EP0499359A1

EP0499359A1 - Fire resistant dielectric fluid

Info

Publication number: EP0499359A1
Application number: EP92300365A
Authority: EP
Inventors: David William Sundin
Original assignee: Cooper Power Systems LLC
Current assignee: Cooper Power Systems LLC
Priority date: 1991-01-17
Filing date: 1992-01-16
Publication date: 1992-08-19
Also published as: NO920221L; NO920221D0; FI920216A; FI920216A0

Abstract

A biodegradable dielectric composition and method for making the biodegradable dielectric composition. The dielectric composition has a natural petroleum derived saturated paraffin hydrocarbon which has been processed to decrease the low molecular weight hydrocarbon content and to remove polar contaminants, and the composition further includes an antioxidant additive and a flow modifier.

Description

FIELD OF INVENTION

This invention relates to a novel composition for a biodegradable dielectric fluid and to a process for the manufacture of the fluid. More particularly, this invention relates to a composition and method that decreases the range of molecular weight species in a biodegradable, fire-resistant dielectric fluid.

BACKGROUND OF THE INVENTION

Dielectric fluids are often used in transformers, electrical switchgears and other pieces of equipment that require fluids that are generally fire and oxidation resistant and which include moderately good heat transfer characteristics and electrical properties. These dielectric fluids, however, are often limited in their use to, for example, equipment that is compatible with a more highly viscous fluid. Furthermore, these known dielectric fluids are typically not compatible with machines that are designed for use with conventional transformer oils. Moreover, these prior art dielectric fluids generally are not eligible for the "less flammable" classification given by the National Electrical Code.
Some of the above inadequacies of the prior art dielectric fluids may be attributed to the fact that it was thought that a wide range of molecular weight species in the fluid was desirable.
This thinking is exemplified in U.S. patent 4,284,522 (the ′522 patent) which discloses a composition and method for forming the composition wherein natural and synthetic hydrocarbons of different molecular weights were selectively blended to achieve a flat molecular weight distribution. According to the ′522 patent, a wide molecular weight distribution improved the physical and chemical properties of the dielectric fluid. However, while a wide range of molecular weight compounds may have improved certain characteristics of the fluid, it also adversely affected various physical and chemical parameters of the fluid in that, for example, it impeded the flow properties of the fluid composition.
Other inadequacies of the prior art dielectric fluids were partially resolved by adding adjuvants, such as antioxidants, for adjusting the viscosity of the liquid. In some, efforts were made to dewater and defuel used oil by selectively removing water, fuel fraction light hydrocarbons, light vacuum gas oils and other impurities by distillation, thin-film evaporators or wiped film evaporates. However, the addition of antioxidants for viscosity purposes or the use of an evaporator for dewatering and defueling of a fluid did not effectively resolve the viscosity and limitation problems found in dielectric fluid. Thus, the known dielectric fluids are, for the most part, extremely restrictive in their use.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novel process for the manufacture of a biodegradable dielectric fluid.
It is another object of the invention to provide a novel process that decreases the range of molecular weight species in the dielectric fluid.
It is another object of the invention to provide a novel biodegradable dielectric fluid.
It is another object of the invention to provide a novel biodegradable dielectric fluid that has a decreased range of molecular weight species.
It is another object of the invention to provide a novel biodegradable dielectric fluid that exhibits a low viscosity at temperatures of use.
It is another object of the invention to provide a novel biodegradable dielectric fluid that exhibits improved heat transfer characteristics and excellent electrical properties.
It is another object of the invention to provide a novel biodegradable dielectric fluid that includes a raised fire point.
It is yet another object of the invention to provide a novel biodegradable dielectric fluid that may be used in machines that were designed of use with conventional transformer oils.
It is a further object of the invention to provide a novel biodegradable dielectric fluid that is economically feasible to produce.
The objectives and advantages of the present invention are achieved, in a preferred embodiment, by providing a composition and method that involves decreasing the range of molecular weight species in the dielectric fluid. This is accomplished by exposing a petroleum fluid to a thin-film evaporator which removes the lighter molecular weight materials from the bulk of the oil after it has been completely processed at the refinery. Polar contaminants are removed from the effluent of this wiped-film evaporation process by allowing the effluent to contact an adsorbent medium. The contacting process can be accomplished with either an adsorbent medium in the form of a slurry or by subjecting the effluent to a percolation-type apparatus. Subsequent to the contacting process, the fluid is fortified with antioxidant additives and a flow modifier.
Thus, my composition and process of manufacturing same has numerous advantages over the prior art dielectric fluids. First, the composition and process therefor, raises the fire point of the resulting fluid and renders it usable as a dielectric fluid classified as "less flammable" by the National Electrical Code. Second, the inventive composition, and process therefor, further maintains a lower viscosity of the fluid at use temperatures than is presently available with either petroleum products or dimethyl silicone fluids. This lower viscosity allows the use of the inventive fluid in transformers and other electrical equipment that have been designed for use with conventional transformer oil. Third, the inventive composition, and process therefor, results in a dielectric fluid having a high dielectric strength and low dissipation loss.

