Non-linear loads became an important problem in now days since the implementation of new power semiconductor devices in electric power systems generating harmonic distortion in transmission systems [1,3,11]. That's the reason why solve these problems for utilities became an important task. In this paper the performance of custom power device known as pure shunt active filter, which deals with this kind of problems, is simulated and tested. At the end of testing section is proved how the total harmonic distortion of the system is reduced and adjusted to an acceptable value.