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3VT5 Molded Case Circuit Breakers up to 1600 A
Accessories and Components
Overcurrent releases
6/15
Siemens LV 36 · 2008
6
■
Technical specifications
The electronic overcurrent release consists of a separate and
interchangeable unit, which is supplied with the 3VT5 716-
3AA3.-0AA0 switching unit. By exchanging the overcurrent re-
lease, the range of the circuit breaker’s rated current can be eas-
ily changed.
Releases for the 3VT5 716-3AA3.-0AA0 switching unit are pro-
duced in four current values
I
n
= 630, 1000, 1250 and 1600 A.
Including their adjustment, the releases cover rated currents
ranging from 250 to 1600 A.
Depending on the needs for adjusting the release’s tripping
characteristics to the protected device and to the variability of
the characteristic with regard to selectivity, the following release
devices are available:
ETU DP
They have one type of characteristic with adjustable
I
r
and
I
rm
.
ETU MP
They have more kinds of characteristics with adjustable
I
r
, t
r
and
I
rm
.
ETU UP
They have universal characteristics, with the greatest variability
in adjustment:
I
r
, t
r
,
I
rmv
, t
v
and
I
rm
.
ETU DP, MP and UP
Proper functioning of releases does not depend on the form of
current in the main circuit. The function of the release is
supported by a microprocessor, which processes a sampled
signal of the power circuit and recalculates it to obtain an rms
value. Therefore, the releases are suitable for protecting circuits
where the sinusoidal current is distorted by high harmonics
(e.g. circuits with controlled rectifiers, power factor compensa-
tors, pulse loading, and the like).
All the releases protect a circuit against short-circuiting and
overloading. Setting of selective cascading of circuit breakers is
especially enabled by the ETU UP release. Tripping characteris-
tics of the releases are independent of the ambient temperature.
The releases are affixed to the switching unit by two bolts. The
translucent cover over the adjustment controls can be sealed.
Adjustment of tripping characteristics for release ETU DP and MP
The tripping characteristics of the overcurrent releases are de-
fined by standard EN 60 947-2. The characteristics are adjusted
in two zones using latched switches on the overcurrent release
unit:
L
- is a zone of low overcurrents and includes the area of thermal
protection.
I
- is a zone of high overcurrents and includes protection against
ultimate short-circuit currents.
ETU DP
ETU MP
1.Independent release (thermal) L
• The dependent release ETU MP is adjusted using two
switches,
I
r
and t
r
. The first of these, the
I
r
switch, is used to
adjust the circuit breaker’s rated current. The characteristic
moves on the current axis. By turning the other switch (t
r
), the
time is adjusted after which the circuit breaker will trip while
passing through 7.2
I
r
. The tripping characteristics thus move
on the time axis. Using the tr switch, it is possible to set a total
of 8 characteristics. Four characteristics are available for mo-
tor protection. Breaking times correspond with the release
class 10 A, 10, 20, 30. By changing t
r
it is possible to select
the characteristic according to the required motor starting
(light, medium, heavy or very heavy starting). For protecting
transformers and lines, 4 characteristics can be set. It is not
possible to turn the device back on right after the dependent
release has been actuated and circuit breaker tripped. The re-
lease must be allowed to cool off, because it has a thermal
memory.
The memory can be disabled by turning the “restart” switch
from the normal “T
t
” position to the “T
0
” position. The depen-
dent release remains active, and only its thermal memory is
inactivated. The thermal memory should be used only in justi-
fied cases, and with the knowledge that there could be rising
temperature in the protected device with repeated tripping.
• The dependent release ETU DP is adjusted using one switch
I
r
. Using the
I
r
switch, the circuit breaker’s rated current is
adjusted, with the characteristic moving on the current axis.
By means of its internal circuitry, the release is set to one type
of characteristic, TV3.
2. Independent instantaneous release (short-circuit trip) I
The independent instantaneous release in designs ETU DP and
MP is adjusted using one
I
rm
switch. The
I
rm
switch is used for
setting up the short-circuit current that, upon its being reached
or exceeded, causes instantaneous tripping of the circuit
breaker. Regulation of the short-circuit release takes in settings
for the characteristic appropriate for protecting lines and motors.
The wave form of the tripping characteristics is adjusted using
latched switches on the release’s front panel according to the
needs of the protected device. A visual demonstration on setting
the tripping characteristic can be found in the SIMARIS design.
NSO0_00506
t
I
L
I
I
r
I
i
NSO0_00454
t
I
L
I
I
r
t
r
I
i