CHAPTER 7 - PROGRAMMING INFORMATION AND SUGGESTIONS
158
1) Initially start the motor some times in the standard thermal class,
but without heating it up excessively;
2) Determine correct starting time. Find an average of the current
through the P002 during the starting time. One can find a current
average for any kind of starting control.
For example:
When an 80A motor is started by voltage ramp, the current at P002
starts at 100A and increases to 300A and after 20s decreases to
the nominal current.
(100A+300A)/2 = 200A
200A/80A = 2.5 x In of the motor
then: 2.5 x In @ 20s.
7.2
PROTECTIONS AND
PROGRAMMING
7.2.1 Thermal Classes
7.2.1.1 Suggestions on How to
Set Thermal Class
Figure 7.23
- Typical current curve when started by voltage ramp
3) Use this time to find the minimum class necessary to start a cold
motor according to the descriptions of P640 in chapter 6;
Figure 7.24
- Determining the minimum thermal class with cold motor
Thus the minimum required thermal class for starting the motor is the
Class 10. The Class 5 requires a shorter time for this current.
This Thermal Class allows motor cold start.
U(V)
Start
100%Un
20s
0
Enable
t(s)
P101
Voltage Ramp
P102
Current
in P002
100A
300A
t(s)
0
20s
2.5 x In of the Motor
5
10
xln
15
Cold
S.F.=1
Summary of Contents for SSW06
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