Development of Silicone Rubber Nanocomposites for High Voltage Insulators

Abstract

High voltage insulators face surface degradation due to contaminant deposition reducing its resistance to erosion. To remedy this, silicone rubber coatings are applied, reinforced with different fillers. This thesis explores the use of hBN-based fillers to improve the erosion and tracking resistance of SiR in the long term. Adding hexagonal boron nitride (hBN) to SiR can significantly enhance its thermal and mechanical properties and make it erosion resistant. Exfoliation and surface modification of hBN to hBNNS and functionalized hBNNS improves dispersion in SiR, increases hydrophobicity, and enhances the mechanical properties critical for erosion resistance.

hBN undergoes treatment through exfoliation and functionalization to produce hBNNS and hBNNS-FTS. To verify exfoliation and functionalization, characterization tests such as FT-IR, XPS, X-Ray Diffraction, surface area (BET), thermal gravimetric analysis (TGA) were done on the nanofillers. Upon verification, SiR composite coatings were fabricated with hBNNS at 0.5%-5% loading amount and hBNNS-FTS at 0.5% - 10%. The composites were spray coated onto ceramic tiles to be tested at high voltage conditions using the inclined plane test (IPT) for 6hrs at 4.5kV following the ASTM D2303 testing standard. The results show that addition of hBN, hBNNS and hBNNS-FTS has improved the thermal stability, hydrophobicity, and mechanical strength of SiR. The coatings with 20% SiR/hBN, 0.5% SiR/hBNNS, and 5% FTS had the highest thermal stability. The 5% hBN, 5% hBNNS, and 5% hBNNS-FTS have the greatest modulus and tensile strength, according to mechanical testing. The IPT testing of SiR/hBN coating with 15% and 20% loadings passed. The tracking and erosion resistance of SiR/hBNNS was demonstrated by the 5% loading for the SiR/hBNNS coating, passing the industrial requirement. The SiR/hBNNS-FTS coating passed the IPT test with just 0.5% filler loading, demonstrating its excellent performance.

While the thermal stability, mechanical strength, and hydrophobicity have improved for filled SiR compared to unfilled SiR, only a few loadings from each set showed increased tracking and erosion resisting, hinting at an optimal loading amount for each set. This indicates the ability of fillers to improve the properties of SiR and its potential for long-term coating for high-voltage insulators. Based on the erosion test, the loadings required to meet the industrial standard for high voltage insulators are 5, 15, and 20% for SiR/hBN coatings, 5% SiR/hBNNS-FTS, and 0.5% SiR/hBNNS-FTS. The results signify that SiR with low loading amounts of hBN based fillers can be used to achieve properties usually associated with higher loading amounts through surface modification. Success through use of low loadings indicates the potential for greater cost efficiency as less amount of material is used to achieve great performance.