DC Transmission Network Fault Isolation via N-1 Security System Segmentation
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Solution Overview
Problem
Current direct current (DC) transmission networks face challenges in quickly isolating faults to prevent widespread outages, as existing circuit breakers may not be able to open fast enough to manage high fault currents, leading to potential network instability and increased manufacturing costs.
Innovation Solution
A method for controlling a DC transmission network with a group of interconnected lines, each with two line circuit breakers, and converter stations associated with security systems capable of interrupting maximum short-circuit currents, where at least N-1 security systems open to isolate the faulty line by reducing current flow through line circuit breakers, allowing them to open even when current is still passing through, and disconnecting faulty converter stations to maintain network stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If all circuit breakers are configured to open immediately upon fault detection, then fault isolation speed is improved, but the breaking capacity requirement increases导致制造成本增加
Solution Approach 1:
The protection system is segmented into two functional layers: security systems at converter stations and line circuit breakers at line ends. Security systems handle the primary fault current interruption by opening N-1 systems, while line circuit breakers perform the secondary isolation function after current reduction, dividing the high breaking capacity requirement across different components with appropriate roles.
Solution Approach 2:
Security systems perform preliminary action by opening first to reduce the fault current before line circuit breakers operate. This preliminary current reduction allows subsequent line circuit breaker operation at lower current levels, reducing their breaking capacity requirements and manufacturing costs while maintaining fast overall isolation speed.
2Ease of manufacture
If circuit breakers wait for current to reach zero before opening, then breaking capacity requirements are reduced, but fault isolation time increases导致网络稳定性下降
Solution Approach 1:
Security systems perform preliminary current reduction by opening N-1 systems before line circuit breakers operate. This creates favorable conditions allowing line circuit breakers to open at reduced current levels without waiting for natural current zero, achieving both manufacturing cost reduction and maintained network stability through coordinated timing.
Solution Approach 2:
Security systems act as intermediaries that mediate between the fault and line circuit breakers. By opening first, they reduce the current stress on line circuit breakers, enabling these breakers to operate reliably at lower current levels without requiring excessive breaking capacity while maintaining fast isolation for network stability.
3Reliability
If N security systems open to isolate a faulty line, then fault isolation reliability is improved, but network availability decreases due to broader current interruption
Solution Approach 1:
The opening decision for security systems is made locally based on which N-1 systems can achieve fault isolation with minimal impact on network operation. This selective local decision-making optimizes the balance between reliable fault isolation and maintaining network availability by opening only the necessary minimum number of systems.
Solution Approach 2:
The system opens N-1 security systems (partial action rather than all N systems) to achieve sufficient fault isolation. This partial action provides adequate reliability for fault containment while minimizing the impact on network availability by keeping at least one converter station connected to the network.
Data Source
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Figure 5~6
AI summary
The control method allows the control of an installation (1) for transmitting electricity comprising a DC transmission network (3) including a group (2) of electricity transmission lines (4) that are linked to one another. The method allows the opening (E1) of at least one N-1 safety system (7) such that, for each safety system (7) being opened, the contribution to the flow of current through the group (2) of transmission lines (4), originating from the converter station (6) associated with said safety system (7) that is opened, is removed. Furthermore, the method also allows a search (E2) for the short-circuit fault in order to identify the faulty transmission line (4), and an operation (E3), implemented after identification of the faulty transmission line (4) by the search step (E2), of isolating the faulty transmission line (4) by opening the line circuit breakers (5a, 5b) of said faulty transmission line (4).