System and method for determining direct-current system fault branch circuits needing to be in in-series connection with alternating currents

Abstract

The invention relates to a system and method for determining direct current system fault branch circuits needing to be in in-series connection with alternating currents. The system comprises an on-line monitoring device, wherein the input of the on-line monitoring device is connected with the positive electrode and the negative electrode of a direct current bus and the ground; a plurality of fault locating devices are arranged in various direct current branch circuits respectively, and the on-line monitoring device is connected with each fault locating device through a communication bus. The method comprises the steps that 1) positive electrode voltage to ground U+, negative electrode voltage to ground U- and in-series connected alternating voltage Uac of the direct current bus are detected, and when the Uac is greater than a set value Uaca, the situation that a direct current system has alternating current in-series connection faults is determined; 2) when the U- is less than or equal to delta U, the situation that the alternating currents are connected to the direct current system in series through the positive electrode is determined; when the U+ is less than or equal to the delta U, the situation that the alternating currents are connected to the direct current system in series through the positive electrode is determined; 3) leak currents of all the branch circuits of the direct current system are detected and ordered, the branch circuit having the maximal leak current value is the branch circuit needing to be in in-series connection with the alternating currents. According to the system and method, an alternating current sensor does not need to be additionally arranged, and system cost is saved. Meanwhile, according to the scheme, signal injection does not exist, and therefore increase of ripples of the direct current system will not be caused, the problems that a relay mistakenly moves and a breaker mistakenly trips are solved, and reliability is higher.

Description

technical field [0001] The invention relates to a system method capable of determining a faulty branch of alternating current connected to a direct current system, and belongs to the field of direct current IT system monitoring. Background technique [0002] In the power system, the reliable operation of the DC power supply plays a very important role in the safety and stability of the system. Due to the wear and tear of the AC and DC cables in the long-term operation, or the damage of the components of the AC and DC devices, or the carelessness of human operation , will cause the alternating current to flow into the direct current system. Accidents in power plants and substations in recent years have shown that after AC is connected to the DC system, it is easy to cause relay protection malfunction or circuit breaker tripping, such as "Analysis of the Causes of Switch Tripping Caused by AC Connecting to DC Circuit" (Relay, The article No. 14 in 2007) introduced the general...

AI Technical Summary

Problems solved by technology

For the DC insulation monitoring device using the signal injection method, the branch where the AC series fault occurs can be located by detecting whether there is an AC current on the branch; while for the insulation monitoring device using the DC leakage current method, because the DC leakage current sensor cannot detect AC current, so the fault location of AC series connection cannot be realized

Because the signal injection increases the ripple of the DC system, it often brings problems such as relay protection misoperation and circuit breaker tripping to the DC system, which has potential safety hazards to the DC system and relay protection system, so the DC system using the signal injection method Insulation monitoring devices are gradually being phased out; and DC insulation monitoring devices using the DC leakage current method need to add AC sensors in each branch to realize the fault location of AC series input, which increases the cost of the system

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