Transformer oil is a kind of mineral oil. It is obtained from natural petroleum through distillation and refining. It has the characteristics of purity and stability, low viscosity, good insulation and good cooling. Normally transformer oil is a light yellow transparent liquid.
The role of transformer oil is not lubrication, but the following aspects.
Insulation Role
Transformer oil has a much higher insulation strength than air. Insulation materials immersed in oil, not only can improve the insulation strength, but also from the erosion of moisture.
Heat Dissipation Role
Transformer oil has a large specific heat, often used as a coolant. The heat generated by the transformer operation makes the oil near the core and winding expand and rise by heat. Through the oil convection up and down, heat through the heat sink to ensure normal operation of the transformer.
Arc Extinguishing Effect:
In the oil circuit breaker and transformer on-load regulator switch, contact switching will produce an arc. Due to the good thermal conductivity of transformer oil, and in the high temperature of the arc can be sub-contact a large amount of gas, resulting in greater pressure. This improves the interrupting performance of the medium, so that the arc is quickly extinguished.
Transformer oil is usually made of mineral oil and is divided into two categories.
Paraffin base oil
Naphthenic base oil
Paraffin based and naphthenic base transformer oils have their own advantages and disadvantages. The main points are as follows：
(1) Paraffin-based oils have better oxidation resistance than naphthenic oils. However, the oxidation products produced by paraffin-based oil are difficult to dissolve. Therefore, the oxidation of paraffin-based oil will produce precipitates at the bottom of the transformer. This affects the convection and heat dissipation of transformer oil.
(2) The low temperature pour point performance of naphthenic base oil is better than that of paraffin based oil.
(3) The heat dissipation of cycloalkyl oil is a little better than paraffin-based oil. Under the same viscosity, the heat transfer coefficient of cycloalkyl oil is 8%~11% higher than that of paraffin-based oil at 40℃.
When buy and use of transformer oil, please consider its performance parameters. Transformer oil is very important for the long and safe operation of transformers. It has a wide range of performance characteristics that fall into three categories.
Electrical performance indicators: including electrical insulation strength, resistivity, dielectric loss factor, etc.
Chemical performance indicators: moisture, acid value, sludge content, etc.
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Physical performance indicators: interfacial tension, viscosity, flash point, pour point, etc.
The operating environment of transformer oil has no direct relationship with transformer capacity. It is usually only related to the transformer's use and the temperature of the installation site.
In China, for example, transformer oil is classified into three sizes: 10#, 25#, and 45#. The difference in numbers indicates that transformer oil has a different freezing point. For example, 25# transformer oil has a freezing point of -25° Celsius.
Under high power operating conditions, transformer oil is usually replaced in about 3 years. During the use of the transformer, the oil level needs to be observed frequently, and new oil is added if the oil level appears to be lower.
Transformer oil failure is related to temperature, moisture, and oxidation.
First, moisture is the key influence factor. It reduces the insulation performance of the oil paper and accelerates insulation aging. And micro water will be transformed into bubbles when heated, which will easily lead to the generation of partial discharge.
The effect of temperature on the oil is often indirect. For example, the temperature resistance of the insulating paper is lower than the oil. When the insulating paper ages, a large amount of degraded furfural will enter the oil and shorten the life of the transformer.
Finally we come to the impact of air on the oil. The oxygen in the air will play a leading role in the deterioration of the oil. For example, the oxidation of unsaturated double bonds in oil produces insoluble aldehydes and ketones. These are the main components of oil sludge. And sludge oil has many side effects, such as affecting heat dissipation, adsorbing wear particles, and so on.
When selecting transformer oil, it may help you to start from the following 7 key points：
Density as small as possible to ease the precipitation of water and impurities in the oil.
Viscosity should be moderate, too large will affect convection heat dissipation, too small will reduce the flash point.
Flash point should be as high as possible, generally should not be lower than 135 ℃.
The freezing point should be as low as possible.
The lower the content of impurities such as acid, alkali, sulfur and ash, the better. To try to avoid their corrosion of insulation materials, wires, oil tanks, etc.
The degree of oxidation should not be too high.
The degree of stability should not be too low.
We at HYDGET have many years of production and business experience in the domestic and overseas markets. We have professional personnel to solve customers' problems at any time. You can browse the relevant product links in our website for more information.
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