The primary objective of power system protection is to prevent equipment damage and ensure the safety of individuals working on or near the power system. Without proper protection, electrical equipment such as transformers, generators, and transmission lines are vulnerable to damage from overloading, short-circuits, and other faults. Power system protection is essential for ensuring the safe and reliable operation of electrical power systems and is a key component of modern energy infrastructure. This paper, therefore, presents the design of a protective system for a three machine nine bus system. A non-directional differential relay is designed and located in input side and output side transformer of the test system. The performance of system is analyzed for various fault condition and the simulation results are presented.