Rtd Overload Biasing - BENSHAW RediStart EXEXMVRMX3 Series User Manual

7 - THEORY OF OPERATION
7.1.7

RTD Overload Biasing

The RTD biasing calculates a motor thermal value based on the highest stator RTD measurement. The motor thermal overload content is
set to this calculated value, if this calculated value is higher than the motor thermal overload content. The RTD biasing is calculated as
follows:
Max measured stator RTD temp < RTD Bias Min Level (RTD27)
RTD Bias Min Level (RTD27) < Max measured stator RTD temp < RTD Bias Mid Point Level (RTD28)
RTD Bias Mid Point Level (RTD28) < Max measured stator RTD temp < RTD Bias Max Level (RTD29)
RTD Bias Max Level (RTD29) < Max measured stator RTD temp
The RTD Biasing levels are generally set by using the motor data as follows:
RTD Bias Min Level (RTD27): This parameter is typically programmed to the ambient temperature rating of the motor.
RTD Bias Mid Level (RTD28): This parameter is typically programmed to the temperature rise rating of the motor.
RTD Bias Max Level (RTD29): This parameter is typically programmed to insulation rating of the motor.
100
90
80
70
60
50
40
30
20
10
0
50
118
BiasOL% = 0
-
RTD max MinBiasTemp
=
BiasOL %
-
MidBiasTemp MinBiasTemp
é -
RTD max MidBiasTemp
=
BiasOL % ê
-
ë
MaxBiasTemp MidBiasTemp
= 99 9
BiasOL% . %
Figure 30: RTD Bias Curve
RTD Bias Curve
RTD BiasMax
RTD BiasMid
RTD BiasMin
0 50 100
Maximum RTD Temperature (C)
´ Hot Cold Ratio
_ _
ù
´ ( . % - ú +
99 9 hot cold ratio _ _ )
û
150 200 250
hot cold ratio _ _
Hot/Cold Ratio