Short-Circuit Fault Current Limiter Using Coupling Reactor
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Solution Overview
Problem
Current fault current limiters face challenges such as increased normal running impedance, high costs, oscillation and overvoltage risks, and resistance heating issues, limiting their effectiveness and practicality in power grid applications.
Innovation Solution
A short circuit fault current limiter using a circuit breaker, transfer current limiting unit, and current detection unit, where the transfer current limiting unit includes precharge capacitors, trigger switches, and a coupling reactor, generating high-frequency reverse currents to rapidly limit fault currents and reduce their impact on the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiting reactor is connected in series to limit fault current, then the short circuit current level is reduced, but the normal running impedance of the system increases, affecting transmission capacity and operation stability
Solution Approach 1:
The patent employs a dynamically controllable current limiting reactor with adjustable impedance that can be switched between different resistance values based on system conditions. During normal operation, the reactor operates at low impedance to minimize impact on transmission capacity, while during fault conditions, it switches to high impedance to effectively limit fault current. This dynamic adjustment resolves the contradiction between fault current limitation and transmission capacity maintenance.
Solution Approach 2:
The patent changes the electrical parameters of the current limiting reactor based on operating conditions. By adjusting the resistance value of the reactor through control circuits and switching devices, the system maintains optimal performance for both normal operation (low resistance for high transmission capacity) and fault conditions (high resistance for effective current limitation), thereby resolving the contradiction between these two requirements.
2Speed
If a solid-state fault current limiter with switch type design is used to rapidly limit fault current, then the response speed is improved, but the cost increases and extremely high response speed requirements are needed
Solution Approach 1:
The patent divides the current limiting function into multiple segments: a controllable reactor for primary current limitation, supplemented by RC damping circuits and metal oxide varistors for oscillation suppression and overvoltage protection. This segmentation allows each component to perform its specific function efficiently, achieving rapid fault current limitation without requiring extremely high response speeds from a single complex solid-state switch, thereby reducing overall system cost and complexity.
Solution Approach 2:
The patent introduces intermediary components such as RC damping circuits and metal oxide varistors that assist the main controllable reactor in achieving rapid fault current limitation. These intermediaries handle secondary functions like oscillation damping and surge protection, allowing the main switching device to operate at moderate speeds while still achieving effective fault current limitation, thus reducing the extremely high response speed requirement and associated costs.
3Reliability
If an arc current transfer type fault current limiter is used to limit fault current through resistance, then the fault current is reduced, but resistance heating problems occur under current-limiting operating conditions
Solution Approach 1:
The patent employs periodic switching action of the controllable reactor, which operates in pulses during fault conditions rather than maintaining continuous high resistance. This periodic operation allows the reactor to limit fault current effectively during critical periods while providing cooling intervals, thereby reducing cumulative resistance heating and improving the thermal performance of the system under current-limiting operating conditions.
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 reduces fault current amplitude and duration, enhances breaking reliability, and lowers device costs, while minimizing system disruptions and equipment damage during short circuit events.
Implementation Method 1
A short circuit fault current limiter using a circuit breaker, transfer current limiting unit, and current detection unit, where the transfer current limiting unit includes precharge capacitors, trigger switches, and a coupling reactor, generating high-frequency reverse currents to rapidly limit fault currents
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention discloses a short circuit fault current limiter comprising: a circuit breaker CB1, a transfer current limiting unit and a current detection unit. The current detection unit is connected to the circuit breaker CB1 in series, and the circuit breaker CB1 and the transfer current limiting unit are connected in parallel into the power system line; an output terminal of the current detection unit is connected to a control terminal of the transfer current limiting unit; and the current detection unit is configured to detect a fault current flowing through a branch of the circuit breaker CB1 under a short circuit fault operating condition and trigger the corresponding trigger switch of the transfer current limiting unit to be switched on, so that the circuit breaker CB1 is disconnected and the secondary side winding of the coupling reactor is connected to the system line in series, which is capable of rapidly limiting the amplitude of the fault current and reducing impact of the fault current on the system.