Grundfos RSI - Page 150

8.2.14 Protections
P3.9.1.2 External Fault
An alarm message or a fault action and message is
generated by an external fault signal in one of the
programmable digital inputs (DI3 by default) using
parameters P3.5.1.11 and P3.5.1.12. The information
can also be programmed into any of the relay
outputs.
P3.9.2.3 ZeroSpeedCooling
Defines the cooling factor at zero speed in relation to
the point where the motor is running at nominal speed
without external cooling. See Motor thermal current IT
curve.
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).
If you change the parameter P3.1.1.4 (Motor Nom
Currnt), this parameter is automatically restored to
the default value.
Setting this parameter does not affect the maximum
output current of the drive which is determined by
parameter P3.1.3.1 alone.
The corner frequency for the thermal protection is 70
% of the motor nominal frequency (P3.1.1.2).
f
f
n
0
I
T
100%
1
3
2
4
9129
Motor thermal current I
T
curve
Pos. Description
1
P
cooling
2 Par. ID706 = 40%
3 Overload area
4 Corner freq
P3.9.2.4 ThermTimeConst
This is the thermal time constant of the motor. The
bigger the motor, the bigger the time constant. The
time constant is the time within which the calculated
thermal stage has reached 63 % of its final value.
The motor thermal time is specific to the motor design
and it varies between different motor manufacturers.
The default value of the parameter varies from size to
size.
If the motor's t6-time (t6 is the time in seconds the
motor can safely operate at six times the rated
current) is known (given by the motor manufacturer)
the time constant parameter can be set basing on it.
As a rule of thumb, the motor thermal time constant in
minutes equals to 2*t6. If the drive is in stop stage the
time constant is internally increased to three times the
set parameter value. The cooling in stop stage is
based on convection and the time constant is
increased. See Motor thermal time constant.
I/I
T
100%
63%
t
T
t
1
2
9077
Motor thermal time constant
Pos. Description
1 Current
2 Motor thermal time constant
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