POWER quality is an issue of interest due to the dissemination of nonlinear loads on one hand and rapid growth of sensitive loads on the other hand. The term Power quality comprises of multitude of phenomenon in voltages and currents which cause them to violate accepted levels in standards. One of the most important power quality events are voltage sags which mainly caused by short circuits or instantaneous large loadings of the lines. However, voltage drop problem may arise when using lateral radial feeders with long length or when feeding large loads. Most of the time, installation of new substation is not economical. Therefore, finding a solution to keep the voltage level within standards becomes imperative. To enhance the voltage and to control the reactive power, distribution systems are equipped with different voltage regulating devices such as tap changing transformers, voltage regulators, shunt/series capacitor banks and etc. The basic function of shunt/series capacitor banks is to regulate voltages by reactive power compensation. Shunt capacitor compensates reactive load current causes reduction in current magnitude drawn by loads and voltage drops due to line current. However, series capacitors compensate impedance of feeder and reduce long and short term variation in voltage. In this thesis, power quality impacts of fixed series capacitor banks and thyristor controlled series capacitor (TCSC) on distribution power systems are investigated. Applications of series capacitive compensation in voltage profile mitigation, increasing transmission capacity, harmonic impacts on distribution systems are investigated by theoretical and simulation techniques. Application guide for series capacitor design and protection for using in distribution long feeders is presented. Also two control methods based on synchronous PI controllers and phasor diagram analysis are introduced to control TCSC’s firing angle and their results are compared. It will be shown that using phasor diagram analysis is much more appropriated approach to improve voltage profile in a wider range of operating points. Fixed series capacitor proper power and placement for voltage profile mitigation in typical real distribution feeder are investigated and impacts of percentage compensation degree of series capacitor are investigated on voltage harmonics and flicker. Key words: Power quality, voltage profile improvement, series capacitor banks, phasor analysis.
