VSC Grounding Arrangement for Safe Maintenance
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Solution Overview
Problem
Existing HVDC transmission systems face challenges in safely grounding voltage source converter (VSC) valves for maintenance, as the indeterminate nature of capacitor discharge failures can result in unpredictable voltages, posing risks to maintenance personnel and requiring complex, bulky, and non-scalable grounding arrangements.
Innovation Solution
A grounding arrangement for VSCs that connects the first and last sub-modules of each converter branch to earth potential upon shutdown, with a plurality of switch units associated with each sub-module to ensure safe voltage limitation, using mechanical or electrical switching devices that can be activated manually or automatically, allowing for scalable and safe maintenance access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a grounding arrangement is provided for converter branches to ensure safety during maintenance, then safety of maintenance personnel is improved, but the complexity and bulkiness of the grounding equipment increases
Solution Approach 1:
The converter branch is divided into multiple modules, and each module is further divided into sub-modules. The grounding arrangement is segmented accordingly, with switching elements associated with individual sub-modules or groups of sub-modules. This segmentation allows the grounding system to be activated in a controlled sequence, grounding sections of the converter branch progressively rather than requiring a single complex bulk grounding mechanism.
Solution Approach 2:
The grounding arrangement is activated automatically upon shutdown of the converter branch. Switching elements are triggered in advance to connect discharge circuits and grounding paths before maintenance personnel access the converter. This preliminary action ensures that residual voltages are dissipated and grounding is established before human intervention, improving safety without requiring complex manual grounding procedures.
2Power
If converter branches comprise multiple serially connected modules and sub-modules to achieve high voltage levels, then voltage capability is improved, but the potential residual voltage after shutdown increases due to capacitor discharge failures
Solution Approach 1:
The converter branch is segmented into multiple modules with serially connected sub-modules, allowing high voltage levels to be achieved through modular stacking. Each sub-module contains its own capacitor and switching elements. The grounding arrangement is also segmented, with switching elements associated with individual sub-modules or groups, enabling progressive grounding of each section to limit residual voltage propagation.
Solution Approach 2:
Discharge circuits are provided in each module or sub-module with switching elements that can be activated upon shutdown. These discharge circuits act as a cushioning mechanism to dissipate residual voltages from capacitors before maintenance personnel access the converter. The switching elements are positioned to connect discharge paths in advance, preventing dangerous voltage accumulation even if some capacitors fail to discharge completely.
3Ease of operation
If switching elements are provided in each sub-module with associated discharge circuits, then control over voltage dissipation is improved, but the device complexity increases
Solution Approach 1:
The converter branch is divided into modular sections, with each module containing sub-modules that have switching elements and discharge circuits. This segmentation allows the complex switching arrangement to be broken down into manageable, standardized units. Each sub-module or group of sub-modules can be independently controlled and grounded, simplifying the overall control strategy despite the large number of components.
Solution Approach 2:
The switching elements are designed to perform multiple functions: controlling power conversion during normal operation and activating discharge circuits during shutdown for grounding. This multi-functionality reduces the need for separate dedicated grounding switches, thereby reducing overall device complexity while maintaining ease of operation for voltage dissipation control.
Data Source
AI summary
A grounding arrangement for a Voltage Source Converter (VSC) in a power transmission system is provided. The VSC comprises at least one converter branch (20) comprising at least one module (221-22N), each module comprising a plurality of serially connected sub-modules (241-248) that can be controllably switched to generate a controlled voltage across the module (221-22N) and each module including a first sub-module (241) at one end thereof and a last sub-module (248) at an opposite end thereof. Each sub-module (241-248) includes a first terminal (381), a second terminal (382), an energy storage element (30) and a switching arrangement (32, 34), wherein at least one of the first (381) or second terminals (382) is coupled to a terminal of the energy storage unit (30). A first terminal (381) of the first sub-module (241) of a module (221) at one end of the converter branch (20) is configured to be connected to earth potential on or after shutdown of the converter, and a second terminal (382) of the last sub-module (248) of the module (22N) at the opposite end of the converter branch (20) is configured to be connected to earth potential on or after shutdown of the converter. A grounding arrangement (40) comprising a plurality of switch units (42) is provided, each switch unit (42) associated with one of the plurality of sub-modules (241-248) of each module (221-22N) and configured to connect the first (381) and second (382) terminals of the associated sub-module (241-248) on remote activation of the grounding arrangement (40), following connection to earth potential of the first (241) and last sub-modules (248) of the converter branch (20).