Cascade Converter Station Bypassing Faulty Components
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Solution Overview
Problem
Cascaded multi-terminal HVDC power transmission systems face challenges in maintaining reliability and safety due to high voltage, large current, and environmental impacts, particularly in isolating faulty components without disrupting the entire system.
Innovation Solution
A cascaded converter station design is implemented, featuring low-voltage and high-voltage end converter stations connected through a middle-voltage DC power transmission line, with grounding and metal return lines, and neutral bus switches to enable flexible bypassing of faulty components, ensuring continuous operation and improved safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If converter stations are connected in series to form a cascaded multi-terminal HVDC system, then power transmission flexibility and economy are improved, but system reliability deteriorates due to vulnerability to high voltage, large current, and environmental impacts
Solution Approach 1:
The converter station is divided into multiple independent converter bridges (first converter bridge, second converter bridge, third converter bridge, fourth converter bridge) connected in series. Each converter bridge can be independently controlled and isolated, allowing the system to maintain power transmission capability even when one bridge fails, thus resolving the contradiction between transmission flexibility and system reliability.
Solution Approach 2:
Bypass switches are pre-configured for each converter bridge and smoothing reactor in advance. When a fault occurs, these bypass switches can be quickly activated to isolate the faulty component and maintain system operation, preventing total system failure and improving reliability while preserving transmission flexibility.
2Power
If converter stations operate with high voltage and large current, then power transmission capacity is improved, but safety deteriorates due to impacts from high voltage, large current, and environmental factors
Solution Approach 1:
Grounding switches are pre-installed for each converter bridge and smoothing reactor. In the event of insulation failure or other faults, these grounding switches can be quickly activated to ground the faulty components, preventing equipment damage and ensuring personnel safety, thus resolving the contradiction between high power transmission capacity and safety.
Solution Approach 2:
The bypass circuit configuration with pre-installed bypass switches provides a protective mechanism that cushions against potential failures. When faults occur, the bypass circuits provide alternative current paths, preventing catastrophic failures and protecting the high-voltage, large-current system from safety incidents.
3Productivity
If converter valves are used for DC/AC conversion, then power transmission functionality is improved, but ease of operation deteriorates when faults require system shutdown
Solution Approach 1:
Bypass switches are pre-configured for each converter bridge and smoothing reactor. When a fault occurs in a converter valve or associated equipment, the corresponding bypass switch can be quickly activated to maintain current flow through alternative paths, allowing the system to continue operating without shutdown and improving ease of operation while maintaining transmission functionality.
4Reliability
If bypassing mechanisms are added to isolate faulty components, then reliability is improved, but device complexity increases
Solution Approach 1:
The converter station is segmented into four independent converter bridges with individual bypass switches and grounding switches for each bridge and smoothing reactor. This segmentation allows faults to be isolated to specific components while maintaining system operation, improving reliability. The modular nature of the segmentation keeps the complexity manageable through standardized repeating units.
Solution Approach 2:
Each converter bridge is designed with identical bypass and grounding switch configurations, creating universal modules that can be independently operated. This multi-functionality allows any bridge to serve as backup for others, improving reliability while reducing overall system complexity through standardization and reuse of the same components across all four bridges.
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
The solution allows for reliable and flexible operation of HVDC power transmission systems by isolating faulty components, enhancing energy availability and safety through effective bypassing mechanisms and the use of smoothing reactors for lightning protection.
Implementation Method 1
a converter valve coupled to the converter transformer for realizing DC/AC conversion
Implementation Method 2
smoothing reactors provided on both ends of the converter valve
Implementation Method 3
a grounding line coupled to a grounding electrode
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~4A
AI summary
A cascade converter station and a multi-end cascade high-voltage direct current (HVDC) power transmission system. The converter station includes a low-voltage end converter station (11) and a high-voltage end converter station (12). Each electrode of the low-voltage end converter station (11) includes a converter transformer (111a, 111b) coupled to a first alternating current (AC) power grid, a converter valve (112a, 112b) coupled to the converter transformer (111a, 111b) and smooth reactors (115a, 115b). The high-voltage end converter station (12) connected in series with the low-voltage end converter station (11) through a medium-voltage direct current (DC) power transmission line (13) and connected to a HVDC power transmission line (14). Each electrode of the high-voltage end converter station (12) includes a converter transformer (121a, 121b) coupled to a second AC power grid, a converter valve (122a, 122b) coupled to the converter transformer (121a, 121b) and smoothing reactors (125a, 125b). A ground electrode line (126) and a metal return line (128) are provided in the low-voltage end converter station (11). A ground electrode line (133) and neutral bus switches (140a, 140b) can be further provided in the high-voltage end converter station (12). With the cascade converter station and the multi-end cascade HVDC power transmission system, HVDC power transmission can be achieved in a flexible, reliable and economical manner.