Study On Transmission Line Parameters On-line Measurement And Application

The strong network structure, powerful power transmissioncapability and secure power supply are the bases of constructing a strong and smart grid. It is obvious that the construction of transmission systemis of great importance. Transmission equipment mainly includes transmission lines, towers, insulator strings and overhead lines, etc. The parameters of overhead transmission line are significant. Transmission line parameters generally refer to the phase or sequence parameters of overhead lines with the frequency of 50Hz. They arethe fundamental basis forsetting value ofprotection devices, fault analysis and location, operation mode selection, power flowand transmission losses calculation in power system. Therefore, getting the transmission lines parameters rapidly and accurately is significant for the safe and reliable operation of power system.Based on summary of previous research achievements, the onlineparameters measurement methods and application of signal line and the double-circuit transmission lines have been proposed in this thesis.These methods were based on synchronous sampling signal at two terminals of transmission line, the 7t-type lumped parameter model.This paper introduced the common parameter type (phase parameters and timing parameters) of overhead transmission lines and mathematical model and deduced theconversion formulabetweenphase and sequence parameters.For low voltage level and short distance transmission line, this article introduces the decoupling algorithm without considering line-to-ground capacitance, In the three-phase single circuit, adopts Karenbauer transformation matrix, decomposes the three-phase unbalanced system into three symmetrical components, then calculates the transmission line parameters according to the online calculation principle of signal phase. Aim at the double-circuits line on the same tower, this article uses anotherphase-mode transformation matrix, decomposes the six-phase unbalanced system into six symmetrical components and calculates the transmission line parameters according to the online calculation principle of signal phase as well.In the high voltage level, the long-distance transmission lines, the line-to-ground capacitance parameters cannot be ignored, thus decoupling algorithm is no longer applicable.Based on π-type lumped parameter model of transmission line, a coupling calculation method of transmission parameters which is based on synchronous sampling signal at two terminals is proposed in this paper. It considers thecoupling resistance, coupling inductance and coupling capacitance in single-circuit and double-circuitstransmission line, derives the parameters formula of couplingalgorithm.Based on the online calculation method of transmission line parameters, this paper adopts SQL server database technology, under the Visual Studio environment, usesC# programming language to design and develop the transmission line parameters on-line measurement system software. It make a brief introduction of development environment and programming language, mainly introduces themixed programming of Matlab and C#, the addition of TeeChart tool in Visual Studio.This software uses the couplingalgorithm and the decoupling algorithm. It can achieve the online calculation of transmission line parameters in single-circuit line and double circuit lines on the same tower. Its features include primary data importing andwaveform viewing, results display, waveform preservation, line parameters exporting and outcome evaluation based on the normal distribution.