Study On The Measurement Of The Zero Sequence Parameters Of Transmission Lines Based On Interference Method And Its Application

With modern power systems becoming more and more complex, the continual expanding of the scale of the power grid, mutual inductance line has been increasing day and day. The role which is played by the line parameter is increasingly important. It not only relates to the power flow calculation, short circuit calculation and relay setting calculation of power system, but also may affects the normal operation of power systems. It is well known that Carson’s formulation is not accurate with the inconstant resistivity of the earth. According to the national standards, they must be measured practically.We point out the shortcomings of the traditional methods and the physical nature of interference voltage, and introduce a measurement method of transmission line zero-sequence parameters taking advantages of interference voltage based on global position system (GPS). This method takes the short transmission lines which ignore distributed capacitance into consideration and the long distance transmission lines put capacitance equivalent to both ends of circumstances into consideration, the mathematical model was established and through the calculation of the transmission lines to solve the zero sequence parameters.In this paper, two mathematical models of the measurement method corresponding to parallel coupled transmission lines and any number of transmission lines with mutual inductance are introudced in detail, including algebra equation, differential equation, especially the models without considering capacitance current. The advantages and disadvantages of are pointed out. We also apply the digital signal process to our system such as Fourier algorithm. Data sampling, processing, calculation, and the whole process are all dealt with in PC and DSP, system, reducing the artificial error and improve the accuracy of the measurement.The paper also introduces the hardware structure and software algorithms design of the measurement system, including signal acquisition process and basic principles of computing.The MATLAB simulation of the measurement method is carried out, considering the influence of different Sampling frequency, capacitance current, comparing the effect of withdrawn line. The presented measurement methods have been successful used to measure the parameter of two220kV transmission lines with mutual inductances in Suzhou power grid in China. MATLAB simulation and engineering practice show that the introduced methods are correct and feasible. The measurement methods have great economic value in measurement and this is of vital significance to the normal operation of the power systems.