Bipolar HVDC Return Path Using AC Current Limiters
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Solution Overview
Problem
High-voltage direct current (HVDC) transmission systems face challenges in fault tolerance and cost-effectiveness, particularly in offshore wind farms, due to issues with electrolytic decomposition of earth electrodes and high costs associated with dedicated metallic return conductors and full-bridge converters.
Innovation Solution
The implementation of a bipolar HVDC system with current limiters in the AC network section to equalize potential between poles, eliminating the need for a dedicated metallic return conductor and using superconducting or non-superconducting current limiters to manage fault currents, along with a bypass in the DC network section for maintaining energy transmission during faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a bipolar HVDC configuration with grounded center potential is used, then voltage distribution between conductors is balanced, but electrolytic degradation of earth electrodes occurs and equalizing current flows through the earth
Solution Approach 1:
A dedicated metallic return conductor (DMR) is introduced as an intermediary element to provide a low-impedance return path for equalizing current. This DMR is connected to a one-sided grounding system, acting as a mediator that prevents equalizing current from flowing through the earth, thereby eliminating electrolytic degradation while maintaining balanced voltage distribution between the two conductors.
2Reliability
If a dedicated metallic return conductor (DMR) with one-sided grounding is installed, then electrolytic degradation is prevented and fault tolerance is improved, but system complexity and cost increase
Solution Approach 1:
The grounding function is extracted from the traditional bipolar configuration and concentrated into a one-sided grounding system connected to the DMR. Instead of requiring two independent grounding systems or complex coordination between multiple grounding points, the solution extracts the essential grounding function and implements it through a single grounding connection, simplifying the overall system structure while maintaining reliability.
3Power
If conventional current limiting methods are used, then fault current magnitude is controlled, but response time and fault isolation capability are insufficient
Solution Approach 1:
The DC circuit breaker is pre-positioned and pre-configured in the HVDC transmission line, ready for immediate operation upon fault detection. The breaker incorporates preliminary protective measures including coordinated control with the AC circuit breaker, enabling instantaneous fault current interruption and rapid system isolation. This preliminary preparation eliminates delays associated with conventional current limiting methods, achieving both effective power control and minimal response time.
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 design enhances fault tolerance and reliability while reducing costs by minimizing earth electrode decomposition and eliminating the need for expensive metallic return conductors, allowing for efficient and cost-effective HVDC transmission with minimal disruption during faults.
Implementation Method 1
The implementation of a bipolar HVDC system with current limiters in the AC network section to equalize potential between poles, eliminating the need for a dedicated metallic return conductor and using superconducting or non-superconducting current limiters to manage fault currents
Implementation Method 2
the other pole not affected by the fault can continue to be operated in a monopolar configuration via the DMR, thus without having to establish an impermissible return path via the earth
Data Source
Figure 1
AI summary
The invention relates to an electrical network (1) with a high-voltage direct current transmission system (2) configured for bipolar high-voltage direct current transmission of electrical energy. The high-voltage direct current transmission system (2) comprises at least one AC network section (3) and a DC network section (4) electrically connected to the AC network section (3). Furthermore, the bipolar high-voltage direct current transmission system (2) is configured with a first pole (5) and a second pole (6), wherein the poles (5, 6) are electrically connected to each other via at least one current limiter (7) implemented in the AC network section (3).