![Characteristics of Modern Transformer Oil](/images/Chris-Kenney-oils-article-1170.jpg)
This article will focus on the characteristics of modern hydrocarbon transformer oil as it relates to current refining technologies being used to guarantee the highest quality finished products available and adherence to all ASTM 3487 standards. In a recent article in Transformer Technology, I presented the fact that refining methodologies used to refine current production hydrocarbon-based transformer fluids have improved greatly over the past number of years. All the major refiners of finished transformer oil stock have completed various degrees of refinery upgrades in terms of hydrotreating severity. The units in place today all meet the minimum standards of heat and pressure that can be used to reform their crude slates to varying degrees of finished quality. Some have significantly upgraded their vessels to produce very high-quality materials which far significantly exceed the minimum standards.
Although we hear much in the news and political sphere about the evils of the hydrocarbons which make our current life so enjoyable, the fact remains, many industries are inextricably linked to the use and dependence on hydrocarbons in various form for many years to come. It is true, new technologies and products have arisen to maybe one day replace conventional oil-based transformer fluid, but for the meantime and at least the foreseeable future, most large OEM substation and large power transformer manufacturers will continue to hydrocarbon-based products to fill their units.
In the standard grouping of ASTM 3487 tests used to prove the quality of current insulating oil acceptance, there are certain tests which speak directly to the improvement in oil refining technology. ASTM D2440 is one of them. ASTM D2440 is a standard test which measures an oil’s resistance to oxidation either in normal operating conditions or under more severe conditions, such as heat, vibration, shock loading, surge voltages or general high electrical stress. The chemical reactions to conditions inside the transformer can result in sludge build up and elevated acidity. Like most chemical reactions, heat is a major accelerator. Much of the severe decay of transformer oil can be and is prevented by regular testing of the oil inside the unit. Like a good doctor who orders regular blood work,
Much of the deterioration of the oil can be prevented by dealing with the factors causing the breakdown in the first place. The reason modern day naphthenic based transformer oils are able to perform their resistance to oxidation so well in the field is due to the plant modernization factors mentioned above. Naphthenic hydrocarbon compounds are classified as closed-chain or ring compounds. They are a non-aromatic ring structure of carbon atoms.
Contained within all petroleum compounds before being severely hydrotreated are also non-hydrocarbons or often referred to as hetero compounds. These hetero compounds may be classified as sulfur, oxygen or nitrogen atoms. There are also naphthenic acids present in the distillate prior to treating as well as trace metals, esters, alcohols, ketones, and peroxide compounds. It should be noted that all these compounds have one thing in common-an oxygen atom. If allowed to proceed, all these compounds will act upon each other and the original oil. The resulting product will be sludge. A finished hydrocarbon-based transformer oil must be relatively free of all these hetero compounds. Today’s naphthenic transformer oils are highly refined to perform the heat transfer and arc quenching demands made upon them. They are very resistant to oxidation and resulting issues that come from oil breakdown.
Over the past few years, type 1 transformer oils have virtually disappeared from user’s RFQ specification requirements. There was a day when these “so called” type 1 oils were the primary oils used among the direct to utility market. The major oil companies, who no longer for the most part, offer transformer oils, all had type 1 offerings. The only difference in the type 1 and type 2 is due to % content in oxidation additive in each product. I assume buyers moved to type 2 oils because price differentials pretty much disappeared, and they received more oxidation protection for essentially the same price.
ASTM D2440 is not normally considered an acceptance specification at the time the oil is received by the buyer. The normal acceptance tests are normally ASTM D1816 which is a dielectric strength test as well as moisture content. In rare instances, power factor is taken at delivery site. Crude selection also plays a role in degree of difficulty for the refiner to overcome when running his crude slate at the refinery. Naphthenic crudes are generally not especially acidic or sour. Some of the best naphthenic crudes are actually quite clean relative to other crudes refineries are asked to deal with.
For the foreseeable future, the transformer industry can look forward to a dependable, stable supply of high-quality hydrocarbon based transformer fluids coming out of a more than a few upgraded naphthenic base oil producers here in North America.
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