Currently, renewable energy sources are being integrated into Vietnam\'s medium voltage system nationwide. According to Circular 39/2015 / TT-BCT of the Ministry of Industry and Trade, issued on November 18, 2015 on \"Regulation of electric distribution system\" referring to a number of technical regulations of the medium voltage network with respect to the frequency, voltage and protective relay systems [1]. However, this provision has not fully considered the changes and effects when connecting the distributed energy sources (DER) such as wind and solar to the medium voltage systems.The actual operation shows that the integration of renewable energy sources into medium voltage systems can cause several power quality problems such as overvoltage, adding more power loss, and affecting the protective relay, which were set up with the unidirectional power flow from the grid to the load [2-7]. This paper will focus on studying the impacts of the distributed energy sources on the protection of the power distribution systems.