Views: 179 Author: Site Editor Publish Time: 2020-10-08 Origin: Site
The power system can be divided into a large current grounding system (including direct grounding, reactance grounding and low resistance grounding) and a small current grounding system (including high resistance grounding, arc suppression coil grounding and ungrounding). Most of the 3~66kV power systems in China adopt the operation mode that the neutral point is not grounded or the arc suppression coil is grounded, that is, the low current grounding system. In the small current grounding system, the single-phase grounding is a common power short circuit fault.
In the actual operation of 10kV distribution lines, single-phase grounding cable short circuit faults often occur, especially in severe weather conditions such as rainy season, strong wind and snow.
After the single-phase grounding occurs, the voltage of the dead short circuit fault place will decrease, and the phase voltage of the non-faulty will increase, but the line voltage is still symmetrical, so it does not affect the continuous power supply to the user. The system can still run for 1 to 2 hours, which is the greatest advantage of the small current grounding system. However, if the power grid runs for a long time after a single-phase grounding electrical short circuit fault occurs, it will seriously affect the safe and economic operation of substation equipment and the distribution network.
1) The wire is broken to the ground or placed on the cross arm.
2) The wire is not firmly tied or fixed in the insulator, and falls off to the cross arm or the ground.
3) The wire is too close to the building due to excessive wind.
4) The high voltage down conductor of the distribution transformer is disconnected.
5) The insulation of 10 kV arrester or 10 kV fuse on the distribution transformer platform is broken down.
6) The single-phase insulation of the high-voltage windings of distribution transformers is broken down.
7) The insulator is broken down.
8) The insulation of branch fuses on the line is broken down.
9) One end of the pull wire of the upper cross arm erected on the same pole falls off and is placed on the lower wire.
10) Other accidental or unknown reasons.
1) Automatic Line Selection Device for the Small Current Grounding System
When the 10kV distribution line grounding short circuit voltage fault occurs, the automatic line selection device for the small-scale current grounding system can be used for automatic line selection. This small current-grounded automatic line selection device can be configured before the distribution line is grounded to measure the electrical circuit.
At the same time, for the practical application of distribution lines, more attention should be paid to the close cooperation between the automatic line selection device for a small current grounding system and the zero-sequence current transformers in the occurrence interval of each distribution line.
2) The Detection System of Single-phase Grounding Faults
In the current power distribution system, most of the substations have started to use signal sources, and their locations are located at the beginning, middle, and end of the power distribution line. The short circuit fault indicator can clearly tell us where the electric wire short circuit fault actually occurs, so we can deal with power line short circuit faults more quickly
3) The Following Preventive Measures Can Be Taken
Carry out regular inspections of power distribution lines, mainly including checking the distance between the wires and trees and buildings, whether there is a bird's nest on the top of the pole, whether the wire is bound or fixed in the insulator firmly, whether the fixing bolts of the insulator are loose, whether the cross arm and pull-line are loose, whether the cable is broken, whether the wire sag is too large or too small, etc.
Insulators, branch fuses, lightning arresters and other equipment on power distribution lines should be regularly tested for insulation, and those that are unqualified should be replaced in time.
4) Treatment Methods After the Single-phase Grounding Fault Occurs
When a short circuit and earth fault occurs in the distribution line, the substation personnel on duty should immediately make a record, promptly report to the on-duty dispatcher and relevant responsible personnel, and search for ground short circuit faults according to the on-duty dispatcher’s orders.
The earthing and short circuiting device is very helpful for troubleshooting cable faults. When troubleshooting cable faults, selecting a suitable fault indicator can greatly improve the accuracy and efficiency of detection.