Exploring the Fallacies in the Overcurrent Relay Coordination Optimization Problem with Simple Cases

Overcurrent relays are used in distribution systems for providing primary and back up overcurrent protection. They have two adjustments: the Plug setting (PS) and the Time multiplier Setting (TMS). Their optimal coordination is necessary to safeguard the system and hence it is stated as an optimization problem. The sum of the operating time of all the relays in the system has been chosen as the index of optimization by researchers all over the world. This paper through simple elementary cases analyzes the overcurrent relay coordination problem, and demonstrates that the PS is more efficient than the TMS, for minimizing the index of optimization The paper then argues that: as it is the PS element responds to the fault current and the TMS was and is merely used to extend the range of the PS, hence it is no wonder that all the optimization algorithms report better and better results by using more of the plug setting than the TMS. It tries to modestly point that researchers have overlooked this reality and drifted away from basic fundamentals.