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Fire risk and preventive measures of transformer

transformer is another kind of electrical energy equipment that uses the principle of electromagnetic induction to convert AC energy into different voltage, current and other parameters. Most of its internal insulation pads and supports use organic combustible substances such as paper, cotton yarn, cloth, wood, and a large amount of insulating oil. For example, the 1000 kW transformer uses about 0.012 cubic meters of wood, 40 kilograms of paper, and 1 ton of insulating oil. Therefore, its fire danger lies in its easy combustion. Once there is a serious overload and short circuit inside the transformer, the combustible insulating materials and insulating oil will be decomposed and burned by high temperature or arc, and a large amount of gas will be generated, which will sharply increase the pressure inside the transformer, causing the outer shell to fully consider the product performance requirements, burst, a large amount of oil injection, and the burning oil flow will further expand the fire hazard and cause a large area of power failure, Affect normal production and life. The causes of fire and explosion of transformer in operation are as follows:

(I) insulation damage

1 Aging of coil insulation

when the transformer is overloaded for a long time, it will cause the coil to heat, gradually aging the insulation, causing inter turn short circuit, inter phase short circuit or short circuit to the ground, causing the transformer to burn and explode. Therefore, the transformer should be tested for insulation strength before installation and operation, and overload is not allowed during operation

2. Poor oil quality and too little oil quantity

the insulation strength of transformer insulation oil will be greatly reduced after water, impurities or other greasy dirt are mixed into the oil due to carelessness in storage, transportation or operation and maintenance. When the insulation strength decreases to a certain value, a short circuit will occur. Therefore, the insulating oil that has been stored for a long time must be tested before being put into operation, such as moisture, impurities, viscosity, breakdown strength, dielectric loss angle, dielectric constant, etc. During operation, the oil quality should also be tested regularly. If problems are found, corresponding measures should be taken in time

3. Aging and damage of iron core insulation

these materials can not only meet the requirements of the shell of the charging pile for weather resistance, drop resistance, environmental protection, etc., but also accelerate the aging of the insulation between silicon steel sheets, or the damage of the bolt sleeve clamping the iron core will cause great eddy current in the iron core, cause heating and increase the temperature, and also accelerate the aging of the insulation

the insulation strength of the transformer iron core should be tested regularly (the test method and requirements are the same as those of the coil). If the insulation strength is lower than the standard, the bolt bushing should be replaced in time or the iron core should be insulated

4. The insulation is damaged due to careless maintenance

the insulation of the coil and the porcelain bushing are often damaged due to carelessness during the maintenance of the hanging core. After the porcelain bushing is damaged, if it continues to operate, it will flash over at first and short circuit at last. Therefore, special care should be taken during maintenance to avoid damaging the insulation. After the maintenance, there should be a special person to count the tools (to prevent accidents caused by omission in the oil tank), check the components, test the insulation, etc., and confirm that they are intact, safe and reliable before they can be put into operation. In addition, pay more attention to the safety distance of the lead during maintenance to prevent flashover during operation due to insufficient distance, resulting in accidents

(II) poor contact of wires

the joints inside the coils, the connection points between the coils, the contacts leading to the high and low voltage porcelain bushings and the contacts on the tap changer will cause local overheating, damage the coil insulation, and short circuit or open circuit if they are in poor contact. At this time, the high-temperature arc will also rapidly decompose the insulating oil and produce a large amount of gas, which will suddenly increase the pressure, with great destructive force and serious consequences

there are the following reasons for poor wire contact:

1 Bolts are loose. 2. Poor welding. 3. The tap changer contact is damaged

for the above, please check whether the main motor source or communication line is connected normally! " For the above reasons, the following measures should be taken:

1 When the transformer is shut down for maintenance, it should be checked, and the bolts with poor contact must be tightened. For the transformer that cannot be shut down, the external contact must be checked

2. During maintenance, the welding surface must be cleaned before welding, and the quality of the welding joint must be carefully checked after welding to prevent accidents caused by the falling off of the welding joint during operation

3. The switch should be switched in place, and the bolts should be tightened one by one. Only when everything is correct can it be put into operation

(III) load short circuit

when the transformer load has a short (original) weight circuit, the transformer will bear a considerable short-circuit current. If the protection system fails or the setting value is too large, it is possible to burn the transformer. Such an accident is not rare in the power supply system

short circuit protection must be installed for this transformer. Small and medium-sized transformers (especially rural transformers) are generally equipped with drop fuses on the high-voltage side, and the melt selection should ensure that it will be fused in the event of a short-circuit accident inside the transformer or at the bushing; The low-voltage side is protected by a low-voltage fuse, and the melt should also be able to be fused in case of short circuit or overload of each outgoing circuit

in addition, the high-voltage side of the transformer can also be protected against short circuit and overload through an overcurrent relay. Gas protection, differential protection, directional protection, temperature protection, low voltage protection, overvoltage protection and other facilities shall be provided according to the operation condition, capacity and voltage level of the transformer

(IV) poor grounding

the neutral point of the secondary side (380/220 V) of the oil immersed power transformer should be grounded. When the three-phase load is unbalanced, current will appear on the zero line. If the current is too large and the contact resistance of the grounding point is large, high temperature will appear at the grounding point and ignite combustibles. For this reason, it is necessary to frequently check whether the grounding wires and points are connected completely and firmly, and regularly test the grounding resistance

in addition, pay attention to the sound of the transformer during operation, monitor the change of temperature rise at any time, check the oil level and oil color, and take timely measures to ensure safety in case of abnormalities

(V) lightning overvoltage

the current of oil immersed power transformer is mostly led by overhead lines, which is easy to be attacked by the overvoltage caused by lightning, puncture the insulation of the transformer, and even burn the transformer, causing a fire, so corresponding lightning protection measures must be taken