Fire behaviour of natural ester transformers

　　In recent years, the transformer explosion and fire events occur frequently, improve the fire safety of the transformer can be said to be imminent. When it comes to transformer fire, let's talk about the reason why it caught fire. First of all, the three elements of combustion: fuel, oxygen and temperature; as long as one element is not satisfied, combustion can not happen. Under normal circumstances, oil-immersed transformer internal insulating oil and other insulating materials and oxygen isolation, and transformer normal operation temperature is generally lower than 105 ℃, so it will not burn. Transformer fire is usually caused by internal body failure, the vast majority of the body of the internal breakdown, caused by the arc, the oil tank can not withstand excessive gas pressure, rupture of the insulating oil escaped by the arc caused by the fire. Therefore, we can see that the fire performance of the insulating oil directly affects the fire performance of the transformer. Therefore, the use of insulating oils with a high ignition point can reduce the risk of fire to a very low level.
　　According to the classification of liquid insulating fluids in the relevant standard IEC 61039, insulating fluids with a flash point of more than 300°C belong to class K insulating fluids. Natural ester insulating fluids, whose ignition point is generally greater than 300°C, are classified as class K flame-retardant insulating fluids, and their fire risk is much lower than that of class O insulating fluids (mineral oils). According to the relevant standards, the experience about 01 grade insulating liquid shows that: the oil pool fire combustion caused by the greatest harm, but there has not been a record of oil pool fire of K grade insulating liquid, even if the K grade insulating liquid is ignited can be quickly terminated combustion.
　　For flammable liquids, the most important fire hazard parameters are flash point and ignition point. In general, the higher the flash point ignition point, the higher the fire safety of the flammable liquid. The following table shows the ignition and flash points of natural esters and conventional mineral insulating oils. It can be seen that: natural ester has higher flash point and ignition point than mineral oil, and has better fire safety. The ignition point of natural ester insulating oil is around 360℃, which is nearly 200℃ higher than the traditional mineral insulating oil. From the perspective of fire prevention, we hope that the flash point and ignition point of the insulating oil are as high as possible; and the ignition point of natural ester is greater than 300℃, which belongs to the K class flame retardant liquid, so it has very good fire prevention characteristics; compared with the traditional mineral insulating oil, the flash point and ignition point of the natural ester insulating oil has a great advantage in the transformer fire performance.
　　We through the natural ester and mineral insulating oil and then test comparison found that: with acetylene gun ignition of the two insulating oils, in the mineral oil has been ignited and continue to burn, the natural ester has not been ignited (the following figure). This also further shows that, under the same conditions, compared with mineral oil, natural ester is less likely to catch fire and has better fire resistance.
　　Fire resistance is a key factor when selecting insulation media for transformers. This is especially true in areas where the fire rating is high and the fire is difficult to control, such as underground tunnels, ships, offshore wind farms, underground factories, densely populated areas, and high-rise buildings.