PCB SPD Module With Piston Electrode for Thermal Runaway
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Solution Overview
Problem
Existing surge protective devices (SPDs) such as varistors often fail due to overheating, arcing, and pinholing, leading to fire hazards and performance degradation, making it difficult to meet new governmental regulations.
Innovation Solution
A surge protective device (SPD) module with a printed circuit board (PCB), housing electrodes, and a varistor stack, featuring a fail-safe mechanism with a meltable member that bypasses the varistor during overheating to prevent thermal runaway, and a sealed chamber with insulating spacers and a piston electrode for enhanced safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional varistor designs are used to absorb surge energy, then surge protection function is provided, but overheating and thermal runaway occur leading to fire hazards
Solution Approach 1:
A piston electrode is introduced as an intermediary component between the housing electrode and the varistor. The piston electrode includes a thermal fuse that acts as a mediator to detect and respond to overheating conditions, preventing thermal runaway before it reaches the varistor.
Solution Approach 2:
The thermal fuse in the piston electrode provides beforehand cushioning by detecting temperature increases before they reach dangerous levels. This early detection mechanism prevents the varistor from experiencing thermal runaway by interrupting the current path before overheating occurs.
2Use of energy by moving object
If conventional varistor designs are used to absorb surge energy, then surge protection function is provided, but arcing occurs causing performance degradation
Solution Approach 1:
The piston electrode serves as a mediator that includes an arc-quenching chamber. When arcing occurs, the piston electrode intercepts the arc and provides a controlled environment for arc extinction, preventing arc damage to the varistor and maintaining performance stability.
3Use of energy by moving object
If conventional varistor designs are used to absorb surge energy, then surge protection function is provided, but pinholing occurs leading to fire hazards
Solution Approach 1:
The thermal fuse in the piston electrode provides beforehand cushioning by detecting temperature increases from pinholing before they propagate. This early detection and current interruption prevents pinhole expansion and potential fire hazards.
4Power
If block varistors with flame sprayed copper electrodes are used for heavy-duty applications, then high surge current capability is achieved, but electrode separation occurs during overheating
Solution Approach 1:
The piston electrode is designed with dynamic response capability through the thermal fuse. When overheating occurs, the piston electrode dynamically changes state by melting the thermal fuse, which automatically interrupts the current path and prevents electrode separation.
Solution Approach 2:
The piston electrode acts as a mediator between the housing electrode and the varistor, providing a controlled current path that prevents direct electrode separation. The thermal fuse in the piston electrode mediates the failure mode to ensure safe operation.
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 SPD module effectively prevents overheating and arcing, ensuring safe failure modes and prolonged device lifespan by bypassing failed varistors, thus protecting equipment and personnel from thermal runaway and fire hazards.
Implementation Method 1
the thermal fuse is responsive to a temperature increase to melt and open the circuit
Implementation Method 2
the varistor forms a low resistance shunt path for the overvoltage current
Implementation Method 3
one or more metal oxide varistors (i.e., voltage dependent resistors) are used to absorb the electric energy during transient events and to keep the voltage to desired low values
Implementation Method 4
One or both of the electrodes include a spring member disposed between the electrode plate and the varistor disk to hold the varistor disk in place
Data Source
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AI summary
A surge protective device (SPD) module (100) includes a printed circuit board (PCB) (150), a first electrode (122), a second electrode (124), and a disc varistor (140) electrically connected between the first and second electrodes. The SPD module forms a housing assembly (121) defining a chamber (123) containing the varistor. The PCB forms a portion of the housing assembly.