8400 BaseLine D | Software Manual
Motor control (MCTRL)
Monitoring functions
108 L Firmware 03.00 - DMS EN 5.0 - 07/2009
5.9 Monitoring functions
5.9.1 Motor temperature monitoring with I²xt
The 8400 frequency inverter is provided with a simple, sensorless monitoring for thermal
"I
2
xt" motor overload of self-ventilated standard motors.
C066
displays the motor utilisation meter I
2
xt, which shows whether the motor is
overloaded or not.
The permissible overload time of the motor is reached with an overload of C066
= 100 %,
the message "Thermal motor overload, I
2
xt" (OC6) is output and the response set in C606
is initiated (default setting: "warning").
C120
serves to enter the overload threshold for I
2
xt motor monitoring
Stop!
The I
2
xt motor monitoring does not provide a full motor protection! Since the
motor utilisation calculated in the thermal motor model gets lost after
switching the mains, the following operating states cannot be determined
correctly:
• Restarting (after mains switching) of a motor that is already very hot.
• Change of the cooling conditions (e.g. cooling air flow interrupted or too
warm).
A full motor protection requires additional measures as e.g. the evaluation of
temperature sensors that are located directly in the winding or the use of
thermal contacts.
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