GE Multilin 489

5–82 489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
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% voltage level, the trip time of 110% will be used (see the figure below).
FIGURE 5–20: Voltage Dependent Overload Protection Curves
Note
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.
489
VOLTAGE DEPENDENT
OVERLOAD PROTECTION CURVES
808831A3.CDR
1
12
3
4
56
7
8
2
3
4
5
6
7
8
9
10
20
30
40
50
60
70
80
90
100
TIME TO TRIP (SECONDS)
MULTIPLES OF FULL LOAD AMPS
200
300
400
500
600
700
800
900
1000
Acceleration Intersect at 80%V
Custom Curve
Acceleration Intersect at 100%V
Safe Stall Time at 80%V,
80%V Stall Current
Safe Stall Time at 100%V,
100%V Stall Current
Safe Stall Points
Extrapolated to 110%V
GE Multilin
Courtesy of NationalSwitchgear.com