Modern society generally expects high reliability power supply. Electricity interruption may cause high damage to consumers. When a fault occurs, the voltage dip or voltage sag will occur. If the customer cannot tolerant the dip, it will be cut off from the supply permanently. Therefore, it is important to consider voltage effect for system reliability. Generally, DG can improve system reliability. But choosing the location of DG have effect on system reliability. According to the results, installing DG in downstream area can make System reliability better. The impact of protection devices and voltage dip is analyzed in this paper. In this paper, Countermeasures against voltage dip are also presented.