Simulation And Analysis On Substitution Of Converter Transformer

With the rapid development of long-distance, high-capacity transmission project, the roleof HVDC in the entire grid is more and more important. As one of the key equipments of theDC transmission system, converter transformer is essential and there must be back-upconverter transformer. There will be no other back-up converter transformer when the mainconverter transformer happens to malfunction during the maintenance of the original back-upconverter transformer. In order to maintain the normal operation of the HVDC system,converter transformer from other station can be temporarily as a back-up. Thus will causeunbalanced three-phase parameters as the capacity, the percentage of short-circuit voltage andother parameters of the back-up may be inconsistent with the converter transformer to besubstituted. So study on the adaptability of substitution is particularly important.This thesis firstly analyzes the selection principle of the simulation tools and theconstruction of simulation model. Simulation models of eight modes including Shenzhenstation’s Y/Y converter transformer to substitute Zhaoqing station’s, Zhaoqing station’s Y/Yconverter transformer to substitute Shenzhen station’s, Shenzhen station’s Y/convertertransformer to substitute Zhaoqing station’s, Zhaoqing station’s Y/converter transformer tosubstitute Shenzhen station’s, Xingren station’s Y/Y converter transformer to substituteAnshun station’s, Anshun station’s Y/Y converter transformer to substitute Xingren station’s,Xingren station’s Y/converter transformer to substitute Anshun station’s, Anshun station’sY/converter transformer to substitute Xingren station’s are built to study the adaptability ofback-up converter transformer. Before Simulation, this thesis carries out preliminaryfeasibility analysis by means of comparing the technique criterions of the two transformers tobe substituted with each other.To sudy the impact on the steady state characteristics of substitution, the impact on ACvoltage and current characteristics is studied, by means of comparing network side voltageand current, valve side current, network side neutral point current, harmonic content ofcurrent before substitution with that after substitution.To sudy the impact on the DC transmission system of substitution, the impact on thefiring angle, extinction angle and reactive power compensation characteristics is studied, andmeasures to reduce the impact are also discussed.Finally, the feasibility of lowering or highering one step in the on-load tap isinvestigated from two aspects of theory analysis and PSCAD/EMTDC simulation to reducethe three-phase unbalanced degree.