Siemens SENTRON 3VL series - Page 121

Parameter assignment / addressing
9.1 Setting the parameters
3VL IEC molded case circuit breakers
System Manual, 11/2013, 110 0110 - 02 DS 03
121
Parameter
Setting buttons
Effect on
characteristic curve
Brief description
Cause
G
I
g
/t
g
Tripping current and
time delay of the
ground-fault protection
I
g
= Off, 1 or 0.6 x I
n
t
g
=
Off, 0.1 s or 0.3 s
Protection from short-circuit to
ground and thus prevention of
arcs. Ground-fault protection is
part of the fire protection.
1)
For LCD ETUs, the ST function must be set to the value "disabled" for t
sd
= 0.
Setting of the protection parameter for line and generator protection
The settings are variable depending on the trip unit (ETU10, ETU12, ETU20, ETU22, LCD-
ETU40 and LCD-ETU42). The following parameters can be set depending on the version:
L overload release I
R
:
The overload release I
R
is set to the operating current I
B
of the circuit to be protected. This
takes place with the help of the left rotary encoding switch I
R
that is set to the factor I
B
/I
n
(example: I
B
= 250 A, I
n
= 315 A => setting factor 250 / 315 = 0.79 corresponds to 0.8 on the
rotary encoding switch).
Delay time t
r
:
The delay time (or time-lag class) t
r
can be set using another rotary encoding switch. The set
time is the tripping time at 6 x I
r
. In this way, selectivity to other molded case circuit breakers
can be achieved in the overload range, for example, when the rated current range does not
differ much.
S short-time delayed short-circuit protection I
sd
:
The short-time delay short-circuit protection can be set with regard to the tripping value of
the current I
sd
and the delay time t
sd
. I
sd
refers to the tripping value of the overload release I
R
and can be set between 1.5 to 10 x I
R
(depending on the molded case circuit breaker).
Delay time t
sd
:
Depending on the requirements and on the trip unit, selectivity to the other molded case
circuit breakers can be achieved with appropriate selection of the delay time t
sd
. If the rotary
encoding switch is in the "ON" range, this means the delay time is current-dependent. The I
2
t
value is constant. For example, the higher the current, the faster the circuit breaker will trip
(equivalent to the overload release I
R
). In contrast, the delay time in the "OFF" position is
current-independent, that is, constant. If the current reaches the set value I
sd
, the circuit
breaker trips after the set time t
sd
. The degree to which the current exceeds the value I
sd
is
not important. The set time is the tripping time at 8 x I
r
.