Transformator adalah komponen utama pada Gardu Induk yang harus dijaga kinerjanya melalui sistem proteksi, salah satunya relay differensial. Cara kerja relay differensial adalah dengan membandingkan arus yang masuk dan keluar dari transformator, dan merespons gangguan secepat mungkin. Dilakukan setting ulang relay differensial akibat terjadinya hubung singkat pada transformator 2. Untuk dapat mengetahui kinerja dari relay differensial dalam melakukan proteksi dapat menggunakan metode kuantitatif dan melakukan simulasi menggunakan perangkat lunak 87T By Sumandari. Hasil menunjukkan kegagalan relay disebabkan oleh kesalahan identifikasi arus gangguan. Setting ulang relay dilakukan dengan rasio CT 300:5A dan 2000:5A, error mismatch 0,88% dan 1,125%, arus differensial 0,481 A, arus restraint 4,089 A, slope1 11,76%, slope2 23,52%, dan arus setting 0,48 A. Setting baru berhasil melakukan trip saat disimulasikan dengan arus gangguan 10 kA pada sisi 20 kV dan 600 A pada sisi 150 kV. Perbandingan sebelum dan setelah pemeliharaan menunjukkan relay differensial berfungsi lebih baik setelah pemeliharaan, dengan lima pengujian relay berhasil trip dalam area kerja slope1 tanpa melebihi slope2, dibandingkan tiga pengujian yang berhasil sebelum pemeliharaan. Dengan penelitian ini, dapat mengetahui kinerja relay differensial untuk melakukan proteksi dan pentingnya setting relay differensial untuk memproteksi secara optimal.

Transformers are the main components in substations that must be maintained through protection systems, one of which is a differential relay. The way differential relays work is by comparing the currents entering and leaving the transformer, and responding to interference as quickly as possible. A differential relay reset was carried out due to a short circuit in transformer 2. To be able to determine the performance of differential relays in carrying out protection can use quantitative methods and simulate using 87T software. The results show that relay failure is caused by fault current misidentification. Resetting the relay is done with a CT ratio of 300:5A and 2000:5A, error mismatch 0.88% and 1.125%, differential current 0.481 A, restraint current 4.089 A, slope1 11.76%, slope2 23.52%, and setting current 0.48 A. The new setting successfully trips when simulated with a fault current of 10 kA on the 20 kV side and 600 A on the 150 kV side. Comparison before and after maintenance showed the differential relay functioned better after maintenance, with five relay tests successfully tripping within the slope1 working area without exceeding slope2, compared to three successful tests before maintenance. With this research, it can determine the performance of differential relays to protect and the importance of setting differential relays to protect optimally.