The paper describes the first step of development of a hybrid twin of a protection device as a tool for validating protection function parameterization and training engineers. The tool uses a closed-loop system and a real-time simulation platform. The process involved studying protection validation techniques, defining the conceptual design of the stages, and validating the results of each stage. A transmission line relay with a differential overcurrent function was developed using a Raspberry Pi 4 as the platform and the Typhoon HIL 402 platform as a real-time simulator. Two types of faults were simulated, and the results were validated.