Siemens SENTRON 3VL System Manual page 138

Parameter assignment/addressing
10.1 Setting the parameters
I t waveform:
2
A I t waveform of the characteristic curve can be switched in (depending on the ETU), the
2
delay time t
form the characteristic curve. As well as a fixed time delay for all currents in the
characteristic curve section, the I
continuously as the current increases, and the product of squared current and time remains
constant.
Figure 10-1
I instantaneous short-circuit protection I
On some trip units, the instantaneous short-circuit release I
the rated current I
instantaneous short-circuit release (I
protection of personnel. The tripping current of the short-circuit release of the circuit breaker
is set to a value that is at least 20% (tolerance of the trip unit) lower than the lowest short-
circuit current at the installation location and simultaneously higher than the maximum
operating current +20%. This guarantees that the circuit breaker will trip within the required
time even with the smallest short-circuit current, and that correct currents will not result in
unwanted trips.
G ground fault protection I
The tripping value of the of the ground fault release I
the ETU12 and ETU22. The tripping current of the ground fault release can be set to
between 0.6 and 1 x I
measuring methods for the ground fault protection are specified on the representation of the
trip unit. On the ETU42, the tripping current of the ground fault release can be set to between
0.4 and 1 x In, and the delay time can be set between 0.1 s and 0.5 s.
Note
Ground-fault protection
It must be noted that the ground fault protection is not an r.c.b. circuit breaker (FI or RCD in
the building installation). Fault currents to ground therefore cannot be detected, only ground
"short"-circuits. However, an RCD module can be used for 3VL.
138
is based on the reference point 8 x I
sd
t characteristic can also be used. The tripping time falls
2
I t
2
of the circuit breaker. It must always be noted that either the
n
:
g
, and the delay time t
n
. Two different procedures are used to
R
:
i
i
) or the delayed short-circuit release (I
sd
is fixed to the rated breaker current on
g
can be set between 0.3 s and 0.6 s. The
g
System Manual, 03/2009, 110 0110 - 02 DS 01
can also be set. This refers to
) handles the
i
3VL molded-case circuit breakers