Treatment of single-phase grounding fault in the h

Treatment of single-phase grounding fault in small current grounding system

when a single-phase grounding fault occurs in a small current grounding system, because the size and phase of the line voltage remain unchanged (still symmetrical), and the insulation and drug release of the system are designed according to the line voltage, it is allowed to operate for a short time without removing the fault immediately. The operation time with grounding fault is generally not more than 2 hours for 10 kV and 35 kV lines, This is mainly limited by the allowable operation time of voltage transformer and arc suppression coil with grounding

1 judgment of grounding fault

one phase high voltage fuse of voltage transformer is blown, and the grounding signal is reported

distinguishing basis: in case of ground fault, the fault phase to ground voltage decreases, the non fault phase to ground voltage increases, and the line voltage remains unchanged. When one phase high voltage fuse of voltage transformer is fused, the voltage to ground decreases in one phase, and the voltage of the other two phases remains unchanged, and the line voltage indication will decrease

and all of them are general brands. When the transformer is used to close and charge the no-load bus, the three-phase closing of the circuit breaker is in different periods, and the three-phase capacitance to the ground is unbalanced, causing the neutral point to shift, the three-phase voltage is asymmetric, and the grounding signal is reported

distinguishing basis: this kind of situation occurs during operation. It can be judged as long as there is no abnormality in the bus and connecting equipment. Input a line or a substation, and the grounding signal will disappear

the three-phase parameters in the system are asymmetric, and the compensation degree of the arc suppression coil is improperly adjusted. When operating in the reverse operation mode, the grounding signal is reported

distinguishing basis: this kind of situation usually occurs when there is reverse operation mode in the system. After reporting and scheduling, we can know when we get in touch with each other. The original operation mode can be restored first, and the arc suppression line 11. Load control accuracy: 1% of the cycle that is better than the indicated value can be cut off, and then the tap can be adjusted, and then it can be put into operation, and then the reverse operation mode operation can be carried out

when closing the no-load bus, ferromagnetic resonance overvoltage may occur and a grounding signal may be reported

distinguishing basis: the voltmeter has one-phase, two-phase and three-phase indications that will exceed the line voltage or swing at low frequency, and the needle will hit the end. It can be divided into fundamental resonance, high-frequency resonance and frequency division resonance

2 search and treatment methods of single-phase grounding fault

2.1 identify the nature and phase of the fault

according to the judgment basis of grounding fault, first identify the nature and phase of the fault, and take measures to search and deal with it after it is determined to be a grounding fault

2.2 reduce the scope of sub operation

sub operation includes sub operation of the system and sub operation in the substation. The sub operation of the system should be carried out under the unified command of the dispatcher, and consider the power balance between various parts, the mutual cooperation of relay protection, and whether the compensation degree of arc suppression coil is appropriate. For the substation, dividing is to operate the bus section by section, narrow the scope, and find a section of bus with grounding signal

2.3 check the equipment in the station

after determining the fault range, a comprehensive external patrol inspection shall be carried out for the primary equipment in the station within the fault range. Mainly check whether the porcelain part of the equipment is damaged, whether there is discharge flashover, whether there is falling objects, small animals and external force damage on the equipment, whether each lead wire is broken and grounded, and whether the mutual inductor, lightning arrester, cable head, etc. are broken and damaged

2.4 but it has stricter specifications and inspection standards. Check the fault treatment of equipment in the station.

the fault point can be isolated by circuit breaker. The equipment outside the circuit breaker such as current transformer, outgoing wall bushing, outgoing lightning arrester, cable head, coupling capacitor, line side disconnector, etc. were found to be faulty. Report to the dispatcher and disconnect the circuit breaker to isolate the fault after transferring the load. Open the disconnectors on both sides of the faulty equipment, report to the relevant superior leaders, take safety measures, and wait for the maintenance personnel to repair the faulty equipment

the fault point can only be isolated with an isolating switch. At this time, the grounding fault and line load current must not be pulled off by the disconnector. Report to the dispatcher and isolate the fault point by using the reverse operation mode according to the main wiring and operation mode of the primary system of the station. For those that cannot operate in reverse mode, the fault point can be transferred by manual grounding method, and then the fault point can be disconnected by circuit breaker

the fault point is on the bus. It is found that the isolation point is on the bus and cannot be isolated. The isolated bus should be powered off for maintenance. If the double bus is connected, the whole load can be switched to another bus for power supply. In other cases, the user's load should be transferred first, and then the bus should be stopped