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The analysis of excessive hydrogen content in transformer insulating oil

1. The presentation and background of the problem

For many years, the stainless steel material of transformer expander often occurs in a period of insulating oil hydrogen content increased, the researchers made a lot of analysis and research, in recent years for the stainless steel corrugated oil storage tank with a similar problem, excess hydrogen produces certain interference to equipment fault diagnosis, so it is necessary to control. In recent years, our company has made an introduction to the judgment and conclusion of this research and experiment.

2. Possible causes of hydrogen enrichment

The reasons for high hydrogen content are as follows:

① The reaction of stainless steel and insulating oil.

It is considered that certain elements in stainless steel (such as nickel Ni) have catalytic effect, causing the dehydrogenation of insulating oil.

For the judgment of many units (including me) have long-term tracking test and simulation test, such as stainless steel materials airtight in insulating oil of qualified, under the running temperature and electric field condition to track the change of the hydrogen content, hydrogen content results found no apparent change. It is found that the increase of hydrogen in the product batch is uncertain, but the growth process is regular. Is often a part of the batch of products appear increasing hydrogen, and usually in the first year of the new product was put into operation, the load increases or the oil temperature rose sharply after the first time, a period of hydrogen content increases sharply, and then leveled off.

According to the reaction of stainless steel and insulating oil, this phenomenon is not explained. Because hydrogen content is not lasting increase continuously, but also is not each have higher hydrogen, even if the same material production of stainless steel expander is often a part of product produce transformer hydrogen content increased, while the other part is not. When the transformer with high hydrogen content is dehydrated by insulating oil, the hydrogen content is usually not increased again.

Therefore, to this day, the reaction of stainless steel and insulating oil is still quoted by many people in the industry, but it can't explain the specific problems, which is not recognized by the industry. As the ideal compensation element, the corrugated expander has been used and entered into the design specification. The self-corrugated oil storage tank has been used in the current market share of nearly 100,000 units.

②. Adsorption of hydrogen by stainless steel materials

That is, the surface of stainless steel has strong adsorption capacity of hydrogen molecules.

In the manufacturing process of some enterprises, hydrogen and argon mixed gas welding corrugated sheets have been used to improve the weldability of stainless steel. According to this judgment, the hydrogen molecules added in the welding process are adsorbed on the inner surface of the material, which causes the addition of hydrogen to the oil at the working temperature of the transformer. According to this conclusion, the majority of production enterprises have stopped using hydrogen and argon mixture welding and switched to pure argon welding. But even so, the companies' products still have a hydrogen problem.

Thus, hydrogen adsorption is not to the point.

③he insulating paint powder that falls off the inner wall may lead to the speculation of excessive oil and hydrogen insulation.

According to the specification, the insulating paint is usually reliable and will not react with the insulating oil.

The current ripple in oil storage cabinet wall insulating varnish is selected with the domestic large transformer factory (change especially, west change, etc.) the same tank wall insulation varnish, its chemical stability performance, insulation performance indicators such as completely conform to the electric power industry standard. In addition, after the mixing of insulating paint and insulating oil in the oil tank, the pressure, medium loss and chromatographic test of the oil tank are up to 500KV transformer oil standard, and the hydrogen content is not exceeding the standard.

④ The problems caused by water and insulating oil in insulating oil lead to excessive hydrogen.

The residual moisture in the manufacturing process leads to the addition of hydrogen.

The hydrogen in the insulating oil may be derived from the manufacturing process of corrugated expander, transformer sheet, etc., and the water that exists in the process of use. We know that if the insulating oil contains water, it is high in hydrogen in the chromatographic test. So where does the water come from?

Corrugated expander and plate radiator is an important process of flooding after production into air tightness test, hard to avoid water enter the process of operation, usually in the inspection after cleaning and drying treatment, expander is into the furnace drying (drying) also known as dehydrogenation, is hot air drying. This process is an extremely important process to prevent future hydrogen enrichment, but its effect is often ignored by some enterprises. Because of corrugated type expander and the oil in the internal corner lot, drying the gasification of moisture not easily from smaller joint discharge, water remains extremely easily, cause the drying process of gasification of moisture volatilizes not fully, after cooling will condense on the inside. After the installation and operation of the product, the water gradually enters the oil, and presents the characteristic law of the first cycle of hydrogen increasing rapidly and gradually stabilizing after a period of time. For the same reason, the internal dead Angle paint is not easy to dry out because of the same reason. The wet paint can also lead to the addition of hydrogen in the insulating oil.

In recent years, there have been many cases of hydrogen overshoot, and the result of the final field judgment is caused by the above reasons. After the operation of the transformer, the hydrogen content in the insulating oil is not too high. After the whole vacuum filter is carried out, the oil can be treated with oil.

In addition to the manufacturing process, the transport and use processes are also prone to moisture and hydrogenation.

Since the expander and oil storage tank are all welded sealed containers, once the water is not easy to be found inside, special attention should be paid to preventing moisture and moisture entering during transportation and use. For example, the valve should be sealed immediately after the factory inspection is qualified to prevent moisture from entering the internal condensation. Special attention should be paid to not opening the upper cover plate during transportation, installation and outdoor placement, otherwise the rainwater will be difficult to remove.

There are many lessons to be learned, but many companies still ignore them. In 2004, the corrugated oil storage tank produced by Shenyang Tiangong was placed in the open air for many days after the installation of a transformer factory and transformer, and it was in rainy weather. When the Shenyang Tiangong sales staff found out in the service of the factory, contacted the quality inspection department of the factory immediately, and asked to take measures to remove water from the storage tank. Results displays lower connection, release more rain water, after the use of hot oil circulation to eliminate internal moisture. But this is a special case that has been discovered in time, and there is no doubt that there will be no hidden dangers. In recent years, the oil storage tank production plant has strengthened the publicity and guidance for the use of the product, so as to arouse the attention of the use unit, especially the transformer factory. In order to prevent rainwater from entering, Shenyang Tiangong has changed the upper part of the product from the straight pipe to the side bend to prevent rainwater and debris from entering.

The problem of insulating oil material leads to the addition of hydrogen.

Transformer insulation oil or insulation material may also cause the transformer to run after the hydrogen.

3. The conclusion

To sum up, the main reason for the increase of hydrogen in the transformer is not the stainless steel material factor, but also the technological factor. The most immediate factor is that the component production process may be stored in water, wet paint, storage tank transportation and storage, etc.

4.Determination method and treatment method after hydrogen content increase.

For transformer or oil storage tank with excessive hydrogen content, oil samples can be extracted from transformer body and storage tank respectively, and chromatographic analysis can be made to determine the source of hydrogen. The results can be divided into:

①The hydrogen content of the transformer is higher than the hydrogen content in the storage tank.

This kind of situation can eliminate the possibility that the oil storage tank causes the excessive hydrogen content, the proposal focuses on the transformer fault analysis.

②The hydrogen content in the storage tank is much higher than the transformer body.

Total reserves, the amount of oil is contained in the transformer oil of 8% ~ 10%, if the oil storage tank is causing hydrogen content rising, so storage cabinet of hydrogen dilution, even if being ontology will be several times higher than that of ontology. If the hydrogen content in the oil storage cabinet is obviously higher than that of the transformer, the treatment should be placed on the storage tank.

③handling method

When the hydrogen content in the oil storage cabinet is high and the hydrogen content of the transformer is not obvious, it is recommended to vacuum the insulating oil in the oil storage cabinet.

The high hydrogen content in the oil storage cabinet and the transformer is recommended as a whole.