Voltage stability enhancement in distribution substation using static var compensator (case study: wolaita sodo distribution substation)

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.