One of the most common and difficult problems to solve in distribution power systems is the location and elimination of the ground fault. For the study of an electrical distribution network in ungrounded system operating at 20 kV on the primary and 380 V on the secondary. The model uses smaller nominal voltages consisting of 380 V on the primary and the secondary. The Ground fault protection system scheme uses over voltage relays and open break delta transformers, whereas for fault location detection using voltage transformers in star star connections.The highest single line to ground fault value is used for consideration of ballast rating selection. The single line to lowest ground fault value is used for setting the threshold on the voltage relay (59N).  Referring to the result of the calculation of the highest single phase to ground voltage at point 1 is 144∠1800 volts, and the lowest point at 4 is 132∠1800 volts. A 200 ohm ballast impedance with 150 watts of power capacity, and an overvoltage threshold setting of 120 volts with TDS of 40. One phase fault protection mechanism works well at each point of interference, and voltage transformers are protected from overheating and damage.

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Various laboratory experiment platforms have been developed to provide students with theoretical knowledge and practical experience. Understanding concepts related to the process for determining the design of protection settings requires practical experience, which can be achieved by repeated trials. In this paper, the mechanism of a ground fault in a medium voltage feeder is done using a simulator substation as a case study. This process must be carried out twice, once for the ground-fault relays protection based on residual currents and then repeated based on residual voltage. For further understanding of the electrical distribution network, the system will be operated at 20 kV on the primary and 380 V on the secondary. The model uses smaller nominal voltages consisting of 380 V on the primary and the secondary. The result of one phase fault protection mechanism works well at each point of interference, and voltage transformers are protected from overheating and damage. The lowest value of the single-phase to ground short circuit that occurs at the fault location at the farthest point of interference from the protection relay location is used for the threshold setting on the voltage relay. The one phase fault protection mechanism works well at each point of interference, and the voltage transformer is protected from overheating and damage. For residual current ground fault protection effective, the threshold setting of phase fault inverse time delay with threshold setting I> is 1.5 ampere, and instantaneous I>> is 7.5 ampere. The effective threshold setting for residual ground fault protection wasUo> = 22% dan UO>> = 33,2%.

The integration of distributed generation in medium-voltage distribution systems requires rapid evaluation of the protection coordination, especially the integration of synchronous generator-based generators where the contribution effect of short-circuit currents is relatively high. This research makes evaluation software for protection coordination based on fuse saving operation. Short circuit calculations on buses using the Zbus matrix. The increase in short-circuits current due to the installation of distributed generations based on variations in the size and location in the medium-voltage network results in need for redesigning the protection system. After a brief literature review, the methods and simulation results are presented. The low penetration level of 20% (0.406 MVA) has only a minor impact on protection coordination. Fuse replacement at limited locations can restore coordination of protection. The high penetration level of 60% (1.075 MVA) indicates that the protection coordination mechanism is still maintained if the installation is near a substation.

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