Analysis Of Shields Of Heavy Current Lead Wire In Power Transformer

Power Transformer is one of the important devices in Power System. Transformer has great significant in power transmission, flexible distribution and safe use. So the safe operation and service life promoting of transformer should be given due attention. When running, especially in larger capability, the heavy current of lead wire in transformer will attain 10-30 k A. The alternating magnetic field and eddy-current loss can not be ignored. Leakage flux in the end of windings will add the losses of metal structures as well as the tank, which may case local overheating and have a bad effect on safe and economical operation of transformer. Nowadays, market competition is going more and more intense, how to reduce loss, weight and cost becomes a key indicator. Current density and flux density should be increased, but the loss will be raised, so as the cost. How to solve this contradiction has already become a problem paid extremely attention in transformer engineering.In engineering practice, shield is used to reduce eddy-current loss and improve local overheating. There is a great diversity of shield material and tank material. Through the analysis of different material combination of tank and shield of heavy current lead wire, more reasonable and feasible plan on design and manufacture of transformer can be put forward. It has great significance in technology and economy. The main contributions are as follows.1 A suitable 3D simulation model based on one real oil-immersed transformer of 500 k V is built. The 3D time-harmonic simulation of heavy current lead wire model and ascending flange model is made. Contrast the simulation flux density in tank and shield with engineering design experience, the error range can be illustrated meets engineering requirements.2 For reducing the eddy-current loss in the tank of large capacity power transformer, the tank can be built of pain steel or low-magnetic steel, the shield can choose magnetic shield or electromagnetic shield. Change the material combination method of tank and shield of heavy current lead wire model and ascending flange model, separately make 3D time-harmonic simulation, compare the sum of magnetic hysteresis loss and eddy-current loss of lead wire, tank and shield, the superior one can be found.3 One-direction analysis of magnetic-thermal coupling simulation of the two models is made. By comparing computed result and empirical data, the error range can meet engineering requirements.4 Change material combination method of tank and shield of the two models, separately make one-direction analysis of magnetic-thermal coupling simulation, and compare same points’ temperature in different material combination method, the superior one can be found.5 For safe cost, in the situation of guarantee the flux density and temperature rise within the specified effective range, the design of lamination thickness should be optimize. According to arithmetic progression, the lamination thickness of magnetic shied on the lead wire model is repeatedly changed. Once more make time-harmonic simulation and one-direction analysis of magnetic-thermal coupling simulation, separately make record of loss, flux density and temperature, and compare the results data, the suitable thickness of transformer magnetic shield can be found out.