Winding Current Calculation And Parameter Optimization Of Controllable Reactor Of Transformer Type

With the construction and operation of the excessively-high voltage long-distancetransmission lines, the power grid is facing the severe problems of reactive power balance andvoltage control. A controllable reactor who can realize swift and smooth regulation with smallharmonic current in a broad range is urgently demanded. As a new type of controllable reactor,the CRT (Controllable Reactor of Transformer Type), on the one hand, can rapidly adjust thereactive power compensation capacity to guarantee the economical efficiency of transmissionlines; on the other hand, it is consistent well with Chinese electromagnetic equipmentmanufacturing industry for the reason that the operation of CRT is not excessively dependentson power semiconductor technologies and related control strategies. Therefore, CRT has beenwidely concerned and explored, but the domestic research work is still far from perfect. Basedon these considerations, the CRT is studied as the main object in this thesis. The thesis makesa deep reaearch on the calculation method of winding short-circuit, the winding currentdistribution, the winding coupled effect, the current rating utilization and the parameteroptimal selection under three different sequential single branch modes.The thesis reveals the inherent relationship between branch parameter of polygonequivalent circuit model and the winding short-circuit impedance, and it gives three methodsto calculate winding short-circuit impedance, these three methods are respectively theshort-circuit impedance formula, the self and mutual impedance analytic method and thefield-circuit coupled finite element method. Also, a simulation model based on equivalentcircuit model is built with MATLAB, and the winding currents under different workingconditions are got.Through the comparison of the simulation results and the ideal distribution of windingcurrent, it is knows that the controlled winding currents are not independent with each other,the input or removal of a controlled winding will cause the current changes of other workingcontrolled windings, which is easy to cause the waste of controlled winding capacity and leadto the inefficiency of CRT. Based on the harmonic grading standard, the current calculationanalytical expression is derived by combining the magnetic potential balance equation andsinusoidal steady-state voltage balance equation, which reveals quantitative relationshipbetween the self and mutual leakage reactance and winding current, also, it materializes theimpact of winding coupled effect to the winding currents. Meanwhile, the thesis gives thedesign requirement of equivalent leakage reactance to guarantee the high efficiency of CRT,and a discriminant based on the equivalent leakage reactance is also given to judge whetherthe winding current rating utilization meets the design target. In order to simplify the winding structure, lower the manufacturing difficulty and thecost of maintenance, the number of windings and the harmonic current are optimized in thisthesis. A principle based on the effective value of harmonic current rather than the harmonicratio is proposed to arrange the controlled winding. Through the analysis of three sequentialsingle branch modes and harmonic current characteristics, the relationship among theharmonic current, the capacity and the number of windings are illustrated in three differentwork modes respectively, and the relevant configuration parameters are given as the form ofnumerical example. Compared to the parameters before, after the optimization, the windingseries (namely the number of controlled winding) becomes less, and the harmonic current islower. Hence, the performance of CRT is improved.