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CHAPTER 6: SETPOINTS
NOTE:
NOTE
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 16: RTD bias curve
80%
60%
40%
20%
TCU
Center
0
0
RDT Bias Minimum, RTD Bias Center, RTD Bias Maximum and HCR are setpoints.
If the maximum stator RTD temperature is below the RTD BIAS MINIMUM setting, no
biasing occurs. If the maximum stator RTD temperature is above the RTD BIAS MAXIMUM,
then the thermal memory is fully biased and THERMAL CAPACITY USED is forced to 100%.
At values between the maximum and minimum, the THERMAL CAPACITY USED created by
the overload curve is compared to the RTD Bias Thermal Capacity Used determined by the
hottest stator RTD temperature.
If the RTD Biased Thermal Capacity Used value is higher than the Thermal Overload
Thermal Capacity Used, then that value is used to replace the Thermal Overload Thermal
Capacity Used. If the RTD Biased Thermal Capacity is lower than the Thermal Overload
Thermal Capacity Used, the Thermal Overload curve does not need to be biased by stator
RTD temperature.
Typically, the RTD BIAS MINIMUM is set as 40
rated motor running temperature, and the RTD BIAS MAXIMUM is set at the stator
insulation rating or slightly higher.
where:
TCU
– the value of the Thermal Capacity Used register when the hottest stator
Center
RTD temperature is equal to the setpoint, RTD Bias – Center T.
(1-HCR)x100%
50
100
o
C, the RTD BIAS CENTER POINT is set at the
S3 PROTECTION
150
896816.cdr
Eq. 12
6–65
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