The Research Of Harmonic Isolated Four Windings Power Transformer

In the 220 kV substations, the heavier harmonic was introduced into the grid by 35 kV and 110 kV load sides. Considering a variety of solutions, this paper studied the four windings transformer, which is a kind of electric power transformer that by using inductive filtering technology. The transformer constitutes two inductive filter groups:220 kV winding, filtering winding and 110 kV winding; 220 kV winding, filtering windings,35 kV winding. Both inductive filter groups meet the inductive filter winding equivalent impedance close to zero that meet the condition of inductive filtering technology. Therefore this transformer can weaken the two load side harmonic magnetic flux in core that improved the magnetic circuit of transformer, thereby suppressed the harmonic flow in the transformer, to achieve the objective of the transformer design that harmonic isolation on 35kV and 110kV sides of the transformer. Paper research content is the national natural science fund project (51077045,51077044,51007020), the state grid corporation of science and technology project ([2008] 1360) and the graduate student research innovation project of Hunan province (CX2012B127), this thesis mainly do the following research:Secondly, the thesis introduces the basic structure, wiring principle and winding arrangement of the harmonic isolated four windings power transformer. In the principle of magnetic flux and the principle of single-phase transformer equivalent model angle to study the working mechanism of the harmonic isolated four windings power transformer. The thesis analyzes the complex equivalent circuit of four windings transformer, from the view point of system principle to introduce the principle of harmonic suppression and reactive power compensation. Conclusions provide theoretical basis for the subsequent simulation.Thirdly, for the problem of special design requirements on transformer short-circuit impedance, uneven load distribution and transformer short-circuit calculation. In the paper, firstly this thesis is deduced the short-circuit impedance formula of the transformer and carried out the related simulation. Then Multiple sets of load simulation distribution data is obtained and compared its results. Finally, the thesis is simulating and calculating the short-circuit current, which reveal the part of running characteristics of the transformer.Then, based on the design requirements of harmonic isolated four windings power transformer, puts forward the design requirements and the corresponding design method of matched filter. In the after designing, it proposed the LC filter topology structure, calculated the result of reactive power compensation, presented capacitor allocation scheme, scheme optimization and capacity checking.Finally, the comprehensive simulations for various cases are carried out on the transformer system, the transformer harmonic suppression effect is also analyzed. The simulation results show that the harmonic isolated four windings power transformer and its matched filter device can effectively suppress the harmonic pollution on both 35kV and 110kV sides, which can improve power quality on transformer substation and achieve the purpose of the transformer design. According to the principle of this paper, the project has designed the engineering prototype (model type:SSZ11-L-180000/220), already put the equipment into operation and Waiting for the test.