Research On Installation And Commissioning Technology Of Converter Transformers

Converter transformer is one of the most important equipments in HVDC transmission system.It bears the function of isolation and energy exchange between AC and DC power grids.It is at the core of the mutual transformation between AC and DC,and it is one of the most important roles in the whole HVDC transmission.In UHVDC transmission system,the withdrawal of any converter from operation will lead to unpredictable consequences.The most common faults in converter transformers are coil insulation damage,oil-paper insulation strength reduction,tap converter,bushing and cooling system(pump)faults.The failure rate of converter transformer is about twice that of AC transformer.Whether the installation process in the early stage and the commissioning process in the later stage can be carried out rigorously,correctly and effectively is the key point to avoid these faults.In this paper,the typical problems in the installation and commissioning of converter transformer are studied.The key role of converter transformer requires its high reliability and high-tech performance.Because of the interaction of AC,DC electric field and magnetic field,the structure of converter transformer is special and complex,which requires strict installation and debugging technology.Developing the research on Key Technologies of installation and commissioning of converter transformers and continuously improving the means of installation and commissioning can further improve the safe operation level of domestic HVDC transmission equipment and lay a solid foundation for the sound development of UHVDC transmission and transformation projects.In this paper,Installation of wall-piercing bushing,tap-changer switch and high-voltage bushing is an important link in the whole process of converter installation.Through detailed fault analysis of typical cases encountered in practice,the problems exposed are summarized and corresponding solutions are put forward;the neutral point offset protection of converter is also proposed.The blocking of the converter and the operation of the converter are mainly studied.The root causes of the problems are found through calculation and analysis,which reflects the importance of commissioning for the operation of the whole converter station.