What is the difference between the mineral oil and vegetable oil?

We all know that an oil transformer requires a lot of transformer oil as an insulating medium. In addition to its insulating function, transformer oil also has a heat dissipation function. The insulating oil in a transformer occupies more than 15% of the weight. Transformer oil plays an important role in transformer insulation performance and function. Now let's learn more about transformer oil.

Table of contents
  1. What is transformer oil?
  2. What are the main functions of transformer oil?
  3. What are the requirements for transformer oil performance?
  4. What is the function of the oil of a 5000kVA transformer?
  5. Types of transformer oil
  1. Daelim transformer factory

What is transformer oil?
From the physical data of transformer oil, it is understood that it is a transparent light yellow liquid with transparency. It is mainly separated out through oil. The components are compounds such as alkanes, naphthenic saturated hydrocarbons, and aromatic unsaturated hydrocarbons. The density of relative properties reaches 0.895. The freezing point reaches <-45°C.


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What are the main functions of transformer oil?
(1) Insulation effect: Compared with the air, the dielectric strength of the transformer oil is much higher. When the internal insulating material of the transformer is immersed in the transformer oil, it also plays a moisture-proof role.

(2) The other is the role of heat dissipation: because the specific heat of the transformer oil is relatively large, it is often used as a cooling material. The entire cooling process is probably that the internal windings will generate heat during operation. After the heat is generated, it is very The oil of the adjacent iron core and winding expands and rises due to heating. At the same time, through the upward and downward convection of the oil, the heat dissipation of the transformer ensures the normal operation and operation of the entire equipment.

(3) Finally, there is an arc extinguishing function: in the transformer circuit, through the circuit breaker and another configuration on-load voltage regulating switch, each contact will generate an arc during the automatic switching process. At the same time, because the transformer oil has a very good thermal conductivity, at the high temperature of the arc, it contacts a large amount of gas and generates high pressure. In this way, on the oil circuit breaker and the on-load voltage regulating switch of the transformer, an arc will be generated when the contacts are switched. The arc performance is improved due to the good thermal conductivity of the transformer oil and the fact that it can contact a large amount of gas and generate a large amount of pressure at the high temperature of the arc.

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What are the requirements for transformer oil performance?

(1) The density of transformer oil should be as small as possible to facilitate the precipitation of moisture and impurities in the oil.


(2) The viscosity should be moderate, too large will affect convection heat dissipation, and too small will reduce the flashpoint.


(3) The flash point should be as high as possible, generally not lower than 136℃.


(4) As low a freezing point as possible should be considered.


(5) Although impurities like acid, alkali, sulfur, and ash are harmful, the lower their content, the better, as these impurities tend to cause corrosion to insulating materials, wires, fuel tanks, etc.


(6) At the same time, the anti-aging ability of oxidized and oil products should not be too high. In addition, the stability performance should not be too low, which will affect the overall quality of the oil. Some sediments that represent material indicators also usually represent the quality and activity of oil products.

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What is the function of the oil of a 5000kVA transformer?


1. The oil in the 5000kva three-phase distribution transformer plays the role of cooling oil in addition to heat dissipation during the operation of the transformer.

2. Ensure the insulation and maintenance of the internal windings and other positions of the transformer. The main purpose is to maintain good insulation performance.

3. Transformer oil also plays an arc extinguishing function, which is the contact of the lead high voltage and the tap changer. In this way, arcing and corona are prevented.

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Types of transformer oil

1. Mineral oiltransformer-oil-25-number

Usually, the mineral oil used in our conventional transformers is #25 and #45 oil. If the transformer is used in extremely cold weather, for example, #45 oil is usually used in Canada. In conventional countries, such as some Asia, and some regions with warmer climates in South America, #25 oil can be used.


Our general understanding is that crude oil that has been mined and processed for the first time is also sometimes oil. We can also understand it as a mineral product buried deep in the ground. At room temperature, we can also call it refined petroleum. It is a physical distillation that separates crude oil into various fractions and substances that are used to obtain different products. However, because of the different separation processes of mineral oil, the extracted components will be very different, for example, it will be divided into various lubricating oils such as crude gasoline and crude kerosene. The ideal of the chemical molecules will not be changed as a whole. Element. However, during the different refining processes, it is not possible to clear any impurities, so the flow pole of the entire mineral oil will be very high, and it is not suitable for use in very low-temperature environments. Therefore, it directly leads to the limitation of the scope of use of mineral oil.


