Techniques to Monitor the Aging of Silicone Oils

Silicone oils are widely used as insulating fluids in many high voltage applications, including cable sealing ends. However, the long-term effects of the service conditions on the properties of silicone oil are relatively poorly understood. Using a range of techniques, we report on the condition of ex-service silicone oils compared to new, unused oil and comment on the suitability of each technique for monitoring the aging process. Analysis of the oils will involve dielectric permittivity measurements, chemical analysis using mass spectrometry, two spectroscopic techniques, and viscosity measurements. We also consider the feasibility of obtaining accurate conductivity measurements: finite element simulations were used to analyze the effectiveness of a conductivity test cell.