Eaton EMR-3MP0 - Page 157

ThermalModel_F03
Multiple of Full Load Ampere
Time in seconds
1000
100
10
1
0.1 1 10 100
SF = 1, TC = 100%
Ith = 150%, Tth = 80%⋅TC
Fig. 38: Thermal Replica Model Limit and Trip Curves with RTD = 100°C.
In the Thermal Replica Model Trip Curves with and without RTD, the unmarked lines are
the thermal limit curves and the marked lines are the trip curves. From the curve without
RTD, it can be seen that one can change the thermal current threshold to shift the upper
portion of the trip curve right to allow the motor to run at a higher overload condition
than is speci󰊎ed with the service factor. From the curve with RTD, it can be seen that the
stator RTD pushes the e󰊍ective thermal current threshold to 2.55 FLA on the thermal limit
curve (unmarked line). The marked line is the trip curve with 80% thermal capacity trip
threshold, so actual e󰊍ective thermal current threshold for the trip curve is about
2.05 FLA. Although in this case, the thermal current threshold is set to 1.50 FLA, it is
e󰊍ectively raised to a higher level with the stator RTD. Keep in mind that thermal limit
and trip curves shown are based on the example above. They will vary with other sets of
the settings.
NOTICE!
When
»WD Trip Function« = “Active”, the thermal model of the motor protection devices
uses the hottest winding “WD” RTD value.
157www.eaton.comEMR-3MP0
4 Protective Elements
4.3 49 – Thermal Model