5–88
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
where: RTD_Bias_TC
used
= TC used due to hottest stator RTD
Temp
actual
= current temperature of the hottest stator RTD
Temp
min
= RTD Bias minimum setpoint
Temp
center
= RTD Bias center setpoint
Temp
max
= RTD Bias maximum setpoint
TC
used at RBC
= TC used defined by the
HOT/COLD SAFE STALL RATIO
setpoint
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 generator heating.
The rest of the thermal model is required during high phase current conditions when
machine 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 machine current must be above the
over-load pickup before an overload trip occurs. Presumably, the machine would trip on
stator RTD temperature at that time.
Note
No biasing occurs if the hottest stator RTD is open or short.
FIGURE 5–24: RTD Bias Curve
808721A1.CDR
Ma
x
imum Stator RTD Temperature
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 = 0.8
5
Rated Temperature=130°C
Insulation Rating=1
55
°C
RTD
Thermal
Capacity
Used
