Is It Possible To Prevent Explosions Caused By Oil-immersed Transformers？

Why did the transformer explode?

Transformers convert alternating current energy into different voltages, currents, and other parameters using the principle of electromagnetic induction. In oil-immersed transformers, the iron core and windings are immersed together in insulating oil to improve insulation, cooling, and heat dissipation. During an overload, short circuit, insulation damage, or other fault inside the transformer, the insulating oil is heated and thermally decomposes to generate a large amount of hydrocarbon gas mixture, the pressure inside the transformer rises sharply, leading to structural damage to the transformer tank and an explosion of the primary transformer.

Through the rupture port of the transformer tank, insulating oil, mixed gas, and oil mist were violently released after the primary transformer exploded. A liquid pool of insulating oil forms on the ground when oil leaks from the transformer, causing a fire when ignited. Upon ignition of the leaked pyrolysis product mixed gas and oil mist, a secondary explosion will occur. Especially in confined or congested areas, these situations can result in very powerful explosions, which can cause serious socio-economic damage to people and equipment.

In transformer fires and explosions, the oil in transformers is a flammable liquid, which vaporizes when mixed with air and explodes when heated. The oil temperature will be higher if the transformer is overloaded. An arc and a short circuit can result when the insulation of the transformer breaks down due to a penetrating fault.As a result of the high temperature of the arc, the oil decomposes, vaporizes, flashes, and ignites, causing the transformer’s casing to burst and a large amount of fuel to ignite.

How can transformer explosion risks be reduced?

For most common primary explosion conditions, engineers will take this factor into account when designing transformers. Considering the serious consequences of the secondary explosion, safety must be the top priority. Safety hazards are eliminated during the design phase by making some important changes.

Explosions can be prevented by strengthening transformer inspections on a daily basis. We must therefore conduct the following inspections every day.

Dry-type transformers are inspected daily for the following items:

1. Coil insulation is intact, and phase color is correct and clear
2. Ferromagnetic debris is not present around the reactor or the air duct
3. A horizontally installed reactor has no tilt, no cracks in the main frame, and no loose deformation in the coil
4. To prevent overheating, the connection parts are in good contact
5. There is a good connection between the lead wire clip and the lead wire
6. No cracks or discharge are visible on the surface
7. To detect abnormal temperature rises and hot spots, use infrared thermal imaging or infrared thermometers
8. It is important to take good care of the transformer’s external rainproof measures

Oil-immersed transformers are inspected daily for the following items:

1. It is important to determine whether the transformer’s oil color and oil level are normal, and whether any parts are leaking oil.
2. It is important to determine if the transformer oil temperature and thermometer indications are normal and whether the remote monitoring and control device indications are accurate.
3. Inspect the busbars on both sides of the transformer for hanging objects and ensure that the hardware connection is tight; Ensure that the leads are not too loose or too tight, that the joints are in good contact, and that the thermometer is not discolored or melted.
4. The respirator should not be obstructed; Discoloration of the silica gel; The level of oil in the gas relay; Make sure that the pressure releaser is intact.
5. The porcelain bottles and casings must be kept clean without damage, cracks, or discharge traces.
6. The grounding point of the main transformer shell must be in good contact, the foundation must be complete, and the cement must not fall off or crack.
7. The on-load tap-changer’s position indication and power indication should be normal.
8. Check to see if the cooling system is functioning properly.
9. Make sure that each control box and secondary terminal box is closed, that the cable perforation is sealed tightly, and that it is dry.
10. The warning signs should be hung correctly, and various signs should be complete and visible.

What can be done to prevent transformer explosions?

1. Overloading an oil-immersed transformer for a long period of time will result in the coil heating up, the insulation gradually aging, the short circuit between the boxes, the short circuit between the phases, or the short circuit to the ground, as well as oil decomposition.
2. Prevent aging of the insulation and damage to the iron core of the oil-immersed transformer: aging of the iron core insulation or damage to the clamping bolt sleeve will result in a large eddy current, and long-term heating of the iron core will cause insulation aging.
3. During maintenance, ensure that the coil or insulating sleeve are protected, and if any scratch damage is detected, it should be addressed as soon as possible.
4. Oil-immersed transformers shall not have an unbalanced current exceeding 25% of their rated value at low voltages; Oil-immersed transformers are allowed to change their power supply voltage within a range of 5% of their rated voltage.
5. Ensure that the wires are in good contact: the internal joints of the coils, the connections between the coils, the contacts leading to the high- and low-voltage side bushings, and the various fulcrums on the tap changer are in poor contact, resulting in local overheating, insulation damage, short circuits or open circuits.Oil-immersed transformers will experience pressure increases when a high-temperature arc decomposes the insulating oil, generates a lot of gas, and decomposes the insulating oil. Gas circuit breakers will trip when the pressure exceeds the protection setting without tripping.
6. Enhance the management and maintenance of transformer operations.In accordance with the regulations, it is necessary to regularly inspect the transformer and to ensure that the oil temperature of the upper layer does not exceed the specified value (85C). Regular oil testing and preventive testing should also be performed on the transformer on a regular basis. It is necessary to prevent the high voltage bushing and low voltage bushing from rotating during transformer installation and maintenance. After installation and maintenance, necessary electrical tests must be conducted according to regulations.
7. When the three-phase load is unbalanced, current will appear on the neutral line in low-voltage systems that use protection to zero. A large current and a large contact resistance will cause the grounding point to reach a high temperature, igniting the surrounding combustible materials.