DETAILED DESCRIPTION OF THE INVENTION

The present invention contemplates preparing a biodegradable dielectric fluid having a reduced range of molecular weight hydrocarbons, a fire point greater than 300°C and a pour point below -15°C. The dielectric fluid will have a high dielectric strength and a low dissipation loss. Generally, the dielectric fluid is prepared from a commercial hydrocarbon normally used for dielectric fluids, i.e. a natural petroleum derived saturated paraffin hydrocarbon having a narrow range of molecular weight hydrocarbons. This commercial hydrocarbon is processed to remove at least 5% by weight of the low molecular weight hydrocarbons therefrom to raise the fire point above 300°C, to remove the polar contaminants by contacting the evaporator-processed fluid or an evaporator effluent with an adsorbent medium. Then added to the processed hydrocarbons is an antioxidant and a flow modifier.
The dielectric fluid is generally biodegradable and is prepared from commercially available natural petroleum-derived saturated paraffin hydrocarbons. The natural petroleum-derived saturated paraffin hydrocarbon has a maximum viscosity at 40°C of 90 cSt., a minimum fire point of 270°C and a maximum color of 1.0 ASTM. One of the hydrocarbons we use was purchased from Chevron and was identified as natural petroleum-derived saturated paraffin hydrocarbon having a fire point of 270°C. This commercial hydrocarbon is processed to remove sufficient low molecular weight hydrocarbons. This may be done with an evaporator, such as a thin-film evaporator.
The paraffinic petroleum fluid that is processed by the above evaporator method should have an initial fire point of at least 270°C, as measured by ASTM standard method D92. Briefly, the ASTM method involves filling a test cup to a specified level with a sample of the transformer oil. The temperature of the sample is increased rapidly at first and then at a slow constant rate as the flash point is approached. At specified intervals a small test flame is passed across the cup. The lowest temperature at which application of the test flame causes the vapors above the surface of the liquid to ignite is the fire point.
The commercial paraffinic petroleum purchased will normally require removal of approximately ten to fifteen percent of the low molecular weight (lower boiling point) hydrocarbons in order to raise the fire point above the 300°C that is mandated by the National Electrical Code Section 450-23.
The effluent from this thin-film evaporation process is then contacted with an appropriate adsorbent medium i.e. Fullers Earth to remove polar contaminants. The contacting process can be accomplished with either an adsorbent medium in the form of a slurry or by subjecting the effluent to a percolation-type apparatus.
After removing the polar contaminants, the treated paraffinic petroleum effluent is fortified with antioxidant additives. The antioxidants used in this invention are the known antioxidants for dielectric fluids. The preferred antioxidants are the hindered phenols which are used at concentrations of less than about 2.0% by volume and preferably between about 0.05% and about 0.50% by volume. The hindered phenolic compound may be 2,6 di-tert butyl phenol or 2,6 di-tert butylated paracresol or mixtures thereof. Alternatively, any one of a number of related compounds may be used which have the ability to increase the oxidation stability of petroleum oils. Examples of oxidation inhibitors that may be used herein include Ethyl 701 and Ethyl 702 which are manufactured by the Ethyl Chemical Corporation, Baton Rouge, Louisiana.
After the addition of the above antioxidant additive, a flow modifier is added to the treated effluent. In the preferred embodiment, the modifier is from the alkylated polystyrene family and is added to the solution at a concentration of less than about 0.10% by weight and preferably between about 0.10% and about 0.70% by weight. The alkylated polystyrene type of flow modifier used is OA-110B, manufactured and sold by Argus Chemical Corporation. Argus also makes variations of OA-110B, such as OA-101 and OA-100A. Other companies make similar compounds that may be used as flow modifiers which include a dialkyl fumarate/vinyl acetate copolymer which is known as Paraflow 387 and is manufactured by Exxon Chemical Company, and an alkyl ester copolymer that is named Lubrizol 6662 and is manufactured by Lubrizol Petroleum Chemical Company.
The final product manufactured by this process will exhibit a fire point in excess of 300°C, a pour point (per ASTM standard method D97) of below -15°C. The fluid will have a high dielectric strength of greater than about 30 Kv and preferably greater than about 35 Kv; and low dissipation loss at 25°C of less than about 0.01% and preferably less than about 0.008%, and at 100°C less than about 0.30% and preferably less than about 0.25%; and a viscosity of less than 112 cSt at 40°C.
The following example illustrates the inventive composition and method of manufacture of the composition.

