WEG SSW-07 - Protections and Programming; Suggestion on How to Program the Thermal Class

CHAPTER 5 - PROGRAMMING INFORMATION AND SUGGESTIONS
39
English
5.2 PROTECTIONS
AND
PROGRAMMING
5.2.1 Suggestion on
How to Program
the Thermal
Class
1) Initially start at the standard thermal class, sometimes, but without
the motor overheating;
2) Determine the correct starting time. Find an average of the current
using a multmeter with a current probe to measure it;
A current average can be found for any type of starting control;
Forexample:
Starting an 80 A motor using a voltage ramp. The current starts at
100 A and goes to 300 A, returning afterwards to the nominal value
in 20 seconds.
(100 A + 300 A)/2 = 200 A
200 A/80 A = 2.5 x ln of the motor
Therefore:2.5xln@20seconds.
Motor
Current
P102
Accel Time
Initial Voltage P101
U (V) Start
100%Un
300 A
t(s)
20 s
0
100 A
Enable
Figure 5.5 - Typical current curve during a voltage ramp start
3)Usethistimetondtheminimumclassnecessarytostartthe
motor in cold condition. In the item 4.8 Overload Protection it is
possible to check the thermal class curves of the motor in cold
condition.
2.5 x In of the motor
t(s)
20 s
0 xln
15
10
5
Cold
F.S.=1
Figure 5.6 - Checking the minimum class of curves in cold condition