Research On Multi-criteria Collaborative Of Transformer Protection

For a long time, the power transformer is always one of the important main elements inthe power systems, the stable operation of the transformer plays a very important role in thesafety of the grid. With the continuous expansion and development of modern powersystems, transformers, as the contact hub of different voltage levels, their continuous andreliable operation become indispensable to power systems. The data show that in recentyears, the correct operation rate of main equipment protection, especially transformerprotection action is less than ideal expectation. The main reasons of this phenomenon mainbe the problems of production sector, problems of operation and management, the principledefects as well as problem of the transformer structure, which provides a larger space tofurther improve the protection of the transformer.Traditional transformer primary protection consists of ratio differential protection,differential quick break protection and magnetizing inrush current detection criterion, anddifferential protection, as the primary protection, has many years’ operating experience.Traditional transformer inrush current detection criterion refers to the second harmonicprinciple, which has dominated the important position of the transformer protection with itssimple algorithm and rich field experience. Traditional transformer primary protection hasalso brought some problems, such as problem of CT saturation caused by the malfunction,high pressure long line with compensation capacitor problems caused by the fault currentharmonic content increases. Over the past decade, due to the rapid development ofcomputer technology, many complex algorithms and techniques can be applied to thetransformer protection. The transformer protection researchers have proposed a newprinciple of magnetizing inrush current identification, including fuzzy logic theory, wavelettransform and the sampled values principles.For the problems discussed above, by reading a large number of domestic and foreignliterature, we proposed a transformer primary protection based on multi-criteriacollaborative. The protection scheme can make full use of advantages of different criterion,which can greatly improve sensitivity and speediness based on improving the protection reliability. And for the magnetizing inrush current identification, we proposed twoalternative magnetizing inrush blocking criteria, with detailed description and analysis. Bymodeling and simulation on EMTDC/PSCAD simulation platform and completing avariety of experiments in dynamic simulation laboratory, we can test that whether these twoprinciples meet the requirements. Finally, we make a summary of the research for thisarticle and point out the research direction in the future.