The transformer skeleton is a power device that is responsible for voltage conversion, power transmission, and terminal distribution in the power system. If there is a defect or fault in the high and low voltage side casing of the transformer frame, it will directly endanger the safe operation of the transformer skeleton and its power supply reliability. For the low-pressure side casing, because of its simple structure, it requires short inspection time and convenient maintenance. For the high-pressure side casing (oil-paper capacitor casing), due to its complicated structure and long maintenance period, it is difficult to overhaul. Therefore, it is very important to timely repair and maintain the oil-paper capacitive casing to reduce and eliminate casing accidents.

First, the cause analysisThrough the analysis of the previous casing failure, the following main reasons are summarized:After the surface of the casing is dirty and absorbs moisture, the insulation resistance is lowered, and the result is that flashover is likely to occur, causing tripping. At the same time, flashover can also damage the surface of the casing. After the dirt absorbs moisture, the conductivity is improved, which not only causes surface flashover, but also may increase the leakage current, causing the insulation sleeve to heat up and cause porcelain damage or even breakdown.Due to the failure of the casing gasket seal, the top seal of the oil-paper capacitive casing is poor, which may cause the water to break through the insulation, and the poor sealing of the lower part causes the casing to seep, resulting in a drop in the oil level. There are two main reasons for the failure of the casing seal: one is due to insufficient experience of the maintenance personnel, the fastening force is not enough; the second is due to the over-period operation or the quality of the rubber pad.Others, such as the failure of the grounding small casing, cause the final screen of the casing to generate a floating potential, and partial discharge occurs; the structure of the casing itself is unreasonable and has defects. For example, the main transformer casing of the substation of the transformer skeleton is soldered by the lead wire and the lead wire. The 220 kV A phase casing is the aluminum tube, the wire head is made of copper, and the rain cap is made of aluminum. The copper-aluminum connection causes an increase in contact resistance, so that the rain cap and the conductive head are sintered, and the lead and the conductive head are boiled.In addition, the casing oil standard pipe is dirty, the oil level is not clear, and the oil is formed after the pre-test sampling every year. For human reasons, for example, in the overhaul of the casing, the vacuum is not completely exhausted, so that the air remains between the screens. After the operation, under the action of the high electric field, partial discharge occurs, and even the insulation layer breaks down, causing an accident. Furthermore, the casing head structure is not properly installed. For example, the contact between the lead head and the rain cap is not tight; the rain cap is not tight with the wiring nose; the contact between the wiring nose and the terminal block is poor, and the contact resistance is increased, and the lead joint is heated and sintered.

Second, countermeasuresThrough the analysis of the operation of the transformer skeleton casing, it is not difficult to find two ways to form defects: one is that the casing itself has weak links; the other is the human factor, which is caused by the casing installation and maintenance personnel in the operation. After analyzing the main causes of casing failure, we can formulate corresponding countermeasures from the aspects of storage, transportation, installation, overhaul, and overhaul.First of all, transportation should pay attention to the problem. Lifting speed should be slow to avoid collision with other objects; when lifting and erecting, use the lifting lugs on the flange and tie the upper part of the casing with hemp rope to prevent dumping; be careful not to lift the casing porcelain skirt to prevent wire rope and porcelain The sleeves are damaged by collision; when erecting the casing, any part should be prevented from landing; when the casing is placed and transported, it should be placed in a special box. There should be two support points at the mounting flange. There should be no support for the porcelain skirt at the upper end, and support points for the tail, and the support points should be padded with soft objects. The casing should be fixed in the box to avoid turbulence damage during transportation.Second, install the issues that should be noted. Check whether the casing type is correct, whether the electrical test oil test is qualified; check whether the oil level of the casing is suitable, whether there is oil leakage or porcelain sleeve damage; check whether the lead length is suitable, wipe the casing clean, check the welding condition of the lead wire The installation of the casing shall comply with the lifting operation regulations, and the transformer skeleton shall be prevented from colliding and damaging the porcelain sleeve. The inclination of the casing lifting shall be determined according to the angle of the riser of the transformer skeleton casing, and the string of the pulling lead shall be strong and hung in the appropriate position. As the bushing is installed, the lead head is gradually pulled out, and the lead wire must not be hung or knotted. If the lead wire cannot be lifted, the cause should be ascertained, and the force cannot be pulled or pulled with a spreader; the tapered insulation of the lead wire If it is damaged, it should be re-wrapped; the lead and terminal should have sufficient contact area and contact pressure. The terminals must be reliably sealed to prevent water ingress.Again, the overhaul should be noted. Place the casing vertically on the bracket, remove the tail pressure equalizing cover, and release the oil from the tail oil plug; first remove the ground small sleeve, then remove the terminal seat washer, remove the expander; support the casing with the bracket Brake the end of the brass tube, tighten the spring pressure plate nut to compress the spring. When the fastening nut on the conductive tube is separated from the spring pressure plate, remove the fastening nut, and then remove the spring pressure plate, spring, spring seat and porcelain sleeve. Hang the brass tube, remove the tail bracket, lift the lower porcelain sleeve, remove the base, then drop the porcelain sleeve, and hang the capacitor core; reassemble the opposite of the above sequence, after assembly, put vacuum immersion oil, strictly in accordance with the process The procedure is carried out.Finally, the problem that the transformer skeleton related operators should pay attention to. Check the pre-test personnel, when disconnecting the small casing lead wire, prevent the guide rod from rotating or breaking the grounding lead. After the test, the original condition shall be restored; after the operation of the oil sample personnel, the sampling block shall be tightened; the personnel of the lead wire shall be disassembled, and the upper and lower casings shall be prevented from being mistakenly stepped on the final screen; the maintenance personnel shall observe the oil level of the casing and timely replenish the oil.

Third, specific measuresThe main reasons for the formation of casing defects are: first, due to product quality problems or improper maintenance methods; second, because the casing is not completely vacuumed during the factory or overhaul, so that the air remains in the casing screen; the third is due to the quality of the rubber pad. Off or super-period operation makes the rubber pad aging; Fourth, the casing structure is unreasonable; Fifth, the contact resistance of the wire connection part is large, causing local overheating.After formulating corresponding countermeasures, we can formulate specific measures from the main defects:Unqualified casing oil sample, including acetylene gas and other defects. The measures taken are: strict inspection of new casings to avoid failure caused by human factors.In case of poor sealing of the casing, there is an ingress or oil leakage phenomenon. The measures taken by the transformer skeleton are: to maintain the seal by replacing the rubber pad, so that the casing has no leakage.Defects such as overheating of the casing head. The specific measures can be made by changing the copper-aluminum transition to copper-copper contact, thereby reducing the oxidation. In addition, in the process of disassembly, connection and introduction, it is necessary to check whether the parts are well connected.