Vacuum Switch Assembly for DC Fault Interruption
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Solution Overview
Problem
Conventional vacuum switch assemblies face challenges in reliably interrupting and isolating dc fault currents, particularly in high power systems, due to re-strike risks and the complexity of hybrid circuit breakers, which incur significant cost, efficiency, and size penalties.
Innovation Solution
A vacuum switch assembly comprising first and second dc lines connected to a primary dc power source, with passive dc power supply units and vacuum switch controllers that synchronize the opening of vacuum switches when the current is below the chopping current, minimizing re-strike risks by controlling the opening and closing of contacts to prevent excessive energy input and transient recovery voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hybrid circuit breakers are used to interrupt dc fault currents, then current interruption capability is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the active current interruption means from the hybrid circuit breaker, removing power electronic switches and their associated switching aid networks. This leaves a simplified vacuum switch that operates passively by opening contacts when current falls below the chopping current threshold, eliminating the need for complex active components while maintaining fault current interruption capability
Solution Approach 2:
The vacuum switch is designed to operate autonomously without external control signals or power electronic assistance. The switch naturally interrupts current when it drops below the chopping current level, using its own inherent characteristics rather than requiring external active means to force current reversal or provide switching aid
2Speed
If vacuum switch contacts are opened during high current flow, then fault current interruption speed is improved, but re-strike risk increases
Solution Approach 1:
The control system monitors current flow and initiates contact opening only when current has naturally fallen below the chopping current threshold. This preliminary condition checking ensures that contacts are opened at the optimal moment when re-strike risk is minimized, rather than opening contacts arbitrarily during high current flow
Solution Approach 2:
The vacuum switch controller continuously monitors the current flowing through the switch and uses this feedback to determine the appropriate moment to open contacts. By base deopening action on real-time current measurement, the system ensures contacts open only when current is sufficiently low, dynamically adapting to prevent re-strike while maintaining fast interruption when safe
3Reliability
If resonant commutation circuits are added to achieve current reversal, then current interruption is improved, but component size and cost increase
Solution Approach 1:
The patent removes the resonant commutation circuit entirely from the system. Instead of adding large inductors and capacitors to force current reversal, the solution relies on the natural decay of fault current to below the chopping current threshold, eliminating the need for bulky passive components while achieving current interruption through passive vacuum switch operation
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 effectively minimizes re-strike occurrences and enhances the reliability of vacuum switch assemblies in interrupting dc fault currents, reducing the risk of thermal excitation and ionized carrier ejection, thereby ensuring safe and efficient operation.
Implementation Method 1
each vacuum switch having a chopping current which is dependent upon the prevailing operating conditions of the vacuum switch before its contacts open
Data Source
AI summary
The present invention relates to a vacuum switch assembly for interrupting and isolating fault current. The vacuum switch assembly includes first and second dc lines that, in use, are electrically connected to the dc output terminals of a primary dc power source and a dc network. Each dc line includes at least one vacuum switch having contacts that are opened and closed under the control of a vacuum switch controller. A passive dc power supply unit is electrically connected to the first and second dc lines and includes a secondary dc power source that provides a substantially ripple-free sensing voltage. The vacuum switch controller is adapted to open the vacuum switch contacts when a fault condition (e.g. a fault current or other fault) or an operator request has been identified and when the current flowing between the vacuum switch contacts is below a chopping current associated with the vacuum switches.