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Vacon
Page 39
Pump control with autochange
Par. 7
.
6
Par. 7
.
7
I
T
f
par. 1
.
7
I
UMCH7_91
Par. 7
.
9
Overload area
Current
limit
7. 7
Motor thermal protection, zero frequency current
The current can be set between 10.0—150.0% x I
nMotor
. This parameter sets the
value for thermal current at zero frequency. Refer to the figure 5-18.
The default value is set assuming that there is no external fan cooling the motor. If
an external fan is used this parameter can be set to 90% (or even higher).
The value is set as a percentage of the motor
name plate data, parameter 1
.
13, motor's
nominal current, not the drive's nominal
output current. Motor's nominal current is the
current which the motor can stand in direct
on-line use without being overheated.
If you change the parameter 1
.
13 this
parameter is automatically restored to the
default value.
Setting this parameter (or parameter 1
.
13)
does not affect to the maximum output
current of the drive. Parameter 1
.
7 alone
determines the maximum output current of
the drive.
7. 8
Motor thermal protection, time constant
The time can be set between 0.5—300 minutes.
T h i s
is the thermal time constant of the motor. The bigger the motor the bigger the time
constant. The time constant is the time when the calculated thermal stage has
reached 63% of its final value.
parameter could be set based on t
6
-time.
As a rule of thumb, the motor thermal time
constant in minutes equals to 2xt
6
(t
6
in
seconds is the time a motor can safely
operate at six times the rated current). If the
drive is in stop stage the time constant is
internally increased to three times the set
parameter value. The cooling in the stop stage
is based on convection and the time constant
is increased.
The motor thermal time is specific for the
motor design and it varies between different
motor manufacturers.
The default value for the time constant is
calculated on the basis of the motor name
plate data given with parameters 1
.
12 and
1
.
13. If either of these parameters is set,
then this parameter is set to default value.
If the motor's t
6
-time is known (given by the
motor manufacturer) the time constant
Figure 6-19 Motor thermal current
I
T
curve.
