Transmission Line Parameter Online Calculating Method Research

Transmission line is one of the main components of the power system. To obtain the transmission line parameter is very important. The accuracy of transmission line parameters has huge effect on power system calculations and even the stability of operation. Above all, actual measurement of transmission line parameters is of great significance.This article describes a variety of current methods calculating the power transmission line parameters and analyzes the shortcomings and disadvantages. Since single lines parameter calculating theory is rather mature, its major problem is that most of the methods are based on simultaneous measurement of two-terminal voltage and current. However, the sampling data is impossible to be completely synchronous. Although GPS can provide basis for synchronous measurement, but difficult to have all lines equipped with GPS. Therefore, the development of non-synchronization algorithm is very necessary. In addition, coupled lines parameter calculating method still need to be studied.First, many different classic transmission line which are usually used in practical are simulated to test the impact on transmission line parameter calculation caused by the asynchronous angle between two terminals of the line. It is found that the impact from the asynchronous angle comply with certain regulations. It is necessary to find the asynchronous angle through this regulation, and calculate the parameter ignoring the impact of the asynchronous angle.Secondly, this paper puts forward a transmission line distribution parameter calculation method based on asynchronous sampling data from two-terminals of transmission line. The line transfer equations are rewritten to eliminate the impact of non-synchronous sampling. Verified by simulation examples, the method can accurately calculate the transmission lines parameter of different sequence, and is not influenced by asynchronous sampling.Problems of coupled lines parameter calculating is studied too. The article have derived coupled lines impedance matrix under a variety of phase sequence arrangements and transposition method (three sections transposition), the result shows that it's better to choose reverse phase sequence using reverse transposition method for coupled lines. Further analysis showed that with reasonable transposition phase sequencer arrangement and transposition method, the main coupled sequence parameter is zero-sequence coupled parameter. The paper also derived lumped parameter model of double lines considering the capacitance coupled to ground. Distributed parameter model of four coupled lines is also derived, and verified by an simulation example, which provides theoretical basis for coupled parameter calculating research. Based on these models, parameter calculating method using asynchronous sampling data is proposed. With specificity of coupled transmission lines on the same tower, its parameter calculating method is proposed and testified.