Analysis Of 220/110kV Electromagnetic Ring Network Affecting Power System Operation

Early in the development of the power grid, the structure of high voltage level is weak. In order to improve the reliability of power supply, the grid of low voltage levels was often built in close interrelated network structure, thus the high and low voltage ring network is formed. Over the years, most of the 220 k V electro-magnetically coupled with 110 k V adopt open-loop operation mode domestically. However, open-loop system that is simple and casual may adversely affect the safety and economic operation of the grid. On one hand, depending only on device, it is difficult to ensure security of power supply in a single line or a single variable run substation, it is common to result in a greater range of lower grid short-term even splitting solution after the grid failure; On the other hand, simple open-loop operation mode may cause high system losses. Currently, in the requirements of the grid facing severe pressure of safe operation and efficient and economical operation, the in-depth study of the above questions was conducted to tap the potential of the grid, which is more significant to improve overall operational level by reducing operating losses and ensuring reliable power supply.Firstly, this paper introduces the research status and significance of electromagnetic ring network, explaining the basic concepts and causes of electromagnetic ring network, analyzing the advantages and disadvantages of electromagnetic ring operation.Secondly, in the background of Hunan 220 k V electromagnetically coupled with 110 k V, the typical operation mode of electromagnetic loop network was summarized, and theoretical analysis for 220 kV electromagnetically coupled with 110 k V open, closed-loop three-phase short-circuit current and single-phase short-circuit current of 110 k V bus was adopted. In PSASP 6.28 environment, 220 k V electro-magnetically coupled with 110 k V in the way of Hunan Power 2013 Fond was applied as the study object. In running of open or closed loop, calculation of 110 k V bus short-circuit current of 220 k V substation, 110 k V substation and 10 k V bus short-circuit current of 110 k V substation was made. When electromagnetic ring open operation,assuming that the short-circuit current value of 220 k V busbar breaker rated is breaking current, determining whether 110 k V and 10 k V bus short circuit current is controlled in the closed-loop running.Once more, it introduces the theory and methods of static security, analyzing Hunan Province 220/110 k V electromagnetic ring static security and stability, and the vast majority of electromagnetic ring can be checked by N-1, in the circumstances of not passing N-1, the majority was belonging to the 220 k V main transformer. This situation also exists in open loop. In the analysis of electromagnetic ring static voltage stabilityload margin index comparised in closed or open loop., obtaining the result that load margin of closed-loop operation has increased to some extent when compared with the open-loop, and load margin index of the partial electromagnetic ring network increase reach around 29%.Finally, it describes the analysis and stability criterion of transient stability, analyzing transient stability of Hunan 220 k V electro-magnetically coupled with 110 k V. Using the Section line fault of the supply area and part generators cutting Machine as perturbations, analysis of the voltage level of the each bus voltage in a closed-loop running was adopted. The results show that 220 k V electro-magnetically coupled with 110 k V closed-loop operation will not appear unstable situation, and the 110 k V substation does not appear unstable situation even in the absence of bus differential protection.