Line selection method for single-phase earth fault line of small current grounding system

Abstract

The invention discloses a line selection method for a single-phase earth fault line of a small current grounding system, and belongs to the electric power cable fault on-line monitoring field. The line selection method comprises a plurality of cables in the same bus with a small current grounding mode, and is characterized in that: transient current signals flowing through each cable outgoing line metal shielding layer grounding line are monitored and recorded through a high speed collection method, the transient current signals are generated by a fault loop when the single-phase grounding fault of the small current grounding system happens; and the fault line is selected by identifying the directions of wave heads of the transient current signals. The method compares the directions of the wave heads of grounding line current traveling waves of all the cables, and distinguishes a fault cable and a non-fault cable. In comparison with other small current grounding line selection methods at present, the accuracy of the line selection is high, and the multi-selection or missing report condition can be effectively avoided.

Description

technical field [0001] The invention belongs to the field of on-line monitoring of power cable faults, in particular to a line selection method for a single-phase ground fault line in a small current grounding system. Background technique [0002] Most of the distribution networks in my country adopt the neutral point not directly grounded system (NUGS), that is, the small current grounding system, which includes the neutral point ungrounded system (NUS) and the neutral point through the arc suppression coil grounding system (NES, also called resonant grounding system). When a fault occurs, since the three line voltages are still symmetrical, especially the NES, the current flowing through the grounding point is very small, which does not affect the continuous power supply to the load, and can still continue to run for 0.5 to 2 hours. However, when the small current grounding system is single-phase grounded, the non-faulty phase voltage will rise to the line voltage, and lon...

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Problems solved by technology

However, the fifth harmonic source in the load, the CT unbalanced current and the size of the transition resistance will all affect the line selection accuracy.

[0013] A serious shortcoming of the fifth harmonic method is that the fifth harmonic content in the fault current only accounts for about 10% of the fundamental wave, and the value will be smaller when the transition resistor is grounded, which is easy to cause misjudgment

If the automatic line selection scheme is adopted in the unattended substation, since the sensitivity of the signal detectors of each line is not consistent, it will bring difficulties to the correct line selection

Therefore, it is not very convenient to install the signal injection device

[0021] To sum up, for the single-phase ground fault of the power cable in the small current system, the existing line selection methods have their own limitations

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