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3VT2 Molded Case Circuit Breakers up to 250 A
Overcurrent releases
3/17
Siemens LV 36 · 2008
3
Tripping characteristics of ETU LP, DP, MP, MPS and DPN
releases with load
The tripping characteristic from the cold state indicates the trip-
ping times during which it is assumed that, up to the moment
when an overcurrent develops, no current is flowing through the
circuit breaker. The tripping characteristic tripped from warm
state indicates the tripping times during which it is assumed that,
before the moment when an overcurrent develops, current is
flowing through the circuit breaker. Characteristics of electronic
releases are independent of the ambient temperature and are
plotted in a cold state. Digital releases enable simulation of a
release in warm state. The tripping times become shorter in a
steady state, as shown in the following diagram. The steady
state is a period during which the characteristic does not
change. If the circuit breaker is loaded with a reduced current for
at least 30 minutes, the tripping times will be cut by a half. If the
load is less than 70% of
I
r
, the tripping time does not become
shorter.
Decrease of tripping time with load
T
- When tripping from the “warm” state, the tripping time of the
characteristic is cut short during the standstill time t
u
by coeffi-
cient
k
.
Thermal standstill time of the characteristics
For all overcurrent releases, the thermal standstill time is t
u
≥
30
min. During this time, the tripping time t
v
is cut short from the
cold-state characteristic by the coefficient
k
.
The real tripping time is t
s
= k x t
v
Example
The shortening constant can be read from the graph. With
steady current 85% of
I
r
the real tripping time will be hortened to:
t
s
= 0.74 x
t
v
k [–] time shortening coefficient
I
r
[A] adjusted rated current of the overcurrent release
t
v
[s] tripping time of the release derived from the characteristic
t
s
[s] real tripping time of the release tripped from warm state
t
u
[s] standstill period for particular characteristics
Overcurrent releases are preset by the manufacturer
I
r
= min
Restart = T
(t)
I
i
= min, 0 ms
t
r
= TV, t
(t)
, min
I
sd
= 0 ms, min
I
N
= 0.5
I
r
Overcurrent releases ETU LP - Lines
Protecting lines with low starting currents
The 3VT9 2..-6AB00 release is intended only for
3VT2725 -.AA36-0AA0 or 3VT2725 -.AA46-0AA0 switching unit.
The release has a thermal memory that cannot be disabled. The
rated currents of the releases are given by their type designa-
tions and correspond to a standardized series of currents
(see specifications table). The short-circuit release is fixed-set at
4 ×
I
n
.
One of the advantages of the releases is its simplicity, because
it does not require any adjustment. Therefore, it is intended for
less complicated applications.
Specifications
Tripping characteristics
NSO0_00217
I
r
[%]
1.0
T
0.8
0.6
0.4
0.2
0.0
50
60
70
80
90
100
k [-]
Order No.
Rated current
I
n
Overload protection
I
r
A
A
3VT9 216-6AB00 160
640
3VT9 200-6AB00 200
800
3VT9 250-6AB00 250
1000
20
200
2000
50
500
5000
10
100
1000
10000
t
[s]
NSO0_00218
2
5
20
50
10
0.5
1
x
I
n
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
I
I
i
L
I
n
= 160 A
I
n
= 200 A
I
n
= 250 A
I
r