DC line relay protection method for multi-terminal flexible medium-voltage DC power distribution system

Abstract

The invention belongs to the technical field of power system relay protection and particularly relates to a DC line relay protection method for a multi-terminal flexible medium-voltage DC power distribution system. The method comprises the steps of main protection and the backup protection. The main protection reflects an inter-electrode short-circuit fault of a DC line and a unipolar grounding fault of a small transition resistor, wherein a fault type and a fault interval are identified based on a current state matrix. The backup protection adopts the duration of the voltage imbalance as a starting criterion, so as to protect a judging fault interval of positive and negative current imbalance state matrixes at an installation part and isolate faults. The method determines the action signal of a DC breaker according to the switching-on/off signals of the main protection and the backup protection. The main protection only depends on the status signal values -1, 0 and 1 of two adjacent protection and transmission current elements, so that the requirement on a communication system is reduced. The backup protection judges the occurrence of a fault only based on the voltage, wherein the unbalanced current calculation is aiming at the positive current and the negative current of the same protection part. Therefore, the generation of errors due to the communication delay or the non-synchronized communication can be avoided.

Description

technical field [0001] The invention belongs to the technical field of relay protection for power systems, and in particular relates to a DC line relay protection method for a multi-terminal flexible medium-voltage DC power distribution system. Background technique [0002] Introducing the flexible DC technology based on Voltage Source Converter (Voltage Source Converter, VSC) into the urban distribution network can solve some problems of the traditional AC distribution network. Its advantages are mainly reflected in: 1) Transforming the urban AC distribution network into Flexible DC distribution network can save line investment, and has the advantages of high power quality, large transmission capacity, high reliability, simple system structure, good economy and low power loss; 2) DC distribution network does not involve frequency stability and wireless 3) The flexible DC distribution network is conducive to the access of distributed power. Compared with the traditional AC ...

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Problems solved by technology

[0004] There are literatures that use overcurrent protection schemes for DC distribution networks, but the application of current-based protection is limited in complex distribution networks due to the difficulty in setting the protection values ​​in adjacent areas and the difficulty in achieving time coordination; another On the one hand, many studies have not considered the impact of converter topology and grounding mode on system fault characteristics when it comes to protection strategies

Some literatures have designed distance-measuring protection for flexible DC power distribution systems. When the distance protection is the main protection, the full length of the line cannot be protected, and it is difficult to calculate the accurate fault distance due to the influence of the transition resistance.

There are also literatures that apply differential protection to DC power distribution systems, but this scheme needs to compare the current values ​​at both ends synchronously. Due to the large current change rate of DC faults, small time differences will cause large calculation errors

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