When the transformer oil is replaced
You read that correctly earlier, the individual turns of a winding are insulated. This is the only way the coil can function at all. But you've also read that the iron core doesn't make an electrical connection. Therefore, the coils must probably be isolated from the iron core. It is therefore worthwhile briefly referring to the isolation of a transformer, because it is certainly not to be neglected.
To isolation Different materials are used for the cables built into a transformer. There are mechanically stable components that are insulated with the help of plastics. In addition, there is insulation made of special paper and other suitable materials. No special materials are therefore used for insulation in a transformer. However, this is also used to isolate a transformer Coolant, because every transformer has to be cooled.
What is special about transformers is that, even though they are mathematically speaking, they are not power accomplish, get warm. The reason lies in the electrical lines through which the current flows. These lines are designed to be as tight as possible in order to reduce weight. The same applies to the products that are used for isolation to be used. This means that a transformer can get warm. We must therefore cool it.
air: You can cool transformers quite normally with air. This is done with the smaller models like you would use them at home. The material becomes warm and is cooled by the surrounding air. Specifically, you will notice this with the charger for your portable computer. It gets warm after you've plugged in the computer. This heat is dissipated through the housing. We therefore cool the material with air.
Air cooling is an easy way to prevent the transformer from getting too hot. However, air has a disadvantage because it can insulate differently. If the air is humid, it conducts electricity rather than when it is dry. Therefore, the isolation the components and lines are made stronger. You can't use the air for insulation without putting a lot of weight into the other insulation.
Even so, for these transformers, often for low Services are designed, this type of cooling is sufficient without any problems. Hence the one used depends Coolant also depends on the structure of the transformer. Transformers that are air-cooled are therefore quite heavy because they are very heavy. The Isolations had to be reinforced because of the modest cooling. But this also applies to the metals in the coils.
Seen in this way, cooling with air is a modest cooling. To the power To increase the number of transformers, one therefore has to use other means of cooling and isolation use, because now we come to the methods of cooling, which also serves as insulation. You will be surprised what kind of means can be used to cool a transformer. So let's continue with the liquids.
The transformer oil: When it comes to cooling with liquids, I start with oil. The reason for this is simple, because these transformers replaced the models that were air-cooled in the locomotives. There was such a possibility to increase the power of the transformers with the same or even lower weight. So I think we need to look at oil cooling as well.
It also offers oil an effective way to do that isolation to improve in a transformer. This allows the weight of the insulation, which consists of solid materials, to be reduced.
Paper continued to be used in place of paper, but with the oil was soaked and was able to isolate better. For this purpose, the water is removed from the paper at 100 ° C in a vacuum and this is then replaced by the oil. The insulating properties of the paper improved significantly.
However, there are special ones developed for this purpose Oils to use. This is why these oils are called transformer oil. They are distinguished by the fact that they insulate well.
Hence this can oil also as an additional isolation to be used. On the other hand, the oil also offers a great advantage when it comes to cooling the transformers. This is why these transformer oils are also used as cooling oil and thus to cool the transformer.
Cooling oils are characterized by good heat absorption. This allows the oil a much larger amount of heat can be dissipated. The consequence of this was that the ladder could be heated more strongly.
This option reduced the weight of the copper so that the transformers were still filled with oil could be built more easily. Therefore, these transformers were able to prevail.
With the help of a circulation pump, i.e. a pump that does the oil Artificially set in motion, targeted cooling can be achieved in the transformer. Such circulation pumps are also used for other oils that are used for cooling.
They make sure there is no oil can heat up too much in one place. However, forced cooling with a circulation pump for the transformer oil has negative effects.
In most cases, the transformer oil moved by the oil pump is fed to an oil cooler. This works on the same principle as the models for water. The oil is fed into a housing that had an enlarged surface. Since the walls were also thin, the heat contained in the oil could easily be released into the air.
As well as cooling with transformer oil works, it has a problem. The oil must be replaced regularly because it decomposes and can suddenly become conductive. Without this change, there would be a short circuit in the transformer. In order to be able to extend these deadlines, the substance PCB was added to particularly heavily loaded transformers. So the time until the change could be increased.
PCB stands for polychlorinated biphenyl. This additive was added to the transformer oil to extend the life of the Oil to improve. However, because the compound contains chlorine, it is considered toxic and carcinogenic. This led to PCBs being banned worldwide as an additive in transformers on May 22, 2001. It is not only its toxicity that is a problem. You could even say that it is the lesser of two evils.
Like transformer oil, PCB is flammable. If such a transformer catches fire due to a short circuit, the combustion residue creates dioxin. Dioxin is a highly toxic substance made famous by the Seveso disaster. The dioxin known as Seveso poison is highly toxic in direct contact and is considered to be carcinogenic. It is also banned worldwide and is no longer used.
