Simple, fast detector for voltage dip or voltage swell

A simple, fast detection scheme for voltage dip and voltage swell is presented. Applying a simple relay and lowpass filter to the supply voltage signal, an in-phase fixed magnitude reference signal with very low total harmonic distortion can be generated. Comparing the supply signal with the in-phased fixed magnitude reference sinusoid, any change of magnitude in the supply signal can be detected. The detection scheme can indicate voltage dip and voltage swell in less than a quarter of the cycle of oscillation. Experimental results are presented to demonstrate the effectiveness of the proposed detection scheme.