Transformers in power systems require different types of protection.This protection is provided by various types of relays, bothelectromagnetic and static. In general, transformer protection servesto protect the transformer in the event of a disturbance, so that thetransformer can be avoided from damage. The relay that will be usedto protect the transformer is a differential relay. This relay workswhen there is a difference in the current of the Current Transformer[CT] on the primary and secondary sides. If the fault occurs outsidethe protection zone, the relay will not work. The method used in thisresearch is R&D (Research and Development), namely research anddevelopment methods, research and development methods areresearch methods used to produce certain products, and test theeffectiveness of these products. An evaluation of the differentialrelay setting on a 150kV power transformer has been carried out atthe Pondok Indah Substation using the Modbus CommunicationsProtocol, where the settings in the field and from the results ofcalculations using the Micom 632 differential relay are obtained: forthe calculation results of Idiff = 0.39 and Idiff max = 8.07 while theactual setting in the field is Idiff = 0.3 and Idiff max = 8. Thedifference in value between the actual setting and the calculationresults is Idiff by 30%, and Idiff max 0.87% is still within theallowed interval . Setting using the modbus communicationsprotocol has advantages, including reducing wiring, makingtroubleshooting or interference easier, reducing the possibility ofhuman-error errors in the configuration process, and making it easyto make changes.