Study On The Parameter Asymmetry Power System Fault Calculation And Its Application

As the application of new power electronics technology and non-linear elements in the power system and extra-high voltage transmission lines are usually untransposed when the voltage is above 500kv, the problem of power system parameter asymmetry becomes obviously. That makes symmetrical components method which is based on the power system parameter balanced lose its big advantage. In order to solve the problem, with the help of computers, the fault calculation method for asymmetrical power system is studied according to the basic theory of linear circuit and the phase-sequence parameter transformation technique.In this paper, by introducing fictitious branches and creating fictitious asymmetry ports, the method to simulate power system parameter unbalanced is proposed; According to the characters of short-circuit fault and open-circuit fault, the method to simulate any kind of fault is given by introducing fictitious branches on faulted points and creating fictitious fault ports.On the basis of these, a new method for parameter asymmetry power system fault calculation is proposed. By taking fictitious fault ports and fictitious asymmetry ports as boundaries, the faulted network is transformed into symmetrical network and asymmetrical network, and then a canonical model for parameter asymmetry power system fault calculation is created under the sequence domain, finally the fault calculation is finished according to the basic theory of liner circuit and the phase-sequence parameter transformation technique.The advantages of the method are:(1) The method can be used both in the parameter symmetry power system and parameter asymmetry power system, and it reserves the advantage of symmetrical components method in the parameter asymmetry power system fault calculation;(2) It does not need to modify the node parameter matrix of the original network, the computation quantity is small and the speed is quickly;(3) The simulations of open-circuit fault and metallic short-circuit fault are accurately;(4) The structure of networks to simulate parameter asymmetry and faults are simple, and it is easily to be realized with the help of computers.Based on the method of this paper, software with a good man-machine interface is designed for asymmetrical power system fault calculation by using programming language Visual Basic 6.0, and then a power system is used for fault calculation.