Power factor correction of three-phase electrical power supply by using of thyristor controlled reactor VAR compensator

Abstract

Low power factor (abbreviated as pf), particularly lagging pf, brings a lot of negative effects to electrical power supply system. Lagging pf is caused by inductive load. Inductive load with low pf draws higher current for the same active power demand. Higher current results in larger kVA rating and size of all electrical equipment connected to the electrical power system, larger conductor size used to deliver electrical power to the load, higher loss hence poorer power distribution efficiency and higher voltage drop hence poorer electrical power system voltage regulation. Considering all these negative effects, reactive power (VAR) compensation is needed. This paper analyses characteristics of a VAR compensation method called Thyristor Controlled Reactor (TCR) applied in three-phase electrical power system supplying an inductive load. A TCR consists of three sets of a capacitor connected in parallel with an inductor. The capacitor will supply a certain amount of reactive power needed by the load. The inductor is connected in series with an electronic static switch named as TRIAC to control the amount of reactive power absorbed by it. When reactive power supplied by the capacitor is higher than reactive power demanded by the load, the switching angle of TRIAC is controlled in such a way that excess of reactive power supply is absorbed by the inductor. In this work, three capacitors in which capacitance of each of it is equal to 50 µF as well as three inductors in which inductance of each of it is equal to 200 mH are used to compensate an inductive load which has power and pf vary from 1.5 kW to 4.6 kW and 0.46 to 0.84 respectively. By controlling the switching angle of TRIAC, pf of the three-phase electrical power system is successfully maintained close to unity at 0.95 following changes of the load. However, further analysis shows that operation of the TRIAC results in increase of current harmonics. Average of total current harmonic distortion (THD) increases from 15.13% to 18.45% due to use of TCR. On the contrary, voltage total harmonic distortion (THDV) after TCR installation is slightly lower than before TCR installation.