Practical solution to prevent failure of grounding transformers in substations due to improper performance of protection system

The grounding transformers (GT) are intended for establishing a neutral point in three-phase ungrounded power systems. Failure of these devices results in power transformer outage and requires subsequent direct and indirect costs. Recently, failure of GTs in many regional electric companies has led to numerous problems. Results show that proper performance of protection system play an important role in preventing failure of these devices. In this paper, MV-side E/F protection system of substations has been described and then simulation of a 63/20 kV substation is presented. Protection system of mentioned substation has been studied practically to evaluate its efficiency against earth faults in different locations. The simulations are carried out by EMTP-RV and results are investigated. This task has been done via characteristic curves of E/F relays. Finally, required tasks to prevent failure of GTs are presented. Moreover, role of resistance tanks to detect high impedance faults and effect of earth fault events occurred in output feeders on failure of GTs have been discussed.