The bolt temperature is too high because the leakage flux of the magnetic flux of the transformer winding is caused by eddy currents on the bolt. Since the magnetic flux in the transformer winding is divided into a main magnetic flux or a leakage magnetic flux, they can be divided into an axial component and a radial component. The axial component distribution is relatively simple and varies little along the winding height; the radial component is distributed along the winding height.
Based on the principle of electromagnetic induction, the leakage current of the transformer in operation will induce a large current between the surface of the transformer body and the raised seat flange of the low-voltage side. Normally, this current passes through the transformer body casing, the transformer base, and the grounding copper. The line is vented to the ground. On the contrary, the temperature is lower. Therefore, tighten all the bolts with the same tightening torque, and connect the flanges of the overheated bolts with a soft copper wire of 25 mm 2 and ground them. Then the result of the test is shown in the number 3, and the temperature of the bolts with too high temperature can be seen. No significant changes.
The 60 mm 6 mm copper row is used to connect the three-phase elevated blocks of A, B and C, and then connected to the connecting plate of the top box of the transformer. The saw blade and the trowel are used to remove the paint from the flange bolt holes and then smear. After the conductive paste is mounted, the purpose is to vent the large current induced between the surface of the transformer body and the riser flange of the low-pressure side to the earth through other means. However, after the copper busbars are connected, it is found that the maximum temperature of phase B has dropped. Obviously, the heat dissipation of the bolts has a better shunting effect on the B phase, but the temperature of the phase C has increased, and the maximum temperature is 154. .
The modified design of the transformer is mainly composed of the eddy current loss caused by the leakage flux in the clamp member, the fuel tank and the like, and the loss caused by the uneven distribution of the magnetic flux density at the joint of the iron core, etc. In addition, in the case of no power failure, the bolts of the low-voltage side riser of the main transformer and the connecting flange of the body are all replaced with stainless steel bolts, and the influence of the magnetic field on the bolts is eliminated by using the characteristics of the stainless steel material; The tightening force is the same, and the bolt tightening torque is set to 80 Nm. Replace the closed busbar between the low-voltage side of the main transformer and the enclosed busbar to replace the rubber expansion joint. The rubber expansion joint is in the form of 470 mm long and 3 bellows (for example). Replace the four outlet pipes on the top of the main transformer with stainless steel pipes of the same diameter to eliminate the influence of magnetic flux leakage on the iron material.
The top of the main transformer is replaced by the four oil outlet pipes at the top of the original transformer, and then the same diameter of the oil pipe is made of stainless steel pipes of the same diameter. In order to prevent the welding slag from falling into the transformer inside the welding, the oil outlet is covered with a 2 mm thick corrugated board, and then the spot welded stainless steel tube is assembled; then the spot welded stainless steel tube is moved to the ground until the welding is completed and cleaned. Clean and press and install. After the above transformation, the test results are shown in the serial number 11. 13. Conclusion After the efforts of the relevant technical personnel of Dongfeng Power Plant, the low voltage side of the main transformer of Dongfeng Power Plant No. 2 and the transformer body connection bolt temperature is too high. Finally solved it completely.
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