CHAPTER 7 - PROGRAMMING INFORMATION AND SUGGESTIONS
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4) To determine the thermal class for starting at hot motor, the motor
thermal class must be known. For this we must determine the
allowed blocked rotor time.
NOTE!
To program the Thermal Class that your motor will withstand, the
allowed locked rotor time must be available. For this data, please
refer to the manufacturer catalog.
With the blocked rotor time we can find the maximum thermal class
that will protect the motor for hot starting, according to the descriptions
of P640;
For example:
6.6 x In @ 6s
Figure 7.25
- Determining the maximum thermal classes through the hot starting
curves
Thus, the maximum thermal class that will protect the motor is Class
25, Class 30 has too long time for this current.
This thermal class allows the motor to start at hot motor, in other
words, it can be started in any condition.
NOTE!
Please consider that this protection adopts WEG standard three-
-phase IP55 motor as a standard. Thus, if your motor is different, do
not program the maximum allowed thermal class, but program the
thermal class near the minimum thermal class required for the start.
Motor Data:
Power: 50 HP
Voltage: 380V
Nominal current (In): 71A
Service Factor (S.F.): 1.00
Ip/In : 6.6
Blocked rotor time:12s at hot
Speed: 1770 rpm
Data about the motor + load Starting:
Starting by Voltage Ramp, average starting current:
3 x the nominal motor current during 25s (3 x In @ 25s).
1) In the chart, at cold at P640, we can find the minimum required
Thermal Class that allows motor start with reduced voltage:
For 3 x In @ 25s, we select the closest higher one: Class 10.
7.2.1.2 Example on How to
Set the Thermal Class
t(s)
0
6s
6.6 x In of the Motor
20
25
xln
30
Hot
Содержание SSW06
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