How to weld and repair oil leakage from transformer welding wires is an issue that all transformer operators attach great importance to. If the power is cut off and the oil is drained for welding repairs, the transformer body is still in the oil tank. Since the insulation of the transformer body has been soaked with oil, some oil, gas and oil will remain in the oil tank. During arc welding repairs, the oil, gas and oil will easily combustion. If the transformer is completely disassembled and the oil is drained for welding repair, a large amount of disassembly work will be required. The transformer body will need to be re-dried if it stays in the air for too long. The oil stuck in the oil tank must be flushed with steam before welding repair can be performed. This workload is too much and the power outage time is too long.
So, can I bring oil to fix the leak? The combustion of oil is conditional. First, it must have a certain temperature; second, it must have enough oxygen. Both are indispensable. When repairing leaks in an oil tank containing a large amount of transformer oil, although a large amount of heat is transmitted to the oil through the tank wall, due to the convection heat dissipation of the oil in the tank, the hot oil is surrounded by a large amount of cold oil, and the high-temperature oil quickly loses heat. At the moment of welding, the temperature in the oil tank close to the welding point is only about 55°C, and the repair welding time with oil is short, so the oil cannot burn. In addition, there is no air in the fuel tank and there is no oxygen in the oil, so there is not enough oxygen to supply the combustion of the oil. Therefore, with proper control, leak repair with oil will not burn.
However, although the inside of the oil leak is not easy to burn during the leak repair process, the leaked oil and the oil in the leaking area are very easy to burn and decompose, forming a strong air flow that makes the droplets reach the leak; excessive oil flow will also directly Extinguishing the arc makes leakage repair impossible, which is the main difficulty.
Secondly, the burning fumes and oil are mixed together, contaminating the leakage point. Even if the air tightness is broken, the leakage will become multiple.
Secondly, the intense convective heat transfer of the oil in the tank prevents the temperature of the tank wall from rising. The leaked oil decomposes rapidly, causing the droplets to quickly cool down and reducing the fusion ability of the droplets.
Based on the above difficulties, in order to achieve welding repair with oil, the following measures can be taken:
a. According to the characteristics that the heat of oil leak repair will dissipate quickly, arc welding should be used for repair, and gas welding should not be used.
b. In order to prevent the oil flow from extinguishing the arc and hindering the fusion of droplets, asbestos ropes and other materials can be used to block the leak in advance before welding. This can eliminate or reduce the oil flow; for leaks that cannot be blocked in advance, such as strips If the leakage is cracked, it can be repaired part by part. After the leakage is reduced to one point, it can be plugged with asbestos rope and repaired; for small leaks on thick plates, they can be twisted with a sharp hammer before welding; for micro-seepage The arc quick point separation method is generally used to bake the surrounding area of the leakage, causing it to heat up and expand, suppressing the oil flow, and then welding is completed in one fell swoop.
In order to resist the decomposition force of the residual Shantou current, a large arc can be used for repair welding. Welding rods of Φ3.2 and below can be used for repair welding, and the current is 65~75A per millimeter in diameter.
c. When repairing welding, transport the welding rod from top to bottom, and weld the leakage quickly after ignition.
d. The welding speed should be fast. If the leakage is large, it is best to weld for a while and then stop for a while to allow the oil to cool down.
e. It is best to use negative pressure and oil repair welding. Use a 2X-0.5 vacuum pump, remove the motor and its chassis, use the hand crank to drive the pump shaft, make the suction port into a tee to install the vacuum pump, and then use a thick-walled hose to connect to the breathing port of the oil conservator. Connect, as shown in Figure 90-1. Measure the vertical distance from the place where welding needs to be repaired to the oil level, and find out the corresponding vacuum degree according to Figure 90-2. The current should be about 180A, and the oil stains at the leaked oil should be wiped clean with 32-1 type cleaning agent. Close the transformer and turn the vacuum pump crank at a speed of 50r/min. After reaching the specified vacuum degree, welding can be performed.
The advantage of negative pressure leak repair is that it can be done with confidence no matter the leakage is in the lower part or the upper part, and it is easy to weld firmly. The molten iron during welding flows into the pores due to negative pressure, and fire will not occur.
It is possible to repair leaks with oil, but you must gain experience in practice; at the same time, prepare sand and foam fire-fighting equipment; there should be no flammable objects on the ground nearby; use iron plates to block places where sparks are likely to splash; the leak repair point should be on the oil surface 100~200mm below the line; welding cannot be carried out for a long time to prevent the pressure in the box from increasing (except for the negative pressure method); welding cannot be carried out when there is no oil in the box. After leak repair with oil, the oil must be filtered. The hydrocarbon gases caused in the oil are filtered out to avoid misjudgment of the results during chromatographic analysis.
