Research On Transfer Capability Of Transmission Section Based On Repeated Power Flow

With the continuous scale-up of power system interconnection and the stesdy advancement of electricity market, transfer capability of power system plays an increasingly important role in ensuring the safe and stable operation of grid and smooth transaction in the electricity market, especially the total transfer capability(TTC). Repeated power flow(RPF) can easily consider various control and regulation means of grid and handle different types of stability constraints. Therefore, it is suitable for TTC calculation of large-scale grid. However, it has some defects in steps of power adjusting elements selection and power flow adjustment, which is worth more attention and study.Firstly, aiming at the blindness existing in power adjusting elements selection of RPF, the concept of transmission channel is introduced in this paper to assist in determining elements to be adjusted in the TTC calculation process. The characteristics of transmission channel are summarized and the search method of transmission channel containing the studied transmission section is proposed. Secondly, reactive power adjustment is not involved in power flow adjustment of RPF, which leads to the fact that the gained power flow solutions do not meet the actual situations of power system operation. A layering and zoning reactive power adjustment method is proposed to make the solutions in line with the actual operation. A power flow convergence adjustment method based on node type switching is put forward to deal with the non-convergence situations of power flow calculation caused by the irrational distribution of reactive power. Finally, as a constraint value of section transfer power, TTC is conservative, which would deteriorate the operational economy. On the basis of the risk theory, the concept of ultimate economical transfer capability(UETC) is proposed in this paper. A benefit model accounting economic and social benefits as well as a risk model considering probability and consequences of failures are established. In addition, a practical UETC calculation strategy is put forward.Examples of CEPRI-36 bus system show that transmission channel can reduce the range of the elements to be adjusted and improve computational efficiency. Reactive power adjustment of power flow adjustment step makes the power flow solutions meet the actual situations and increases the value of TTC significantly. As a constraint value of section transfer power, UETC considering benefit and risk would ensure the operational safety and improve the operational economy of power system at the same time.