Eaton EMR-3MP0 Installation, Operation And Maintenance Manual page 156

4 Protective Elements
4.3 49 – Thermal Model
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Fig. 36: Effective Current Threshold vs. Maximum Stator Temperature.
The diagram shows the following relationship: The lower the stator temperature, the
higher the effective 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 effective 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
Fig. 37: Thermal Replica Model Limit and Trip Curves without RTD.
156
0
0 50
Stator Temperature [°C]
1000
100
10
1
0.1
Multiple of Full Load Ampere
100 150 200
1 10
SF = 1, TC = 100%
Ith = 120%, Tth = 80%⋅TC
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250
100
EMR-3MP0