20
Siemens · 10/2014
General data
3WL Air Circuit Breakers
3WL air circuit breakers/non-automatic air circuit breakers up to 6300 A (AC), IEC
Measurement method
Vectorial summation current formation (measurement method 1)
The three phase currents and the N conductor current are
measured directly.
The electronic trip unit determines the ground-fault current by
means of vectorial summation current formation for the three
phase currents and the N-conductor current.
Direct measurement of the ground-fault current (measurement
method 2)
A standard current transformer with the following data
is used for measurement of the ground-fault current:
1200 A/1 A, Class 1 (the internal load of the 3WL circuit breaker
is 0.11 ). The current transformer can be installed directly in the
grounded neutral point of a transformer.
3-pole circuit breakers, current transformers in the N conductor
3-pole circuit breakers, current transformers in the grounded neutral
point of the transformer
4-pole circuit breakers, current transformers in the grounded neutral
point of the transformer
Setting
How the module is set depends on the measurement
method used (see above):
Measurement method 1: in position
Measurement method 2: in position
This setting can be implemented for the electronic trip unit
version ETU76B with Menu/Comm.
Ground-fault protection with I
2
t characteristic curve
With the exception of the ETU27B electronic trip unit, all
versions of the ground-fault modules are supplied with
an
I
2
t characteristic curve which can be activated.
Selection criteria for 3WL circuit breakers
Basic criteria for selecting circuit breakers are:
• Max. short-circuit current
at place of installation of circuit
breaker
I
k max
.
This value determines the short-circuit breaking capacity or
short-circuit current carrying capacity of the circuit breaker
• It is compared with the value
I
cu
,
I
cs
,
I
cw
of the circuit breaker
and essentially determines
the size of the circuit breaker.
See Figure "Overview of 3WL circuit breakers/non-automatic
air circuit breakers"
• Rated current
I
n
which is to flow through the branch circuit.
This value must not be larger than the maximum rated current
for the circuit breaker.
The rated current for the 3WL circuit breaker is set with the
rated current module. See Figure "Overview of 3WL circuit
breakers/non-automatic air circuit breakers" in "Design"
• Ambient temperature
For the circuit breaker.
This is usually the control cabinet internal temperature
•Design
of the circuit breaker
• Minimum short-circuit current
Which flows through the switching device. The trip unit must
still detect this value as a short-circuit and must respond by
tripping
Protection functions
of the circuit breaker.
These are defined by selection of the corresponding electronic
trip unit, see the table "Functions of the electronic trip units"
under "Functions"
L1
L2
L3
N
T5
PE
NSE0_00946a
L1
L2
L3
N
T6
PE
NSE0_00947
To Next Page
Loading...
