Transient overvoltage and overcurrent in extra-high-voltage networks can have a significant impact on system design and operation. This work investigates various types of faults in the high-voltage transmission network of practical power system, 400 kV in Oman’s electrical network. Power Systems Computer Aided Design (PSCAD/EMTP) software is used to model and simulate the high-voltage grid and the fault models. The research focuses on various abnormal scenarios, including short-circuit faults, supply disconnections, line energizations, and lightning strikes, to analyze their impact on system performance and fault currents. Different types of short-circuit faults, such as single line-to-ground, double line-to-ground, and three-phase faults, are applied to the power system network at different locations to monitor the maximum transient current. The current response is detected when a three-phase fault is applied at different buses of the system and also when disconnecting the supply. The study focuses on studying the faults along the transmission line. The study also examines the influence of parameters such as fault duration, fault resistance, and fault location on short-circuit current magnitudes. The transient overvoltage and overcurrent are calculated due to line energization, and it is detected at the sending and receiving ends of the transmission line. The highest current magnitude during short-circuit faults occurs with a three-phase fault, where the current reaches 6.34 p.u. at the midpoint of Line 7 for a fault duration of 0.05 s. The other objective of this study was to compute the highest current magnitude along the transmission line due to the standard lightning surge injected in different locations (at the middle of the line and at each end). The highest current magnitude reaches 15.9 p.u. on Bus 7 in the middle of the line, and the transient time from the lightning surge injection to return the waveform at power frequency oscillations is approximately 0.065 s. The traveling wave time is calculated when injecting the surge at one end of the transmission line and measuring the current at the other end.