DC Grid Switching Circuit for In-Rush Current Isolation
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Solution Overview
Problem
Existing DC electric grid switching apparatuses face issues with high manufacturing costs and limited current breaking performance due to in-rush currents during opening maneuvers, particularly in solid-state switching devices with self-powered control stages, which require bulky input capacitors to withstand these currents.
Innovation Solution
A switching apparatus with a secondary switching arrangement controlled by a control unit to alternate the connection of the power supply stage to either the power source or load section of the electric line, preventing in-rush currents and allowing a smaller, cheaper power supply stage design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a self-powered control stage is used in solid-state switching devices, then the control stage can be fed directly from the electric line, but in-rush currents occur during opening maneuvers that require bulky input capacitors
Solution Approach 1:
A secondary switching arrangement is introduced as an intermediary between the power supply stage and the electric line. This intermediary component controls the connection timing to prevent direct in-rush current flow to the input capacitor during opening maneuvers, thereby protecting the capacitor without requiring it to be oversized.
Solution Approach 2:
The control unit activates the secondary switching arrangement before the primary switching devices open,预先 disconnecting the power supply stage from the electric line. This preliminary action prevents the in-rush current from occurring in the first place, allowing the use of smaller input capacitors.
2Reliability
If bulky input capacitors are used to withstand in-rush currents, then the power supply stage can survive opening maneuvers, but the current breaking performances of the switching devices are limited
Solution Approach 1:
The secondary switching arrangement acts as a mediator that isolates the power supply stage during fault conditions. This allows the primary switching devices to handle full current breaking requirements without being constrained by the power supply stage's capacitor sizing limitations.
Solution Approach 2:
The switching apparatus is segmented into primary switching devices for current interruption and a secondary switching arrangement for power supply management. This segmentation allows each component to be optimized for its specific function, with the primary devices handling high-current breaking while the power supply stage uses smaller capacitors.
3Ease of operation
If the power supply stage is electrically connected to the power source side to enable black start operation, then the control stage can be fed as soon as the electric line is powered, but in-rush currents occur during opening maneuvers
Solution Approach 1:
The control unit uses the secondary switching arrangement to preliminarily disconnect the power supply stage before opening the primary switching devices. This preliminary disconnection prevents in-rush currents while maintaining black start capability, as the control stage can still be fed during normal operation and reconnect after opening.
Solution Approach 2:
The electrical connection configuration of the power supply stage is made dynamic through the secondary switching arrangement. The connection state changes based on operating conditions: connected during normal operation for black start capability, disconnected during opening maneuvers to prevent in-rush currents.
Data Source
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AI summary
A switching apparatus for DC electric grids comprising: - first and second electric terminals for electrical connection with corresponding conductors of an electric line; - a primary switching arrangement including one or more primary switching devices configured to conduct or block a current along a conductive path between said first and second electric terminals; - a control stage including a control unit configured to control one or more controllable components of said switching apparatus; - a power supply stage electrically connected to said control stage to feed said control stage with electric power drawn from said electric line; - a secondary switching arrangement including one or more secondary switching devices controllable by the control stage. Said secondary switching devices are configured to electrically connect the power supply stage with said first electric terminals or with said second electric terminals, according to the needs.