Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heterocyclic ring compound; a heterocyclic ring is one...
Reexamination Certificate
1999-05-21
2001-04-10
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heterocyclic ring compound; a heterocyclic ring is one...
C508S280000, C508S584000
Reexamination Certificate
active
06214776
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrical and transformer oils and more particularly to electrical oils suitable for use in electrical devices operating under severe electrical stress such as circuit breakers, switchgear and load tap changers.
BACKGROUND OF THE INVENTION
Present commercial practice is to use conventional naphthenic transformer oils in electrical devices operating under severe stress such as transformer load tap changers. Unfortunately such oils have poor oxidation and chemical stability under severe loading conditions of high current, fast contact switching speeds and arcing. Over time a deposit of carbonaceous material tends to build up on the contacts, distorting the contact surface, insulating the contacts and resulting in overheating of the contact and loss of temper of the contact spring.
Also over time the silver overlay on load top changer contacts may become worn away leaving the copper contact exposed. Exposure of the copper surface to conventional transformer oils tends to catalyze oil oxidation.
One object of the invention is to provide improved transformer load tap changer oils which reduce the build up of deposits on the tap changer contacts and thus extend their in-service life.
Another object of this invention is to provide an oil with improved oxidation stability to minimize the formation of oxidized products in the transformer oil.
A further object of the invention is to provide a load tap changer oil that will provide a film covering any exposed copper surface resulting from wear of contact silver overlay.
Yet another object is to provide an oil that will extend the in-service life of electrical devices such as circuit breakers, switchgear and load tap changers.
These and other objects of the invention will become apparent upon a reading of the description which follows.
SUMMARY OF THE INVENTION
Briefly stated, an oil composition is provided comprising a major amount of a low viscosity paraffinic or naphthenic oil, such as less than about 20 cSt @ 40° C., preferably 5 to 15 cSt @ 40° C. and an effective amount of an additive system which includes:
i) at least one hindered phenol anti-oxidant, and
ii) a metal deactivator
The composition is especially useful as an electrical and transformer oil.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the present invention utilizes a major amount of a low viscosity paraffinic oil having a viscosity less than about 20 cSt @ 40° C., preferably 5 to 15 cSt @ 40° C. An example of such an oil is a solvent refined 75N paraffinnic basestock sold by Exxon Corporation, Dallas, Tex.
The composition also utilizes an additive system which includes (i) at least one hindered phenol antioxidant, (ii) metal deactivator.
Typical hindered phenolic antioxidants suitable in the compositions of the present invention may be represented by formula I and formula II:
where R
1
and R
2
may be the same or different alkyl groups, especially branched alkyl groups, containing 3 to about 9 carbon atoms. Preferred phenolic antioxidants include 2,6 di-tert-butylphenol, 2,6 di-tert-butylparacresol and mixtures thereof.
The additive system also includes a metal deactivator such as an alkyl substituted benzotriazole present as a reaction product of the benzotriazole and a diphenyl amine. The preferred metal deactivator is 1,2,3 tolytriazole. This reaction product of the benzotriazole and the diphenyl amine is used in place of the benzotriazole and diphenyl amine as separate components to facilitate blending of the oil, since the benzotriazole typically is a solid and must be dissolved in the oil, whereas the blend of the two is a liquid. A typical benzotriazole diphenyl amine may be represented by the formula III
wherein R
1
and R
2
may be the same or different alkyl groups having from about 3 to about 15 and preferably about 4 to about 9 carbon atoms and R
3
is an alkyl group of from 1 to about 15 carbon atoms and preferably 1 carbon atom.
In general, the additive system in the composition is present in a minor but effective amount. For example, the hindered phenol or mixtures thereof typically will comprise from about 0.05 to about 3.0 wt % based on the weight of the paraffmic oil, and preferably 0.5 wt % to 2.0 wt %. The metal deactivator typically will comprise from about 0.01 to about 1.5 wt %, based on the weight of the paraffinic oil, and preferably from about 0.10 to 1.0 wt %.
Finally, the additive system may also include a pour point depressant capable of lowering the pour point to below the lowest temperature expected for the climate in which the tap changer is to be used. This would normally be a temperature of −30° C. to −40° C. A particularly preferred class of pour point depressants is alkylated polystyrenes. The pour point depressant will comprise from about 0.10 to about 1.0 wt %, based on the weight of paraffinic oil and preferably from 0.4 to 0.8 wt %.
Alternatively this low temperature performance can be provided through the use of a base oil having the requisite pour point achieved for example by catalytic dewaxing or solvent dewaxing.
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patent: 6046144 (2000-04-01), Karol et al.
patent: 0499359 (1992-08-01), None
patent: 0497467 (1992-08-01), None
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Angelo Jacob B.
Gragg Frederick Michael
Kent Christopher Jeffrey Still
Dvorak Joseph J.
Exxon Research and Engineering Company
Johnson Jerry D.
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