01/02 AWB8230-1413GB
Electronic motor protection
135
Electronic motor protection
Using an electronically simulated bimetallic strip, the DF6
frequency inverters can provide thermal monitoring of the
connected motor. With PNU b012, match the electronic motor
protection to the motor’s rated current. If the values entered here
exceed the rated motor current, the motor cannot be monitored
with this function. In this case, PTC thermistors or bimetal contacts
in the motor windings must be used.
Let us assume you have a DF6-340-11K. The motor full load
current is 22 A. The setting range goes from 4.4 A = 0.2
x
22 A
to 26.4 A = 1.2
x
22 A. figure 135 shows the tripping
characteristic when PNU b012 contains the value 22.
Use PNU b013 to match the overload protection to your load
conditions. You have three options (
a
fig. 136 to fig. 138):
• Increased overload protection; value: 00
• Normal overload protection; value: 01 (default)
• Adjustable overload protection; value: 02
Tripping characteristics with increased overload
protection
With increased overload protection (PNU b013 = 00), the tripping
current is reduced, for example, by 80 % at 20 Hz (
a
fig. 136).
Accordingly, the tripping characteristic is offset to smaller current
values (
a
fig. 139).
Caution!
At low motor speeds, the output of the motor cooling fan
is diminished, and the motor may overheat despite its
overload protection. You should therefore provide
protection with PTC thermistors or bimetal contacts.
Figure 135: Tripping current characteristic at
I
e
= 22 A
Figure 136: Increased overload protection (PNU b013 = 00)
60
0
25.5 A
116 %
33 A
150 %
44 A
200 %
0.5
[s]
J
1
100
80
60
5
20
60
f
[%]
[Hz]
I
Figure 137: Normal overload protection (PNU b013 = 01)
Figure 138: Adjustable overload protection (PNU b013 = 02)
Figure 139: Tripping characteristic for increased overload protection at
20 Hz and
I
e
= 22 A
100
80
90
5
2.5
60
f
[%]
[Hz]
I
PNU b020
PNU b018
PNU b016
PNU b015 b017
b019
A004
I
f
60
0
20.4 A
92.8 %
26.4 A
120 %
35.2 A
160 %
0.5
[s]
J
1
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