9424200996 84-35
BE1-11m Settings Calculation Examples
=
10% +
=
(
80°1.10
)
+ 40°
= 88°+ 40°= 128°
Equation 84-24. Center RTD Bias Temperature
A good starting point for the center point Thermal Capacity (%TC) is the percentage difference between
the Hot Safe Stall Time and the Cold Safe Stall Time. This point can be modified later after observation
and motor monitoring. The initial calculation for %TC is given in Equation 84-25.
%= 100% 1
= 100% 1
9
10
= 10 %
Equation 84-25. Center Point Thermal Capacity
Set the Center RTD Bias Temperature (point 2) to 128°C and 10 percent thermal capacity per the results
from Equation 84-24 and Equation 84-25.
The Maximum RTD Bias Temperature (point 3) is set to 155°C and 100 percent thermal capacity. These
values are determined by the maximum insulation factor of F according to the motor manufacturer data.
Adding More Points
Once the basic curve is set, more points can be added to the curve to make it correspond to an actual
thermodynamic curve found in a thermodynamic black box. Figure 84-43 shows this capability, yielding
better motor protection at high operating temperatures.
Figure 84-43. Adding More Points Increases Motor Life
Resistance Temperature Detector (49RTD)
The RTDs can be used as a direct source for protection as well. RTDs serve as backup protection to the
49TC thermal model because of the inherent slow reaction time of these devices. The maximum stator
winding insulation temperature is 155°C per the motor manufacturer data.
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