Protections And Programming; Suggestion On How To Program The Thermal Class - WEG SSW-07 Manual Del Usuario

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5.2 PROTECTIONS
AND
PROGRAMMING
5.2.1 Suggestion on
How to Program
the Thermal
Class
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Chapter 5 - prOGraMMING INFOrMatION aND SUGGeStIONS
For each application exists a range of thermal classes, which might
be set. The overload protection should not trip during normal starting.
Therefore it is necessary to know the starting time and current, to
determine the minimum thermal class. The maximum thermal class
depends on the motor limit.
Determine the minimum thermal class:
1) Initially start at the standard thermal class, sometimes, but without
the motor overheating;
2) Determine the correct starting time and find an average of the
current using a multimeter 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.
U(V)
Initial Voltage
P101
0
Figure 5.9 - Typical current curve during a voltage ramp start
3) Use this time to find the minimum class necessary to start the
motor in cold condition. In the item 4.8 Motor Electronic Overload
Protection it is possible to check the thermal class curves of the
motor in cold condition.
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Start
100 A
P102
Enable Accel Time
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100 % Un
300 A
Motor
Current
t(s)
20 s
43
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