C I R E D C I R E D C I R E D C I R E D 22 nd International Conference on Electricity Distribution Stockholm, 10-13 June 2013 Paper 100 CIRED2013 Session 3 Paper No 100 1 INVESTIGATION OF THE IMPACT OF DG ON THE BEHAVIOUR OF NDEDC PROTECTION SYSTEMS Heba BEDER Ebrahim A. BADRAN Magdi M. El-SAADAWI North Delta Electric Distribution Company Faculty of Engineering, Faculty of Engineering, (NDEDC) - Egypt Mansoura University - Egypt Mansoura University - Egypt islam.girl@live.com ebadran@mans.edu.eg saadawi@gmail.com ABSTRACT The current global trend in the distribution networks is to use Distributed Generation (DG). The coordination problem between protection devices is a challenge which faces DG insertion to the distribution network. In this paper, the effect of DG on the distribution networks protection system is investigated. The real network of the North Delta Electric Distribution Company (NDEDC) in northern Egypt is studied. The study focuses on the over- current, the earth fault relays and auto-recloser (AR), where they represent the protection system used in distribution networks. The NDEDC real data are implemented with all of the protective devices which are modelled with their practical settings using Matlab/Simulink. Different scenarios for integrating the DG with the studied system have been implemented and discussed. Finally, recommendations are introduced for NDEDC protection systems. INTRODUCTION The traditional power system grid in most of the developing countries has a structure with an up-down power flow. The International Energy Agency (IEA) estimates that by 2020, the developing countries will need to double their electrical power output [1]. DG provides an attractive alternative solution for the world energy crisis. DG is an electrical power source connected directly to the distribution network and/or the customer site [2-3]. In [4] the positive impact of DG is presented. It mainly includes provision of voltage support, improved power quality, reduction in network losses, release of addition transmission and distribution capacity and improved reliability. The protection issue is one of the main technical constraints which face DG insertion to the distribution network [5]. Relays false tripping and blinding of protection are mainly issues from the protection issues. False tripping occurs when a generation installed on a healthy zone contributes to the fault in another zone connected to the same substation; this can lead to false tripping of the relay in the healthy zone. The protection blinding occurs because the DG contribution to the fault which reduces the grid contribution to the fault. Therefore, the short circuit current may be undetected by the grid protection relays [6]. In this work the impact of DG on the protection of traditional distribution networks in developing countries is studied. The study is applied on a part of the Egyptian distribution network; NDDEC, in northern Egypt. NDEDC is a sample of a traditional network designed for unidirectional electricity feeding. The main objective of the paper is to find the maximum allowable DG penetration level that maintains the same protection system before DG integration. A Matlab/Simulink model is used to implement the investigated system. The study includes the over-current, earth fault relays and auto- recloser. NETWORK DESCRIPTION AND MODELING NDEDC Network Description NDEDC network is supplied from the 220 kV Egyptian grid through 220/66/11 kV substations (SS). The 11 kV substations sides supply 167 Distribution Panels (DP). The 11 kV network feeders consist of either rural lines (OHL) or urban underground cables. The NDEDC real data are implemented with all of the protective devices which are modeled with their practical settings. Three real selected systems are used to simulate all protection systems in NDEDC: cable systems, OHL systems, and OHL-AR systems. Cable System Modeling Fig. 1 illustrates EL-Mokhtalat DP as a section of NDEDC network. It is a cable system which consists of three incoming feeders and eight outgoing feeders. Modeling has been performed in Matlab/Simulink with the help of Sim- Power-Systems toolbox (SPS) [7]. The loads of the outgoing feeders are centralized using constant impedances based on 11 kV. The cable data is verified with the actual onsite measured cable impedance. Then, the aging factor of the cables is calculated and implemented in the simulation. The system parameters are given in Table 1. Both over current and earth fault relays are modeled in Simulink. The overcurrent relay model is picked from [8]. The vectorial sum of the three phase currents is used to represent the earth fault relay operation. A logic function is used to combine the output signals of the earth fault relay and the three overcurrent relays outputs, as shown in Fig. 2. The time delay is set to 0.2 seconds for outgoing and 0.5 seconds for incoming feeders. The current setting is given in Table 1.