Frequency stability and digital protection coordination of multi-source power system

Nowadays, the interconnection issues of different power plants are interested and must be highlighted, such as the frequency stability and voltage stability, which are a basic principle in the power system operation. Many reasons such as, load shedding, load restoring, and short circuits cause large frequency fluctuations, which threaten the system security and could lead to complete blackouts as well as damages to the system equipment. Hence, this paper proposes a coordination of Load Frequency Control (LFC), which uses an optimized PID controller-based new Moth Swarm algorithm (MSA) and digital under/over frequency relay for a realistic multi-source power system considering different cases study of load shedding and restoring. The digital relay will be energized by the data conversion system under normal and fault conditions. The presented digital frequency relay will cover both over and under frequency conditions. To validate the effect of the proposed coordination, the Egyptian Power System (EPS), which contains three dynamics subsystems, hydro, reheat, and non-reheat power plants, was investigated for the MATLAB/SIMULINK considering the effect of system nonlinearity. The obtained results stated the effectiveness of the proposed coordination to maintain the power system frequency stability and security. Furthermore, the superiority of the under/over digital frequency relay has been approved.