Studies Of Paralleling Operation Simulation In Power System Restoration

Since the 1960s, large-scale power outages have taken place in many countries, covering broad area and long time. These outages seriously affect people's normal life, causing enormous social impacts and economic losses. Though the blackout is not probably happened, fundamentally the outages are inevitable. Therefore, research on how to restore the power system quickly and effectively after the outages is of major importance.With the deepening of research, the study on power system restoration has expanded from the black-start to skeleton restoration. As an important component of skeleton restoration, the paralleling operations between bilateral systems appear in the whole restoration process. There are many problems in paralleling operation. The choice of location and conditions has great effect on the security and speed of power system restoration, which should be considered as a factor in the development and optimization of skeleton restoration strategy. Due to the influence of two bilateral systems for each other, the system will appear oscillation after paralleling, which is more serious when two systems are in similar scale or paralleling occurs in the initial period of power system restoration. In order to guarantee the safety and the speed of paralleling operation, we should simulate and analyze the transient process of paralleling.A simulation method for transient process after paralleling between bilateral systems is proposed in this paper. The method simulates the function of the automatic synchronizing devices and sets the initial state of the power grid before paralleling through altering the result of the power flow, and simulates the close of breaker through modifying the admittance matrix of power grid, and guarantees the frequency difference setting and rotor angular calculation through different setting of generators rotate speed and the same basic value of frequency. In addition, considering different grid environment has different paralleling conditions requirement, this paper further estimates the reasonable conditions for specific grid. According to the estimation results, we should set the value of automatic synchronizing devices and adjust power grid, which can make the paralleling conditions more suitable for the specific grid and be benefit for the speed and accuracy of automatic synchronizing devices.Based on the paralleling simulation method, this paper builds the simulation model and simulates the paralleling operation between Linyi and Rizhao subsystems in Shandong power grid restoration strategy using internal power source, and the paralleling operation on 500kV backbone skeleton in restoration strategy using external power source from Huanghua and Xin'an substation in Hebei grid. Through simulation, the security of paralleling operation and the feasibility of restoration strategy are checked. In addition, the main factors of paralleling and some adjusting measures can be obtained through simulation analysis. The simulation results demonstrate the proposed method is feasible.This paper also simulated the paralleling operation between the black-start testing system and the main operating system in Shandong power grid. The simulation checks the security of paralleling operation and estimates the reasonable conditions. Some improvement measures are provided through simulation calculation, such as enlarging frequency of test system suitably above the main grid, and maintain it's stability through some controlling measures, and enlarging the angle difference setting value of automatic synchronizing devices and so on. The simulation results and countermeasures are proved feasible through the comparison with experimental data.