Research On Magnetic Performance Of High Magnetic Induction Grain-Oriented Silicon Steel Based On UHV Transformer Core Model

The high magnetic induction grain-oriented silicon steel is the basic composition material of UHV transformer core,and its excitation performance directly affects the whole machine performance and operational reliability of UHV transformer operation.When high magnetic induction grain-oriented silicon steel used in UHV transformer are made into the transformer core through shearing,laminated and other processes,the excitation performance will produce a certain change,so the high magnetic induction grain-oriented silicon steel need to be studied further in the application of UHV transformer excitation conditions.The three kinds of silicon steel sheets which have been applied to UHV transformers are selected.By analyzing the principle of Epstein square ring,the excitation characteristics of three kinds of grades of silicon steel sheets under ideal conditions are contrastive studies.The result shows that the excitation performance of silicon steel sheet corresponds with nameplate and excitation performance of the same grade is fair.To the core structure of a typical UHV single-phase transformer,study the corresponding magnetic circuit and the magnetic flux distribution of each part,and analysis the correspondence between the excitation characteristics of the silicon steel sheet and the no-load characteristic of the transformer deeply,on this basis,give the calculation method of no-load current and no-load loss of transformer.The equivalent reduction model with same flux density and construction under different ratio rated voltages of UHV single-phase transformer core is developed,and the magnetic performance test system of silicon steel sheet is set up with the core model as the test transformer.According to the requirements of IEC and GB test to the transformer,the test scheme of excitation test of core model under frequency saturation excitation condition and DC bias condition is designed respectively.Aiming at the core model made of three grades,the test and analysis of the excitation characteristics under the conditions of frequency saturation excitation,DC bias and repeated over excitation are carried out respectively.The test results of the frequency saturation excitation are compared with those of the silicon steel sheet.The no-load loss and no-load current of the core model are compared and analyzed.The results show that there is a certain deviation between the no-load performance data obtained by the traditional calculation method and the measured value.Based on the deep analysis and research on the no-load characteristics of the three types of core models under different excitation conditions,a series of reference indexes for the evaluation of the excitation performance of the high magnetic induction silicon steel sheet based on the core model are proposed,and the three grades of silicon steel chip excitation performance by the index are evaluated.These indexes reflect the excitation performance of the high magnetic induction silicon steel sheet under the extreme application conditions,such as deep excitation saturation and DC bias,which can evaluate excitation performance of UHV transformer with oriented silicon steel chip more scientific and reasonable,which has important engineering application value in the UHV transformer core Material selection.