Calculation On The Limit Of Transfer Capability In The Tie-lines Based On The Most Serious Fault

With the more development of national economy, interconnected networks' emergence has become the certainty for the network's development. The interconnection between network can bring a series of economic benefits, such as stagger peak, fire and water electricity inter-complementarities, urgent power support. But it also makes it necessary to solve many important technique problems, for example, the control of power flow and stability of interconnected line between big network and other network. Nowadays, it is the most important thing to insure the stable run in power system. If there is a fault happened in the supplied side of network, the transmitted power is so large in tie-lines that the power system will be easy to be transient instability, even to be voltage collapse, which will affect a lot to national economy. Therefore, it is necessary to calculate the limited transmitted power in tie-lines considering transient stability constrains.A new method of calculating the most power transmitted in tie-lines is presented in this paper. Comparing the transient energy margin of system which has a three-phase short circuit fault among each branch of supplied side and a bout of tie-lines, the branch having the most serious fault in the system can be found. It can be confirmed that the most power transmitted on this branch is the limit of power transmitted in tie-lines. In this paper, numerical integration method is adopted to calculate the sensitivities of transient energy margin by each generator. The output of generator should be adjusted according to that sensitivity, and the tie-lines'transmitted power is adjusted by regulation strategy which combines equal step method and dichotomy method. The paper also indicates that fault clear time can affect the limit of transmitted power in tie-line. The longer fault clear time is, the smaller transient energy margin of instable system is, and the smaller the most power transmitted also is. The calculations of twenty-six and sixty node system have proved the efficiency and rationality of the method presented in the paper.