In the meantime, however, these transformers have been replaced. Transformers on locomotives are not part of this group transformers contaminated with PCBs. That is, the Oilsthat are used here are not contaminated with PCB. However, this does not mean that these oils are harmless should they get into the environment. So you had to find other remedies that have similar properties but are more compatible with the environment.
The polyol ester: Polyol ester offers a solution to replace transformer oil. This liquid has similar properties to transformer oil. Polyol ester is abbreviated as POE and consists of several alcohols that have been esterified. The advantage of these coolants is the fact that they can be broken down in nature. They are therefore no longer as burdensome as the transformer oils.
Polyols are polyhydric alcohols that come from a large group consists of individual substances. Well-known polyols are, for example, glycerine or ethylene glycol, which is used as frost protection. Polyols are made from Oil from petrochemicals or from vegetable oils. The latter in particular are environmentally friendly and are therefore used in the corresponding transformers in place of the previous transformer oil.
This alcoholic Coolant is therefore well suited for transformers. Polyol ester is similar to transformer oil in its application. However, it is difficult to combine with mineral ones Oilsuch as transformer oil. Oil residues therefore do not cause a problem with the isolation. The polyol ester as a coolant in transformers could only be described as an interim solution, because there were much better and more environmentally friendly coolants.
The cooling water: A better liquid for cooling heated components is water. Water has therefore been used for cooling since ancient times. It is also a substance that is widespread in the environment and that is well tolerated because it is also present in the natural environment. Only, water, as we know it from the water pipe, cannot be used in a transformer.
We basically drink mineral water with the drinking water. The water is interspersed with minerals and salts. The proportion is so small that we do not notice these substances in the water. Special named mineral waters that can be bought in bottles have an increased proportion of these additives. However, this water is not suitable for the transformer, because the minerals make it electrically conductive and you don't want that.
You have to rid this water of the minerals. This can be achieved, for example, by heating and cooling again. This creates distilled water. This water is chemically pure and cannot electricity manage more. The reason is the composition, which now only consists of hydrogen and oxygen. Such water is well suited for cooling transformers and is extremely environmentally friendly.
However, water has one disadvantage. Due to the forced cooling, it can wash out metals. This leads to the formation of trace elements in the water again. This can lead to the water suddenly becoming conductive again, which can lead to a short circuit. However, when this article was written, these transformers are still very new, so that little information can be given about the long-term problems.
With that we are almost finished with the possibilities to cool a transformer. However, we started with the air and got back to the air through the liquids. Strictly speaking, you can take a transformer with you very well gas cool. Before you get scared, it's special gas that is used here, so let's look at gas cooling for transformers.
The gas cooling: In the case of cooling with gases, we now come to the second variant. We already got to know the first one, because it was done with normal air. But now let's look at a variant that contains a clearly defined gas instead of air. At the main switch you learned that electricity cannot spread in a vacuum. Certain gases also offer this possibility. It is therefore worthwhile if we consider gas cooling.
By the gas you don't have the problems of oil and water. Gas is not liquid and therefore cannot wash out metals and thus suddenly become conductive. You can use the gases forever and don't have to change them regularly. However, it must be noted that not every gas is suitable for cooling with gases. There are also conductive gases. It is therefore only used for cooling transformers6 Gas used.
With the abbreviation SF6 there is not much you can do. SF6 is the abbreviation for sulfur hexafluoride. The name of this Gas sounds dangerous just because of the sulfur part. Sulfur hexafluoride consists of sulfur and fluorine. This chemical compound resulted in a gas that is inert and therefore the group the noble gases can be counted. That just SF6 The said gas is therefore non-flammable and non-toxic.
Because SF6 is very heavy due to its high density, but it can be asphyxiating for humans or animals. It is very difficult for the lungs to push inhaled sulfur hexafluoride out of the body. The gas therefore remains in the lungs. This means that no more oxygen can get into the lungs. You need to do a handstand to allow the sulfur hexafluoride to flow out of your lungs.
SF6 can be used as insulating gas isolation used by transformers. There it is characterized by its high insulating capacity. This is above the values of others Gases, so that sulfur hexafluoride is also suitable for high voltages of up to 800,000 volts. The gas is also non-flammable, which can be particularly helpful with transformers, as it can even be used as a special extinguishing gas in the event of a fire.
However, sulfur hexafluoride is on the list of the worst greenhouse gases. However, such transformers come with locomotives and Railcar not applicable. Transformers in the locomotives are cooled either with air or with liquids. With liquids in particular, great advances in environmental protection have been made with polyol ester and water, so you don't have to Gases must put. As you know, gases are banned on the railways in Switzerland.
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