THE · EFFECT OF AN ANTI-OXIDANT ON THE BREAKDOWN VOLTAGE OF PALM OLEIN " AMPLES

The effect of the anti-oxidant (hydroquinone) on the breakdown voltage of palm olein samples was studied. The oil samples had different acid values resulting from the different degrees of neutralization treatments given. The hydroquinone addition ranged from 0.23 to 1.13 weight percent of the oil. 
The hydroquinone had a positive effect on the breakdown voltage of the oil samples. The increase in the breakdown voltage was rapid at low concentrations of the hydroquinone with the increase tending towards an asymptotic value at higher concentrations. the effect of the hydroquinone on the breakdown voltage was also dependent on the acid value of the oil. Oil samples with lower acid values had sharper increases in their breakdown voltages. Percentage increase in the breakdown voltage of 66.67(vis-a-vis the additive-less samples) was recorded for oil sample of acid value of 1.515 mg KOH/g oil and containing 0.45% by weight hydroquinone.These results show that the one major problem (oxidative stability) in the use of vegetable oil as transformer oil can be overcome without an adverse effect on their electrical properties. 
Key words: Breakdown voltage, Anti-oxidant, Palm olein, Neutralization, Acid value. 
[Global Jnl Engineering Res. Vol.1(1) 2002: 23-30]


INTRbOUCTION
Any oil whether of synti4C!tic, vegetable, mineral .~>r.animal origin, if free from water, acid, alcohol, amines and similar condu~ting liquids, will withstand the minimum electric strength test prescribed for insulating oils (Sillars, 1973).Vegetable oils -Soybean oil, cotton seed oil etc -consist principally of glyceride esters of fatty acids and are characteristically soluble in organic sblvents ( Kirk-Othrner, 1978).Transformer oils are used in power transformers for the purpose of ir;sulation and cooling.The production of satisfactory insulating oils is partly dependent on choosino suitable crude stocks and partly on refining technig,ues .inrelation to the stocks being used (Sillars, 1973).
•: One of the most inter~stihg recent developments is a growing realization that vegetable oils present a pr,ctlcal alternative to fuels, iubricants derived from fossil fuels (Weiss, 1983).
In tile formulation of.:-transformeroils from 'base stocks, the use of additives is necessary since no oil -vegetable or mineral possesses all the properties required by modern technology.Such additives are often specific in• function and are used' io concentrations varying from parts per million up to about 20 percent (Halton, 1962).Types c;>f additives include; viscosity index improvers, pour point depressants, oxidation inhibitor~ {anti-oxidants) anti-corrosion agents etc.The aromatic cont~nt of oil increases its tendency to absorb oxygen when subjected to discharge, HYMORE, F. K., FacultyofEf1$1ineering,•Unlversityof8enln.Nigeria WARA, S. T.   Tho ~cid values of the oil• sa~1ples'wero rneasured affer and before ea~h KOH' r1eutralization stop.The acid value• of oli'ls expressed i11 •tarms of milligran1s' of KOH required to r1eLrtrallza tho fruo fatty acids in one gram of oil.The ocld value dotermir1atio11 was made by weighing accurately f.lbout 1 Og. of tho oil in a flask and adding 100 ml of a mixture of 60ml of 'oluene and 40ml.,Of alcoh()l which has been neutralized: This was titrated with 0.1 M potassi~rn hydroxide soh.Jtion usir1u phenolphthalein as indicator.The acid values of the samples were calculated from tl1e formula: '! where AV is the acid value in mg KOH/g of oit.

•
V is the volume of KOH solution at end point.
W is the weight of oil sample M is the molarity of potassium hydroxide solution Degumming of oil: The essence of degumming is to remove the phosphatides present in tile oil.The oil .was weighed into a beake,r. in a water bath maintained at 70°C.While til~ oil was being stirred, water (about 5% by weight of the oil) was added.The mixture was stirred continuoi,Jsly for 30 minute after which it was allowed to cool.The_,"gums" separated out from the oil and settled' at the bottom of the beaker.The oil was finally separated from the gums in a separating funnel.

• • • Neutralization
In the neutralization process, the free fatty acids reacted with the potassium hydroxide according to equation 2 to form soap. ..

61•
The oil was warined to 40nc.While stirring, the potassium hydroxide was ndded drop wise to the oil to neutralize the free fatty acid.Different degrees of neutralization were achieved by adding.different amounts of potassium hydroxide solution.The mixture was then warmed to 60°C and th'e stirrii•,g• stopped only when the soap stock showed signs of separating.The soap stock was separated from the oil in a separating funnel.The neutralized oil samples were washed with warm water t~ remove any remaining soap particles.
• .The oil samples Were then dried .to remove all traces of moisture that must have bee1i introduced during the degumming, neutralization and washing steps.The oil was heated in a flask indirectly through a water bath to a temperature of about 60°C.The flask was connected bY means of a rubber tubing to a vacuum pump to suck the water vapour above the oil.

Measurement of the breakdown voltage of oil
Five different measuremehts were made on each of the oil samples each measuremeqt with a •.different concentration of anti-oxidant ranging from 0.23 to 1.13 weight percent of Vail.The breakdown voltage is the maximum voltage the oil can withstand while remaining as an insulator.The m~thod consists of immersing two electrodes from a voltage source in the oil and continually increasing the voltage until the oil starts conducting.The test cell consists of a glass vess•el 55mm by 90mm and 1 OOmm high with two spherical electrodes 13mm in diameter made of brass with a gap of exactly 4mm.The alternating current was supplied through a transformer so that •it shall be approximately of sine wave form and having a frequency of between 25 and 100 Hz., and capable of being raised uniformly from zero.The oil was placed to a depth of 40mm above the electrodes and left undisturbed for 10 minutes for air bubbles to escape.The power was switched on• and the voltage across the electrodes was steadily increased to a specified value in 10 seconds.The voltage at which the breakdown of .theinsulation.occurs between the electrodes is the breakdown voltage.Five different readings were taken lor each sample after a time interval of 1 0 minutes.The average of the readings is taken as the Breakdown voltage of each.sample of oi~ , .
-----.::::::-..In figure 1, the breakdown voltage of the !;amr;..i~'S ?! room temperature is presented as a •• • function of anti-oxidant concentration.The trend is the sc.11e for all the oil samples.The addition of anti-oxidant increased the breakdown voltage and the stability of the oil samples.This observation"js in line with some findings (Sillars, 1973).The tim A-taken under stand~rd conditions for inhibited oil to absorb the equivalent of 300 ml of oxygen per 1 OOg of oil, which broadly corresponds to the ' production of an acid value of 1 mg of KOH per gram of oil was measured.'This was called thy useful • life period.They found that th•e useful life period is approximately proportional to the quantity of inhibitor used.The rate of increase in breakdown voltage was higher :13!' low concentrations of anti• oxidant.At higl1 concen'trations of anti-oxidant.the rate of increase :in breakdown voltage with concentration decreased.This is evident in figure 2.The reasons for the increase in the breakdown voltage with anti-oxidant "concentration include tlole folloyving: • a) Anti-oxidant•is not ionic and therefore will not increase the conductivity of the oil.
The antl-oxidandnt~/~~1 ,pt~ the ti~e radic'al mechanism of glyceride au,to oxidation and hence stop the production of ions,sucl) as, free fatty acids from the natural degradation of the.oil (Sherwin,