43315-239036

METHOD TO DEACTIVATE CORROSIVE SULFUR IN INSULATION OIL

Cross-reference To Related Application

This application claims priority to U.S. provisional patent application 60/754,625 filed

30 December 2005.

Field of the Invention

The present invention relates to removing corrosive sulfur from insulation oil, such as insulation oil in transformers.

Background of the Invention

Power transformers, distribution transformers and reactors usually include an insulation system consisting of oil and cellulose These two components have been used for a long time due to their relatively low price and good performance. The dielectric strength of such an insulation system is strongly dependent on its insulating properties.

One problem that occurs with insulating oils used in power transformers, distribution transformers and reactors is copper sulfide, such as copper(I)sulfide, deposits forming on conductors and in solid insulation in transformers. Copper sulfide deposits can lower the initiation level for partial discharges (PD). With deposition in areas of the windings, with high electrical stresses and under certain operating conditions, especially the abundance of transients,

PD activity may lead to degradation of the solid insulation and ultimately to dielectric breakdown. In extreme cases copper sulfide growth may be so extensive that conductive bridges are formed through several layers of conductor covering paper. In such cases failures may occur even in the absence of extra-ordinary stresses.

An example of an area where the electrical stress is high is between turns in the windings. This turn-to-tum insulation is typically built up by conductor insulation, which may include paper wrapping, for example, and sometimes also spacers separating the conductors from each other. The conductors may be insulated with paper wrapping. Both the conductor insulation and the spacers will then be very sensitive for copper(I)sulfide deposits.

Problems of copper sulfide formation in transformer insulation have increased in the last ten to fifteen years. This appears to be due at least in part to increased corrosivity of insulating oils. Many transformers are filled with corrosive oil. While new less corrosive oils are being developed, it may take several years for new specifications take effect world wide. Also, it may take years to secure sufficient supplies of harmless oils. As a result, many more transformers and reactors will be filled with corrosive insulting oils. Furthermore, it will take time for cycles of transformer and transformer oil replacement to result in the elimination of corrosive insulating oils.

Reactions leading to copper sulfide formation can be prevented or suppressed by removing or reducing active copper and sulfur containing components. However, conventional insulating oil processing techniques, such as reconditioning and reclaiming have little or no effect. Reclaiming, which is typically carried out by treating the oil with a sorbent for polar

contaminants, such as Fullers earth or alumina, has as its primary purpose to remove oxidation products from aged oil, and restore it to a condition similar to that of new oil. Copper mercaptides and other copper-organic compounds can be removed with this process. However, the effect on active sulfur species can vary depending on the process used, and the effect on compounds like mercaptans, sulfides and disulfides can be small.

Summary of the Invention

The present invention provides simple methods for addressing problems resulting from use of corrosive insulation oil. According to one aspect, the present invention provides a method of deactivating corrosive sulfur in insulating oil. The method includes adding at least one sulfide forming compound to the insulating oil in oil soluble form in an amount sufficient to react with corrosive sulfur compounds in the oil.

Further objectives and advantages, as well as the structure and function of exemplary embodiments will become apparent from a consideration of the description and examples.

Detailed Description of Embodiments of the Invention

Embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and

configurations can be used without parting from the spirit and scope of the invention.

The present invention provides methods for deactivating corrosive sulfur in insulation oil. One or more compounds that react with sulfur compounds may be added to the insulation oil. The added compound(s) can react with the corrosive sulfur compounds. Through the reaction with the added compound(s), the corrosive sulfur compounds are prevented from forming copper sulfide deposits in the insulation and/or on conductors. It is thought that the present invention operates by the added compounds, such as copper containing compounds, react with corrosive compounds, such as corrosive sulfur species, in the oil, thus rendering the corrosive compounds harmless.

The added compound(s) typically are oil soluble. Also, the added compound(s) typically are sulfide forming compounds. The sulfide forming compound(s) may include one or more metals. According to one particular embodiment, the added compound(s) include sulfide forming copper compounds. One particular example of such an embodiment includes adding copper naphthenate to the insulating oil. Other oil-soluble salts and preparations of copper or of other metals such as iron and zinc can also be used.

The amount of compound(s) added to the oil may depend upon the level of corrosive sulfur compounds that the oil contains and the relative number of added compound molecules that react with corrosive sulfur compound molecules. The amount of compound(s) added to the oil may also depend upon the speed with which it is desired to deactivate the corrosive sulfur compounds. More added compounds may be added to the oil if is it desired to deactivate the corrosive sulfur compounds quickly. The amount of added compounds may be sufficient to

suppress and/or prevent the corrosive sulfur compounds from forming copper sulfide deposits on conductors, insulation, and/or other surfaces.

According to one particular embodiment, the added compound(s) may include copper naphthenate at a concentration range of from about 10 to about 500 mg Cu/kg of insulating oil. Whichever sulfide forming agent is used, a guideline for estimating a suitable dose is that a small surplus may be added, based on the stochiometric proportions of the sulfide and the amount of reactive sulfur in the oil. For a specific combination of agent and oil type, the dose may be determined by lab-scale treatment on small samples.

The added compounds may be introduced into the insulating oil with any procedure currently in use for adding materials to insulation oil. For example, procedures currently utilized for adding antioxidant or metal passivator may be utilized. No special procedures or means may be necessary to introduce the added compounds into the oil.

After the introduction of the added compounds into the insulating oil and the reaction of the added compound(s) with corrosive compounds in the oil, reaction products resulting from reactions between the added the added compound(s) and the corrosive compounds as well as excess unreacted added compound(s) may be removed. However, it is not necessary to carry out any removal process. In many cases, the insulating oil may have acceptable properties even without carrying out any reclaiming process.

In other cases, the reaction products and excess added compound(s) may be removed from the oil. The amount of time that the added compounds may remain in the oil can vary.

Typically,' the compounds may remain in the oil until the presence of corrosive compounds, particularly corrosive sulfur compounds, is reduced or eliminated. According to one embodiment, when the corrosivity and ability of the oil to form copper sulfide has disappeared, reaction products resulting from reactions between the added compounds and corrosive sulfur compounds and excess added compounds, such as copper, can be removed from the insulating oil. The reaction products and excess added compounds may be removed by utilizing standard procedures. For example, standard oil reclaiming processes may be utilized. According to one particular example, on-line processing may be utilized.

_. The present invention can fulfill the potentially large demand for methods to reduce corrosive components in insulating oil. The simplicity of the present invention makes the present invention particularly attractive to reduce corrosive components in insulating oil. The lack of special equipment necessary to carry out the present invention makes this particularly true.

The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.