Varistor Surge Protection with Thermal Expansion Bypass
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Solution Overview
Problem
High voltage devices, particularly HVDC circuit breakers, face challenges in protecting against voltage surges and DC currents without zero current crossings, leading to potential device failure and costly replacements.
Innovation Solution
A voltage surge protection device using a varistor with an expandable member that generates heat and gas upon threshold voltage, triggering a bypass process without external control or power supply, allowing for safe short-circuiting of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a varistor is used to protect high voltage devices from voltage surges, then the device can shunt current away from protected equipment, but the varistor requires external control or auxiliary power supply to activate the bypass mechanism
Solution Approach 1:
The bypass mechanism is designed to activate automatically through thermal expansion of the varistor material when threshold voltage is reached, without requiring external control signals or auxiliary power supplies. The system serves itself by using the thermal energy generated during overvoltage events to trigger the bypass contact closure.
Solution Approach 2:
The patent replaces electronic control systems with a thermal-mechanical activation mechanism. The varistor material's thermal expansion properties are utilized to physically move the bypass contact, substituting complex electronic control circuitry with a simpler thermal-responsive mechanical system.
2Power
If a high voltage device operates without zero current crossings (DC current), then continuous current flow enables higher power transmission, but fault current interruption becomes difficult without natural current zeros
Solution Approach 1:
The bypass contact is pre-positioned and ready to close immediately when thermal activation occurs. The mechanical structure is designed so that thermal expansion directly and rapidly actuates the bypass contact, creating a predetermined failure mode that automatically establishes a low-impedance path without requiring complex interruption control.
3Reliability
If an IGBT chip is destroyed by overvoltage, then the internal short-circuiting device protects the rest of the system, but the short-circuiting device has limited current carrying capability and requires complete unit replacement
Solution Approach 1:
The protection system is segmented into a reusable main unit and a sacrificial bypass contact component. The bypass contact is designed as a separate, replaceable element that absorbs the thermal and mechanical stress of repeated activation, allowing the main IGBT unit to be preserved and reused while only the inexpensive contact needs replacement.
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 effectively provides a self-triggered bypass mechanism for high voltage devices, enhancing their protection against voltage surges and reducing the need for frequent replacements by utilizing thermal energy to activate a movable contact for short-circuiting, thus ensuring reliable operation.
Implementation Method 1
The varistor material, when subjected to the threshold voltage, produces heat
Implementation Method 2
The varistor material, when subjected to the threshold voltage, produces heat and/or gas
Implementation Method 3
The varistor material, when subjected to the threshold voltage, produces heat and/or gas expanding the expandable member
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
The invention relates to a voltage surge protection device 1, 21, 31 for protection of a high voltage device. The voltage surge protection device 1, 21, 31 comprises a varistor 2, 22, 32 having a first part 2a, 22a, 32a and a second part 2b, 22b, 32b separated by varistor material 4, 24, 34. The voltage surge protection device 1, 21, 31 further comprises an expandable member 5, 25, 35 arranged to act on a movable electrical contact 7, 27, 37 for short-circuiting the voltage surge protection device 1, 21, 31 upon a threshold voltage being applied between the first part 2a, 22a, 32a and the second part 2b, 22b, 32b of the varistor 2, 22, 32. The invention also relates to high voltage circuit breakers.