Momentary Circuit Interrupter for DC Fault Current Reduction
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Solution Overview
Problem
Existing circuit protection technologies for DC power systems face challenges in quickly and efficiently interrupting DC fault currents due to the lack of zero crossings in DC power circuits, leading to high conduction losses and slow response times, which are inadequate for applications like turboelectric aircraft and electric ships.
Innovation Solution
A momentary circuit interrupter with a pulse transformer is used to inject a transient voltage into the DC circuit branch, reducing the fault current to near zero within microseconds, allowing a series-connected mechanical switch to safely disconnect the faulty branch, while minimizing power losses during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If solid-state circuit breakers are used to interrupt DC fault current quickly, then response time is reduced to tens of microseconds, but conduction losses increase significantly
Solution Approach 1:
The circuit protection function is segmented into two distinct components: a momentary circuit interrupter (MCI) that operates only during fault conditions to provide fast current reduction, and a mechanical disconnect switch that provides low-loss isolation during normal operation. This segmentation allows each component to be optimized for its specific function, resolving the contradiction between fast response and low conduction losses.
Solution Approach 2:
The power semiconductor devices in the MCI operate in a periodic pulsed manner during fault interruption rather than continuously. The devices are activated only when a fault is detected, providing fast current reduction, then remain inactive during normal operation, thereby achieving fast response when needed while avoiding continuous conduction losses.
2Loss of energy
If hybrid circuit breakers are used to reduce conduction losses, then energy efficiency improves, but response time increases to 1-20 milliseconds
Solution Approach 1:
The system dynamically switches between two operational modes: during normal operation, the mechanical disconnect switch provides the current path with minimal conduction losses; during fault conditions, the MCI dynamically activates to provide fast current reduction. This dynamic operation allows the system to achieve both low conduction losses and fast response time as needed.
Solution Approach 2:
The MCI acts as an intermediary device between the power source and the load, specifically activated during fault conditions to provide fast current reduction. This intermediary component enables the system to achieve microsecond-range response during faults while the mechanical disconnect switch maintains low conduction losses during normal operation.
3Ease of operation
If parallel hybrid circuit breakers are used to commutate fault current to electronic path, then current zero crossings are created to aid mechanical switch opening, but fault current continues to rise through electronic path during mechanical switch opening time
Solution Approach 1:
Instead of using the electronic path to commutate current and create zero crossings to aid mechanical switch opening (as in parallel HCBs), this invention inverts the approach: the MCI actively forces the fault current to zero using power semiconductor devices, and this forced current zero is then used to aid the opening of the mechanical disconnect switch. This inversion eliminates the problem of current rising through the electronic path during switch opening.
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 solution achieves ultrafast fault current reduction and low on-state power losses, providing a response time between 5 microseconds and 1000 microseconds, significantly faster than existing technologies and reducing conduction losses.
Implementation Method 1
A momentary circuit interrupter with a pulse transformer is used to inject a transient voltage into the DC circuit branch
Implementation Method 2
A momentary circuit interrupter with a plurality of capacitors and operable in combination with a DC circuit branch
Data Source
AI summary
A momentary circuit interrupter in series connection with a mechanical switch to provide protection against short circuit faults in a DC power circuit. The momentary circuit interrupter injects a transient voltage pulse via a pulse transformer to reduce a DC fault current to near zero in a DC circuit branch, thus allowing the mechanical switch to disconnect the faulty branch under a near zero-current condition. The power electronic circuit on the primary side of the transformer controls the discharge of a plurality of pre-charged capacitors to generate the transient voltage pulse during the fault interruption process, but otherwise does not incur any power loss during normal operation. The secondary winding of the pulse transformer conducts the main DC current, and is highly conductive to minimize the conduction power loss. The invention provides ultrafast response to a short circuit fault (even faster than solid-state circuit breakers and much faster than hybrid circuit breakers), significantly reduced overcurrent stress in the power system, and/or ultralow conduction power losses.