Investigating the relationship between light transmittance, dissipation factor (tan α) and transformer oil quality

• Main Authors: Sinclair, Noel, Muir, Dave D., Chambers, Therese
• Format: Conference Proceeding
• Language: English
• Subjects: Capacitance; Capacitors; dissipation factor; Insulating oil quality; Moisture; Oil insulation; Phase transformers; Power transformer insulation; real-time; refractive index
• ISSN: 1091-0050; 1558-058X
• DOI: 10.1109/SECON.2015.7132955

The reliable operation of power transformers depends on utilities having the insulating system in good condition. For power transformers, the insulating system consists of the solid insulation such as kraft paper and press board along with the insulating oil, which has to be monitored to ensure system reliability and improved economic viability of the company. The current practice of visiting the site semi-annually to take samples for testing has led to transformer failures and can be improved with real time monitoring. Using light to monitor the quality of the insulating transformer oil for the purpose of recycling is the main focus of this paper. Research has shown that the refractive index n of a material is directly proportional to the square root of its relative permittivity, εr. Real time monitoring of the dissipation factor was achieved by monitoring the light transmittance through oil. The dissipation factor of transformer oil is a function of the relative permittivity of the oil. The research has shown that owing to the relationship between refractive index and electrical permittivity, the principle of light transmittance can be used to monitor the dissipation factor in oil. Using the visible spectra will ensure that the photon energy is less than the band gap energy of the oil and hence any decrease in transmittance will only due to the presence of absorbing species and scattering in the transformer oil. The aging process explored was to increase moisture, by adding water to samples and agitating at increase temperature. Based on the results of the transmittance and dissipation factor test a novel method of monitoring power transformer oil is proposed using the visible spectra.