GE 489 - Page 97

GE Power Management
489 Generator Management Relay 4-59
4 SETPOINT PROGRAMMING 4.10 S9 THERMAL MODEL
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The 489 takes the information provided and create protection curves for any voltage between the minimum and 100%. For
values above the voltage in question, the 489 extrapolates the safe stall protection curve to 110% voltage. This current
level is calculated by taking the locked rotor current at 100% voltage and multiplying by 1.10. For trip times above the 110%
current level, the trip time of 110% will be used (see the figure below).
Figure 4–15: VOLTAGE DEPENDENT OVERLOAD PROTECTION CURVES
The safe stall curve is in reality a series of safe stall points for different voltages. For a given voltage, there can be
only one value of stall current, and therefore only one safe stall time.
808831A2.CDR
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TIMET OTRIP (SECONDS)
MULTIPLES OF FULL LOAD AMPS
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Acceleration Intersect @ 80%V
Custom Curve
Acceleration Intersect @ 100%V
Safe Stall Time @ 80%V,
80%V Stall Current
Safe Stall Time @ 100%V,
100%V Stall Current
Safe Stall Points
Extrapolated to 110%V
489
VOLTAGE DEPENDENT OVERLOAD
PROTECTION CURVES
GE Power Management
NOTE