EMR-5000
IM02602012E
Thermal Model
Available Elements:
49
General – Principle Use
Thermal Protection and Alarm
This protective device provides a thermal model that is similar to Eaton’s MP-3000 motor relay to approximate the
thermal capacity used. The thermal model can work with or without the URTD. The RTD-based direct temperature
trips and alarms are independent of the thermal model. Without the URTD, meaning the URTD is not connected to the
protective device or it is connected but not configured for the thermal protection trips, the thermal model protection will
be solely based on the following settings:
1.Full Load Ampere (FLA);
2.Locked Rotor Current (LRC);
3.Maximum Allowable Stall Time (Tc);
4.UTC (Ultimate Trip Current) or Service Factor (SF);
5.Cooling Time Constant;
6.Thermal Model Trip Threshold if enabled;
7.Trip Delay;
8.Thermal Model Alarm Threshold if enabled; and
9.Alarm Delay.
The first four settings (1-4) dictate the maximum allowable thermal limit curve of the protected equipment, and the last
four settings (6-9) define the thermal trip and alarm curves relative to the thermal limit curve. Setting 5 is used for
cooling or damping.
Mathematically, the thermal limit curve can be expressed as the following:
TripTime
=
I
LR
2
∗
T
LR
I
ef
2
when
I
ef
SF
∗
FLA
If the direct stator temperature measurements are available, the thermal replica model will be modified to include the
heat loss between stator and rotor. As a result, the motor will be able to run longer under overload conditions. The
heat loss serves as a cooling. At some point, the cooling effect will cancel the heat increment so that the thermal
capacity used will reach some steady-state level that may be below the trip or alarm limit. This equivalently raises the
service factor and shifts the trip curve right.
If the thermal capacity used is held at a level that is below the trip threshold, the thermal model will not trip. To prevent
the protected equipment from overheating, the direct temperature trip function must be enabled. Keep in mind that in
order for the stator temperature to be effective in the thermal replica model, the following conditions must be met:
•
Some RTD channels must be configured to measure the winding temperatures; and
•
These RTD channels must be enabled for trip.
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