A. During normal conditions, both the feeder Circuit Breaker 1 and the DER Circuit Breaker at the
Point of common coupling (PCC) are closed. The Distributed energy resource (DER, e.g.,
photovoltaics, wind etc.) are synchronized with the source.
B. When a transient fault occurs on the overhead line, the SEL Relay sees the fault and sends signal
to open Circuit Breaker 1.
C. Circuit Breaker 1 opens, however the DER Circuit Breaker remains closed. The SEL-3780 signals
the SEL Relay that DER is still energized. The SEL Relay doesn’t reclose the Circuit Breaker 1
immediately even after the transient fault is cleared.
D. If the following conditions are fulfilled, the SER relay sends “Trip” command to the DER Circuit
Breaker.
1. Breaker 1 Open
2. Line hot (DER Online)
3. SEL Relay in Reclose cycle state (Wants to Autoreclose)
DER Circuit Breaker “Trips” because of SEL Relay communication through the network.
E. The SEL-3780 output contact signals the SEL relay that DER is deenergized. The SEL Relay closes
the Circuit Breaker 1 while in it’s reclose cycle state.
F. The DER inverter autosynchronizes the DER with the source and the normal condition is
restored.