The safe and reliable operation of the main transformer of the nuclear power plant is of vital importance to the safety of nuclear power production. Each nuclear power plant has managed the main transformer according to nuclear equipment. Qinshan Phase II main transformer consists of three single-phase 500kV transformers, model DFP-250000/500TH, Y/Δ wiring. The transformer is located in the East China region. With the increase of the DC drop point, the DC bias has caused the main transformer vibration to increase several times, and the transformer has been running for nearly 15 years. In order to grasp the vibration of the main transformer, it is closed at no load. The vibration characteristics were tested and analyzed under rated operating conditions. The test uses the ADRE-Sxp24 channel high-precision vibration tester and the 9200 vibration sensor.
The vibration of the transformer is mainly composed of two parts: the vibration of the body and the vibration of the cooling system. The main body vibration includes core vibration and winding vibration. The main sources are: 1 periodic vibration caused by magnetostriction of silicon steel sheet. 2 The vibration of the core caused by the electromagnetic attraction between the seam of the silicon steel sheet and the lamination. 3 The tank vibration caused by magnetic leakage. 4 When the load current passes through the winding, dynamic electric power is generated between the windings, between the line cakes and between the turns, and the winding vibration is caused. The vibration of the cooling system is caused by the vibration of the submersible pump and the cooling fan.
The running transformer continuously vibrates, and its hazards mainly include: 1 magnetostriction causes the core vibration to increase, the silicon steel sheet creeps, and the surface insulating paint film wears, causing the core eddy current loss to increase. 2 The fastening bolts of the core structure are loose, so that the contact surface of the structural member is poorly connected, forming a suspension discharge, causing abnormal oil chromatography. 3 The winding pressing force is insufficient, the insulating paper on the surface of the electromagnetic wire is abraded, and the winding axial direction is gradually loosened; 4 The insulating member is displaced and broken, such as the radial protruding of the wire cake transposition pad and the breakage of the lead frame bakelite bolt. 5 causes winding deformation, reduces the ability of the transformer to withstand short-circuit current surges, and induces serious accidents. 6 causes oil leakage at the tank seal boundary.
In the case of no-load closing and power transmission, the magnetizing inrush current of the transformer can reach 6 times to 8 times of the rated current, and the vibration value is larger. The strong impact vibration easily induces transformer failure or damage. In order to deal with transformer vibration problems, it is recommended to: 1 periodically test the transformer vibration. When the vibration value is 10%~20% stable compared with the historical value, it should be paid attention to; when the vibration increases by more than 20%, it should be comprehensively determined whether there is a serious fault inside the transformer. 2 Transformer DC resistance measurement should use a small current, demagnetization should be performed after the test to reduce the residual magnetism, thus reducing the magnetizing inrush current. 3 After the transformer is powered, the oil chromatographic analysis should be carried out in time. 4 During the internal inspection, the inspection of the fasteners in the transformer was strengthened, and it was found that the looseness was corrected in time. 5 The manufacturer shall use high-quality insulation materials to improve the strength of the insulation fasteners; improve the insulation process of the transformer core pad and improve the anti-vibration capability of the transformer.
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