ABSTRACT
The project was aimed at the modeling and simulation of a definite time overcurrent relay for power system protection. Different types of faults that occur in power systems and various types of protective relays were explained.
The project was simulated using Matlab/Simulink. A typical power system with a Generator (40MVA, 11KV, 20% reactance), Bus-bars, Step-up transformer (40MVA, 11/220KV, 15% reactance), Transmission line (100KM length, ⅉ60Ω impedance), Step-down transformer (40MVA, 220/11kv, 15% reactance) and a Motor (30MVA, 11KV, 30% reactance) was incorporated into the project. Design of the system parameters was also carried out in order to determine the equivalent per unit reactance, short circuit MVA and fault current.
The power system was modeled on three working conditions: when operating without a fault, when operating with fault applied and when operating with a definite time over-current relay introduced.
The definite time over-current relay was also modeled in Matlab/Simulink with Simulink blocks such as the relational operator, logic gates, data conversion block and the transport delay. The relay operating time was designed for 0.1s
Finally, the over-current protection scheme was tested on three fault conditions: three phase (line-line-line) fault, two phase (line-line) fault, and three phase-to-ground (line-line-line-ground) fault conditions.
