Capacity Increasing Strategy Of Power Transmission Line Around Access Point Of Uhv

With the developing of UHV technology, the capability of power transmission line increases significantly. In the early time of UHV, the 10000kV network is not complete, so it has to cooperate with 500kV network whose capability is much smaller than UHV. The capability of UHV is limited seriously, especially around the access point of UHV. The cause of the problem is that the capability of 500kV power line around the access point of UHV is too small to cooperate with UHV. Effective methods have to be taken to increase the capability of 500kV power line around the access point of UHV.To meet the demands of developing UHV, this paper is working on a solution which can increase the capability of 500kV without building new power lines.There are two different methods:static method and dynamic method. Static method means raising the temperature of power line from 70℃ to 90℃. Dynamic method means dynamically increasing capacity of power line according to environmental parameters.In this paper, firstly mechanism of power line is analyzed by ANSYS. Result shows that environmental parameters have a huge effect on the capability of power line. So the parameters specified in our country is too conservative, which means the capability of power line can be increased.It comes to a conclusion that the temperature of power line should be increased properly. The maximum temperature is 90℃. Meanwhile, system stability should be checked to ensure the security of power system.Three capacity calculation models of power line are proposed in this paper. They are "inside model", "outside model" and "pull model". The power line temperature prediction model based on BP neural network is introduced into the strategy. Then, hybrid method is proposed. It uses dynamic power line temperature according to the needs. The maximum temperature is 90 C. The pull parameter is used to fix the error.The hybrid method makes the most use of the advantages of both static method and dynamic method. It can increasing the capability without influencing the stability of power system.The hybrid method may makes the system electric current change rapidly. So high performance reactive power compensator is needed so that the voltage of the system won’t fall. In this circumstances, a new kind of dynamical reactive power compensator is proposed.For the reactive power compensator such as Static Var Compensator (SVC) and Static Var Generation (SVG), there is a contradiction between performance and price. SVC is cheap but its performance is not satisfactory, particularly in inhibiting voltage flicker and voltage harmonic filter. SVG performs excellently but it is too expensive. In order to solve this contradiction, a new kind of dynamical reactive power compensator with a small SVG inside is proposed in this paper. SVC firstly compensates most of the reactive power, and SVG is responsible for inhibiting voltage flicker and voltage harmonic filter finally. This model makes the most use of their advantages and find a balance between the cost and its performance. By analyzing different kinds of circuit structures, the best one is selected. It is able to reduce the interference between the SVC part and the SVG part significantly. Meanwhile, a new kind of Improved Dynamic PI Controller based on support vector machines and artificial immune algorithm is proposed in this paper to coordinate the SVC part and the SVG part.Finally, the hybrid method and the new compensator are verified by the simulation based on ANSYS and PSCAD. The result shows that compared to static method and dynamic method, the hybrid method performs the best. The capability can be increased by 65%. Even in the worst situation, the capability can be increased by 50%. And the new dynamical reactive power compensator performs faster and compensates better and it reduces harmonics significantly. The cost of the compensator is only half of the old ones.