The power quality improvement faces different significant problems due to the wide use of power electronics and voltage instability. To overcome these different power quality problems, an active power filter is used. The active power filter in general has four main categories, shunt, series, unified power quality conditioner and hybrid active power filter. The shunt active power filter is usually used to mitigate source current harmonics and compensate reactive power for power factor improvement. The series active power filter is usually used to mitigate voltage problems (sags, swells, transients, dips, distortions….). The unified power quality conditioner is used for all voltage and current problems. In this paper, the three phase three-wire series active power filter is utilized alone to mitigate all power system problems (voltages and currents) for this case study, such as voltage sag, voltage swell, voltage harmonics, and source current harmonics to comply with the harmonics limits given in IEEE 519-1992, and IEC 61000-4-7 standards. The source current harmonic problem mainly exists due to, 1) distorted voltage source, and 2) non-linear loads. The series active power filter can effectively eliminate the source current harmonics in case of distorted voltage source. Consequently, the series active power filter can be used alone as a power quality improvement for all voltage and current problems as mentioned in this case study.