Over-Current Protection in Transmission Systems Using Analog and Digital Relays - Case Study and Comparison

This paper focuses on studying a complete comparison between analog and digital overcurrent relays. Analog term is given to the first generation of the electromechanical relays whereas digital term is associated with the up-to-dated relays. Digital relays are presently used for secured, dependable and efficient operation of power systems. In power systems, overcurrent protection is essentially required against short circuit faults. The parameters of overcurrent relays are critical and sensitive as incorrect settings of them can cause improper tripping leading to a big problem. Accordingly, these parameters must be tested in order to validate the relay performance subjected to different fault cases. Thus, a radial power system with different fault conditions is taken as a case study using both analog and digital relays individually. The whole proposed system is designed, implemented and simulated using MATLAB program software. The most suitable overcurrent relay adequate with radial power systems is based on time definite characteristics. The overall model is then simulated twice to analyze, study and differentiate the performance of both digital and analog relays when subjected to short circuit faults. Finally, A brief comparison is presented between the analog and digital overcurrent relays showing the features and benefits of digital overcurrent relays over the analog relays.