Externally Controlled Thermal Trip for Varistor Fire Prevention
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Solution Overview
Problem
Aging voltage dependent resistors (VDRs) can short-circuit and fail to disconnect power during overvoltage conditions, leading to potential fires due to inadequate heat generation for meltable materials, causing incomplete disconnection and increased risk of short circuits.
Innovation Solution
An externally-controllable thermal tripping device is introduced, featuring a VDR chip, thermal tripper, and controllable heating element, where the tripping electrode is connected through meltable welding material, allowing external control to generate heat and disconnect the tripper from the VDR chip, enhancing safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the VDR chip deteriorates and leakage current is insufficient, then the meltable material cannot melt, but the VDR may still short-circuit and cause fire
Solution Approach 1:
The patent introduces a controllable heating element that can be activated externally to pre-generate heat and melt the welding material before the VDR chip fails or when leakage current is insufficient. This preliminary action ensures the tripping mechanism is activated proactively rather than relying solely on passive heat generation from deteriorated VDR, thereby preventing short-circuit fires even when leakage current is inadequate.
2Reliability
If the VDR chip short-circuits, then resistance becomes zero, but heat generation stops and the tripper fails to work
Solution Approach 1:
The patent introduces a controllable heating element as an intermediary device that can generate heat independently of the VDR chip's leakage current. When the VDR chip short-circuits and resistance drops to zero, this intermediary heating element can be externally activated to melt the welding material and trigger the tripping mechanism, ensuring the protection function remains reliable even when the VDR chip itself cannot generate sufficient heat.
3Device complexity
If the meltable material is used for passive thermal protection, then the structure is simple, but the tripping response is delayed and insufficient
Solution Approach 1:
The patent adds a controllable heating element that can be externally activated to pre-generate heat and melt the welding material before actual failure occurs or when passive thermal accumulation is too slow. This transforms the protection mechanism from purely passive to actively controllable, significantly improving tripping response speed while maintaining relatively simple structural complexity.
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 actively ensures electrical disconnection of the thermal tripper from the VDR chip, preventing fires by generating heat to melt the welding material, even in cases of insufficient leakage current, thus enhancing the safety and reliability of VDR applications.
Implementation Method 1
the controllable heating element is controlled by an external control device to generate heat and transmits the generated heat to a commissure (i.e., junction, joint or surface) of the meltable welding material to melt the meltable welding material
Implementation Method 2
the commissure between the controllable heating element and the meltable welding material is formed by heat conduction
Data Source
AI summary
An externally-controllable thermal tripping device comprising a voltage dependent resistor including a voltage dependent resistor chip; a thermal tripper including a tripping electrode; and a controllable heating element. The tripping electrode is connected to an electrode of the voltage dependent resistor chip through a meltable welding material, and the controllable heating element is controlled by an external control device to generate heat and transmit generated heat to a commissure of said welding material to melt said welding material and electrically disconnect the tripping electrode from the voltage dependent resistor chip.