9424200996 84-11
BE1-11m Settings Calculation Examples
Figure 84-12. Protection, Thermal, RTD Bias Curve Screen
Set the Center RTD Bias Temperature (point 2) to the motor hot running temperature. Recall from the
motor manufacturer data that the insulation is class F and the manufacturer allows an 80°C stator
temperature rise. Allow for a 10 percent overage for hot spots. Refer to the Center RTD Bias Temperature
Equation 84-4.
=
10% +
=
(
80°1.10
)
+ 40°
= 88°+ 40°= 128°
Equation 84-4. 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 84-5.
%= 100% 1
= 100% 1
9
10
= 10 %
Equation 84-5. 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 84-4 and Equation 84-5.
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.
Resistance Temperature Detector (49RTD)
The RTDs can be used as a direct source for protection as well. The maximum stator winding insulation
temperature is 155°C per the motor manufacturer data.
Set the 49RTD-1 protection element as shown in Figure 84-13 to protect the stator winding insulation.
Voting is set to 2, meaning at least 2 RTDs must be at 155°C or higher to result in a trip. A delay is not
required for the reason that temperatures change slowly because of the large motor thermal mass.
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