Operating Instructions

Siemens Industry, Inc. • 82 Siemens Application
24-hour support [phone] (Dial 2)
Motor thermal time constant (P3.9.9)
The time constant is the time within which the calculated thermal stage has reached 63% of its final val-
ue. The bigger the frame and/or the slower the speed of the motor, the longer the time constant.
The motor thermal time is specific to the motor design and it varies between different motor manufactur-
ers. 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 based on it. As a
rule of thumb, the motor thermal time constant in minutes is equal 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 Figure 23.
Motor thermal load (P3.9.10)
Setting the value to 130% means that the nominal temperature will be reached with 130% of the motor’s
nominal current.
Figure 23. Motor temperature calculation.
Stall current (P3.9.12)
The current can be set to 0.0…2*I
L
. For a stall stage to occur, the current must have exceeded this limit.
See Figure 24. If parameter P3.1.1.7 Motor current limit is changed, this parameter is automatically cal-
culated to 90% of the current limit. See page 49.
NOTE: In order to guarantee desired operation, this limit must be set below the current limit.
105%
Q = (I/ I
T
)
2
x (1- e
-t/T
)
I/I
T
11099.emf
Tr i p ar e a
Motor temperature
Ti m e
Motor temperature
Ti m e con st ant T
*)
*)
Changes by motor size and
adjusted with P3.9.9
Faul t / al ar m
P3.9.6
Motor
current