BENSHAW RediStart EXEXMVRMX3 Series, User Manual

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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)
BiasOL %
=
0
RTD Bias Min Level (RTD27) < Max measured stator RTD temp < RTD Bias Mid Point Level (RTD28)
BiasOL
RTD MinBiasTemp
MidBiasTemp MinBiasTemp
%
max
=
-
-
´
Hot Cold Ratio _ _
RTD Bias Mid Point Level (RTD28) < Max measured stator RTD temp < RTD Bias Max Level (RTD29)
BiasOL
RTD MidBiasTemp
MaxBiasTemp MidBiasTemp
%
max
=
-
-
´
( . % _ _ ) _ _ 99 9
-
é
ë
ê
ù
û
ú +
hot cold ratio hot cold ratio
RTD Bias Max Level (RTD29) < Max measured stator RTD temp
BiasOL % . %
=
99 9
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.
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7 - THEORY OF OPERATION
10
0
20
30
40
50
60
70
80
90
100
0 50 50 100 150 200 250
Maximum RTD Temperature (C)
RTD
B
ias
V
alue
(%)
Hot/Cold Ratio
RTD BiasMin
RTD BiasMid
RTD BiasMax
RTD Bias Curve
Figure 30: RTD Bias Curve