4. SETPOINT PROGRAMMING S5 THERMAL MODEL
4-39
In simple terms, the RTD bias feature is real feedback of 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 thermal 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.
Maximum Stator RTD Temperature
Thermal Capacity Used
0
20
40
60
80
100
-50 0 50 100 150 200 250
RTD Bias Maximum
RTD Bias Center Point
RTD Bias Minimum
Hot/Cold = 0.85
Rated Temperature=130 C
Insulation Rating=155 C
Figure 4-22 RTD BIAS CURVE
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