Nontraditional Relay Curves for the Coordination of the Ground Overcurrent Function With Downstream Fuses

This paper describes the details for the application of some nontraditional relay curves for the coordination of the ground overcurrent function with downstream fuses. These curves have a segmented shape in order to achieve the best combination of sensitivity, speed, and selectivity. For this segmented shape, greater current does not necessarily imply a shorter time. These curves can be programmed in different ways, according to the available features in the commercial relays, and the expected behavior of two options is analyzed. Both options would have satisfactory behavior although they would have different dynamic behavior.