WO2011134050A1 - Apparatus and method of dehydration of transformer insulating oil by continuous fluid flow - Google Patents

Abstract

The invention deals with increasing the quality of insulating mineral oil in transformers, by providing an isolating layer of flowing nitrogen over the oil's surface to keep ambient air from combining or absorbing with or in the oil, also removes water from the oil. The invention has application in the field of transformers where it is useful to provide self-sufficient and environmentally friendly equipment and methods to prolong service life and reliability between service or inspection of medium, high, and extra-high voltage power. A method and apparatus is provided which by continuously flowing a fluid, preferably gaseous nitrogen, across the surface of insulating oil in an electrical transformer both segregates the oil from atmospheric oxygen and picks up and removes water (among other things) from the oil. This reduces dangerous and harmful water buildup in the transformer on a continuous basis.

Description

APPARATUS AND METHOD OF DEHYDRATION OF TRANSFORMER INSULATING OIL BY CONTINUOUS FLUID FLOW

FIELD OF THE INVENTION The Invention relates to the field of power transformers. In particular, the Invention, in one embodiment, is a method and apparatus to reduce decay of mineral insulating oil used in power transformers by removing water from in solution in the oil and absorbed by the paper insulation of windings.

The Invention has particular application, but is not thereby limited, in the field of power transformers, where it is useful to use a self-sufficient and environmentally friendly method or apparatus to prolong the service reliability and life expectancy of medium, high and extra high voltage power transformers by removing water from the oil and paper insulation.

BACKGROUND OF THE INVENTION

It is commonly understood that insulating liquid, commonly an oil or hydrocarbon is used in power transformers. A number of methods exist for various treatments relating to transformer oil. See Canadian Patent No. 1,227,026 (United States Patent No. 4,498,992), which claims a process for treating contaminated transformer oil by heating the oil and passing it through an absorber, then chilling the oil, and Canadian Patent No. 2, 143,580, a method for eliminating the oxidation of dielectric fluid using a continuous flow of inert gas and an expansion chamber. Also see United States Patent No. 5,942, 121 , which claims a method for filtering and removing products of aging in oil using a mechanical filter, an adsorbent and degassing process, and United States Patent No. 4,806,276, an additive for transformer

WSLegal\064562\00007\ 5994900v] oils comprised of a non-ionic fluorosurfactant and a halogenated hydrocarbon. Further, United States Patent No. 6, 193,786 claims a method and device for portable degasification, reducing the concentration of combustible gases in insulating oils, by forming a combustible gas-inert mixture and venting the mixture.

It is also known to use a gas or liquid analyzer with a transformer. See Canadian Patent No. 2,014,619, which claims a method and apparatus for analyzing gases in dissolved insulating oil, involving the use of separate gas stripping zones communicating with a flame ionization detector side and thermal conductivity detector side of a chromatograph. Also see Canadian Patent No. 1,082,774, which claims an apparatus and method for detecting and measuring fault gases in oil insulated transformers using a cell loop and hollow tubes, and Canadian Patent No. 2,054,616, which provides a method of determining the stability of insulating oil by ionizing and determining the concentration of free radicals in oil, and absorption spectra of oil before and after ionization of the oil.

Several technologies exist that attempt to prevent the deficiency presented by the absorption of elements in air that jeopardize the service reliability and shortens the life expectancy of power transformers. The presence of water in insulating oil is known, and is thought to occur due to either or both of: (i) absorption from atmosphere where the oil's surface is exposed to air (for instance in a conventional freely breathing transformer's expansion chamber); and (ii) as a by product of chemical reactions in the oil during operation of the transformer (for instance, a combination of oxygen and hydrogen component of the hydrocarbon oil). The water is found both in the oil and absorbed in paper insulation elements of the transformer; an equilibrium is reached between the levels of water dissolved in the oil and water absorbed in the paper, as the oil and paper are situated together in the transformer. Water is deleterious to the long-term operation of a transformer

WSLegal\064562\00007\ 5994900v l - 2 SUMMARY OF THE INVENTION

A method and apparatus is provided which by continuously flowing a fluid, preferably gaseous nitrogen, across the surface of insulating oil in an electrical transformer both segregates the oil from atmospheric oxygen and picks up and removes water (among other things) from the oil. This reduces dangerous and harmful water buildup in the transformer on a continuous basis.

