This study provides an in-depth analysis of short-circuit faults and overcurrent phenomena in electrical power systems. A short circuit is one of the most critical disturbances, as it can cause a sudden surge of current that may damage electrical equipment and disrupt the continuity of power supply. Therefore, it is essential to calculate the short-circuit current values for each feeder connected to the substation to determine whether the equipment can continue to operate reliably during fault conditions.
In a three-phase short circuit disturbance on the Porsea feeder, the current at 10% is 2,515.68 and at 100% is 1,482.26. For two phases, the current value at 10% is 2,178.41 and at 100% is 1,334.40, and for one phase, it is 267.15 and at 100% is 253.785. In a three-phase short circuit disturbance on the Siantar feeder, the current at 10% is 2,314.02 and at 100% is 977.73. For two phases, the current value at 10% is 2,004.008 and at 100% is 846.74, and for one phase, it is 264.092 and at 100% is 250.18. In a three-phase short circuit disturbance on the Tebing 1 feeder, the current at 10% is 1,708.136 and at 100% is 378.09. For two phases, the current value at 10% is 1,479.28 and at 100% is 327.34, and for one phase, it is 215.63 and at 100% is 148.37. In a three-phase short circuit disturbance on the Tebing 2 feeder at 10%, the current is 2,050.97 and at 100% is and at 100% the current is 617.057, at 2 phases the current value at 10% length is 1.774.622 and at 100% length is 534.373 and at 1 phase it is 261.29 and at 100% length it is 235.415. This pattern is also found in other feeders, indicating a correlation between the location of the disturbance and the disturbance current values. Then, in the calculation of the relay settings for overcurrent short circuit disturbances for each feeder, where the previous setting at the Siantar substation was 0.15, it must be changed to a setting value that provides a more selective relay operation where the Tms values are: for Porsea Feeder Tms is 0.134 seconds, for Siantar Feeder Tms is 0.137 seconds, for Tebing 1 Feeder Tms is 0.108 seconds, for Tebing 2 Feeder Tms is 0.15 seconds, and for the 20 kV Side Tms is 0.16 seconds. Therefore, the time coordination of the overcurrent relay tripping on the 20 kV must provide a relay opportunity for each feeder to operate first so that if a short circuit occurs in that feeder, only that feeder will trip.