84-12 9424200996
Settings Calculation Examples BE1-11m
Figure 84-13. Protection, Thermal, Resistance Temperature Detector (49RTD-1) Screen
Set the 49RTD-2 protection element as shown in Figure 84-14 to protect the motor bearings. The
maximum bearing temperature of 95°C is supplied in the motor manufacturer data. Voting is set to 1,
which provides a sensitive bearing overtemperature trip. Only one RTD must be 95°C or higher to result
in a trip.
Figure 84-14. Protection, Thermal, Resistance Temperature Detector (49RTD-2) Screen
Protection - Current
Five instantaneous overcurrent elements, one current differential element, and one instantaneous
undercurrent element are used in this settings example.
Instantaneous Overcurrent (50-1) - Short-Circuit Protection
The 50-1 protection element is used to protect the motor stator windings for a short circuit. The pickup is
set as low as possible without causing a trip to occur during motor starting. The pickup setting is derived
using a dc offset of 1.7, 125 percent of LRA, and a BE1-11m pickup tolerance of 2 percent. Reference the
secondary FLA (Equation 84-1) and LRA (Max Locked Rotor Current) of 600% per motor manufacturer
data. See Equation 84-6.
= 1.7
(
125% + 2%
)
(600%)
= 1.7
(
1.25 + 0.02
)
(
6 4.54
)
= 71.77
Equation 84-6. 50-1 Pickup
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