Theoretical Study On Design To Magnetic Integration Structure Of Controllable Reactor Of Transformer Type

With the power system developing to the extra-high voltage(EHV) and high capacity, the demands for the security and reliability of the transmission line are higher than before and the security and reliability of the system can be improved by reactive power compensation. Controllable reactor of transformer type(CRT), as a reactive power compensation device, is of great significance for the study.CRT has several control windings. In the control winding loops, there are antiparallel thyristors installed in series. By adjusting the conduction angle of the thyristor, fast smoothing regulation of CRT capacity can be achieved and the voltage of control windings can be reduced by transformer. Therefore, CRT gets wide application prospect in EHV large power system.Based on the analysis of CRT operating principle, when designing the CRT structure the thesis uses the magnetic integration technology to realize the “high resistance and weak coupling” design principle and proposes 3 CRT structures: array type magnetic integration structure, magnetic integration structure composed by a variety of magnetic materials and split magnetic integration structure. To the array type magnetic structure, magnetic flux between the control windings is analyzed, “transformer-inductance” equivalent circuit of the structure is established, and the formulas of short circuit impedance and short circuit current of structure which has four control windings are deduced. To magnetic integration structure composed by a variety of magnetic materials, not only the generalized computing equations of short circuit impedance and short circuit current are deduced which is based on the equivalent circuit,but also the simulation model is built in MATLAB. The simulation of work winding current waveform, control characters and transient process are carried out. The result shows that the current harmonic is low and the CRT can realize graded smooth regulation and quick response under fluctuation of load. To split magnetic integration structure, the equivalent circuit of the basic structure unit is built up, the realization theory of the high resistance is analyzed, and the simulation model of 2-dimension finite element is built up in ANSYS. When control windings are short in turn, current distribution and magnetic distribution are calculated by using “magnetic field and circuit” coupling method. By calculating the 3 structures in an example, the results show that all the structures can s meet the design principle of “high resistance and weak coupling” and prove the validity and effectiveness of these 3 structures. The array type magnetic integration structure can realize full decoupling and the non-load current is zero, while the structure is complicated and hard to expand. Magnetic integration structure composed by a variety of magnetic materials is relatively simple and easy to expand. However, the non-load current of this structure is not zero and it can’t realize the full decoupling among control windings. The split magnetic integration structure realizes the full decoupling among control windings, has a simple structure, and is easy to expand. Although the non-load current of this structure is not zero, it is only 1.08% of the total current. So the split magnetic integration structure is more accessible to engineering application.Though the analysis above, to realize the design principle of “high resistance”, the core limb or the discus can be added between work winding and control winding. To realize the design principle of “weak coupling”, the split core(low magnetic resistance core) can be added in the structure.