Some measures to reduce partial discharge of the h

Some measures to reduce partial discharge of power transformer

among the factors causing partial discharge, foreign matters and dust are very important inducements. The test results show that, ф one point five μ Metal particles of more than m may produce a discharge much greater than 500pc under the action of an electric field. Whether metallic or non-metallic dust exists, it will produce a concentrated electric field, which will reduce the initial discharge voltage and breakdown voltage of insulation. Therefore, in the process of transformer manufacturing, it is very important to maintain a clean environment and body, and dust control must be strictly implemented. Strictly control the extent to which the products may be affected by dust during the manufacturing process, and establish a sealed dust-proof plant. For example, when leveling wires, wire wrapping paper, winding winding, winding suit, iron core stacking, insulator manufacturing, body assembly and body finishing, foreign matter residues and dust are absolutely not allowed to enter. Strictly control the extent to which the products may be affected by dust during the manufacturing process, and establish a sealed dust-proof plant. For example, when leveling wires, wire wrapping paper, winding winding, winding suit, iron core stacking, insulator manufacturing, body assembly and body finishing, foreign matter residues and dust are absolutely not allowed to enter

2. Centralized processing of insulating parts

insulating parts are very taboo to contain metal dust, because once the insulating parts are attached with metal dust, it is very difficult to completely remove it. Therefore, it is necessary to conduct centralized processing in the insulation workshop and set up a machining area, which should be isolated from other areas producing dust

3. Strictly control the machining burr of silicon steel sheet

the transformer core sheet is cut and formed by longitudinal shear and transverse shear. These shear cuts all have burr to varying degrees. Burr can not only cause inter chip short circuit, form internal circulation, increase no-load loss, but also increase the thickness of iron core and actually reduce the number of laminations. More importantly, when the iron core is inserted into the yoke or vibrated during operation, burrs may fall on the body and discharge. Even if the burrs fall on the bottom of the box, they may be orderly arranged under the action of the electric field, resulting in ground potential discharge. Therefore, the burrs of the core piece should be as few as possible. The burr of 110kV core piece shall not be greater than 0.03mm, and that of 220kV core piece shall not be greater than 0.02mm

4. Using cold pressed terminals for leads

using cold pressed terminals for leads is an effective measure to reduce the amount of partial discharge. Because a lot of spatter welding slag will be generated when phosphorus copper welding is used, which is easy to be scattered in the body and insulating parts. In addition, the welding boundary area needs to be separated by soaking asbestos rope, so that water will enter the insulation. If the moisture is not completely removed after the insulation is wrapped, the local discharge of the transformer will be increased

5. Sometimes there are sightseeing boats on the circular bridge at the edge of parts through rounding.

the purpose of rounding the edge of parts is to: 1) improve the distribution of field strength and increase the starting voltage of discharge. Therefore, the metal structural parts in the iron core, such as clamps, pull plates, pads and support edges, pressing plates and outlet ductile iron and some high-strength cast iron edges, the wall of the casing riser and the magnetic shielding guard plate inside the box wall, should be rounded. 2) Prevent iron filings caused by friction. For example, the contact part between the lifting hole of the clamp and the hanging rope or hook shall be rounded

6. Product environment and body cleaning during final assembly

after the body is vacuum dried, the body should be cleaned before packing. The larger the product, the more complex the structure, the longer the finishing time. Since the pressing of the body and the fastening of fasteners are carried out when the body is exposed to the air, moisture absorption and dust scattering will occur during this period, so the body finishing should be carried out in the dust-proof area. If the finishing time (or the time exposed to the air) exceeds 8 hours, it needs to be re dried. After finishing the body, carry out the vacuum pumping and oil filling stage of the fastening oil tank. We should always pay attention to the problems found in the use of the experimental machine. Because the insulation of the body will absorb moisture during the finishing stage, 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 products. The vacuum degree of vacuum pumping is determined according to the body, environmental humidity and water content standards, and the vacuum pumping time is determined according to the furnace discharge time, environmental temperature and humidity

7. Vacuum oiling

the purpose of vacuum oiling is to vacuum the transformer, remove the dead corners in the insulation structure of the product, completely exhaust the air, and then inject the transformer oil in the vacuum state to make the body completely saturated. The transformer after oiling can only be tested after standing for at least 72 hours, because the permeability of insulating material is related to the thickness of insulating material, the temperature of insulating oil and the time of oil immersion. The better the degree of immersion is, the less likely it is to discharge. Therefore, there must be enough static discharge time

8. Sealing of oil tank and parts

the sealing structure is directly related to the leakage of transformer. If there is a leakage point, moisture will inevitably enter the transformer, resulting in the moisture absorption of transformer oil and other insulating parts, which is one of the factors of partial discharge. Therefore, it is necessary to ensure the reasonable sealing performance