138 / 267
3VT3 Molded Case Circuit Breakers up to 630 A
Overcurrent releases
4/18
Siemens LV 36 · 2008
4
Tripping characteristics of ETU LP, DP, MP, MPS and DPN
releases with load
The tripping characteristic from the cold state indicates the
tripping 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 release’s “warm” state, the tripping
time of the characteristic is cut short during the standstill time t
u
by coefficient
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
sd
is cut short from the
cold-state characteristic by the coefficient
k
.
The real tripping time is t
s
= k . t
sd
Example
The shortening constant can be read from the diagram. With
steady current 85% of
I
r
the real tripping time will be decreased
to:
t
s
= 0.74 .
t
sd
k [–] time shortening coefficient
I
r
[A] adjusted rated current of the overcurrent release
t
sd
[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
Protecting lines with low starting currents
The 3VT9 3..-6AB00 release is intended for the 3VT3763-.AA36-
0AA0 and 3VT3763-.AA46-0AA0 switching unit. The release has
a thermal memory that cannot be disabled. Releases’ rated cur-
rents are given by their type designations and correspond to a
standardised series of currents (see specifications table). The
short-circuit release is fixed-set at 4
I
n
.
One of the release’s advantages is its simplicity, because it does
not require any adjustment. Therefore, it is intended for less
complicated applications.
Specifications
Tripping characteristics
NSO0_00355
I
r
[%]
1.0
T
0.8
0.6
0.4
0.2
0.0
50
60
70
80
90
100
k [-]
Type
Rated current
I
n
Overload protection
I
rm
A
A
3VT9 325-6AB00
250
1000
3VT9 331-6AB00
315
1260
3VT9 340-6AB00
400
1600
3VT9 350-6AB00
500
2000
3VT9 363-6AB00
630
2520
20
200
2000
50
500
5000
10
100
1000
10000
t
[s]
NSO0_00356
1
2
5
20
50
10
0.5
x
I
n
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
I
L
I
r
I
i
I
n = 630 A
I
n = 500 A
I
n = 400 A
I
n = 315 A
I
n = 250 A
I
n
= 250 A
I
n
= 315 A
I
n
= 400 A
I
n
= 500 A
I
n
= 630 A