Reed Switch Differential Current Sensor for DC Protection
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Solution Overview
Problem
Existing residual current circuit breakers are ineffective for DC voltage and lack independence from mains voltage, as they rely on summation current transformers that do not function with direct current and require separate power supplies for evaluation.
Innovation Solution
A differential current sensor utilizing a reed switch or magnetic switch wound with two coils, where the magnetic fields cancel out under balanced currents, triggering the switch to close and interrupt the circuit when a current difference exceeds a threshold, allowing for DC circuit protection independent of mains voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If summation current transformers are used for residual current detection, then AC residual currents can be detected, but the device does not work with DC voltage and requires separate power supply
Solution Approach 1:
The differential current sensor uses the circuit's own current to generate the magnetic field that actuates the reed switch. The first and second coils are connected in series with the conductors, so the circuit current directly creates the magnetic effect without requiring external power supply, making the device self-powered and suitable for DC circuits
Solution Approach 2:
The patent replaces the electromagnetic transformer system (which requires AC power and complex windings) with a direct magnetic field approach using reed switches. The reed switch contacts are directly actuated by the magnetic field from the coils, eliminating the need for transformer-based detection and separate power supply
2Reliability
If two coils are wound on the reed switch with same number of turns and symmetric arrangement, then optimal symmetry of magnetic fields is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies different properties to different parts of the system: the coils are designed with specific winding directions (first coil in one direction, second coil in opposite direction) to create opposing magnetic fields. This local differentiation in winding direction compensates for any minor variations in turn count or positioning, maintaining field symmetry without requiring extreme manufacturing precision
Solution Approach 2:
The invention changes the winding direction parameter of the coils rather than relying solely on identical turn counts. By winding the first coil in one direction and the second coil in the opposite direction, the system achieves magnetic field symmetry through parameter variation rather than parameter uniformity, reducing manufacturing precision requirements
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
Enables effective detection and interruption of fault currents in DC circuits without a separate power supply, providing reliable and energy-efficient protection across various electrical configurations.
Implementation Method 1
a first coil (S1) and a second coil (S2), each having a different winding direction, are applied to the reed switch RS... both coils have an electrical two-wire line... the magnetic fields of the coils cancel each other out when the outward and return currents are the same... the resulting magnetic field causes the reed switch or magnetic switch to close
Data Source
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AI summary
The invention relates to an electrical circuit with a first and a second conductor, wherein the first conductor has a first coil and the second conductor has a second coil, both coils being arranged on a reed switch whose contact is connected to a trip circuit for interrupting the electrical circuit. When a first current difference in the first and second conductors is exceeded, the resulting magnetic field of both coils causes the reed switch to close, thereby interrupting the electrical circuit.