DC Circuit Breaker Parallel Switch Commutation
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Solution Overview
Problem
Existing DC circuit breakers for extra-high-voltage power transmission systems face challenges in efficiently interrupting direct current due to the need for generating an arc voltage across mechanical switches, leading to high costs and power losses, especially when using semiconductor switches in series configurations.
Innovation Solution
A DC circuit breaker design that includes a mechanical switch and a semiconductor switch connected in parallel, where the mechanical switch is made nonconductive to commutate the current to the semiconductor switch, reducing power loss and allowing for a lower voltage withstanding capability, thus lowering costs and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical switch is used to interrupt direct current, then the current can be interrupted, but an arc voltage higher than the ON voltage of semiconductor switches must be generated which may not be sufficient in vacuum contactors
Solution Approach 1:
A forced commutation circuit is introduced as an intermediary to generate the necessary arc voltage for commutating current from the mechanical switch to the semiconductor switches. This circuit includes a commutation capacitor and commutation inductor that work together to create the required voltage spike, solving the problem of insufficient arc voltage in vacuum contactors without requiring the mechanical switch to inherently generate high voltage.
2Strength
If a large number of semiconductor switches are connected in series to achieve extra-high-voltage withstanding capability, then the voltage withstanding capability is improved, but the device complexity and cost increase
Solution Approach 1:
The voltage withstanding capability is segmented between two types of switches: mechanical switches (vacuum contactors) that handle the bulk of the voltage blocking requirement, and semiconductor switches (IGBTs) that handle only the commutation voltage. This segmentation allows the use of fewer, lower-voltage-rated semiconductor switches while maintaining the overall extra-high-voltage capability of the system.
3Ease of operation
If semiconductor switches are used to interrupt direct current, then the current can be interrupted without forcing current to zero, but power loss is generated due to resistance component
Solution Approach 1:
The system dynamically switches between mechanical switches for normal current conduction (low power loss) and semiconductor switches for fault current interruption (easy operation). The mechanical vacuum contactor has extremely low contact resistance during normal operation, minimizing power loss, while the semiconductor IGBTs provide fast, controlled interruption capability when faults occur.
4Reliability
If the mechanical switch is opened when current becomes zero, then the mechanical switch can be opened safely, but the disconnector must withstand extra high voltage requiring expensive circuit breakers
Solution Approach 1:
The forced commutation circuit acts as an intermediary that enables the mechanical switch to open safely by first commutating the current to the semiconductor switches. This eliminates the need for the mechanical disconnector to withstand the full extra-high voltage, as the semiconductor switches assume the voltage blocking responsibility during the commutation process.
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 configuration reduces power loss and costs by allowing normal current flow through the mechanical switch, shortening interruption time, and enabling the use of a lower voltage withstanding capability, making it suitable for extra-high-voltage applications with reduced size and price.
Implementation Method 1
it is necessary to generate, across the mechanical switch, an arc voltage higher than a voltage (ON voltage) at which the series-connected GTOs are turned on
Implementation Method 2
Joule heat is generated due to a resistance component of the semiconductor switch and accordingly a power loss is generated
Data Source
AI summary
A DC circuit breaker includes: a mechanical switch provided on an electrical path through which a direct current flows; and a semiconductor switch connected in parallel with the mechanical switch. The mechanical switch includes a gas disconnector and a vacuum circuit breaker connected in series. Normally, the direct current flows through the mechanical switch. When interrupting the direct current, the vacuum circuit breaker is made nonconductive to allow the direct current to be commutated to the semiconductor switch, and subsequently the gas disconnector and the semiconductor switch are made nonconductive. A vacuum circuit breaker having a low withstand voltage can be used.