The solvent used is separated. The production process is basically based on physical processes without changing the structure of hydrocarbons. The base oil produced depends on the content and properties of the ideal components in the raw material; the mineral oil cannot be cleaned of impurities during the refining process. The base oil has a high flow point and is not suitable for use in cold regions; therefore, mineral oil base oils are limited in nature.
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2. Vegetable oil

Environmental pollution will also be the main defect in the use of mineral oil for transformers. A vegetable oil transformer is a transformer that uses vegetable insulating oil (natural ester insulating oil) as an insulating liquid. Natural ester insulating oil is made from renewable resources, more than 98% of which are vegetable oil, which is not toxic and dangerous in water and soil. It can be completely degraded within 28 days, which can effectively solve environmental problems in reservoirs, water surface photovoltaics, agricultural greenhouses, and other fields. This clean, green and environmentally friendly equipment is suitable for areas with high environmental protection requirements (such as offshore wind power, complementary fishing, solar power, tourist areas, charging piles, etc.). In addition, compared with traditional mineral insulating oil, vegetable insulating oil is a high Ignition, environment-friendly, renewable liquid insulating medium with better safety performance. The vegetable oil transformer is small in size, the load capacity can be more than 20% higher than the mineral oil transformer, and the service life is 5-8 times that of the mineral oil system.


Environmentally friendly:

Due to the use of non-toxic, harmless, and biodegradable natural ester insulating oil, the natural ester transformer has excellent environmental-friendly properties. The 28-day biodegradation rate of natural esters exceeds 97%, while mineral oils are generally less than 30%. Natural ester has no acute oral toxicity and is harmless to organisms. Even if the natural ester transformer leaks, it will not cause pollution to the surrounding environment. Natural esters are derived from renewable crops, do not rely on petrochemical raw materials, have low carbon emissions, and are sustainable insulating oils.

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Fire Safety:transformer-vegetable-oil-FR3

The ignition point of natural ester exceeds 300°C, which is much higher than that of mineral oil. It belongs to the K-class flame-retardant insulating liquid specified by IEC 61039-2008. Its initial boiling point, saturated vapor pressure, kinematic viscosity, explosion limit, and flue gas generation rate are all better than mineral oil. Compared with mineral oil, the natural ester is more difficult to ignite and has certain self-extinguishing characteristics after ignition, which can effectively reduce the failure probability of transformer combustion and explosion14-5.

Longer insulation life:


Natural ester molecules are more polar than mineral oil and have strong hydrophilicity. At the same temperature, the relative water saturation of natural ester is about 4-30 times that of mineral oil (the higher the temperature, the smaller the difference). During the aging process, in order to maintain the dynamic balance of moisture in the oil-paper insulation system, natural esters can absorb the moisture in the insulating paper better than mineral oil, thereby delaying the aging of the insulating paper. Secondly, the hydrolysis reaction of the natural ester can consume the moisture in the insulating paper, thereby inhibiting the influence of moisture on the degradation of the insulating paper. In addition, natural esters inhibit the cellulose hydrolysis of insulating paper, thereby reducing the aging rate of insulating paper.


Higher heat resistance level:

The heat resistance grade of the natural ester is B (130 ℃ C), which is higher than the heat resistance grade A (105 ℃) of mineral oil, and the combination with cellulose paper can improve the heat resistance of the insulation system. Natural ester can be combined with high temperature resistant solid insulating material of E class (120 ℃) ​​and above to form a hybrid insulation system and high-temperature insulation system to improve the temperature rise limit of natural ester transformers

3. Silicone oil

The biggest disadvantage of silicone oil is that the price of silicone oil is too expensive. The price of silicone oil in the world is about 6 times that of transformer oil, while it is about 8 times in my country. This will increase the cost of the transformer accordingly. Price increases. However, due to the relatively simple manufacturing process of silicone oil transformers, as well as good dynamic and thermal stability and electrical insulation properties, it can reduce a lot of daily maintenance, especially the high flash point and high ignition point of black wire, as well as the self-resistance of silica decomposition products With flammability, the period has fire safety performance. With the gradual narrowing of the price difference between silicone oil and mineral oil, silicone oil transformers are still very promising.


Silicone oil transformers have the advantage of being difficult to catch fire, but they are not suitable for environments that are too humid. The large-scale production and development of this product are limited because the domestic supply of silicone oil cannot be solved at present. Silicone oil transformers will first be widely used in underground railways and electric locomotives and will be used in other areas later.


Daelim transformer factory

Daelim is a factory specializing in the production of transformers. The transformer oil we use has been strictly screened and has high quality and insulation performance. According to customers' requirements, Dalin's transformers can use mineral oil, vegetable oil, and FR3 oil.


Daelim International Transformer Cases


If you have transformer-related projects or questions, please feel free to contact Daelim.


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