Earth fault protection failure in the distribution transformer 110.4 kV supply

Abstract EN

This research studies a miss-coordination problem in the protection of 11 kV distribution network in Iraq.

The problem arises when an underground cable is exposed to an earth fault at a location between the High Rupturing Capacity (HRC) fuses and the high voltage windings of the distribution transformer.

In this case, the protective relay of the main circuit breaker of the feeder operates at a time faster than the HRC fuses of the faulty transformer.

The distribution network considered in this work is an underground 11kV distribution network at Al-Rusafa General Directorate geographical region in Baghdad city.

The problem was studied using mathematical analysis and software analysis.

The mathematical results and the analysis of the simulated network using CYME 7.1 program show that the relay will operate before the HRC fuses as a response to an earth fault occurrence on that part of the network.

To solve this problem several solutions are proposed and discussed in this research.