Flexible arc suppression method for single-phase to ground fault in distribution network based on Z-type grounding transformer
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摘要: 煤矿供配电系统通常采用中性点非有效接地方式，该方式下的供电线路多数采用电缆线路，井下供电系统复杂，使用的电压等级较多，发生单相接地故障时极易在接地点形成间歇性电弧。而现有中性点非有效接地配电网单相接地故障消弧技术存在消弧效果不佳、难以精准测量配电网对地参数等问题。我国煤矿10 kV变电站中变压器绕组最常用的接线方式是三角形接线，该方式需通过专用接地变压器（大多是Z型接地变压器）人为引出中性点连接消弧线圈。针对上述情况，设计了一种基于Z型接地变压器的配电网单相接地故障柔性消弧系统。当配电网发生接地故障初始时刻，首先实时测量配电网的三相电源电动势和中性点电压，当中性点电压幅值大于三相电源电动势的15%时，可判断为接地故障；对比三相电源电动势，其中电源电动势最小相为故障相。在单相接地故障发生后，迅速闭合故障相对应的快速投切开关，同时投入有源逆变器和Z型接地变压器功率转换模块，其中Z型接地变压器功率转换模块将中性点电压反相钳制接近于故障相电源电动势，中性点电压与故障相电源电压差值的幅值和相位由有源逆变器精确补偿，实现将故障点电压和电流抑制至零的控制目标。一定时间延时后切除快速投切开关，若中性点电压有效降低则可判断该故障为瞬时性接地故障，即可恢复配电网正常运行，否则判断为永久性故障，采取故障馈线隔离措施，恢复配电网正常运行。仿真结果表明，当单相接地故障过渡电阻为500 Ω和3 000 Ω时，仅通过Z型接地变压器功率转换，故障点电压和电流抑制率达79%~83%，不能完全达到消弧效果；投入柔性消弧系统可有效抑制故障点电压和电流，抑制率达98%以上，实现配电网单相接地故障的可靠消弧。Abstract: The coal mine power supply and distribution system usually adopts the neutral point non-effectively grounded method. Most of the power supply lines in this method use cable lines. The underground power supply system is complex and uses many voltage levels. When a single-phase to ground fault occurs, it is easy to form intermittent arcs at the grounding point. Moreover, the existing single-phase to ground fault arc suppression technology of the neutral point non-effectively grounded distribution network has the problem of poor arc suppression effect and difficulty in accurately measuring the parameters of the distribution network to the ground. The most common connection method of transformer winding in 10 kV substation of coal mine in China is delta connection. This mode needs to lead out neutral point and connect arc suppression coil artificially through special grounding transformer (mostly Z-type grounding transformer). In order to solve the above problems, a flexible arc suppression system for single-phase to ground fault of distribution network based on Z-type grounding transformer is designed. When the initial time of grounding fault occurs in the distribution network, the three-phase power supply electromotive force and the neutral point voltage of the power distribution network are firstly measured in real time. When the amplitude of the neutral point voltage is greater than 15% of the three-phase power supply electromotive force, it can be judged as a grounding fault. Compared with the three-phase power supply electromotive force, the phase with the smallest power supply electromotive force is the fault phase. After a single-phase to ground fault occurs, the fast switching switch corresponding to the fault phase is quickly closed. And the active inverter and the Z-type grounding transformer power conversion module are simultaneously put into operation. The Z-type grounding transformer power conversion module clamps the voltage of a neutral point in an opposite phase to be close to the electromotive force of the fault phase power supply. And the amplitude and the phase of the difference between the neutral voltage and the fault phase supply voltage are precisely compensated by the active inverter. Therefore, the control target of suppressing the voltage and the current at the fault point to zero is achieved. After a certain time delay, the fast switching switch is cut off. If the voltage of the neutral point is effectively reduced, it can be judged that the fault is a transient ground fault. And the normal operation of the power distribution network system can be restored. Otherwise, it is judged as a permanent fault. The measures to isolate the fault feeder are taken to restore the normal operation of the distribution network. The simulation results show that when the single-phase to ground fault transition resistance is 500 Ω and 3 000 Ω, the power conversion is only through the Z-type grounding transformer. The voltage and current suppression rate at the fault point reaches 79%-83%, which cannot fully achieve the effect of arc suppression. The flexible arc suppression system can effectively suppress the voltage and current at the fault point, with a suppression rate of more than 98%, realizing reliable arc suppression of single-phase to ground faults in the distribution network.
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图 4 中性点非有效接地配电网单相接地故障仿真模型
Figure 4. Simulation model of single-phase to ground fault of neutral point non-effectively grounded distribution network
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图 5 故障相电源电压相反数和中性点电压仿真波形(过渡电阻500 Ω)
Figure 5. Simulation waveforms of the opposite number of the fault phase power supply voltage and the neutral point voltage (transition resistance 500 Ω)
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图 8 故障点电压、故障点电流和消弧装置注入电流仿真波形(过渡电阻3 000 Ω)
Figure 8. Simulation waveforms of fault point voltage, fault point current and injection current of arc suppression device (transition resistance 3 000 Ω)
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图 6 故障点电压、故障点电流和消弧装置注入电流仿真波形(过渡电阻500 Ω)
Figure 6. Simulation waveforms of fault point voltage, fault point current and injection current of arc suppression device (transition resistance 500 Ω)
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图 7 故障相电源电压相反数和中性点电压仿真波形(过渡电阻3 000 Ω)
Figure 7. Simulation waveforms of the opposite number of the fault phase power supply voltage and the neutral point voltage (transition resistance 3 000 Ω)
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图 9 故障相电源电压相反数和中性点电压仿真波形(过渡电阻500 Ω)
Figure 9. Simulation waveforms of the opposite number of the fault phase power supply voltage and the neutral point voltage(transition resistance 500 Ω)
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图 12 故障点电压、故障点电流和柔性消弧系统注入电流仿真波形(过渡电阻3 000 Ω)
Figure 12. Simulation waveforms of fault point voltage, fault point current and injection current of flexible arc suppression system (transition resistance 3 000 Ω)
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图 10 故障点电压、故障点电流和柔性消弧系统注入电流仿真波形(过渡电阻500 Ω)
Figure 10. Simulation waveforms of fault point voltage, fault point current and injection current of flexible arc suppression system(transition resistance 500 Ω)
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图 11 故障相电源电压相反数和中性点电压仿真波形(过渡电阻3 000 Ω)
Figure 11. Simulation waveforms of the opposite number of the fault phase power supply voltage and the neutral point voltage(transition resistance 3 000 Ω)
表 1 不同过渡电阻下仿真结果
Table 1 Simulation results under different transition resistances
过渡电阻/Ω −EA/V UN/V Uf/V If/A I1/A 500 未投 5 759 4 810 3 032 6.06 无 投入 5 759 5 854 649 1.30 2.42 3 000 未投 5 759 1 530 5 169 1.73 − 投入 5 759 5 841 910 0.30 3.36 
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表 2 不同过渡电阻下仿真结果
Table 2 Simulation results under different transition resistances
过渡电阻/Ω −EA/V UN/V Uf/V If/A I1/A 500 未投 5 759 4 810 3 032 6.06 无 投入 5 759 5 765 61.06 0.12 3.49 3000 未投 5 759 1 530 5 169 1.73 无 投入 5 759 5 852 62.79 0.02 3.55
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