en Electrical railway Electrical railway پژوهشي Research <strong>Abstract</strong><br> General faults in regular electrical railways system could be detect by implementing the specific protection functions such as ground fault or sensitive earth fault. Otherwise, in ungrounded electrical railway systems which using both feeding and return contact rail at the same time, fault detection cannot done with above-mentioned function. Due to recent growth in electrical railway network especially in metropolises, it is an essential requirement to improve operation and safety indexes by using efficient fault preventing and fault clearing method in minimum time.<br> In this applied research, a new fault diagnosing method developed by using frequency response of contact rails system. This technique based on observing pattern changes caused by expected faults such as broken contact rail, contact rail to ground faults on feed or return circuit frequency response.<br> &nbsp; frequency response, contact rails, fault, ungrounded electrical railways 29 38 http://ijrare.iust.ac.ir/browse.php?a_code=A-10-88-13&slc_lang=en&sid=1 S Akbari Akbari_sa@mapnagroup.com 180031947532846001453 180031947532846001453 Yes Electrical Railway Expert, MAPNA Group, Electrical Railway Expert, MAPNA Group z Rosami A.rostami.eng@gmail.com 180031947532846001454 180031947532846001454 No ALZAHRA University ALZAHRA University A Khoshharf Khoshharf_a@mapnagroup.com 180031947532846001455 180031947532846001455 No Electrical Railway Expert, MAPNA Group Electrical Railway Expert, MAPNA Group SS Fazel fazel@iust.ac.ir 180031947532846001456 180031947532846001456 No School of Railway Engineering, Iran University of Science and Technology School of Railway Engineering, Iran University of Science and Technology