A DC grounding search method with self-compensating current

Abstract

A DC grounding search method with self-compensating current. First, use a clamp DC ammeter to measure the line current value I, and then the DC current source outputs the compensation current I through the shielded wire. The shielded wire passes through two precision clamp meters successively in opposite directions, and then Make the two clamp meters respectively clamp the two conductors of the DC system to be tested. The direction of the jaws is opposite to the direction of the compensation current. Adjust the compensation current so that the reading of the clamp meters is close to zero and then maintain the output. The two clamp meters are connected to the wave recorder and other data acquisition. The instrument is used for integration, and the integration is divided by time to obtain the average value of the current. If the difference between the two average values ​​is close to the deviation of the calculated leakage current, then there is a grounding point in the branch. The invention solves the problem of insufficient measurement range of the precision clamp meter, and at the same time, two clamp meters perform data comparison, which can conveniently measure and compare currents at different locations on the wire. Therefore, this method accurately finds the grounding point of the DC system by finding the leakage current.

Description

technical field [0001] The invention relates to the field of fault detection of electric power systems, in particular to a method for finding DC grounding in electric power systems. Background technique [0002] DC grounding is one of the common faults of DC operating power supplies in power systems. When a point ground fault occurs in the DC system (directly grounded or the insulation resistance to the ground is reduced), there will generally not be immediate harmful consequences, but if two points are grounded at the same time, it may cause damage to the signal device, control circuit and relay protection device. The malfunction of the circuit breaker will cause the trip of the circuit breaker, or directly cause the short circuit of the DC operating power supply, thus causing serious power system accidents. Therefore, the DC system is not allowed to run for a long time with one point grounded. The DC operating power supply must be continuously monitored online. When a gr...

AI Technical Summary

Problems solved by technology

Since the field device is inconvenient for power failure operation and cannot be connected to the ammeter for measurement, only some indirect methods can be used to find the grounding point

[0004] The more commonly used DC grounding methods are: ①The method of pulling the road, that is, by cutting off the loads of each circuit, the grounding point is obtained by the method of elimination. This method requires load reversal, and the operation is complicated and extremely dangerous.

② clamp DC ammeter measurement method, such as figure 1 As shown, the load line is simultaneously clamped with a clamp DC ammeter, and the reading of the ammeter is the leakage current I', but this method has shortcomings: First, because the value of I' is very small, even lower than 1mA, it can measure the precision voltage lower than 1mA The jaws of the clamp ammeter are very small to achieve high precision. The site conditions may not be able to clamp two specific wires at the same time, or the wires are too thick to clamp two wires at the same time.

Second, this method can only measure the current difference between two parallel wires, but cannot measure the current difference between two specified points on one wire, and the field application range is limited

Therefore, this method is not convenient to find the DC grounding point

③Injecting AC signal method: By connecting an external 10V AC current source, use a clamp AC ammeter to measure the AC signal flowing in the line to determine the grounding point. The disadvantage of this method is that 5% to 10% of the AC signal brings safety hazards to the DC system, and there is currently no industry standard for this aspect, and neither the manufacturer nor the power supply bureau has conducted a risk assessment on it

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