Abstract:
One of the major concerns of power system is the voltage instability. Voltage instability is a
problem of overload or underload of a power system. The main factor causing voltage
instability is the inability of the power system to meet the demand for reactive power. Static
Var Compensator plays a major role in voltage stability enhancement due to its fast response
and high capability. So, it is very important to study the use of static Var compensator for
distribution substation voltage stability enhancement under normal operating conditions.
Data collection is carried out to study the voltage profile and reactive power compensation of
Wolaita Sodo distribution substation. Wolaita Sodo distribution substation has one incoming
feeder and eight outgoing feeders. There are three transformers 132/15 kV, 132/33 kV,
132/66 kV, the rating of the transformers are 20 MVA, 25 MVA, 16 MVA respectively. The
132/15 kV transformer suppling to four 15 kV outgoing feeders, the 132/33 kV transformer
suppling to three 33kV outgoing feeders and the 132/66 kV transformer suppling to one 66
kV outgoing feeder. The total load of Wolaita Sodo distribution substation is 17.9 MW and
14.74 MVAR. The total connected load to the four 15 kV feeders is 13.9 MW and 10.36
MVAR.
Static Var compensator modeling and simulation studies have been carried out using ETAP
software. Simulation results with and without Static Var compensator has been performed.
Line Voltage stability index (Lmn) at various lines are calculated to identify the critical lines
and weak buses. Then Static Var compensator device is introduced at the bus connected the
critical lines and its effectiveness is evaluated for voltage enhancement. The size of the
selected Static Var compensator is 11.544 MVAR.
After connected the Static Var compensator the voltage profile of the weakest bus is
improved from 0.9489pu to 0.9925pu. The voltage profile of the other buses which
connecting with the critical line also improved. Additionally the power and current flows of
the distribution substation buses and lines increased, the reactive power loss decreased, the
voltage deviation decreased and transformer loading decreased. Thus, based on the findings
of this research, I concluded that use of static Var compensator could be a very effective
FACTS device for voltage stability enhancement.
