Various non-linear loads such as variable speed drives (ASDs), bulk rectifiers, ovens, computer supplies, etc. draw non-sinusoidal currents containing harmonics from the power supply, which causes voltage. harmonics. Current harmonics cause increased losses in the electrical system, excessive heating of rotating machinery, interference with nearby communication circuits and control circuits, etc. It has become vital to maintain the sinusoidal nature of voltage and currents in the electrical system. Various international agencies like IEEE and IEC have published standards that impose limits on various current and voltage harmonics. The limits for various harmonics of current and voltage specified by IEEE-519 for different frequencies are shown in Table 2.1 and Table 2.2. Table 2.1 IEEE 519 Voltage LimitsBus Voltage MinimumIndividualHarmonicComponents (%)MaximumTHD (%)69 kV and below 3 5 115 kV to 161 kV 1.5 2.5 Above 161 kV 1 1.5 Purposes and functions active power filters have been extended from reactive power compensation, voltage regulation, etc. through to harmonic isolation between utilities and consumers, and harmonic damping throughout the distribution as harmonics propagate through the system. Active power filters are installed either in individual consumer premises, or in substations and/or on distribution feeders. Depending on the compensation objectives, different types of active power filter topologies have evolved, a suitable overview of which is provided in [3-4].Table 2.2 IEEE 519SCR current limits=Isc/Il h