The Research Of The Unbalance Of Three-phase Low Voltage Large Current Leads Of The Special Transformer

The system of low voltage large current windings and leads are widespread in the rectifier transformer and the electric furnace transformer.for getting the larger low voltage current, the low voltage windings are only few turns,even only one turn.So the impedance of lead can not be ignored,especially the complicated electric network’s influence on the balance of low volage current.Test a transformer(7200KVA/10KV) and find that the DC-resistance unbalance rate is close to 35%,the load current unbalance rate is 56%. The calculate of low volage loop’s DC-resistance is easy,but through the DC-resistance to adjust the unbalance rate of three-phase current is no obvious effect.Analysis shows that the leakage reactance of leads is more influence on the low volage impedance for low volage and less turns transformer.Traditional computing method of the resistance and the reactance is not suitable for the complicated electric network. Calculating and adjusting the load current in this way is not exact.The finite element method can calculate the complicated winding under the condition of working.but there is no literature which is about the simulation and analysis of the leakage reactance of the large current leads. Using the method of field-circuit coupling can not only calculate the three-phase current but also reduce the manufacturing costs and time.Useing the advanced electromagnetic field analysis software MagNet can adjust the designing scheme and grant user’s wish.Based on the modeling and the finite element analysis for 3D leakage magnetic field and the magnetic field of the low voltage large current fuses,we get the three-phase AC-current of the complicated electric network.The simulation results are close to the measured,that prove the availability of model analysis.