Research On Protection And Internal Faults Simulation Model Of Inductive And Phase-Shifting Filtering Rectifier Transformer

Converter transformers are important electrical equipments. Aiming at thedeficiency of the traditional converter transformer, coupling-compensation andharmonic-shielding converter transformer, that is, the new converter transformer, andits corresponding inducing filter technology are proposed. In order to accelerate itsengineering application, this paper mainly opens out the research based on thedifferential protection of the new converter transformer and distinguishing themagnetizing inrush current from differential protection.Base on the wiring mode of the new converter transformer, this paper analyze thefundamental working principle of the new converter transformer, and from essentiallyanalyze the harmonic suppression principle, which based on the harmonic ampere-turnequilibrium of the coupling winding.Based on the analysis of the principle of differential protection for ordinarytransformer, the principle of differential protection for new converter transformer isresearched. Its connecting scheme of differential protection is proposed based on theestablishment of the current transform matrix. Adopting the ratio braking characteristicwith three-broken line, and taking these effects into account including the unbalancecurrent under the normal condition, current-transformer performance and existingoutput current when internal fault occurring, the setting values for the differentialprotection of the new-type converting transformer are calculated. At last, thesimulation model of the differential protection in Matlab/Simulink is established basedon the new-type converting transformer technical parameters, by means of thesimulating analysis of various operating conditions of transformer, the feasibility ofthe proposed scheme and the correctness of the setting calculation are verified.Based on the analysis of the mechanism of transformer inrush current, theultimate reasons why inrush current maybe cause the differential protection scheme actincorrectly has been analysis deeply. Considering the shortage of differentialprotection scheme in distinguishing inrush current of the new converter transformer,the principle of a new microcomputer protection scheme based on an equivalent circuitwhich casts the method of differential protection and utilize synthetically theinformation of voltage and currents of a transformer is studied. Based on an equivalentcircuit composed of inverse inductance is proposed, which composed of transferbranch and magnetizing branch. The correctness of the equivalent circuit is verifiedfrom the three network theory. According to the value of the magnetizing branch parameters, the operating criteria for distinguishing the magnetizing inrush currentfrom differential protection is provided. At last, the simulation model of the protectionscheme in Matlab/Simulink is established, by means of the simulating analysis ofvarious operating conditions of transformer, the correctness of the protection schemeare verified.