and current, dependent on the function(s) implemented. For a non-export system, the relay would be set to trip the circuit breaker if reverse power is sensed for longer than a short delay time or, alter
According to the IEEE Buff Book, static relays should have a minimum 0.2 s coordination time. Different protection devices, such as a fuse, a low voltage circuit breaker, have other minimum coordination times, as shown in Table 2 [ 35 ]. Table 2. IEEE Buff Book minimum clearing time [ 35 ].
In [ 25 ], the time delay for an overcurrent relay was re-evaluated after several trippings due to variations in wind turbine output power. The new settings were implemented using electrical transient analyzer program (ETAP) software.
The relay operating time was calculated based only on the standard IEC curve. Time delay setting limitation is considered a constraint and affects the minimum allowable time coordination between relays.
Different vendors have different designs and parameters. For instance, manufacturer 1 relay has three decimal time delay settings, manufacturer 2 has two decimal time delay settings, and manufacturer 3 has only one-time delay setting. This change affected the selected curve type and time delay.
The overcurrent relay curve can vary depending on the selection by the protection engineer. The standard curves include IEC standard inverse time (SI), IEC very inverse time (VI), IEC extremely inverse time (EI), IEEE moderately inverse time (MI), IEEE very inverse time (VI), and IEEE extremely inverse time (EI).