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Talking about the Characteristics of Single Phase Earth Fault
Power grid short circuits generally fall into four categories, with the three-phase short circuit being the most severe. Among them, single-phase grounding faults are the most common. In practical operations on 10kV distribution lines, single-phase grounding issues frequently arise, particularly during harsh weather like rainy seasons, strong winds, or snowstorms. For instance, in 2005, out of 24 anomalies at the Longsha Power Supply Bureau in Heilongjiang Province, seven were due to single-phase grounding. In 2006, this number rose to eight out of 31 anomalies. After a single-phase grounding fault occurs, the voltage at the fault point drops, while the phase voltages of the unaffected phases increase. However, the line voltage remains symmetrical, ensuring uninterrupted power supply to users. This small current grounding system has the advantage of allowing the system to continue operating for up to two hours. Nevertheless, prolonged operation post-fault can severely impact the safety and economic performance of substation equipment and the distribution network.
To prevent such incidents, there should be no obstructions like buildings or trees within a specific range around the wires, creating what’s known as a “transmission corridor.†These problems mostly stem from load imbalances. Common causes include wire breaks, insulator failures, or tree contact leading to short circuits.
When a ground fault occurs, the system triggers an alarm: the bell rings, signaling "a certain kV bus ground" with a lit light panel. Additionally, in an arc suppression coil neutral point grounding system, the "arc suppression coil operation" light illuminates. On an insulation monitoring voltmeter, the fault phase voltage decreases (in partial grounding) or becomes zero (in complete grounding), while the other two phases experience an increase in voltage, either higher than the phase voltage (partial grounding) or equal to the line voltage (complete grounding). If the voltmeter pointer does not oscillate, the grounding is steady; if it swings continuously, it indicates intermittent grounding.
In an arc suppression coil grounding system equipped with a neutral point displacement voltmeter, the indicator shows a certain reading (partial grounding) or displays the phase voltage value (complete grounding), accompanied by an arc suppression coil grounding alarm light. During arcing, overvoltage occurs, causing the voltage of the non-faulted phase to rise. This can lead to the blowing of high-voltage fuses in the voltage transformers and, in some cases, burn out the transformers themselves.
Understanding these phenomena helps operators respond promptly and effectively to mitigate risks and maintain grid stability.