The Research On The Transformer Microcomputer Protection In Power System

The power transformer is a very important equipment in power system, so, ever since the microcomputer protection of transformer came along, it has been improved and developed continuously by people, and now it has been widely used in the power system with its unique advantage. But when the theory of microcomputer protection is combined with practice, there are questions and questions still exist. The artical concentrates on these questions, mainly analyze and study the following aspects.In the first place, on the basis of the theory of transformer differential protection in-depth understanding, emulate and analyze the cause of unbalance current and solutions, as well as the current transformer(CT) saturation influence on the transformer differential protection, especially study further about the remnant magnetism influence on the CT saturation. The result shows that the remnant magnetism is directly proportional to the time of CT saturation, and increase of the time of CT saturation is good for transformer differential protection. So it should take measures to reduce the influence of the remnant magnetism, besides, emulate and verify it.In the next place, comprehensive analyze and compare the currently inrush current and internal fault current identification principle's strengths and weaknesses. on the basis of some correlated reference, propose a new inrush current identification method based on the theory of instantaneous reactive power, it is not same as the traditional identification method which adopt the theory of instantaneous reactive power based on theαβ0 coordinate system, but adopt the theory of instantaneous reactive power based on the dq0 coordinate system to identify, it is much more practicability. The emulate system model is builded by the use of MATLAB, and make lots of simulation and analysis when the transformer in different circumstances, such as inrush current, internal fault current, and the internal fault of transformer when closing. The result of simulation shows that this method can make a valid discrimination between the currently inrush current and internal fault current. But it is not conspicuous to identify when the transformer occur slight turn-to-turn fault, so it becomes the most important study point in the next work.In addition, there are some questions about fourier improved algorithm confuse the real part with the imaginary part. So, in the article, on the basis of deduce the right fourier expression, to amend some typical improved fourier algorithm, and compare these algorithm performance comprehensively through the simulation, point out their strengths and weaknesses and the scope of application, it can offer some theoretical instruction for the distinct occasions.At last, in order to catch up with the trend of the microcomputer protection, meet its requirement for software and hardware, there gives a software and hardware of microcomputer protection program based on the dual DSP structure, design and introduce the main hardware circuit and software flow diagram in detail.