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Characteristic curves
The tripping characteristics show the relationship between the
tripping time and tripping current as multiples of the current
setting I
and are given for symmetrical three-pole and two-pole
e
loads from the cold state.
The smallest current used for tripping is called the minimum trip-
ping current. According to IEC 60947-4-1, this current must be
within specified limits. The limits of the minimum tripping current
for the 3RB22/3RB23 solid-state overload relays for symmetrical
three-pole loads lie between 105 and 120 % of the current
setting.
The tripping characteristic starts with the minimum tripping cur-
rent and continues with higher tripping currents based on the
characteristics of the so-called trip classes (CLASS 10,
CLASS 20 etc.). The trip classes describe time intervals within
which the overload relays have to trip with 7.2 times the current
setting I
from the cold state for symmetrical three-pole loads.
e
The tripping times according to IEC 60947-4-1,
tolerance band E, are as follows for:
Trip class
CLASS 5
CLASS 10
CLASS 20
CLASS 30
The tripping characteristic for a three-pole overload relay from
the cold state
(see illustration 1)
simultaneously loaded with the same current. In the event of a
phase failure or a current unbalance of more than 40 %, the
3RB22/3RB23 solid-state overload relays switch off the contac-
tor more quickly in order to minimize heating of the load in ac-
cordance with the tripping characteristic for two-pole loads from
the cold state
(see illustration
Compared with a cold load, a load at operating temperature ob-
viously has a lower temperature reserve. The tripping time of the
3RB22/3RB23 solid-state overload relays is reduced therefore to
about 20 % when loaded with the current setting I
ded period.
Tripping time
3 ... 5 s
5 ... 10 s
10 ... 20 s
20 ... 30 s
only apply if all three phases are
2).
for an exten-
e
Overload Relays
3RB2 Solid-State Overload Relays
3RB22, 3RB23 for high-feature applications
Tripping characteristics for 3-pole loads
1000
800
600
400
s
200
100
80
60
40
20
10
8
6
4
2
1
0,6
1
2
4
Tripping current
Illustration 1
Tripping characteristics for 2-pole loads
1000
800
600
400
s
200
100
80
60
40
20
10
8
6
4
2
1
0,6
1
2
4
Tripping current
Illustration 2
The above illustrations are schematic representations of charac-
teristic curves. The characteristic curves of the individual
3RB22/3RB23 electronic overload relays can be ordered from
"Technical Assistance":
• Either by e-mail to:
technical-assistance@siemens.com
• Or on the Internet at:
http://www.siemens.com/automation/service&support
NSB0_01525
CLASS 30
CLASS 20
CLASS 10
CLASS 5
6
8 10×
e
NSB0_01526
CLASS 30
CLASS 20
CLASS 10
CLASS 5
6
8 10×
e
Siemens · 2011
37
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