EXEMPLE 1

A biodegradable dielectric fluid was prepared from a natural petroleum-derived saturated paraffin hydrocarbon purchased from Chevron. The paraffinic petroleum had an initial fire point of 270°C.
The paraffinic petroleum is then processed by a thin-film evaporator to lower the range of molecular weight species represented by the fluid. This step removes 10 to 15% of the lighter molecular weight materials from the saturated paraffinic hydrocarbon. These are the lower boiling point constituents.
The effluent from the above evaporation process is treated by contacting the effluent with an adsorbent medium, such as Fullers Earth to remove polar contaminants. The adsorbent medium was in the form of a slurry.
Then the treated effluent was fortified by adding 2,6 di-tert butyl phenol as the antioxidant additive.
Finally the flow modifier is added.
Specifically, alkylated polystyrene was added to the composition. The amount of polystyrene added is consistent with the required flow properties of the composition. The polystyrene that is used is OA-100B manufactured by Argus Chemical Corporation.
The following tests were then performed on the dielectric fluid to verify its superior heat transfer characteristics.
The foregoing description is for purposes of illustration, rather than limitation of the scope of protection accorded this invention. The latter is to be measured by the following claims, which should be interpreted as broadly as the invention permits.

Claims

A process for preparing a biodegradable dielectric composition, which comprises treating a saturated paraffin hydrocarbon to remove at least 5% by weight of the low molecular weight hydrocarbons and a substantial portion of the polar contaminants, and formulating the hydrocarbon with an antioxidant and a flow modifier.
A process according to claim 1, wherein the composition comprises, as the antioxidant, 0.05 to 0.5% by volume of a hindered phenol.
A process according to claim 1 or claim 2, wherein the antioxidant is 2,6-di(tert-butyl)phenol and/or 2,6-di(tert-butyl)-p-cresol.
A process according to any preceding claim, wherein the flow modifier is an alkylated polystyrene.
A process according to claim 4, wherein the composition comprises 0.1 to 0.7% by weight of the alkylated polystyrene.
A process according to any preceding claim, wherein the hydrocarbon is petroleum-derived.
A process according to any preceding claim, wherein the composition has a fire point of at least 300°C and a pour point of less than -15°C.
A process according to any preceding claim, wherein the composition has a dielectric strength of greater than 35 Kv, a dissipation loss of less than 0.008% at 25°C and less than 0.25% at 100°C, and a viscosity of less than 112 cSt at 40°C.
A process according to any preceding claim, which comprises the steps of:
processing the hydrocarbon in an evaporator to remove at least 5% by weight of the low molecular weight hydrocarbons;
contacting the processed hydrocarbon with an adsorbent medium to remove polar contaminants;
adding the antioxidant to the processed hydrocarbon solution; and
adding the flow modifier to the processed hydrocarbon.
A process according to any preceding claim, wherein the composition is a solution, and the hydrocarbon is processed by an evaporator to remove at least 10% by weight of the low molecular weight species in the solution.
A biodegradable dielectric composition, comprising a petroleum-derived saturated paraffin hydrocarbon having at least about 5% by weight of the low molecular weight hydrocarbons and a substantial portion of the polar contaminants removed, a hindered phenol antioxidant and a flow modifier.
A composition according to claim 11, as obtained by a process according to any of claims 1 to 10.