Charge transport in thermally aged paper impregnated with natural ester oil

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link ABSTRACTSamples of a dried composite oil-paper system were thermally aged in the laboratory under N 2 in a sealed container and analysed using their dielectric response. The contributing loss processes were separated using an equivalent circuit model containing constant high frequency capacitances, dc-conductances, a dispersive capacitance, and a low frequency quasi-dc (q-dc) dispersion process as circuit elements. This low frequency dispersion in oil-paper samples is a bulk property of the system that is often mistaken for a dc conduction process when only the imaginary capacitance or acconductance is measured. The Dissado-Hill response function is proposed for the frequency dependence of the dispersive capacitance in the mid-frequency range rather than the Debye function because its cluster concepts correlate with the sample morphology of a matrix of oil-filled cavities. The quasi-dc dispersion is assigned to the transport of mobile charges between charge-clusters associated with locally connected oil filled cavities, which is a process that can be represented on a global scale by the form of hierarchical circuit system that leads to constant phase angle responses, and is here modelled by the Dissado-Hill q-dc function. It was found that the two dispersions moved together to higher frequency with thermal ageing of the composite material. The characteristic frequency common to the dispersions had an activation energy that decreased with thermal ageing, whereas their amplitude increased. This behaviour is discussed in terms of possible changes to the oil-paper composite caused by the ageing process.

Enhancing Insulating Performances of Presspaper by Introduction of Nanofibrillated Cellulose

“…Enhancing electrical properties of cellulose insulation is therefore of great significance. However, only a few studies deal with the modifications of presspaper despite of the extensive research on mineral oil and other polymers [8,9].…”

Condition monitoring of biodegradable oil filled transformer

“…Effective DC conductivity is 1/(1/σ2+1/σ2), because these two elements are electrically in series [255]. Figure 7.15 manifests that effective DC conductivity 170 | P a g e exponentially increases with moisture content.…”

“…Generally, three main polarisation mechanisms can be observed in insulation materials, namely deformation (electron or atomic), ionic and dipolar polarisation. Moreover, some of the insulation materials possess different types of polarisation mechanisms such as interfacial polarisation (space charge polarisation) and hopping charge carrier polarisation [109,[111][112][113][114][115][116].…”

“…This circuit is somewhat similar to that of [114] and has the dispersive capacitive elements of DHq-dc and DH loss peak. In the proposed circuit, these two capacitive elements are in series because DH loss peak and q-dc processes behave sequentially.…”

“…It is generally accepted that NE insulating oils are highly oxidation susceptible and oxidation of NE oils produces gummy waxes. These waxes deposit on the wall of cellulose fibres and it enhances the long range charge transport along the surfaces of fibres [114]. This may also be a cause for having higher conduction and polarisation phenomena in pressboard aged in NE than that of aged in mineral oil.…”