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Hi, I am running a fairly large system and observing that during 3 phase fault, a few synchronous machines trip due to underspeed and overspeed. Even though, 1. The tripped generators do not have relays. 2. DYR-file has no call of 'NRCGP3U'. [Checked also spreadsheet Dynamics Data - Protection Models - Machine for any tripping models.] 3. Dynamic Simulation Option of 'Scan generators exceeding speed deviation threshold is disabled. [ierr = psspy.set_genspdev(0, 10, 0, 0) #status, speed, trip, icode]

Can you please help me understand the reason of the trip?

The simulation progress files show messages like below. * MACHINE 1 AT BUS 400 TRIPPED BY UNDERSPEED RELAY AT TIME = 5.2125 SECS. * MACHINE 1 AT BUS 300 TRIPPED BY OVERSPEED RELAY AT TIME = 5.0750 SECS.

Best Regards,