Complex Fault Analysis Method Based On Multi-port For Asymmetrical Power System

With the rising of our country’s economy development level, power grid construction has stepped into a new stage that UHV transmission line, AC/DC transmission system and inter regional transmission network are widely used which has made the power system getting larger and more complex. At present UHV transmission line usually dosen’t replace, and power electronic technology has being gotten more and more extensive application in power system which make asymmetry in power grid becoming more and more obvious. In the asymmetric case, components cannot be decoupled in symmetrical components coordinate, which has limited the use of symmetrical components method in fault calculation of power system.This paper presents a new complex fault calculation method for asymmetry and large-scale power grid. Using piece-wise method to solve the large scale problem, remove the contact lines from the original network and use them build the piecewise port. Introducing dual port to solve the asymmetry problem, simulate the asymmetric part of transmission line to achieve error free fault calculation of the whole line. Building the equivalent variable configurations port to handle power network operations, such as remove some line. Introducing virtual node and virtual unit branch to to simulate all kinds of faults in power grid and create virtual fault port. So the original asymmetric network is transformed into a symmetry network with no faults, and all the equivalent Simple networks are connected to its corresponding port. And the model of asymmetric large-scale power system fault calculation in symmetrical components coordinate is finished.Meanwhile, the method mentioned in this paper is also suitable for distribution network fault calculation. A new distribution network fault calculation method based on multi-port is proposed which applies to the condition that proportion of asymmetric line of distribution network is not so high. This method can solve the following problems, loop network structure, distributed power accessing, asymmetry parameters of transmission line and frequent network operations. If the scale of distribution network is small, piecewise method can not be used.Besides, this paper has developed the power system complex fault calculation software by mixed programming with Visio VBA and Matlab based on the method mentioned. In the process of software development, drawing function of Visio and storage function of shapesheet are fully used, mixed programming based on MatrixVB lib is adopted to complete matrix computation. So the software has a short development cycle and a fast calculation speed.