Industrial Control Engineering

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Browsing Industrial Control Engineering by Author "Abebaw, Yalew"

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    Study on Power Transfer Capability and Voltage Stability Improvement Using Static Var Compensator Case Study: Holeta 500 /400 Kv Substation
    (Addis Ababa University, 2019-05) Abebaw, Yalew; Getachew, Biru (PhD)
    Voltage stability is a major concern while planning and operating an electrical power system. As electrical power demand increases, power system networks should be used in maximum of their capacity to meet the demand growth. In such case Flexible AC Transmission System (FACTS) can be used so that maximum capacity of system equipments utilized keeping the thermal limit and maintaining system voltage stability. Static Var Compensators (SVCs) can endlessly provide or consume the reactive power which is necessary to control the dynamic voltage oscillation helping to get stable transmission system and also help to achieve maximum power transfer. Power transmission can always be improved by upgrading or adding new transmission lines. But sometimes due to financial constraints and lack of corridors for new transmission lines (environmental reasons), this may not be practical solution. SVC is feasible alternative for optimizing the existing transmission system so that maximum possible power will be transferred in the range of thermal limit and without affecting system stability. Great Ethiopian Renaissance Dam (GERD) which is now under construction is going to generate around 6450 MW. This energy is far more than the current total generation capacity of the country. HOLETA 500 /400kV substation will be the gate way for this power to the grid. There are four 500 kV transmission lines coming from GERD to HOLETA 500/400 kV substation. SVCs are installed at HOLETA 500/400 kV substation to enable in evacuating the power generated at GERD power plant. This thesis focuses to investigate the impact of the SVCs in HOLETA 500 /400kV substation on voltage stability and power transfer improvement. Three SVCs of total capacity 900 MVAr are used at HOLETA 500/400 kV substation. They are connected to the AC 400 kV system using 400/33 kV coupling transformers. The study also evaluated possible installation of SVCs at DEESA or GERD substation and observes the effect on the voltage stability and transferred power. In this study, the system is simulated using MATLAB 2017a /simulink environment. It is observed that the best location of the SVCs is HOLETA 500/400kV substation as the power transferred and voltage stability is better than if it is in DEDESA or GERD. Using the SVCs in the network, didn’t improve transfer of power. But the voltage at GERD bus bar becomes 509.3 kV from 568.6 kV. The voltage at HOLETA 400 kV bus bar becomes 338.4 kV from 362.8kV. The SVCs improve the voltage stability margin in the 500 kV network at GERD bus bar. The simulation also depicts that while the SVCs are used, reactive power of the system increases and system voltage reduces. The PV and QV curve Study shows that SVCs improve over voltage problem. During 50% loading in the absence of SVCs, the voltage at HOLETA 400 kV bus bar is 418.5 kV. But when the SVCs are present it is 396.3 kV which is very good for the system. Since the system is facing both over voltage and under voltage problem, the SVCs are helpful in controlling the over voltage problem. When The SVCs are used with Reactors on the line, the voltage is reduced to 314.1kV from 338.4kV.The system is having 620 km of 500 kV transmission line length and heavy loading, 2591 MW at HOLETA 400 kV bus bar leading to under voltage. But GERD bus bar has no any load and very far away from the load center leading to over voltage. So for better voltage stability and power transfer improvement, series capacitive compensator should be inserted in the GERD-DEDESA-HOLETA 500/400 kV network as they reduce inductive reactance and boost receiving end voltage. In long term, additional FACTS device should be considered for better stability and transfer of power.