Due to high penetration of distributed generation (DG) in distribution networks, transmission networks are no longer responsible solely for security issues in low-voltage distribution networks. DG units may also participate in security as well as power generation depending on their locations. In this paper, a DG placement problem is solved based on voltage stability analysis as a security measure. Modal analysis and continuous power flow are used in a hierarchal placement algorithm. Also, a modified equivalent reactive compensation method is proposed to provide a priority list of DG locations for compensating reactive power during occasions of reactive power shortage. Simulations are carried out on the well-known 33-bus radial distribution network. The results show the effectiveness of the placement algorithm and the ranking method.