AC Ground Fault Detection Circuit With Intermittent Self-Test
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Solution Overview
Problem
Existing fault detection devices for AC supplies, such as RCDs, face inefficiencies and high costs due to the need for high energy test pulses, which complicate the design and increase costs.
Innovation Solution
The implementation of a test circuit that utilizes intermittent test pulses generated by a pulse generator, allowing for an efficient design by separating the pulse generator from the high energy requirements, and incorporating a self-test and end-of-life detection mechanism using a test resistor and capacitor to verify the integrity of key components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high energy test pulses are used to test the device, then the testing capability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent divides the testing function into two separate components: a simple pulse generator that produces low-energy triggering pulses, and a test circuit that contains the energy-storing capacitor and switching elements. This segmentation allows the pulse generator to be simple and low-cost, while the complex high-energy functions are isolated to the test circuit that is only activated during testing.
Solution Approach 2:
The patent introduces an intermediary test circuit between the simple pulse generator and the device under test. This test circuit acts as a mediator that converts the low-energy pulses into the high-energy test conditions needed, without requiring the pulse generator itself to be complex or high-powered.
2Reliability
If high energy test pulses are used to test the device, then the testing capability is improved, but the cost increases
Solution Approach 1:
By segmenting the testing system into a simple pulse generator and a separate test circuit with energy-storing components, the patent reduces the cost of the main device while maintaining full testing capability. The expensive high-energy components are only present in the test circuit that is activated intermittently.
Solution Approach 2:
The testing is performed periodically using intermittent pulses rather than continuous high-energy operation. This allows the system to use small, low-cost components for the pulse generator, with the high-energy test circuit only activated during periodic test intervals, reducing overall system cost.
3Reliability
If the pulse generator is designed for high energy pulses, then the testing capability is improved, but the pulse generator complexity increases
Solution Approach 1:
The patent extracts the high-energy functions (energy storage capacitor, switching elements) from the pulse generator and places them in a separate test circuit. This leaves the pulse generator itself simple and low-complexity, while the extracted components form a dedicated test circuit that provides the necessary high-energy testing capability.
4Reliability
If self-test function is added to verify component integrity, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The test circuit serves multiple functions: it provides the high-energy test pulses needed for testing, it verifies the integrity of the pulse generator and test circuit components through the self-test capability, and it can trigger protective actions. This multi-functionality reduces the need for separate verification circuits, offsetting the added complexity with consolidated functionality.
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
This approach reduces design complexity and costs while ensuring reliable fault detection and end-of-life indication, providing a fail-safe feature and efficient operation.
Implementation Method 1
a pulse generator for generating intermittent test pulses, wherein the test pulses do not in themselves test the device for faults, but rather they intermittently enable a test circuit to test the device
Implementation Method 2
they intermittently enable a test circuit to test the device. This allows the pulse generator to be designed without regard to the high energy characteristics of the pulses needed to test the device, which are instead provided by the test circuit
Implementation Method 3
incorporating a self-test and end-of-life detection mechanism using a test resistor and capacitor to verify the integrity of key components
Data Source
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AI summary
A device for detecting a fault in an AC supply comprising a detection circuit (CT1, W1a, U1) for detecting a fault in an AC supply to a load and providing a corresponding output (30). A disconnect circuit (SCR1, SCR2, K1, SW1, SW2) disconnects the load from the supply in response to an output (30) from the detection circuit. The device also includes a generator (40) of intermittent test pulses, and a test circuit (Q2, D11, R12, W2, K1, R9) coupled to the detection circuit (CT1, W1a,U1) and containing a first solid state switch (Q2). Each test pulse turns on the solid state switch (Q2) for the duration of the test pulse so that a current simulating the fault flows intermittently in the test circuit and a corresponding output (30) is provided by the detection circuit (CT1, W1a,U1). The device further comprising means to disable the disconnect circuit (SCR1, SCR2, K1, SW1, SW2) in response to each test pulse.