Yin Xin2
1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Wuhan 430074 China; 2. School of Electrical and Information Engineering Changsha University of Science & Technology Changsha 410114 China
Abstract：The excitation and control methods of variable speed pumped storage units (VSPSU) are complex and prone to the loss of excitation (LOE) fault. Therefore, it is very important to configure targeted protection to ensure its safe operation. Due to the special three-phase AC excitation method used in VSPSU, its LOE fault is quite different from that of conventional units. At present, the LOE protection scheme of the traditional DC excitation synchronous machine is relatively mature, but there are few studies on the LOE fault characteristics and LOE protection of the AC excitation doubly-fed machine, and a reliable protection scheme has not yet been formed. To ensure the safe operation of VSPSU, this paper analyzes the characteristics of the LOE fault of the VSPSU in detail and puts forward the corresponding LOE fault protection scheme on this basis. Firstly, based on the difference analysis between the DC excitation system and the AC excitation system, the LOE fault of VSPSU is divided into two types: symmetrical LOE and asymmetrical LOE, and the research is mainly carried out on the symmetrical LOE. Secondly, the fault characteristics and fault hazards of VSPSU symmetrical LOE are analyzed from the point of view of the fault located on the machine side and the grid side, respectively, and the importance of configuring LOE protection for VSPSU is clarified. Then, the adaptability of the traditional LOE protection criterion based on impedance circle when applied in VSPSU is deduced and analyzed. Finally, based on the characteristics of the operating power of the VSPSU after LOE and the corresponding relationship with the impedance, the criterion of the downward throwing impedance circle is proposed for machine-side symmetrical LOE fault; based on the reflection characteristics of DC voltage on the damage of rotor-side power exchange channel, a DC voltage criterion for grid-side symmetrical LOE fault is proposed. The combination of the two forms a protection scheme against the symmetrical LOE fault of the VSPSU. The research has the following conclusions: (1) When a symmetrical LOE fault occurs on the machine side, the operating power of the VSPSU will quickly drop to the operating power point of the LOE Leading Phase Operation. At this time, the VSPSU is no longer under control and will absorb a large amount of reactive power from the grid. When a symmetrical LOE fault occurs on the grid side, it will have different characteristics of the LOE fault based on different rotor active power flow directions, but all of them will cause the DC capacitor voltage to jump or drop. The symmetrical LOE fault of VSPSU will cause harm to the power grid and the unit itself, so it is necessary to be equipped with LOE protection. (2) The traditional LOE protection scheme based on a statically stable boundary impedance circle and asynchronous operation impedance circle has misoperation and refusal to operate when applied in VSPSU, which cannot meet the reliability requirements of VSPSU for LOE protection. (3) The PSCAD/EMTDC simulation results show that the proposed downward throwing impedance circle criterion and DC voltage criterion can effectively detect the symmetrical LOE fault of VSPSU under various operating conditions, and meet the reliability requirements of VSPSU for LOE protection.
卢庆辉, 尹项根, 乔健, 王义凯, 尹昕. 变速抽蓄机组失磁故障分析及保护研究[J]. 电工技术学报, 2024, 39(5): 1390-1403.
Lu Qinghui, Yin Xianggen, Qiao Jian, Wang Yikai, Yin Xin. Study on Loss of Excitation Fault Analysis and Protection of Variable Speed Pumped Storage Units. Transactions of China Electrotechnical Society, 2024, 39(5): 1390-1403.
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2024, Vol. 39 
