Physico-chemical analysis of transformer oil and stability studies of their blends with synthetic and natural antioxidants.
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Date
2012
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Abstract
This study is focused on the analysis of transformer oil commonly used in South African
transformers and the characterisation of the blends of these oils with either synthetic antioxidants
or those extracted from natural sources.
The virgin naphthenic based uninhibited transformer oil was shown to have no acidic or
saponifiable constituents. Although the oil used in this study is naphthenic based it was found to
contain bicyclic compounds identified as tetralin (aromatic) and decalin by GC-MS. The oils
were void of typical wear metals and only additive metals/non-metals were present. The blending
of transformer oils with synthetic antioxidants was successful as confirmed by ¹H NMR, ¹³C
NMR and FT-IR data. The blending showed increased antioxidant activity of the oils as well as
thermal stabilities (DPPH assay and TGA respectively). Apparent activation energy for the
decomposition reaction was determined by means of the Ozawa, Flynn and Wall (OFW) and
Kissinger models. The apparent activation energy for BHT-B, DBP-B and VO were found to be
57.0, 63.7 and 69.3 kJ molˉ¹
, respectively for 10% mass conversion obtained from TGA data
(OFW model). The dissipation factor for the oil blends was established to be favourably lower
than that of unblended oils; however an undesirable decrease in the dielectric breakdown voltage
of the blends was observed (16, 26 and 50 kV for BHT-B, DBP-B and VO respectively).
The blending of transformer oil with synthetic antioxidants is a common practice, however
greener approaches are always favoured. In this study, a greener approach was employed by
blending the transformer oil with turmeric plant extract in an effort to improve the oil’s
performance. Turmeric is known for its antimicrobial, antioxidant and anticarcinogenic
properties. Solvent extraction of turmeric powder and subsequent blending into transformer oils,
revealed the dissolution of 5 components from turmeric into the oil, viz., curcumene,
sesquiphellandrene, ar-turmerone, α-turmerone and β-turmerone (curlone). In this work, we
analysed novel turmeric-oil blends in terms of oxidation and thermal stability in comparison to
that of virgin transformer oil. The DPPH assay confirmed that addition of these blends into the
oil increased its ability to scavenge the free radical DPPH. Thermogravimetric analysis showed
an increase in thermal stability when compared to that of virgin unblended oil. Evidently
blending of synthetic antioxidants/turmeric extract has potential to enhance the performance and
increase the life-span of transformer oils.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.
Keywords
Electric insulators and insulation--Oils., Theses--Chemistry.