Analysis On Vulnerability Area Of Voltage Sag Based On The Virtual Node Method

Sensitive loads have been widely used in modern power system,which make the requirement of power quality is higher and higher by power users.It is found that voltage sag has become one of the most prominent of all power quality problems.The voltage sag in the power system is mainly caused by short circuit fault.When a short circuit fault occurs,how to define the influence of the voltage sag caused by the short circuit fault is a practical problem.The vulnerable areas of voltage sag proposed by this paper can solve the problem well.At first,the calculation method of voltage sag amplitude is discussed in this paper.By using the symmetrical component method to calculate the asymmetric fault,the relationship between the value of the voltage sag and the impedance is obtained.And through the calculation of the amplitude of the voltage sag,this paper classifys the types of voltage sags.Then,this paper discusses the influence of the connection mode of the transformer to the voltage sag and the change of the voltage sag type.In addition,this paper discusses the influence of other factors in the system for the voltage sags,including the structure of the system,the access of the distributed generation(DG),the reactive power compensation device.In this paper,the analysis of voltage sag sag based on virtual node method is proposed,the concept of fault distance and the relationship between the amplitude of the bus voltage and the fault distance in the system based on the virtual node method is also proposed.On this basis,the construced nonlinear equation is solved by Newton Raphson method,which can obtain the critical fault point and determine the vulnerable areas of the voltage sag.In this paper,the new England 39 bus system is used as a simulation example to discuss the voltage sag sag under different voltage sags and different fault types.At the same time,the influence of the distributed power supply and the operation mode of the neutral point of the system on the vulnerable areas of the voltage sag is analyzed.