Silicone Rubber Insulator with Al2O3 Particles for Varistor Cooling
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Solution Overview
Problem
High voltage surge arresters face challenges in efficiently transferring heat due to limited thermal conductivity of silicone rubber insulators, which can lead to overheating as they operate with higher electric field strengths, necessitating longer and more costly designs to accommodate heat sinks.
Innovation Solution
Incorporating particles such as Al2O3, BN, and ZnO into the silicone-based rubber to enhance its thermal conductivity to at least 0.8 W/mK, allowing for improved heat transfer and reduced need for heat sinks, resulting in a more compact surge arrester design without increased complexity or space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicone rubber insulator is used to enclose varistor blocks, then hydrophobic properties and dielectric properties are improved, but thermal conductivity remains insufficient (below 0.6 W/mK)
Solution Approach 1:
The patent creates a composite material by incorporating particles of aluminium trihydrate, aluminium oxide, boron nitride, and zinc oxide into the silicone rubber matrix. This composite structure combines the hydrophobic and dielectric properties of silicone rubber with the high thermal conductivity of the added particles, achieving a thermal conductivity of at least 0.6 W/mK while maintaining the insulator's reliability properties.
2Temperature
If aluminium trihydrate particles are added to increase thermal conductivity, then cooling of varistor blocks is improved, but the thermal conductivity increase is still restricted (maximum 0.6 W/mK)
Solution Approach 1:
The patent combines multiple particle types (aluminium trihydrate, aluminium oxide, boron nitride, and zinc oxide) in a composite structure within the silicone rubber. This multi-component composite approach synergistically enhances thermal conductivity beyond what single particle additions can achieve, reaching at least 0.6 W/mK while maintaining flame retarding properties and effective varistor block cooling.
3Power
If varistor blocks operate at higher electric field strengths, then protection performance is improved, but heat generation increases leading to overheating risk
Solution Approach 1:
The patent develops a composite insulator material with enhanced thermal conductivity (at least 0.6 W/mK) by incorporating specific particles into silicone rubber. This composite structure enables more efficient heat dissipation from varistor blocks, allowing them to operate at higher electric field strengths and power levels without overheating, thus improving protection performance while managing thermal loads.
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 enhanced thermal conductivity of the silicone-based rubber effectively cools the varistor elements, reducing the risk of thermal runaway and enabling higher continuous operating voltages while maintaining mechanical and electrical properties, thus improving protection performance and reducing arrester length and cost.
Implementation Method 1
the thermal conductivity of said silicone-based rubber is equal to or above 0.8 W/mK... the increase of thermal conductivity obtained as a result of the addition of the aluminium trihydrate is a welcome effect, since it promotes the cooling of the varistor blocks
Implementation Method 2
blocks made of a material that, upon being subjected to a predetermined voltage, turns from a highly resistive state into an electrically conducting state... the varistor blocks are heated both during normal operation and, in particular, when limiting transient overvoltages
Implementation Method 3
the thermal conductivity of said silicone-based rubber is equal to or above 0.8 W/mK... promotes the cooling of the varistor blocks and reduces the risk of overheating thereof
Data Source
Figure 1
AI summary
A high voltage surge arrester (1), comprising an varistor element (2) arranged so as to be connected to a high voltage source and to carry a high voltage when being positioned in its operative position, and an electric insulator (3) that encloses and is in contact with said varistor element (2) and forms an outer surface of the apparatus (1), wherein said electric insulator (3) comprises a silicone-based rubber. The silicone based rubber comprises particles chosen from the group consisting of Al2O3, BN and ZnO, to such an extent that the thermal conductivity of said silicone-based rubber is equal to or above 0.8 W/mK.