GE MOTOR MANAGEMENT RELAY 469 Instruction Manual page 95

4 SETPOINT PROGRAMMING
In simple terms, the RTD bias feature is real feedback of the measured stator temperature. This feedback acts
as correction of the thermal model for unforeseen situations. Since RTDs are relatively slow to respond, RTD
biasing is good for correction and slow motor heating. The rest of the thermal model is required during starting
and heavy overload conditions when motor heating is relatively fast.
It should be noted that the RTD bias feature alone cannot create a trip. If the RTD bias feature forces the ther-
mal capacity used to 100%, the motor current must be above the overload pickup before an overload trip
occurs. Presumably, the motor would trip on stator RTD temperature at that time.
GE Power Management
100
Hot/Cold = 0.85
80
Rated Temperature=130 C
Insulation Rating=155 C
60
40
20
RTD Bias Minimum
0
-50 0 50
Maximum Stator RTD Temperature
Figure 4–18: RTD BIAS CURVE
469 Motor Management Relay
4.6 S5 THERMAL MODEL
RTD Bias Maximum
RTD Bias Center Point
100 150 200 250
4
4-45