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.

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Due to the high growth of DG installation in power systems, besides active power production, the DGs can also play an important role to fulfill reactive power requirements. Future smart grid is envisioned to be based on Distributed Resources (DR) and system security issues should be tackled by these units. In this paper, a method is used to rank the reactive power supported by DGs at different locations considering reactive power requirement in emergency conditions. Also, a new index is proposed in order to show the effect of DG's reactive power output on voltage profile. In order to illustrate the effectiveness of the proposed method, simulation results of a low-voltage distribution system are reported and discussed.

A B S T R A C TTraditionally, conventional generation units were used to provide ancillary services e.g. reactive power support, and spinning reserve. Nonetheless, with the emergence of highly penetrated distributed energy resources (DERs) systems and considering how beneficial they can be; it appears reasonable to use them as reactive power providers. Therefore, this paper introduces a new procedure for DERs to participate in the reactive power market. To do that, an algorithm is proposed to calculate the deliverable reactive power capability of DERs from distribution networks to transmission systems. Furthermore, a reactive power procurement model is introduced to consider DERs participation in the reactive power market. Finally, to show the effectiveness, and validity of this method many case studies are carried out on 33-bus distribution and CIGRE 32-bus transmission test systems

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