Study on Power Transfer Capability and Voltage Stability Improvement Using Static Var Compensator Case Study: Holeta 500 /400 Kv Substation
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Date
2019-05
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Addis Ababa University
Abstract
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.
Description
Keywords
Stability, simulation, power transfer, FACTS, SVC, MATLAB, simulink, PV, QV curves