5–58 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUALCHAPTER 5: SETTINGSIn 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. SinceRTDs are relatively slow to respond, RTD biasing is good for correction and slow motorheating. The rest of the thermal model is required during starting and heavy overloadconditions when motor heating is relatively fast.Note that the RTD bias feature alone cannot create a trip. If the RTD bias forces thermalcapacity used to 100%, the motor current must be above the overload pickup before anoverload trip occurs. Presumably, the motor would trip on stator RTD temperature at thattime.FIGURE 5–16: RTD Bias CurveMaximum Stator RTD Temperature020406080100–50 0 50 100 150 200 250RTD Bias MaximumRTD Bias Center PointRTD Bias MinimumHot/Cold = 0.85Rated Temperature=130°CInsulation Rating=155°CRTD Thermal Capacity Used
