Arab J Sci Eng DOI 10.1007/s13369-017-2931-2 RESEARCH ARTICLE - ELECTRICAL ENGINEERING DC Fault Protection Strategy for Medium Voltage Integrated Power System: Development and Assessment Syed Imran Ahmad Shah 1 · Munira Batool 2 · Abdul Khaliq 1 · Fawad Nawaz 3 Received: 2 March 2017 / Accepted: 24 October 2017 © King Fahd University of Petroleum & Minerals 2017 Abstract In medium voltage direct current (MVDC)-based power distribution scheme DC faults can cause instant disrup- tion in service continuity to various connected loads. Many integrated power systems (IPS) found MVDC as a better replacement of MVAC for detection, isolation as well as protection against DC faults. DC fault protection strategy for developed MVDC-IPS system (which is accompanied by LVDC subsystem), is proposed here by introducing a modi- fied series Z-source breaker circuitry which minimize fault or transient current that reflects back at the DC source by keep- ing its common ground return path and to re-energize the DC load after fault clearance. The versatility of the proposed idea also include to energize the loads after the fault clear- ance. The main problem is that a large value of fault/transient current 0 that reflects back at the source and SCR (when it stops commutation). This large reflective current value is much greater than the value of the SCR peak cycle surge value and can damage the SCR permanently. To overcome this problem in the developed technique, an addition of series resistance is made with capacitors which minimize the effect of transient level on SCR and source. Furthermore, due to this resistance the other component size or value is decreased which helps in minimizing the effect of transient current at SCR and source. Another aim is to build the breaker struc- ture in such an optimize way so that to minimize dissipation B Munira Batool munirabatool@postgrad.curtin.edu.au 1 Department of Electrical Engineering, Center for Advance Studies in Engineering, Islamabad, Pakistan 2 Department of Electrical and Computer Engineering, Curtin University of Technology, Bentley Campus, Perth, WA 6102, Australia 3 COMSATS Institute of Information and Technology, Lahore Campus, Islamabad, Pakistan and weight as compared to its classic structure along with enhancement of efficiency. The proposed strategy of DC fault for IPS is validated through two case studies done in PSCAD simulations. Keywords Z-source · SCR · Topologies · Transient currents · MVDC · IPS Abbreviations MVDC Medium voltage direct current LVDC Low voltage direct current IPS Integrated power system MVAC Medium voltage alternating current SCR Silicon controlled rectifier C–L Capacitor–inductor R–L Resistance–inductor I C Capacitor current V C Capacitor voltage I L Inductor current V L Inductor voltage I SCR Current through SCR V SCR Voltage across SCR G f Fault conductance HFC High frequency conduction 1 Introduction In recent years power system area of electrical technology has brought up a vast revolution in the life and industry and new developments are in progress. In order to estab- lish distribution networks as more independent and safe, extreme efforts are made through comprehensive research 123