Fire risk of oil immersed power transformerInsulating gasket and support inside oil immersed power transformer. Most of them use organic combustible substances such as paperboard, cotton yarn, cotton cloth and wood, and there is a large amount of insulating oil (mineral oil with flash point no less than 135 is easy to decompose when heated and can burn in case of open fire).
For example, the 1000KVA transformer uses about 0.012 cubic meters of wood, more than 40 kilograms of paper and 1 ton of insulating oil. In case of serious overload and short circuit inside the transformer, the combustible insulating materials and insulating oil will decompose, expand and gasify under the action of high temperature or arc, resulting in a sharp increase in the pressure inside the transformer, which will seriously cause shell explosion and a large amount of oil injection, The burning oil flow will further expand the fire hazard, cause power failure in the factory and even the whole power supply area, affect normal production and life, and cause huge losses.
Fire causes of oil immersed power transformer(1) Insulation damagea. Coil insulation aging. b. Poor oil quality, too little oil. c. Aging and damage of iron core insulation. d. The insulation is damaged due to careless maintenance.
(2) Poor contact. Local overheating, damage to coil insulation, short circuit or open circuit, high temperature and arc, rapid decomposition of insulating oil, large amount of gas (80% hydrogen) and sudden increase of pressure. There are three reasons: loose bolts (the transformer often operates under impact load, and the vibration will cause contact looseness), loose welding and damage of tap changer contact.(3) Lightning overvoltage. The overvoltage generated by lightning strikes breaks down the insulation of the transformer, burns the transformer and causes a fire.(4) Load short circuit. When the load is short circuited, the transformer bears huge short-circuit current. If the protection system fails or the setting value is adjusted too much, the transformer may be burned. Short circuit protection device shall be installed, and the melt selection must meet the requirements. In case of internal short circuit of the transformer, the high-voltage side shall be able to fuse quickly. In case of short circuit or serious overload of each outgoing circuit of the transformer, the low-voltage side can be fused.
(5) If the transformer is overheated, the service life of the transformer will be affected at least (for example, the service life of the transformer will be 20 years under the normal working temperature of 90 ; if the temperature rises to 105 , the service life will be 7 years; if the temperature rises to 120 , the service life will be only 2 years), or fuel injection combustion or explosion will occur at most. The causes of transformer overheating are: poor contact and high contact resistance; Long term serious overload operation causes coil heating; If the voltage is too high, the iron loss will increase (when the voltage increases by 10%, the iron loss will increase by 30% 50%); The ambient temperature is too high and the ventilation is poor;
(6) The transformer is ignited by an external fire source. The combustibles stacked around the transformer ignite the transformer or transformer chamber after combustion, causing the transformer to catch fire.Fire prevention measures for oil immersed power transformer
The selection is reasonable and of high quality, which can withstand the sudden short circuit at the secondary line end without damage; Provide explosion-proof pipe (diameter and shape suitable) lightning protection facilities, fuse and other protective devices as required; The transformer shall be carefully inspected and tested before installation and after maintenance to prevent insulation damage; During operation, patrol inspection shall be carried out carefully to pay attention to whether the transformer oil leaks, whether the oil level is too low and whether the oil temperature is too high (no more than 75 ); Whether the load exceeds the rated capacity. The transformer oil shall be sampled and tested regularly. If the flash point is lower than 135 , it shall be treated or replaced in time. If you hear abnormal sound in the transformer, check it immediately.
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