During experimentation with the invention of US Patent 7,205,874 an unexpected and beneficial result was observed and measured in real life conditions: the removal of water from transformer insulating oil by the continuously flowing nitrogen gas blanket which was provided to segregate the oil from atmosphere (and remove dissolved oxygen from the oil). Briefly, a conventional freely breathing transformer system was modified to replace the continuously varying air layer in the expansion chamber and the associated dehydrator/filter which scrubs water from air coming into the chamber when the oil's volume declines (prior art) (due to reduced temperature or load variation, for instance); with a gaseous nitrogen source (in the case of the experiment, a bottle of compressed dry nitrogen equipped with a pressure regulator to flow nitrogen into the expansion chamber with an added (regulated) vent to permit the nitrogen introduced to the expansion chamber to exit, thus providing a continuous flow of nitrogen into the chamber in the space above the oil, in order to effectively isolate the insulating oil from atmosphere.

It was expected that the nitrogen would eliminate the exposure of the oil to atmospheric oxygen, which was confirmed. The nitrogen gas also captured water dissolved in the insulating oil. The replacement of dissolved oxygen and dissolved water in the oil by nitrogen follows Henry's Law and takes place because of the respective partial pressures of the oxygen, nitrogen and water in the oil. The discovery was experimentally confirmed when the nitrogen exiting the expansion chamber was bubbled through a vessel filled with insulating oil, and the observation

WSLegal\064562\00007\ 5994900v l - 3 - that the oil in the vessel became clouded; this initiated further laboratory investigation which uncovered unexpected amounts of water in the nitrogen gas leaving the chamber, as well as an unexpected reduction in the amount of water in the oil and paper insulation after the nitrogen flow had been operational for some time period. We also discovered that the amount of water in insulating oil was high prior to operation of the apparatus of this invention, pointing to an unrecognized need to remove this unexpectedly high concentration of water from the oil. Water inside a highly electrified transformer system can cause unexpected short circuits (water being electrically conductive) causing operational failure and equipment damage; in addition to being conductive, water is also corrosive, causing increases in the rate of deterioration of paper and oil insulation and metallic parts, among other things, in the transformer, and increasing needs for maintenance, reducing insulating oil useful life, and reducing transformer service reliability.

We note that, while the use of nitrogen is preferred due to the other benefits associated with the prior art (e.g. US 7,205,874), the benefit of water removal would be provided by any number of fluids flowed past and in contact with the insulating oil, if the provided fluid has suitable characteristics, such as having a useful partial pressure in relation to the oil and dissolved water, being hydroscopic or capable of accepting water in solution or replacing water dissolved in the oil, and carrying the water away from the oil, thus dehydrating the oil.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure One (1) schematically illustrates an embodiment of the Invention comprised of transformer 1 , gas compressor 2, nitrogen membrane generator 3, nitrogen 4, oil expansion chamber 5, oil 6, trace gases 7, trace gas analyzer 8, gas relay 9, transformer tank 10, oil pump 1 1 , reactivable adsorption tower 12 and Fuller's Earth 13.

WSLegal\064562\00007\ 5994900vl - 4 - Figure Two (2) schematically illustrates an embodiment of the Invention as an apparatus comprised of a transformer 1, with gas compressor 2, nitrogen membrane generator 3, nitrogen 4, oil 6, trace gases 7, trace gas analyzer 8, transformer tank 10, oil pump 1 1, reactivable adsorption tower 12 and Fuller's Earth 13.

DETAILED DESCRIPTION

The descriptions here are meant to be exemplary and not limiting. It is to be understood that a reader skilled in the art will derive from this descriptive material the concepts of this Invention, and that there are a variety of other possible implementations; all components used in the Invention may be comprised of any suitable material or materials and substitution of different specific components for those mentioned here will not be sufficient to differ from the Invention described where the substituted components are functionally equivalent.

The following described embodiments of the Invention display preferred compositions but are not intended to limit the scope of the Invention. It will be obvious to those skilled in the art that variations and modifications may be made without departing from the scope and essential elements of the Invention.

A known embodiment of the Invention is a method comprised of a transformer, gas compressor, nitrogen membrane generator, oil, gases, oil expansion chamber, trace gas analyzer, gas relay, transformer tank, oil pump, reactivable adsorption tower and Fuller's Earth, without expansive chamber or gas relay.

