706 MOTOR THERMAL PROTECTION: MOTOR COOLING FACTOR AT ZERO SPEED 234567 (2.7.10)
Gives the cooling factor at zero speed in relation to the point where the motor operates at
nominal speed without an external cooling. See Fig. 72 The motor thermal current IT curve.
The default value is set for conditions where there is no external fan. If you use an external
fan, you can set the value higher than without the fan, for example at 90%.
If you change parameter Motor Nominal Current, this parameter is automatically set to its
default value.
Although you change this parameter, it does not have an effect on the maximum output
current of the drive. See Chapter 8.4 Parameters of motor thermal protection (IDs 704 to 708).
The corner frequency for the thermal protection is 70% of the value of the parameter Motor
Nominal Frequency (ID111).
f
fn
ID706=40%
0
IT
100%
Overload area
Pcooling
Corner freq
Fig. 72: The motor thermal current I
T
curve
707 MOTOR THERMAL PROTECTION: TIME CONSTANT 234567 (2.7.11)
This time can be set between 1 and 200 minutes.
The time constant is the time during which the calculated warming curve becomes 63% of its
target value. The length of the time constant is in relation with the dimension of the motor.
The bigger the motor, the longer the time constant.
In different motors, the motor thermal time constant is different. It also changes between
different motor manufacturers. The default value of the parameter changes from dimension
to dimension.
The t6-time is the time in seconds that the motor can safely operate at 6 times the rated
current. It is possible that the motor manufacturer gives the data with the motor. If you know
the t6 of the motor, you can set the time constant parameter with its help. Usually, the motor
thermal time constant in minutes is 2*t6. When the drive is in the STOP state, the time
VACON · 322
PARAMETER DESCRIPTIONS
8
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