Abstract
This study reports experimental investigations of the effects of different surfactants (CTAB, Oleic acid and Span 80) on silica based synthetic ester nanofluids. The positive and negative potential observed for the ionic (CTAB) and non-ionic surfactant (Span 80) from zeta potential analysis indicates an improved stability. The optimization of nanofillers and surfactants is performed considering the corona inception voltage measured using ultra high frequency (UHF) technique and fluorescent fiber. Rheological analysis shows no significant variation of properties with shear rate, implying Newtonian behavior even with the addition of surfactant. In addition, the permittivity of the nanofluid is not much affected by adding surfactant but a marginal variation is noticed in the loss tangent with the effect of temperature. The fluorescence spectroscopy shows no change in the emission wavelength with the addition of silica nanofiller and surfactants. Flow electrification studies indicate an increase in the streaming current with the rotation speed and temperature, with a higher current magnitude observed in the case of nanofluids.
Highlights
Oil filled power transformers form an important part of the power system network
A negative zeta potential was seen on the addition of Oleic acid and Span 80, which could be due to its higher pH value compared to cetyl trimethyl ammonium bromide (CTAB) surfactant [19], with a higher negative zeta potential observed on the nanofluids containing Span 80 as a surfactant
The results were in accordance with the corona inception voltage showing better properties with Span 80 compared to other surfactants
Summary
Oil filled power transformers form an important part of the power system network Their insulation design is critical for long and reliable operation. Mineral oils have long been used as an insulant and coolant Their low degradability level and environmentally toxic nature have led to much research on finding alternative fluids for transformers, that are being tested. Ester-based fluids have gained importance because of their higher fire class properties and excellent biodegradability compared to mineral oil [1, 2]. There is need to design and develop suitable insulating structures for transformers with better dielectric properties due to increased voltage levels of operation, space constraints and other economic concerns. The performance of silica (SiO2) nanoparticles was investigated because of its increased breakdown voltage and excellent dielectric properties [7, 8]. It remains difficult to determine an optimal quantity of nanofiller, in this case SiO2 nanoparticles, to achieve optimum breakdown strength, which is one of the major objectives of this work
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