Ground Return Transfer Switch for Bipole DC Current Path Change
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Solution Overview
Problem
Current bipole direct current power transmission systems require complex and bulky DC breaker functionality for changing current return paths, which is maintenance intensive and expensive due to the need for resonance circuits and nonlinear resistors.
Innovation Solution
A simplified arrangement using a ground return transfer switch that operates between open and closed states to change the current return path without requiring resonance circuits or nonlinear resistors, allowing for fast and economical path changes by controlling power from a steady-state level to zero.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DC breaker functionality with resonance circuit and nonlinear resistor is used to change current return path, then the current path can be changed, but the breaker becomes complicated, bulky, maintenance intensive and expensive
Solution Approach 1:
The patent extracts and removes the resonance circuit and nonlinear resistor from the DC breaker, keeping only the essential switching functionality. This eliminates the complex components while maintaining the core capability to change current return paths by switching between ground electrode and metallic return paths.
Solution Approach 2:
The patent replaces the complex, expensive DC breaker with a simpler switch that can be integrated into the converter station's existing switching infrastructure. The simplified switch requires less maintenance and has lower cost, while still achieving the required path changing functionality through coordinated operation with the converter.
2Ease of operation
If DC breaker with resonance circuit is used, then current zero crossing can be achieved for switching, but the arrangement becomes bulky and expensive
Solution Approach 1:
The patent replaces the mechanical DC breaker system with resonance circuit with an electronic switching approach. The converter's electronic control system generates artificial current zero crossings through power modulation, eliminating the need for physical resonance circuits and bulky mechanical breaker components.
Solution Approach 2:
The patent makes the converter station multi-functional by enabling it to perform both power conversion and current path switching functions. The same converter and control system that manages power flow also generates the current zero crossings needed for switching, eliminating the need for separate dedicated breaker equipment.
3Reliability
If conventional DC breaker is used for path changes, then reliable switching is achieved, but the system becomes maintenance intensive and expensive
Solution Approach 1:
The patent merges the path switching function with the converter's existing control and switching infrastructure. By integrating the current return path changing capability into the converter's normal operation, the system eliminates separate breaker components that would require independent maintenance, while maintaining reliable switching through the converter's proven control systems.
Data Source
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AI summary
An arrangement for changing current return path in a bipole direct current power transmission system comprises a converter station (10) having an active and a passive converter (14, 16) connected in series between an active and a passive pole line (P1, P2) via a first neutral bus (NB1), a metallic return transfer switch (30) in an electrode line (L1), a ground return transfer switch (24) in a current redirecting path (CRDP1) between the passive pole line (P2) and the neutral bus (NB1) and a control unit (40) which in case of change to the passive pole line (P2) for providing a return current path is configured to, upon control of power related to the active converter (14) from steady-state to zero, close the ground return transfer switch (24) and thereafter open the metallic return transfer switch (30), whereupon power related to the active converter (14) may be controlled back to steady state.