Reliability Evaluation of Differential Relay as Primary Safeguard of Transformer against Short Circuit

A transformer is an electrical device that converts high voltage into low voltage or vice versa. The dry-type transformer used at the CHARUSAT Healthcare campus is a stepdown transformer. Transformers, which are devices connected between one voltage level and another voltage level, frequently experience external interference or internal fault. Internal faults have the potential to inflict damage, as was the case in the CHARUSAT Healthcare campus System. The damage is a result of external interferences involving highly high currents. The interference resulted in internal damage, triggering the activation of all protection devices in the transformer, including the differential relay. The characteristics of a differential relay indicate that it must operate in the event of any disturbance occurring within its protected zone, which is situated between a set of Current Transformers in both the primary and secondary circuits. The operation is carried out by comparing the current between the primary and secondary. The reason for the differential relay's functionality can be determined by analyzing the setting and short circuit calculation and examining the internal relay record of the Digital Fault Recorder (DFR). Based on the calculations, it was determined that the differential relay functioned correctly with a value of 0.3 Ampere and an instant time setting. To enhance the dependability of the differential relay, which serves as the primary protection for the transformer, it is possible to activate a high set setting (12 times the rated current). This setting allows the relay to operate in the presence of high-magnitude interference.