AC Electronic Trip Circuit Arc Fault Detection
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Solution Overview
Problem
Current DC circuit breakers face challenges in accurately detecting arc faults at low current levels, particularly in photovoltaic applications, where thermal and magnetic trip units are prone to nuisance tripping and lack adequate protection, while DC electronic trip units are costly and may fail to initiate trips when current drops below rated levels.
Innovation Solution
An electrical switching apparatus incorporating a transductor circuit with current transformers, a current sensor, and an alternating current electronic trip circuit with an arc fault detection circuit, powered by both AC and DC sources, which senses DC current and outputs AC proportional to it, enabling accurate arc fault detection and tripping even at low currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermal and magnetic trip units are used in DC circuit breakers, then the circuit breaker can provide overload and short circuit protection, but they are prone to nuisance tripping at low current levels and do not provide adequate arc fault protection
Solution Approach 1:
The patent replaces mechanical thermal and magnetic trip units with an electronic trip unit that uses a transductor circuit to sense DC current. The transductor converts DC current into an AC signal that can be processed by electronic circuitry, enabling precise detection of low current levels and accurate arc fault detection without the limitations of mechanical systems.
Solution Approach 2:
The transductor circuit acts as an intermediary between the DC current and the electronic trip circuit. It converts the DC current into an AC signal proportional to the DC current magnitude, allowing the electronic circuit to accurately measure and detect arc faults at low current levels where thermal and magnetic trip units fail.
2Reliability
If a DC electronic trip unit is used to improve control and tripping accuracy, then arc fault detection capability is enhanced, but the cost of the circuit breaker increases significantly
Solution Approach 1:
The patent makes the electronic trip unit universal by enabling it to operate with both AC and DC power sources. The circuit can derive power from AC utility power or from the DC protected circuit through the transductor, allowing the same electronic trip unit design to be used in both AC and DC applications, thereby reducing development and manufacturing costs.
Solution Approach 2:
The transductor circuit serves a dual function: it converts DC current to AC signal for the electronic trip unit while also providing power to the electronic trip unit itself. This self-powering capability eliminates the need for separate power supply circuits and reduces overall system cost.
3Adaptability or versatility
If self-powered electronic trip units are used, then they can operate without external power sources, but they fail to initiate trips when current drops below rated levels
Solution Approach 1:
The patent introduces dynamic power sourcing capability where the electronic trip unit can switch between AC power source and DC power source depending on availability. This dynamic adaptability ensures continuous operation and reliable trip initiation across all current levels, overcoming the static limitation of self-powered units that rely solely on circuit current.
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 provides reliable arc fault protection across a range of current levels, ensuring timely tripping and reducing the risk of nuisance tripping, while maintaining cost-effectiveness by utilizing existing power sources, thus addressing the limitations of existing DC circuit breakers.
Implementation Method 1
a transductor circuit with current transformers, a current sensor, and an alternating current electronic trip circuit with an arc fault detection circuit, powered by both AC and DC sources, which senses DC current and outputs AC proportional to it
Implementation Method 2
an alternating current electronic trip circuit with an arc fault detection circuit
Data Source
AI summary
An electrical switching apparatus includes a transductor circuit that senses a direct current between an input terminal and an output terminal and outputs an alternating current proportional to the direct current. The electrical switching apparatus also includes a current sensor configured to sense an alternating current component of the direct current. The electrical switching apparatus further includes an alternating current electronic trip circuit including an arc fault detection circuit configured to detect an arc fault based on the sensed alternating current component. The alternating current electronic trip circuit is also configured to control pairs of separable contacts to trip open based on the alternating current output from the transductor circuit or the detected arc fault. The electrical switching apparatus also includes a power supply structured to provide direct current power to the alternating current electronic trip circuit.