Abstract：The stator grounding arc fault is a technical bottleneck that restricts the safe and reliable operation of large generators. The continuous burning arc is prone to burn or melt the stator winding insulation and iron core. residual currents, active and harmonic currents of grounding faults is not eliminated completely by the existing methods. And it is difficult to limit the residual currents of grounding faults to the allowable value of safe grounding currents and cannot meet the requirements of existing regulations. By analyzing the variation characteristics of stator grounding arc suppression fault voltage and arc resistance, the flexible grounding method for stator grounding arcing fault voltage reduction and arc suppression is proposed. Firstly, the analytical relationship between the stator grounding arc resistance and the arc voltage was established. Then, during the voltage reduction at the stator grounding fault point, the stator arc resistance increase. The voltage at the grounding fault point is suppressed below the arc reignition voltage. So, the suppression method can achieve returning the breakdown gap of the stator winding to the normal insulation state. When the method of generator stator is the flexible grounding, the grounding fault point is output with the power frequency and third harmonic reverse electromotive. The voltage of the fault point is reduced to below the gradient of the arcing electric field. And the stator grounding arc is extinguished. By injection signals to sense the stator grounding fault status, the vector angle change trend of stator winding damping rate is real-time monitored. And the grounding arc fault is monitored during the voltage reduction and arc suppression process. In the proposed method, the fault point voltage is not required reducing to zero. The risk of breakdown in the slot of the stator winding is effectively avoided during the voltage rise of the non-fault phase. The proposed method was experimentally validated by simulating the arcing conditions of stator grounding faults in the PSCAD/EMTDC simulation environment. The experimental results showed that the flexible grounding voltage source was put into operation. The input potential amplitude was changed, and the fault point voltage was regulated. The fault point voltage value was lower than the arc breakdown voltage, and the stator grounding arc extinguished within 100 ms. The stator grounding arc is unable to reignite. After the flexible grounding voltage source is put into use for voltage reduction and arc suppression, the damping vector angle is less than 12°. And the change value is negative. The state of stator grounding arc burning out is effectively distinguished during the voltage reduction and arc suppression process. The following conclusions can be drawn from the analysis: (1) The field strength of the stator grounding fault through the gap is inversely proportional to the arc resistance. By reducing the voltage at the stator ground fault point, the electric field strength of the arc is reduced, and the arc resistance is increasing. So, the current at the fault point is reduced. (2) By utilizing a controllable voltage source in parallel with the stator neutral point, the voltage at the fault point is reduced to achieve reliable suppression of grounding fault arcs. (3) The voltage asymmetry of the stator system is reduced during the voltage reduction and arc suppression process in the method. the degree of voltage rise of the non-fault phase winding and the risk of breakdown can be reduce. The maximum displacement voltage shall not exceed the rated voltage of the system and shall be consistent with the stator voltage offset caused by natural ground faults.
李理, 喻锟, 曾祥君, 王沾, 贺世庚. 基于发电机定子接地燃弧电阻变化特征的主动降压熄弧机理与抑制方法[J]. 电工技术学报, 2024, 39(17): 5379-5393.
Li Li, Yu Kun, Zeng Xiangjun, Wang Zhan, He Shigeng. Mechanism and Suppression Method of Active Arc Extinguishing Based on the Variation Characteristics of Arc Resistance of Stator. Transactions of China Electrotechnical Society, 2024, 39(17): 5379-5393.
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2024, Vol. 39 
