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Abstract
When designing an industrial MV network, a suitable neutral earth arrangement must be selected. The neutral point can either be isolated or it can be connected to earth. The use of isolated neutral in MV network has the advantage of ensuring operational continuity since it does not trip on the first fault. An earthed neutral generally implies mandatory tripping on
the first fault.This scientific report represents a case study for an already existing plant situated in one of fertilizers and chemical industrial companies.As it known about the electrical power systems in such industries, the main operating voltage is considered to be in kV due to the high power needed. And also the arrangement of the earthing system is being isolated in order to prevent sudden stopping of process due to one of the most commonly faults which is known as single phase-to-ground fault.
In this system, the star point of the main generator is earthed via a limiting resistance 1200 so that in case of a single phase-to-ground fault the fault current will be limited to lower values of ampers.The shortage in the protection system of that plant is that there is no earth fault protection found to indicate that a certain feeder (such like a M.T motor or distribution transformer) is subjected to single phase-to-ground fault. Only a flap indicator supplied from an open delta voltage transformer of the main 6.6 kV busbar - which is the main operating voltage of the.