Simulation Study On Electromechanical Disturbance Propagation Of Power Systems

The increasing conflict between energy demand and the uneven distribution of energy will inevitably leads to power grid interconnection of regional, national and some other levels. Under this interconnection, the structure of the grid will become more substantial complex, and its dynamic process will also be more complex. Since the 1000kv UHV tie line between the Central China Power Grid and the North China Power Grid being put into operation, there will be a large amount of power fluctuation in the UHV tie line when power disturbances occurs in the Central China Power Grid or the North China Power Grid. This power fluctuation’s amplitude will even reach more than 90% of the load rejection, which cause a lot attention in the indursty. In this paper, we are going to study how electromechanical disturbance propagates in power system though simulation study. And we will also study how the internal faults in the North China Power Grid influence the power fluctuations of UHV tie line between the Central China Power Grid and the North China Power Grid through simulation study, among which the Sichuan Power Grid will be emphatically study. By doing so, we are going to provide some relevant experience for UHV system’s operation and its expansion.In this paper we will first introduce the research status of the electromechanical disturbance propagation, and we will analysis the electromechanical wave equation, the electromechanical wave velocity equation and the reflection and transmission mechanism of the electromechanical wave. Based on electromechanical disturbance propagation theory, we are going to have some simulation study in the 60 machines uniform chain system and the real power system to study how electromechanical disturbance propagates in power system. In the 60 machines uniform chain system simulation study a Gauss angle disturbance and a power disturbance will be added to the system to see how the disturbance propagates in the system. And the forty -first machine’s rotational inertia will changed to find out how electromechanical disturbance propagates under this case. In these three cases, we find that electromechanical disturbance propagates in form of wave, which is consisted of the electromechanical disturbance propagation theory. The propagation velocities we find in the simulations are similar to theoretical values of the continuum theory. In the real power system simulation study, a large cutting machine disturbance is added to the system to see how all the other machines react to it. And time delays are found in the other machines’ reactions, which prove the propagation of electromechanical disturbance among other machines.Based on simulation study in PSASP, we study how the internal faults in the internal faults in the Central China Power Grid influence the power fluctuations of UHV tie line between the Central China Power Grid and the North China Power Grid. After a series of simulations we find that a fault in Sichuan has the biggest influence in the power fluctuation of the UHV tie line. After calculating the transient energy inject into all the provincial grids after different disturbances, we find that among all the disturbances the disturbance in Sichuan generates the largest amount of transient energy. And the transient energy inject into the North China Power Grid from the Central China Power Grid through the UHV tie line of the Sichuan disturbance is the largest, that is why the Sichuan disturbance has the greatest influence in the power fluctuation of the UHV tie line.In the paper many simulations were carried out based on PSASP, and the impact of different faults in Sichuan Power Grid to the power fluctuations of the tie line between Sichuan and Chongqing and the 1000kV UHV tie lines between North China Power Grid and the Central China Power Grid were studded. Simulation results show that in the case of tie-lines buckling, the same failure of different locations affect the amplitude of tie-line power fluctuations, on the other hand the power shortfalls in the same place is proportional to the amplitude of tie-line power. Different types of disturbances have influence on the amplitude and frequency of tie-line power fluctuations, in which 500kv bus’three-phase earthing short circuit affects the tie-line power fluctuations more seriously. If 500kv bus’s three-phase earthing short circuitwas kept for longer time in certain buses in Sichuan, tie-line power fluctuations will get instability. Under the situation of buckling the same fault will lead to that the amplitude of power fluctuations in Sichuan and Chongqing tie-line greater than that in UHV tie-line.