DC Switch Yard with Unidirectional Main Circuit Breakers
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Solution Overview
Problem
Existing DC switch yards require costly main circuit breakers with bidirectional breaking capacity, which limits cost savings in high-voltage, medium-voltage, or low-voltage DC power grid interconnections.
Innovation Solution
Implementing a DC switch yard with at least two busbars interconnected through an intermediate main circuit breaker and fast disconnectors, where the main circuit breaker operates with unidirectional breaking capacity, allowing for sequential disconnection of DC lines from one busbar and subsequent disconnection of remaining lines from another, reducing the need for bidirectional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If main circuit breakers with bidirectional breaking capacity are used in DC switch yards, then the switch yard can handle faults in both directions, but the cost increases significantly
Solution Approach 1:
The invention divides the switch yard into multiple sections with separate main circuit breakers for each section. Each main circuit breaker only needs to handle faults in one direction (unidirectional breaking capacity), which reduces the cost of each breaker. The segmentation allows the system to achieve bidirectional fault protection through multiple unidirectional breakers rather than requiring expensive bidirectional breakers.
Solution Approach 2:
The invention introduces transfer switches that can dynamically reconfigure the circuit connections. When a fault occurs, the transfer switches redirect the fault current path so that unidirectional main circuit breakers can effectively protect against faults in both directions. This dynamic reconfiguration allows the system to maintain high reliability while using cost-effective unidirectional breakers.
2Ease of manufacture
If unidirectional main circuit breakers are used, then cost is reduced by approximately half, but the ability to handle bidirectional faults is limited
Solution Approach 1:
The transfer switches serve multiple functions: normal circuit switching, fault isolation, and reconfiguration of current paths. By making the transfer switches multi-functional, the system compensates for the limited unidirectional capability of the main circuit breakers, enabling the overall system to handle bidirectional faults effectively while maintaining cost savings from using unidirectional breakers.
Solution Approach 2:
The transfer switches act as intermediaries between the unidirectional main circuit breakers and the bidirectional fault currents. When a fault occurs in either direction, the transfer switches mediate by redirecting the fault current through appropriate paths, allowing the unidirectional breakers to effectively protect the system against faults in both directions.
3Reliability
If multiple main circuit breakers with bidirectional capacity are installed, then comprehensive fault protection is achieved, but the device complexity and cost increase
Solution Approach 1:
The switch yard is segmented into multiple independent sections, each protected by its own unidirectional main circuit breaker. This segmentation reduces the complexity compared to using fewer bidirectional breakers, as each breaker has a simpler, more specialized function. The modular structure makes the system easier to maintain and manage while achieving comprehensive protection.
Data Source
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AI summary
DC switch yard (1) comprising at least two busbars (2, 3) and two or more DC lines (5 - 8) forming a grid, wherein each DC line (5 - 8) is connected or connectable to said at least two busbars (2, 3) through an intermediate circuit breaker, wherein the at least two busbars (2, 3) are interconnected or connectable to each other through an intermediate main circuit breaker (4), and wherein each of said two or more DC lines (5 - 8) are connected or connectable to each of said at least two busbars (2, 3) through intermediate fast disconnectors. The switch yard is arranged to operate such that upon identification of a DC line to be disconnected from the grid, one of the fast disconnectors of said DC line is operated to disconnect said DC line from a first of the two busbars, and disconnectors of the remaining DC lines are operated to disconnect said remaining DC lines from a second of the two busbars, whereafter the main circuit breaker is operated to disconnect the two busbars from each other. The main circuit breaker and preferably also the fast disconnectors are arranged with unidirectional breaking capability.