EMC Filter Switching for Residual Current Device Protection
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Solution Overview
Problem
Existing EMC filters in multi-phase power networks can cause incorrect tripping of residual current circuit breakers due to asymmetry in phase voltages during switching on and off, leading to unnecessary shutdowns and potential damage.
Innovation Solution
A method and circuit arrangement that deactivates the current path of the EMC filter with a switch-off delay time shorter than the tripping time of the residual current circuit breaker, ensuring that asymmetry-related leakage currents are minimized and the filter is only reactivated when the network is symmetrical, using a detector to analyze pulsating direct voltage for rapid asymmetry detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-capacity loads are switched on and off, then power supply capability is improved, but phase voltage asymmetry occurs causing false tripping
Solution Approach 1:
The patent applies preliminary action by detecting the voltage asymmetry caused by load switching before it can cause false tripping. The detector monitors phase voltages and automatically disconnects the EMC filter as soon as asymmetry is detected, preventing the false tripping from occurring. This allows high-capacity loads to be switched freely without compromising breaker reliability.
Solution Approach 2:
The patent implements feedback by continuously monitoring phase voltage symmetry and automatically controlling the filter connection based on the detected state. When load switching causes voltage asymmetry, the feedback mechanism triggers immediate disconnection of the filter, preventing false tripping. This allows the system to maintain high power capability while ensuring breaker operation reliability.
2Ease of operation
If the switch-off delay time is extended to ensure complete switching, then switching completeness is improved, but leakage currents flow longer causing false tripping
Solution Approach 1:
The patent uses feedback to automatically detect when phase voltage asymmetry occurs during switching and immediately triggers disconnection of the EMC filter. This eliminates the need for extended switch-off delay times, as the feedback mechanism responds in real-time to the actual switching state, ensuring complete switching while preventing false tripping by disconnecting the filter as soon as asymmetry is detected.
Solution Approach 2:
The patent applies self-service by enabling the system to automatically detect and respond to switching-induced voltage asymmetry without requiring manual intervention or fixed delay timing. The detector and switching device work together to self-regulate the filter connection based on real-time voltage conditions, ensuring both switching completeness and prevention of false tripping without compromising either aspect.
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
Prevents incorrect tripping of residual current circuit breakers by minimizing leakage currents during asymmetry, allowing for safe and reliable switching of high-capacity loads without inducing false alarms, and enabling more cost-effective EMC filter design with reduced inductance.
Implementation Method 1
a detector (22) is provided, which detects an asymmetry of phase voltages (UL1, UL2, UL3) of the multiphase power network (SN)
Implementation Method 2
a switching device (21) is provided, by which the at least one current path (28) of the EMC filter (2) carrying the leakage current is deactivated
Data Source
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AI summary
The invention relates to a method and a circuit arrangement for operating an EMC filter (LF) on a multiphase power network (SN) having phase voltages (UL1, UL2, UL3), in particular a three-phase power network, or in a component connected to the multiphase power network (SN), such as an inverter (UR), to prevent a faulty tripping of a residual current device (RCD) upstream of the EMC filter (LF) and having a tripping time T_a, caused in at least one current path of the EMC filter by an asymmetry of the phase voltages (UL1, UL2, UL3), in particular by switching the multiphase power network (SN) on or off, and flowing to a protective conductor (PE) of the multiphase power network (SN), and wherein the occurrence of an asymmetry of the phase voltages (UL1, UL2, UL3) is detected by means of an asymmetry detector (AD).wherein at least one leakage current path of the EMC filter (LF) is activated by means of a switching device (SE) when the phase voltages (UL1, UL2, UL3) exhibit essentially the same voltage without interruption for at least a turn-on delay time dT_ev. To prevent a false tripping of the residual current device (RCD) in the event of a phase voltage asymmetry, it is provided that at least one leakage current path of the EMC filter (LF) is deactivated by means of the switching device (SE) within a turn-off delay time dT_av after the occurrence of the asymmetry, wherein the turn-off delay time dT_av is shorter than the tripping time T_a of the RCD.