Charge Dynamics in Vegetable Oil-Based Ester Dielectric Fluid

Abstract

Alkyl ester derivatives of palm kernel oil have been prepared for use as bio-dielectrics in oil filled HV electric equipment. Conduction and loss characteristics of the ester derivatives were studied to understand the behaviour of the material under electric field. Frequency response analyzer was used to study electrical conduction within the fluids since dielectric loss occurring at low frequencies under AC condition is dominated by mobile charge carriers. This is particularly important since power dissipation at power frequency, 50 Hz, may lead to dielectric heating. The dielectric response analysis of the samples with the range 10-3 - 104 Hz show a constant real relative permittivity at high frequency region. As the frequency drops below 101 Hz, there is interfacial polarization at the electrode-liquid interface, which results in a significant dielectric increment in the real part of the relative permittivity at low frequencies with a negative slope greater than 1 and a frequency independent conductance (εʹ slope = -1). This is an indication of Maxwell-Wagner interfacial effect where electric double layer (EDL) is formed. The real part acquired a slope of about -1 around frequency of 103 Hz. This suggests that the establishment of the EDL may be tending towards steady state. This change in the low frequency dispersion could be due to the ionic species undergoing interfacial electrochemical processes, or ions of lower mobility may have contributed to the EDL formation within the frequency region. This may have limited the effect of the strongly divergent processes at the interface.