Compute And Research On The Complex Structure Transmission Line Grounding Short-circuit And The Current Distribution Of OPGW

In order to adapt to the needs of the modern large-scale power system and build a strong and accurate communication system, Optical Fiber Composite Overhead Ground Wire (OPGW) as a phenomenon of the side of the overhead ground wire is commonly used in modern power system. However, when fault occurs in power system or power system is struck by lightning over-voltage(short duration), the relatively large current will flow through OPGW, the heating effect of current will increase the temperature of wires, even devastate its internal composite fiber, and result in paralysis of the electric power communications. The structure of actual power system transmission lines are complex, how to improve the calculation accuracy of the OPGW’s maximum fault current to provide the basis for its thermal stability verification is an urgent problem. The thesis focuses on the line ground fault of the power system’s complex transmission structure and the OPGW current distribution in the modeling calculations and correlation analysis, the main work and results are as follows.The research of this OPGW thesis is on the distribution of the current computational model and algorithm, which is based on the phase component method.The research of model. The complex structure of the transmission line model consists of two parts, the line model and the terminal model, the building process of the model is as follows:(1)Line model adopts an extension component method which takes the mutual influence into account between the phase line system and ground system, and it is the extension of the phase component. Extension component method takes phase line systems and ground systems into modeling, in the model each wire is connected with the tower through a virtual resistor. If wire is directly connected to tower, the virtual zero resistance, and if the wire and the tower is insulation, the virtual resistance is infinite. So, adjusting the virtual resistor values can describe the variety wiring of towers.(2)The line terminal is divided into the power supply terminals and load terminals. The power supply terminal uses multi-port Thevenin equivalent model which is based on phase component. The load terminal at the assumption is not connected with the external system, in order to ensure the unity of the model, exports in the substation to transformer neutral point of fill phase line system take the file line impedance is infinite.(3) According to the same principles of the line structure, the complex structure of transmission lines are split into blocks, and across the board by multiple sub-intervals, so each subinterval according to the number of towers are divided into the appropriate gear. On each subinterval using the model based on the expansion of the phase component in the principle of expansion phase component method, and then blocks are linked together by the intersection, and the OPGW fault current calculated by the full model of the complex network.Algorithm to be determined. According to the extended phase components method we establish the whole line model, whose amount of data is many times greater than the method of mesh method. In order to overcome this disadvantage, according to the block tri-diagonal characteristics of the coefficient matrix, this paper uses "chasing method" to simplify and solve, which greatly improves the computational speed, and makes up the deficiency of large computational complexity.Applications and examples.(1) Using the proposed model to analysis the simple circuit we can learn the result curves using extended phase components method are in good agreement with the curves using the traditional mesh method, which shows the rationality of the extended phase component method; From the comparison of the calculation results we can find that, by using the extended phase component method compared to using the traditional algorithm the OPGW fault current values are bigger about10%.(2) This paper uses the extension phase component method and the principle of the junction points to analysis and calculate the Africa city network; the programs of the OPGW fault current analysis give the details of the OPGW fault current distribution; Also the programs can realize the fault points automatic circulation function, and can get OPGW maximum fault current distribution curve, according to the curve, it is easy to get the fault current distribution under the most severe case This provides the reference to the city net OPGW selection.The extended phase component method can achieve the unifying admittance calculation of earth wire system and phase wire system, and avoid OPGW maximum fault current calculation error caused by factors such as ignoring mutual influence of earth wire system and phase wire system when work are divided; combined with extended phase component method and the principle of junction point, we can solve the calculation problems of OPGW fault current distribution in complex structure of transmission line; Using the method proposed in this paper can also obtain the fault current distribution in the phase wire system under the influence of the overhead ground wire line; The OPGW value of fault current calculated by using expanded phase component method are bigger than the traditional algorithm, which illustrates that the calculating results of traditional algorithm are overly optimistic; for the OPGW maximum fault current calculation, grounding fault programs of the complex transmission line can automatically run the calculation for each tower in turn served as the fault point, in the end, according to the OPGW maximum fault current in the case that tower is served as the fault point, we can draw the OPGW maximum fault current curve.In short, the extended phase component method can visually and accurately find OPGW fault current in the most serious cases, which provides a reliable basis to the selection of the OPGW modeling, and provides a strong guarantee to the reliable operation of the power system and economic development. Therefore, it has an important significance for both OPGW type checking and fault analysis of power system.