Under the new method and apparatus used by the Invention, a nitrogen source provides a nitrogen blanket 4 above the surface of the oil 6. The dynamic nitrogen blanket 4 prevents atmospheric oxygen from contact with the oil 6 and the absorption of water by the nitrogen in the expansion chamber and removal of the

WSLegal\064562\00007\ 5994900v l water (and nitrogen) from the oil and the chamber via the vent, so the initial properties of the oil are maintained and even improved, thus both preventing the decline of the transformer service reliability and extending life expectancy. By eliminating the dissolved oxygen that deteriorates the chemical stability of the oil and removing water which is harmful to the oil and the solid (paper) insulation, the purity of liquid oil insulation can be maintained for the lifetime of the power transformer. The oxidation process is eliminated and any absorbed water initially present decreases until it disappears, improving the quality of the oil during use.

In a preferred embodiment a flow of roughly 99.8% purity nitrogen 4 is supplied by a gas compressor 2 and a membrane nitrogen generator 3, and it is continuously injected at one end of the expansion chamber 5 into its gas space and vented at the other end into the atmosphere.

According to Henry's law, the content of gases dissolved in oil of a power transformer is proportional with the partial pressure of gases above its surface. Therefore, when gases are generated inside a transformer tank 10 due to the decomposition of oil under the impact of an incipient electrical failure (hot spot or partial discharge), the arising gases that dissolve in the oil will partially diffuse into the dynamic nitrogen blanket 4. As a result, while the dynamic nitrogen blanket 4 transforms an existing free breathing transformer into an effectively closed or at least oil isolated one, arresting the access of atmospheric oxygen to the surface of the oil without modifying the original design, it also removes water form the insulating oil, which in turn removes water absorbed in the paper insulations in the main immersion tank.

Essentially, the method utilized in the Invention provides a system whereby the initial purity of the oil is maintained for the entire lifetime of the transformer and the liquid insulation provides a method of removal of water that may damage the solid insulation. This lessens the decay of mineral insulating oil while in

WSLegal\064562\00007\ 5994900vl - 6 - service. A further economic advantage of the Invention is that separate desiccators are no longer necessary.

According to conventional transformer design, the role of an expansion chamber is to minimize the surface of oil in contact with the gas space connected to the outside atmosphere by a back and forth circulation pipe, and to introduce the gas relay 9 between the tank and the conservator to isolate dissolved gases in the one chamber from the other. The application of the new transformer apparatus consisting of a one way dynamic nitrogen blanket system free of both oxygen and moisture renders the expansion chamber redundant although the system can be retro-fitted to older two-chamber design if desirable.

In the foregoing descriptions, the Invention has been described in known embodiments. However, it will be evident that various modifications and changes may be made without departing from the broader scope and spirit of the Invention. Accordingly, the present specifications and embodiments are to be regarded as illustrative rather than restrictive.

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Claims

An electrical transformer with components immersed in an insulating oil, the insulating oil being provided with a continuous flow of fluid over a surface of the oil, the fluid removing water from the oil on a continuous basis.

The transformer of claim 1 where the fluid is gaseous nitrogen.

The transformer of claim 1 where the fluid is chemically inert.

An electrical transformer with components immersed in an insulating oil, provided with an expansion chamber connected by a fluid passage to the main transformer chamber where the components are immersed, the expansion chamber to hold part of the insulating oil when the oil expands due to elevated transformer operating temperatures, the expansion chamber' s useful volume providing for a vent to atmosphere to provide for approximate pressure equalization between the expansion chamber and atmosphere which involves ensuring that the expansion chamber will always have a space above the oil which is not occupied by the oil whether the oil has expanded due to high temperatures or contracted due to low temperatures, that space being occupied by a fluid separate from the oil but in continuous flow from a source, with controlled fluid pressure and flow rate to the space over the surface in the oil in the expansion chamber and out the vent in a controlled manner, the fluid absorbing water molecules from the insulating oil thus removing water in the insulating oil.

The transformer of claim 4 where the fluid is gaseous nitrogen.

WSLegal\064562\00007\ 5994900vl

6. A method of removing water from insulating oil in an electrical transformer by causing a continuous flow of fluid over the surface of the oil, the water moving from the oil into the fluid in flow and being exhausted with the fluid from the transformer. 7. The transformer of claims 1 or4 or 6 where the water removed from the oil has first been removed from a solid insulation transformer component by the oil.

8. The method of claim 6 where the fluid is gaseous nitrogen.

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