International Journal of Power Electronics and Drive System (IJPEDS) Vol. 10, No. 3, Sep 2019, pp. 1317~1323 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v10.i3.pp1317-1323  1317 Journal homepage: http://iaescore.com/journals/index.php/IJPEDS Investigation of distributed generation units placement and sizing based on voltage stability condition indicator (VSCI) Arvind Raj 1 , Nur Fadilah Ab Aziz 2 , Zuhaila Mat Yasin 3 , Nur Ashida Salim 4 1,2 Department of Electrical Power Engineering, Universiti Tenaga Nasional, Malaysia 3,4 Faculty of Electrical Engineering, Universiti Teknologi MARA, Malaysia Article Info ABSTRACT Article history: Received Aug 8, 2018 Revised Feb 2, 2019 Accepted Mar 6, 2019 Voltage instability in power distribution systems can result in voltage collapse throughout the grid. Today, with the advanced of power generation technology from renewable sources, concerns of utility companies are much being focused on the stability of the grid when there is an integration of distributed generation (DG) in the system. This paper presents a study on DG units’ placement and sizing in a radial distribution network by using a pre- developed index called Voltage Stability Condition Index (VSCI). In this paper, VSCI is used to determine DG placement candidates, while the value of power losses is used to identify the best DG placement. The proposed method is tested on a standard 33-bus radial distribution network and compared with existing Ettehadi and Aman methods. The effectiveness of the method is presented in terms of reduction in power system losses, maximization of system loadability and voltage quality improvement. Results show that VSCI can be utilized as the voltage stability indicator for DG placement in radial distribution power system. The integration of DG is found to improve voltage stability by increasing the system loadability and reducing the power losses of the network. Keywords: Distributed generation Maximum loadability Power losses Voltage stability Voltage stability index Copyright © 2019 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Nur Fadilah Ab Aziz, Department of Electrical Power Engineering, College of Engineering, Universiti Tenaga Nasional (Uniten), Jalan Ikram-Uniten, 43000 Kajang, Selangor, Malaysia. Email: nfadilah@uniten.edu.my 1. INTRODUCTION Distributed generation attributes to generation of power at the point of consumption or the location of load [1, 2]. Distributed generation also refers to small scale generation that is not directly connected to the bulk distribution system and non-centrally dispatched [3]. In published works, there are a number of different terms and definitions are used for the description of distributed generation [4]. The term ‘embedded generation’ is often used in Anglo-American countries, ‘dispersed generation’ is used by North American countries and the term ‘decentralised generation’ is applied in Europe and parts of Asia [4, 5]. The name ‘distributed generation (DG)’ is recommended to be used all over the world based on the literature survey [4, 5]. Power generation at the location of load decreases the losses due to transmission over long distances as well as other costs associated with the distribution systems. The complexity and the inefficiencies from the systems are also minimized with the emergence of DG [6]. In many cases, DG can supply electricity at a lower cost with improved power reliability and security and resulted to fewer environmental issues compared to conventional generators [7]. Voltage stability is defined as the ability of a power system to maintain acceptable voltage levels at all buses within the system [8]. The definition includes the voltage of buses under normal condition and after disturbance in the network. A state of voltage instability is experienced in a system when there is a continuous or uncontrollable drop in the magnitude of voltage either after a disturbance, load increase or after