35 / 2018-08-13 12:10:13

Aging Characteristics and Repairing Evaluation of Long-term Operating LSR Bushings

liquid silicone rubber; aging; chalking layer; Fourier transform infrared spectrum; X-ray diffraction spectrum;

Because of its excellent performance, liquid silicone rubber(LSR) is often used as external insulation material for important equipments in substations. However, the LSR sheds of 500kV wall bushings(running for over 15 years) showed significantly aging, such as chalking, cracks and low hydrophobicity. One of the aging bushings ran out of service after it was repaired by RTV coatings. In this paper, the adhesion strength, hydrophobicity and electrical performance of new-made RTV coatings were test first. Thereafter the status of the bushing after repairing was evaluated by comparing test results of new-made RTV and RTV coatings on the bushing. Then the macroscopic aging characteristics of LSR sheds were investigated by using hydrophobicity and hydrophobicity transfer test, tensile and tear strength test. The microscopic characteristics of the aging sheds were obtained by using Scanning Electron Microsope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). It was found that the aging of the LSR shed developed from outer surface into the inside, and the layer structure including the chalking layer and the inner layer was obviously observed. The hydrophobicity, hydrophobicity transfer, tensile strength and tear strength of the aging sheds had different decrease. At microcosmic angle of view, the aging sheds appeared irregular shaped patches with a reduced surface roughness and adhesion; FTIR and XPS results indicated that the side chain groups of PDMS in the chalking layer were oxidized, crosslinked with other polysiloxane chains, forming more Si-O-Si groups, accompanied by the precipitation of TiO2 and white carbon black fillers. Due to the change of silicone rubber material from organic to inorganic, the content of C and Si elements in the chalking layer decreased, and the content of O element increased.The research also shows that, the hydrophobicity and hydrophobicity transfer of the aging LSR sheds can be improved by RTV repairment, but the appearance and hydrophobic changes still needs to be regularly monitored in the operation.