Dynamic Equivalents Based On Electrical Distance And Coupling Index And Its Influence On Probabilistic Insecurity Index

Because of the development of power systems, the power system transient stability analysis is facing the problem that the time spent on computing is too long. Dynamic Security Region (DSR) is a useful solution to this problem, which provides more operating information to system operators.The coefficients of DSRs are necessarily to be updated regularly, because of the randomness of the network structure and the possible failure parameters, when DSRs are used online. Furthermore, it takes very long time to obtain DSR coefficient as the power systems'scale is expanding.The system's dimensions can be reduced a lot, and thus reduce the calculation time of DSRs dramatically with the dynamic characteristics being ensured basically, by using dimension reduction techniques. The way of choosing the study area has important influences on the precision and speed of calculation when reducing the system dimensions. The main work of the paper including:1) A conceptual expanded definition of electrical distance is proposed. The concept of coupling index is introduced on the foundation of electrical distance. Electrical distance is the main criterion while the coupling index serves as a supplement. It makes up the disadvantage that there is not enough description of system's transient character.2) A new method of dividing power systems based on the new expanded concept of electrical distance is proposed. It is more reasonable. The dividing result is unique, which solved the problem of the randomness of the dividing result when using traditional method.3) Probabilistic insecurity index is used to evaluate the precision of dimension reduction, which accords with facts better.4) The 10-generator 39-bus test system is used to prove the effeteness and rationality of the proposed method in the paper.