Dynamic Overhead Transmission Line Rating Based On Tension Measurement

Transmission line"bottleneck"is a major obstacle of power transmission in different countries and regions. The current thermal ratings are based on the assumption that it is the worst weather conditions which maintain the safe ground clearances of transmission line at all times. In fact the probability of co-incidence of the worst weather conditions is exceedingly little. So it makes dynamic line rating (DLR) system possible monitoring the real-time weather conditions and line parameters. We have mainly done the follwing research work:Sag has influence on transmission line thermal rating. Mechanical actions for overhead line concerned wind speeds and wind direction in a deflection plane were analyzed in this thesis. The safe ground clearances and deflection sags could be monitoring on-line using the measured tension.Conductor temperature is related to line load, tension and environment, such as wind speed and wind direction, et al. The relationship of influence factors was discussed and studied in the thesis. The conductor temperature modeling affected by multiple factors was established. The field test results showed that this conductor temperature module is effective in describing relationship between conductor temperature and environment factors in question. The method is superior to existing state equation and experiment method in calculating conductor temperature.State equation of overhead transmission line was improved. In general, state equation of overhead transmission line is used in designing the overhead transmission lines. After the line being in power, conductor temperature calculated by state equation introduced much error, and changed smoothly even with heavy load. It was shown in the test that the stretch of conductor length was not just about linear temperature, which is also related with ambient temperature. The state equation was corrected in the thesis, which accord with line operating.The solar heat gain of conductor depends on complex factors, such as solar altitude, the intensity of the direct solar on a surface, turbulence of the atmosphere, et al. But hardly any field tests have been carried out to correlate these affected factors on a probabilistic basis. A solar heating sensor for transmission line was designed in the thesis. Solar heating gain of conductor was modeling according to the data of the field tests.It is proved that rating time series is chaotic series in the thesis. So the short-term line rating could be forecasted by chaos theory. The improved C-C method is used to determine appropriate delay time and embedding dimension in state space reconstruction. In this thesis, an approach which combines radial basis function neural network (RBFNN) with chaos theory is presented to predict the rating and thermal overload risk. The prediction is tested to be effective and feasible in the thesis, which is useful for on-line decision making in the line operation.A DLR monitoring system was developed on the project background of 110kV overhead transmission line of South grid. The DLR system can evaluate transmission capacity dynamically through measuring the real weather condition and conductor tension. The results of field operation indicated that the system operated stably and could effectively increase line capacity without violating the legal ground clearance, and monitor the important parameters of transmission line, which avoid unnecessary contingency accident.