Some measures to reduce partial discharge in power transformers

Measures to reduce partial discharge:

1, dust control

Among the factors that cause partial discharge, foreign matter and dust are very important incentives. The test results show that metal particles above φ1.5μm may generate discharges much larger than 500pC under the action of electric field. Whether it is metal or non-metallic dust, a concentrated electric field is generated, which lowers the initial discharge voltage of the insulation and lowers the breakdown voltage. Therefore, it is very important to maintain a clean environment and body during the transformer manufacturing process, and dust control must be strictly implemented. Strictly control the degree to which the product may be affected by dust during the manufacturing process to establish a sealed dust-proof plant. For example, in the case of flat wires, wire wraps, winding windings, winding sets, core stacking, insulation manufacturing, body assembly, and body finishing, foreign matter residue and dust entry are absolutely not allowed. Strictly control the degree to which the product may be affected by dust during the manufacturing process to establish a sealed dust-proof plant. For example, in the case of flat wires, wire wraps, winding windings, winding sets, core stacking, insulation manufacturing, body assembly, and body finishing, foreign matter residue and dust entry are absolutely not allowed.

2. Insulation processing

Insulating parts are very taboo with metal dust, because once the metal dust adheres to the insulating parts, it is very difficult to completely remove them. Therefore, it is necessary to centrally process in the insulation workshop and set up a machining area, which should be isolated from other areas where dust is produced.

3. Strictly control the processing burrs of silicon steel sheets

The transformer core piece is formed by slitting and shearing shearing, and these shearing cuts have different degrees of burrs. The burr not only causes short circuit between the sheets, but also forms an internal circulation, which increases the no-load loss, and also increases the thickness of the core, actually reducing the number of laminations. More importantly: when the core is inserted into the yoke or subjected to vibration during operation, the burr may fall on the body and discharge. Even if the burr falls on the bottom of the box, it may be arranged in an orderly manner under the action of the electric field, causing the ground potential to discharge. Therefore, the core piece burr should be as small as possible and as small as possible. The burr of the core piece of 110KV product should be no more than 0.03mm, and the burr of the core piece of 220KV product should be no more than 0.02mm.

4, the lead is cold pressed terminal

The use of a cold-pressed terminal form is an effective measure to reduce the amount of partial discharge. Because of the use of phosphor bronze welding, many spatter slags are generated, which are easily scattered in the body and the insulation. In addition, the welding boundary zone needs to be separated by soaked asbestos rope so that water enters the insulation. If the moisture is not completely removed after the insulation is wrapped, the partial discharge of the transformer is increased.

5. Rounding of the edges of components

The purpose of rounding the edge of the component is to: 1) improve the distribution of the field strength and increase the initial voltage of the discharge. Therefore, the metal structural members in the core such as the clips, the pull plates, the legs and the edge of the bracket, the edge of the pressure plate and the outlet, the wall of the casing riser, and the magnetic shield on the inner side of the box wall should be rounded. 2) Prevent friction from generating iron filings. If the lifting hole of the clip is in contact with the lanyard or the hook, it needs to be rounded.

6. Product environment and body finishing during total assembly

After the body is vacuum dried, the body should be finished before packing. The larger the product, the more complex the structure, the longer the finishing time. Since the body is tightly pressed and the fasteners are fastened, the body is exposed to the air, moisture absorption and dust scattering occur, so the body should be arranged in the dust-proof area, such as finishing time (or exposed to the air). The time) is more than 8 hours and needs to be re-dried. After the body is finished, the fuel tank is vacuumed and oiled. Because the insulation of the body during the body finishing stage will absorb moisture, it is necessary to dehumidify the body. This is an important measure to ensure the insulation strength of high-voltage products. The method adopted is to vacuum the product. According to the body and the ambient humidity and water content standards, the vacuum degree of vacuuming is determined, and the vacuuming time is determined according to the time of the furnace, the ambient temperature and the humidity.

7, vacuum oiling

The purpose of vacuum oiling is to completely remove the dead air by vacuuming the transformer, remove the dead space in the insulation structure of the product, and then inject the transformer oil under vacuum to completely soak the body. The oil-filled transformer can be tested for at least 72 hours after the test. This is because the degree of penetration of the insulating material is related to the thickness of the insulating material, the temperature of the insulating oil, and the time of oil immersion. The better the degree of soaking, the less likely it is to discharge, so there must be enough rest time.

8, the seal of the fuel tank and parts