Short Circuit Trip This function is intended to protect the stator windings of the motors against phase-to-phase faults. Equipped with an overreach filter, the RTD Thermal Capacity Used (%) RTD Bias Maximum RTD Bias Minimum RTD Bias Center Point 100 90 80 70 60 50 40 30 20 10 0 -50 0 50 100 150 200 250 Maximum Stator RTD Temperature (C) 806809A4.cdr RTD Bias curve. Thermal Capacity Used Time in Minutes 100 75 50 25 0 0 50 100 150 200 250 806810A3.cdr Iavg @ 100% FLA Iavg @ 50% FLA Exponential cooldown (hot/cold curve ratio 60% 1.00 0.95 0.90 0.85 0.80 0.75 0.70 0 1 2 3 4 5 k=2 k=4 k=6 k=8 k= 10 Derating Factor Percent Voltage Unbalance Motor derating factor due to unbalanced voltage 400 469 Motor Protection System Motor Protection www.GEDigitalEnergy.com 469 removes the DC component from the asymmetrical current present at the moment a fault occurs or motor starts. A trip backup feature is also available as part of this function, used to issue a second trip if the fault is not cleared within a given time delay. The backup feature can also be assigned to an auxiliary contact for annunciation or remote tripping of upstream protection devices
Ground Fault This function is designed to protect motors against phase to ground faults. There are two dedicated ground current inputs in the relay, which support the following types of ground current detection. • Core balance (Zero sequence) current transformer. • Core balance (Zero sequence) 50:0.025 A (sensitive) current transformer. • Residual connection of phase current transformers. The function is equipped with an overreach filter, which removes the DC component from the asymmetrical current present at the moment a fault occurs, or a motor starts. Two pickup levels ( trip and alarm) with individual time delays are available for ground fault detection. A trip Backup feature is also available as part of this function. The operational principal of Ground Fault Trip Backup is the same as of Short Circuit Trip Backup