HVDC Interconnection Equipment Using Superconductor Current Limiters
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Solution Overview
Problem
High-voltage direct current (HVDC) networks face challenges in rapidly and selectively breaking short-circuits, particularly in multinode transmission systems, where existing solutions are costly and imperfect in ensuring protection and selectivity.
Innovation Solution
An interconnection equipment item with at least three terminals connected to a node, each equipped with a superconductor current limiter and a controlled switch in series, where a capacitor injects energy to trip the limiter closest to the short-circuit, allowing selective opening of the switch without triggering other limiters, thereby isolating the fault without communication between equipment items.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a very rapid deep direct current circuit breaker is positioned in series with reactances to limit the rate of growth of short-circuit current, then the breaking time is reduced and selectivity is improved, but the cost increases and energy losses are not inconsiderable
Solution Approach 1:
The patent utilizes the phase transition property of superconductors (from superconducting state to normal resistive state) when exposed to high current. The superconductor remains in zero-resistance state during normal operation, then transitions to high-resistance state during fault conditions, providing rapid current limitation without continuous energy loss. This resolves the contradiction by achieving fast breaking capability only when needed, eliminating continuous energy losses associated with traditional reactance-based solutions.
Solution Approach 2:
The patent changes the electrical resistance parameter of the current limiter dynamically through superconductor transition. During normal operation, the superconductor maintains zero resistance for efficient power transmission. During short-circuit conditions, the superconductor transitions to high resistance state to limit current growth rate. This parameter change enables both fast breaking and reduced energy losses, as the high resistance is activated only during fault conditions.
2Loss of time
If a very rapid deep direct current circuit breaker is used to achieve fast breaking, then the breaking time is reduced, but the cost of the circuit breaker becomes particularly high
Solution Approach 1:
The patent employs a superconductor current limiter that acts as a protective device activated only during fault conditions. The superconductor remains in its normal low-resistance state during regular operation and is only 'consumed' or triggered during short-circuit events to limit current. This approach replaces expensive very rapid deep circuit breakers with a more economical superconductor-based solution that provides the necessary protection only when needed.
Solution Approach 2:
The patent introduces a superconductor current limiter as an intermediary device between the power source and the load. This superconductor acts as a mediator that limits current growth during faults, protecting the downstream circuit breaker from excessive current stress. The intermediary superconductor enables the use of less expensive, less rapid circuit breakers while still achieving adequate protection and breaking times.
3Reliability
If superconducting fault current limiters are positioned at network intersections to avoid failure propagation, then network protection is improved, but the ability to rapidly locate and isolate failures is reduced
Solution Approach 1:
The patent implements selective tripping capability that enables differentiating between local and remote faults. When a superconductor transitions during a fault, the local interconnection equipment detects this transition and can selectively trip only the affected terminal, rather than causing widespread network disruption. This local quality enhancement allows rapid failure location and isolation while maintaining overall network protection.
Solution Approach 2:
The patent incorporates monitoring of superconductor transition states as feedback signals. When a superconductor current limiter transitions from superconducting to normal state, this provides immediate feedback about the location and nature of the fault. This feedback mechanism enables rapid detection and localization of failures, resolving the contradiction between network protection and failure detection capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables robust and selective current breaking, reducing the risk of damage to power electronics and maintaining network continuity by isolating the affected terminal without requiring communication between interconnection equipment items, thus enhancing the network's robustness and reducing costs.
Implementation Method 1
a current limiter configured to limit a current passing through it
Implementation Method 2
a device configured to inject an electrical current into the node upon a voltage drop on this node (in particular a capacitor connected between the node and the ground stores energy)
Data Source
AI summary
An item of interconnection equipment for a high-voltage DC grid includes first and second terminals for connection to first and second lines of a high-voltage DC grid, a third terminal for connection to a local station or a line of the high-voltage grid, a node connected to the first to third terminals, a first superconductor current limiter and a first controlled switch connected in series between the first terminal and the node, a second superconductor current limiter and a second controlled switch connected in series between the second terminal and the node, a third superconductor current limiter and a third controlled switch connected in series between the third terminal and the node, and a current injector configured to inject an electrical current into the node.