Analisis Sistem Proteksi Relai Diferensial pada Transformator Daya 60 Mva di Gardu Induk Jajar Menggunakan Software ETAP

A power transformer is an electric power equipment that has the function of increasing and decreasing the electric voltage. The power transformer is a very important main component in the transmission system so it must have protection from disturbances that can reduce the performance of the transformer. The differential relay is the main protection in power transformers. Differential relays work by comparing the current entering the relay with the current leaving the relay. The relay will detect a fault and instruct the circuit breaker (CB) to trip. The correct and correct setting value will make the differential relay work properly and optimally. The method used is to collect the necessary data at the 150 kV Jajar substation which is then processed by mathematical calculations or manually and by simulating the work of the differential relay using ETAP software. In mathematical calculations there are several calculations, namely: calculation of the CT ratio value, mismatch error, secondary current on CT, differential current, restraint current, percent slope and calculation of setting current value. The results of the mathematical calculations are: the CT ratio value on the primary side is 300:1 A and on the secondary side is 2000:1 A, the mismatch error value on the primary side is 0.89% and on the secondary side 1.125%, the secondary current value on the CT side on the primary side is 0.77 A and on the secondary side is 0.87 A, the value of the differential current is 0.1 A, the value of the retention current is 0.82 A, the value of pecent slope1 is 12.19% and the value of percent slope2 is 24.39%, the setting current value is 0.1 A. The results of the simulation of the differential relay working system using ETAP software, the internal fault shows the differential relay works at 0 ms and CB1 and CB2 work at 10 ms and 52 ms, while when there is an external fault the relay the differential doesn't work, but two OCR relays, namely relay1 and relay2. Relay1 works at a time of 1,138 ms and commands CB1 to work at a time of 10 ms, while relay2 works at a time of 1,608 ms and commands CB2 to work at a time of 52 ms