Eaton EMR-3MP0 - Page 156

Current Threshold Multiple of FLA
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0 50 100 150 200 250
Stator Temperature [°C]
ThermalModel_F01
Fig. 36: E󰅠ective Current Threshold vs. Maximum Stator Temperature.
The diagram shows the following relationship: The lower the stator temperature, the
higher the e󰊍ective current threshold. Without stator temperature, given the current
threshold of 1.0 FLA and 2.0 FLA of the stator phase current, the thermal model will use
the full thermal capacity in 139.54 seconds. However, if the stator temperature is known
as 100°C (212°F), the e󰊍ective ultimate trip current threshold is raised to 2.55 FLA and
the thermal capacity used will reach a steady state of 77.5%. As a result, the thermal
model will never trip under this condition. From this example, it can be seen that the
stator RTD could keep the motor running under overload condition. In this case, the
appropriate direct stator temperature trip function must be enabled.
Thermal Replica Model Trip Curves
Multiple of Full Load Ampere
Time in seconds
1000
100
10
1
0.1 1 10 100
SF = 1, TC = 100%
Ith = 120%, Tth = 80%⋅TC
ThermalModel_F02
Fig. 37: Thermal Replica Model Limit and Trip Curves without RTD.
156 www.eaton.com EMR-3MP0
4 Protective Elements
4.3 49 – Thermal Model