Current Limiting Circuit with Dynamic Capacitor Bypass
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Solution Overview
Problem
The increasing risk of large fault currents in electrical power supply networks due to higher power transmission poses challenges in limiting currents during faults without adversely affecting normal network operation, as existing solutions like high-impedance coils or transformers interfere with normal load flow.
Innovation Solution
A current-limiting circuit comprising a coil unit and a capacitor unit connected in series, with a bypass device that can electrically bypass the capacitor unit during overcurrents, utilizing power semiconductor switches, spark gaps, and mechanical switches to manage impedance and limit currents effectively, while maintaining low impedance during normal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-impedance coils or transformers are used to limit fault currents, then fault current limitation is achieved, but normal load flow is worsened
Solution Approach 1:
The patent applies a dynamically switchable impedance configuration where the capacitor unit can be bypassed during faults to provide current limitation, while being connected during normal operation to maintain low impedance and minimize impact on load flow. The bridging device dynamically changes the circuit configuration based on operating conditions.
Solution Approach 2:
The patent changes the electrical impedance parameter of the circuit by switching the capacitor unit in and out of the circuit. During normal operation, the capacitor provides reactive compensation maintaining low impedance. During faults, the capacitor is bypassed to increase impedance and limit fault current.
2Productivity
If the capacitor unit remains connected during overcurrents, then normal operation is maintained, but fault current limitation is insufficient
Solution Approach 1:
The bridging device dynamically switches the capacitor unit out of the circuit during overcurrent conditions. The control unit detects overcurrent and activates the bridging device to bypass the capacitor, providing fault current limitation when needed while maintaining normal operation when not needed.
Solution Approach 2:
The patent extracts the capacitor unit from the circuit during fault conditions by closing the bridging device across it. This removes the capacitor's low-impedance path from the circuit, forcing fault current through the higher-impedance coil unit for current limitation.
3Reliability
If a bridging device is added to bypass the capacitor unit, then fault current limitation is improved, but device complexity increases
Solution Approach 1:
The bridging device serves multiple functions: it bypasses the capacitor unit during faults to limit current, and can be controlled by the control unit based on various detection signals. The same basic structure handles both protection and normal operation transitions.
Solution Approach 2:
The control unit acts as an intermediary that detects overcurrent conditions and controls the bridging device accordingly. This mediator coordinates the switching action to achieve fault current limitation without requiring direct complex interconnection between all components.
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 limits fault currents without significantly impacting normal current flow, reducing the dynamic and thermal load on network components and ensuring reliable operation by quickly switching to bypass modes during overcurrents and faults, thus extending component lifespan.
Implementation Method 1
the capacitor unit has such a capacitance and the coil unit has such an inductance that at the nominal frequency of the alternating current the amount of the capacitive reactance of the capacitor unit corresponds to the amount of the inductive reactance of the coil unit
Implementation Method 2
the capacitive reactance of the capacitor unit corresponds to the amount of the inductive reactance of the coil unit
Implementation Method 3
the first bridging branch has a first bridging element, in particular a power semiconductor switch
Implementation Method 4
the second bridging branch having a second bridging element, in particular a spark gap
Implementation Method 5
A first damping circuit (in particular a further coil unit) can be connected electrically in series with the power semiconductor switch. This first damping circuit limits the flow of current through the power semiconductor switch
Implementation Method 6
the third bridging branch having a third bridging element, in particular a mechanical bridging switch
Data Source
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AI summary
The invention relates to a current-limiting circuit (1) for limiting the magnitude of an alternating current (20), comprising a coil unit (23) and a capacitor unit (26), which are connected electrically in series, and comprising a bridging device (29) for electrically bridging the capacitor unit (26) when an overcurrent occurs.