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Wu W.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Song S.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Zhang X.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2012

A mal-operation of line No.I zero-sequence protection of 110 kV wind farm booster station is resulted from a out-area single-phase ground fault occurring on 110 kV regional power grid grounding system. The unearthed transformer neutral point protection gap strike and discharged in booster station is the fault cause, which is found by the recorded fault waveforms and scene investigation. In addition, it also points out the existing problems due to relay settings improper coordination in substation and problem of neutral point protection gap arrangement for main transformer. Through detailed theoretical analysis on the mal-operation according to the area power system situation, an improving measure to avoid protection malfunction is put forward. The application results on site of substation are verified effective. Source


Wu W.-C.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Wu Z.-Y.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Bian J.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Wang Y.-F.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company
Gaoya Dianqi/High Voltage Apparatus | Year: 2011

In the power system without neutral grounding, due to the nonlinear characteristic of excitation inductance of three-phase electromagnetic potential transformer, the ferroresonance overvoltage is easy to occur under a certain condition, leading to breakdown of the inner insulation, discharge of the external insulation, and blowing of the fuse. This accident often results in outage in large area because of delay in dealing with. This paper analyzed two ferroresonance overvoltage accidents caused by 10 kV single-phase grounding and 35 kV single-phase grounding, which induced the capacitor at 10 kV side to transfer overvoltage. The causes of the accidents were found, and the prevention measures were suggested correspondingly. Examples support the measures. Source


Wu W.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Bian J.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company | Wu Z.,Wuzhong Electrical Power Bureau of Ningxia Electrical Power Company
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2011

The switch-on of an electric transformer without load or the voltage recovery after its external fault is removed will induce the sympathetic inrush in its adjacent transformer, which may result in the misoperation of differential protection and back-up protection of the adjacent transformer. Based on the flux variation, the principle of sympathetic inrush generation is summarized and its characteristics in waveform and variation are analyzed. Simulation with two single-phase transformers demonstrates that, the flux variation caused by the terminal voltage change induces the sympathetic inrush. It is pointed out that, one of three phase sympathetic inrushes is symmetry when three-phase transformer is switched on without load and the difference of harmonic current decay between two sides of transformer causes the misoperation of differential protection. Source

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