THE IMPACT OF WEAK INTERNECTION OF BULK POWER GRIDS TO DAMPING AND DYNAMIC STABILITY OF POWER SYSTEMS

The interconnection of national power grids in China brings new issues into power system stability and control especially low-frequency oscillation. In this paper, we analysis the low-frequency phenomena from the viewpoint of damping torques. First, damping torques of strong and weak connected systems are compared, and the results show that the relatively large impedance of tie-lines in weakly interconnected systems could greatly reduce the damping of these systems. Then, this conclusion is validated by tests in national grids of China. These tests also demonstrate that reinforcement of the connection between two bulk power grids is an effective way to mitigate oscillations in systems. Finally, we introduce the not well-known concept of damping coefficients matrix and re-deduce its analytical forms in a two-generator system, then it is concluded that damping of a power system not only depends on models and parameters of the system itself, but also depends on reactance of tie-lines, as well as parameters of other systems participating in interconnection with this system.