Siemens SENTRON 3WL Reference Manual page 20

3WL Air Circuit Breakers
3WL Air Circuit Breakers/Non-Automatic Air Circuit Breakers up to 6300 A (AC)
General data
Measurement method
Vectorial summation current formation (measurement method 1)
The three phase currents and the N conductor current are
measured directly.
The solid-state release 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 SENTRON 3WL is 0.11 Ω). The current trans-
former can be installed directly in the grounded neutral point of
a transformer.
SENTRON WL
3-pole circuit breakers, current transformers in the N conductor
SENTRON WL
T6
T6: 1200 A/1 A
3-pole circuit breakers, current transformers in the grounded neutral
point of the transformer
SENTRON WL
T6
T6: 1200 A/1 A
4-pole circuit breakers, current transformers in the grounded neutral
point of the transformer
20 Siemens · 2009
L1
L2
L3
N
T5
PE
NSE 00946
L1
L2
L3
N
PE
NSE 00947
L1
L2
L3
N
PE
NSE 00948
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 solid-state release ver-
sion ETU76B with Menu/Comm.
Ground-fault protection with
With the exception of the ETU27B solid-state release, all
versions of the ground-fault modules are supplied with an
characteristic curve which can be activated.
Selection criteria for SENTRON 3WL circuit breakers
Basic criteria for selecting circuit breakers are:
• Max. short-circuit current at place of installation of circuit brea-
"
ker .
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
and essentially determines the size of the circuit breaker.
See illustration "Overview of SENTRON 3WL Circuit
Breakers/Non-Automatic Air Circuit Breakers".
• Rated current which is to flow through the branch circuit.
I n
This value must not be larger than the maximum rated current
for the circuit breaker.
The rated current for the SENTRON 3WL is set with the rated
current module. See "Design", illustration "Overview of
SENTRON 3WL Circuit Breakers/Non-Automatic Air Circuit
Breakers".
• 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 release must
still detect this value as a short-circuit and must respond by
tripping.
Protection functions of the circuit breaker.
These are determined by the selection of the
corresponding solid-state release,
"Functions of the solid-state releases" under "Functions".
.
.
2
t characteristic curve
I
I 2
t
, , of the circuit breaker
I cu I cs I cw
see the table