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Functions
Temperature
Behaviour during
Changing
Operating States
222
For the rotor temperature equilibrium time, a setting of. T EQUAL = 1 min has proven
to be a good value. The value for the minimum inhibit time T MIN. INHIBIT depends
of the requirements made by the motor manufacturer, or by the system conditions. It
must in any case be higher than T EQUAL. In this example, a value has been chosen
that reflects the thermal profile (T MIN. INHIBIT = 6.0 min).
The motor manufacturer's, or system requirements determine also the extension
factor for the time constant during cooldown, especially with the motor stopped. Where
no other specifications are made, the following settings are recommended:
Kt at STOP = 5 and Kt at RUNNING = 2.
For a proper functioning, it is also important that the CT values for side 2 (addresses
0211 and 0212), the power system data (addresses 0251, 0252) and the threshold
current for distinction between stopped and running motor (address 0281
BkrClosed I MIN, recommended setting ≈ 0.1 ⋅ I/I
An overview of the parameters and their default settings is given in the tables at the
end of this section and in the Appendix.
For better understanding of the above considerations, two of the many possible
operating states will be discussed in the following paragraph. The examples use the
settings indicated above. 3 cold and 2 warm startup attempts have resulted in a restart
limit of 66.7 %.
Figure 2-106 illustrates the temperature behaviour during 2 warm startup attempts.
The motor is always operated at nominal current. After the first shutdown, T EQUAL
takes effect.
30 s later the motor is restarted and immediately shut down again. After another
pause, the 2nd restart attempt is made. The motor is shut down once again. During
this 2nd startup attempt, the restarting limit is exceeded, so that after shutdown the
restart inhibit takes effect. After the temperature equilibrium time (1 min), the thermal
profile cools down with the time constant
restart inhibit is effective for about 7 min.
1st startup
p.u.
1.0
0.8
0.6
0.4
0.2
0
100
200
Figure 2-106 Temperature Behaviour during Two Successive Warm Starts
τ
⋅ Kt at STOP ≈ 5 ⋅ 204 s = 1020 s. The
L
2nd startup
Inhibit time
Temperature in p.u.
Restarting limit
Motor current in I/I
300
400
500
) have been set correctly.
N Motor
N
t/s
600
700
7UM62 Manual
C53000-G1176-C149-3
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