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| Generator Stator Winding Ground Fault Location Algorithm Based on Third Harmonic Potential Distribution Characteristic |
| Wang Yikai1,2, Yin Xianggen1,2, Tan Liming1,2, Qiao Jian1,2, Zhu Lingjin1,2 |
1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Wuhan 430074 China;
2. Hubei Electric Power Security and High Efficiency Key Laboratory Huazhong University of Science and Technology Wuhan 430074 China |
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Abstract Floating nuclear power plant operates in a wet and salty environment. The main equipment in the power system is easy to be corroded, and generator stator winding ground faults occur frequently. To avoid the power loss of the nuclear reactor loads caused by the generator's blind and rapid tripping, the active arc suppression technology is adopted to realize stator ground fault arc suppression and achieve smooth load transfer. The difference between the active arc suppression technology of the generator and the distribution network lies that: the applied voltage in the neutral point is different for ground faults at different fault points on the stator windings. Therefore, reliable fault point location should be realized.
For the problem of generator stator ground fault location, the influence of the winding structure and operating condition should be considered. The existing ground fault location methods usually utilize the fundamental zero-sequence voltage. They can obtain accurate location results in most fault scenarios. However, in some fault scenarios, when the fault transition resistance is large or the fault point is close to the neutral point, multiple solutions are easy to be located. And it cannot provide reliable location guarantee for active arc suppression technology. Aiming at the problems of the existing fundamental potential based location methods, a new location algorithm based on the third harmonic potential distribution characteristics is proposed. Based on the 180° phase-band distribution of the third harmonic potential of each coil, the geometric relation between the third harmonic fault potential and the third harmonic phase potential is constructed. Taking the third harmonic fault current as the intermediate quantity, the analytical location equation containing the third harmonic fault potential, neutral grounding voltage and neutral grounding voltage variation is established. Grounding transition resistance is not included in the equation, which is suitable for the generator in the floating nuclear power plant without injection protection equipment.
Simulation results show that under different generator stator windings ground fault scenarios, the location error is within ±1%, which has a high accuracy under different fault points and fault transition resistances. Dynamic test results show that the proposed method can realize accurate ground fault location under different load conditions, and it is not affected by operating conditions and excitation regulation. In engineering application, the existing fundamental voltage based method can be combined with the proposed third harmonic based method proposed in this paper. When the fundamental voltage based method has multiple location solutions, the closest solution of the two location methods is taken as the final localization result.
The following conclusions can be drawn from the simulation analysis: (1) The existing ground fault location methods based on fundamental zero-sequence voltage have some problems and cannot provide reliable location guarantee for active arc suppression technology. (2) Based on the distribution characteristics of the 180° phase-band of the third harmonic potential of the stator windings, the analytical locating equation including the third harmonic fault potential, the third harmonic neutral point voltage and the third harmonic neutral point voltage variation is established in this paper. It does not include the fault transition resistance and is applicable to floating nuclear power plant generators without injection protection equipment. (3) Simulation and dynamic model test results show that the proposed method has high accuracy and is not affected by fault location, fault transition resistance and operating conditions. This method can cooperate with the fundamental location method to eliminate the location dead zone and solve the multi-solution problem of the fundamental voltage based location method. (4) The proposed method is applicable to generators whose stator windings meet the characteristics of 60° phase-band distribution and whose neutral point is grounded by high resistance.
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Received: 04 May 2022
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2023, Vol. 38 
