Comparative analysis of differential relay settings in Langsa substation transformer to avoid protection failure

This paper discusses the arrangement of differential relays at the Langsa substation. The ratio of CT mounted on the transformer to the primary side is 150/1 A and on the secondary side is 1000/1 A. This result is taken with consideration of the current value calculated from 127.02 A on the primary and 952.62 A on the secondary side. For the sensitivity of the mismatch error is still good because it is still under 5% on the primary side which is 0.89% and the secondary side is 1.13%. The differential current also shows the normal condition of 0.1 A and the restraint current 1.205 A. Using the ETAP 12.6.0 simulation, relay can work well when interference occurs at the current setting indication 1.29 A is greater than the operating current 1.65 A and the relay does not work during an external fault with a setting current of 1.29 A equals to an operating current of 1.29 A.