In distribution systems, voltage sag/swell is known as the most hazardous disturbances which distort voltage stability in sensitive loads. In order to compensate these voltage disturbances via custom power devices, fast and accuracy detection of voltage sag/swell is the most significant issue for effective compensation. Therefore, this paper aims to examine and compare detection capabilities of the most common sag/swell detection methods. In this study, EPLL, SOGI-PLL, FFT and ISRF are assessed among the detection methods. The common point of these methods is that they are applicable for both three-phase system and single-phase system as well. The performances of proposed methods are analyzed and compared for both single phase sag/swell condition and three-phase asymmetrical sag/swell conditions. The methods are compared through constructing sag/swell generation system in PSCAD/EMTDC.