Analysis of Differential Relay Performance in the Bakaru Hydroelectric Power Transformer Protection System

Abstract

A differential relay is a piece of equipment installed on both terminals of a power transformer coil to detect abnormal operating conditions in a power plant. Its function is to detect disproportionate differences in current flowing at both ends of the power transformer coil terminals as an indicator of a disturbance in the power transformer. Next, it sends a signal to the power breaker, thereby cutting off the power supply to the power transformer. This research aims to determine the correct way to set the differential relay, based on its characteristics so that it can work accurately according to its function. Determining the differential relay settings using the steep point slope. From the analysis, it was found that the slope 1 setting was 9.51% and slope 2 was 19.02%, while the installed data (existing) setting slope 1 was 8.87% and slope 2 was 17.74%. Based on determining the differential relay settings using steep point slopes through analysis and existing data on the power transformer, it was found that the differential relay settings from the analysis results were more sensitive with an angle of 5.43° than the installed settings with an angle of 5.02°. Then, when simulated in the ETAP 19.0.1 software, internal and external three-phase short circuit fault currents were obtained, where during an internal short circuit fault, the differential relay on the Bakaru PLTA power transformer immediately worked to detect abnormal conditions/faults in the transformer, whereas in external short circuit fault, the differential relay does not work detecting an abnormal condition/fault outside its working area