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Wind energy is becoming the most viable renewable energy source mainly because of the growing concerns over carbon emissions and uncertainties in fossil fuel supplies and the government policy impetus. The increasing penetration of wind power in distribution systems may significantly affect voltage stability of the systems, particularly during wind turbine cut-in and cut-off disturbances. Currently, doubly fed induction generator wind turbine (DFIG-WT) is the most popular wind turbine. This paper investigates the issues of voltage stability improvement and grid-loss reduction of distribution systems which include DFIG-WTs under unbalanced heavy loading conditions. Simulation studies are carried out in IEEE 34-bus test system using DIgSILENT software to examine these issues during steady-state and transient operations of the system. Optimal locations of the WTs are determined based on this analysis. A new index (system unbalanced voltage variance) is proposed to evaluate system unbalanced voltage. The dynamic impacts between WTs and motor loads are also examined.