Transformers are devices that carry high current and voltages. Especially it’s the core-coil of the transformer that carries more current and voltage than the other parts. Transformer oil is used in the oil filled transformers and in some other systems such as high voltage capacitors, circuit breakers, etc. and other similar systems that have to work with high voltages and currents. People in general have less knowledge about transformer oil and its importance so due to that, a lot of transformers in Nepal seem to suffer and even get damaged.
Before getting further into the subject matter, we should first know about what a transformer oil is. Well, transformer oil or insulating oil is a special type of oil which has excellent electrical insulating properties and is stable even at very high temperatures. Transformer oil is used in transformers with the prime purpose of insulating, stop arcing and prevent corona discharge. On top of that, transformer oil also acts as a coolant and helps to dissipate or maintain the heat of the transformers.
A proper use of transformer oil will also help a lot in preserving several other parts of the transformer. A transformer’s core and windings will be fully immersed in the oil, increasing the protection to these parts. The advantage to using transformer oil in transformers doesn’t just stop there. It also prevents oxidation and acts as a barrier between the atmospheric oxygen and cellulose.
Transformers in Nepal suffer and along with themselves, the people also frequently suffer. One of the main reasons behind this is the lack of knowledge about maintaining transformers along with transformer oils. So, if we want the best operating transformers in Nepal, we should use transformer oils properly and use good quality oil along with proper and timely maintenance. Then only general public will be able to live without constant troubles caused by the breakdown of transformers.
Types of transformer oil
Mineral oil and synthetic oils are the types of oil used in transformers. Synthetic oils are the chemical products such as silicon oil and act as fire retardant. Hence, synthetic oil is used in fire prone areas and this type of is also more costly than mineral oils. On the other hand, mineral oils are basically different types of petroleum products which can be categorized into two main types.
Paraffin based transformer oil
The oxidation rate of paraffin oil is comparatively lower than that of Naphtha oil. But the disadvantage of using paraffin oil is that the oxidation product or sludge is comparatively insoluble and precipitates at the bottom of the transformer. This causes obstructions in the cooling system of the transformer and due to this, the entire system break down may even occur. Another commonly occurring problem with paraffin oil is that the dissolved waxes inside of it may lead to high pour points. However, this issue may not occur in warmer climate of plains and hills in Nepal. Despite its drawbacks, paraffin oil is a popular choice for transformers simply due to its high availability.
Naphtha based transformer oil
Naphtha oil is more easily oxidized than paraffin oil. The oxidation product or sludge in naphtha oil is also more soluble than the product obtained from paraffin oil. Its advantage over paraffin oil is that the sludge does not precipitates as much in case of use of naphtha oil. The bottom of transformer contains less precipitated products. This also helps to maintain temperature in the machine, causing less heating and the normal circulation of oil is also not interrupted due to this. Naphtha oil is much more suitable for use in transformers and its use has been increasing rapidly in transformers.
Apart from these types of oils, pentaerythritol tetra fatty acids and natural and synthetic acids are also found to be used. These have characteristics like low flammability, high tolerance capacity and is also more environment friendlier than mineral oils. Vegetable based oils are also used in some cases but they are often considered unsuitable for colder environment and surroundings.
Transformer oil properties
Physical Properties
Interfacial tension between water and oil interface is the way to measure the attractive molecular force between oil and water and a good quality oil always exhibits high interfacial tension. This can be measured in Dyne/cm or milli-Newton/meter. The flashpoint of transformer oil in general should be more than 140 degrees. Flashpoint is important as it is the temperature at which oil gives vapors to produce a flammable mixture with air and specifies the chances of fire hazard. Good oil should also possess low viscosity and offer less resistance to the conventional flow of oil, thereby, it won’t affect the cooling of the transformer.
Electrical properties
Dry and clean oil gives breakdown voltage (BDV) results which are better than the oil with moisture and other impurities. The minimum breakdown voltage or dielectric strength of transformer oil at which it can be used safely in a transformer is considered to be 30 KV. Specific resistance of a transformer oil is also a very important property that just cannot be missed. The specific resistance is the measure of DC resistance between opposite sides of one cm cube block of oil. The minimum standard specific resistance of transformer oil at 90oC is 35 × 1012 ohm–cm and at 27oC it is 1500 × 1012 ohm–cm. Dielectric dissipation factor is also known as loss factor of transformer oil. This is the measure of the imperfection of the dielectric nature of the insulation materials like oil. We try to keep the value as small as possible and high value is a presence of containments in the transformer oil.
Chemical properties
Presence of moisture or water is highly undesirable as it hugely affects the dielectric property of oil. Water also affects the paper insulation of the core and winding of transformers. In transformers, as the oil becomes hotter, solubility of water also increases. Water content up to 50 ppm is allowed and if the water content rises above the specified level, the transformer may be affected. Acidic transformer is a harmful thing for a transformers it deteriorates the insulation. Acidity increases oxidation and also promotes rusting of iron in presence of water. Acidity test should be conducted in the transformer oil to measure and remove contaminants.
Not only transformer oil, but transformers in Nepal in general are not tested. This results in constant break down of transformers. When it comes to transformer oil, it needs to be tested constantly as it gives idea about need of filtering and will be able to know if the soil is suitable for future use. By timely testing, we can enhance the transformer’s life and even prevent untimely failures and increase safety and reduce risks at the same time. Transformer oils can easily up to 30 years so by taking proper care of them, you will be able to save a lot of money and time.
BN Mahto Group not only is a manufacturer and distributor of transformers in Nepal, but is the top name when it comes to transformers in Nepal. We provide you with highest quality products that will not only keep you satisfied but also help in promoting your life, work and growth.