Power quality is a significant issue that has become increasingly important to both electric power utilities and their customers because of financial losses caused by insufficient. In this work, the Fourier transform (FT) has been exploited for the statistical investigation of the disturbances affecting the electrical distribution networks (HTA) in South-Benin. The data coming from the overhead line disturbances and underground cables, especially from the source substations of MARIA-GLETA, VEDOKO, AKPAKPA, GBEGAMEY and SEME have been treated. These data have been collected and made in our disposal by the Beninese Electricity Energy Company (SBEE) over the period from 2010 to 2017. Harmonic Distortion Rate (TDH) and the Disturbance Rate (D R ) have been used to evaluate the variation coefficient of the different disturbances registered at the each source substation, in order to characterize the harmonic pollution and the reactive power consumption. According to the EN 50160 N standard, the results obtained show that VEDOKO registered 500 to 2000 interruptions of duration between 0.4x10 5 and 1.8x10 5 minutes, between 2013 and 2016 especially due to a very critical load shedding. The dominance of the disturbances observed has been due exclusively to the incidents setting off and the load shedding incidents in 2017. 2013 and 2015 have been characterized by the frequent blackouts of long living, and occasion considerable damages, and consequently slow down the economic activities, social and cultural life of consumers.