A method to secure the generator reactive power reserve by adjusting the transformer tap to improve the power system penetration of renewable energy has been proposed in this study. The tap is adjusted based on the voltage and reactive power sensitivity in the power system network. That is, the transformer tap sensitivity is calculated and analyzed to adjust the tap variation to gain sufficient or the least necessary amount of reactive power reserve. This method can be effective for generators without any margins in the reserves. The optimization problem based on the calculated sensitivities and effectiveness are presented. The optimum solution derived from such a problem provides the minimum control amount necessary to maintain the system voltage and dynamic reactive power reserve at their pre-specified levels to improve the power system acceptability of renewable energy. To demonstrate the effectiveness of the method proposed, a simulation has been performed for an IEEE-25 bus system. The results from simulations prove that the voltage has been well maintained while securing a dynamic reactive power reserve through optimal control based on the sensitivity analysis.
-The paper analyzes reactive power flow characteristic in power system by reactive power tracing. In addition, virtual buses are inserted in the algorithm to consider losses of transmission lines, and shunt capacitor treated as a reactive power generator. The results of simulation are analyzed by two points of view. The one is load's point of view and another is generator's point of view. Classic purpose of the reactive power tracing consists in the reactive power pricing. However, it is significantly used to select vulnerable area about line outage in this paper. To find the vulnerable area, reactive power tracing variations between pre-contingency and post-contingency are calculated at all load buses. In heavily load area, buses which has highest variation become the most vulnerable bus. This method is applied to the IEEE 39-bus system. It is compared with voltage variation result and VQ-margin to verify its effect.
-Voltage instability results from a lack of reactive power support in a power system. One effective solution for supplying reactive power to a power system is utilization of flexible alternatingcurrent transmission system (FACTS) facilities. Currently, two FACTS facilities are operated for stable operation of the power system on Jeju Island in South Korea. Both FACTS respond to disturbances to stabilize voltage fluctuations in the island power system, however there is potential for mutual interference between them because they are operated using measured voltage without a coherent system operation strategy; cooperative control between the two would result in more effective system operation. Here, a multiple FACTS control algorithm is developed for effective operation of the island power system. The algorithm is based on two methods: calculation of the effective reactive power (Q) reserve (EQR) to obtain an accurate reactive power for the system, and GV analysis to account for the two HVDC interconnections between Jeju Island and the Korean Peninsula.
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