Description
2.8 Electronic trip unit ETU
3VA27 molded case circuit breakers & 3WL10 air circuit breakers
Manual, 10/2018, L1V30499596002-01
67
Basic rules of parameterization and basic protection functions
Parameter
Effect on
characteris-
tic curve
Description
Cause
Example
L I
r
Current setting value of the
overload protection:
I
r
=0.4…1.0 × I
n
absolute values in A
Setting of the over-
load protection to the
load current of the
circuit to be protected
I
r
= 0.9 x I
n
(where I
n
=1000A)
Overload range as of I
r
= 900 A
t
r
Delay time in the overload
range The set time is the
tripping time at 6 × I
r
.
Use for current and
time selectivity
The set delay time t
r
of, for exa-
mple, 10 s always applies at the
reference point 6 x I
r
.
In this case, it is therefore
6 x 900 A = 5400 A
The tripping characteristic in the
overload range can be plotted in
the same way as for I²t depen-
dency.
S I
sd
Operating current of the
short-time-delayed short-
circuit protection
I
sd
= 1.0 … 10 x I
n
Limitation of the
short-circuit range in
which the current has
to be interrupted as
quickly as possible,
but with a defined
time delay
I
sd
= 8 x I
n
= 8000 A
(at I
n
= 1000 A)
Range of the short-time delay as
of 8000 A
t
sd
Delay time of the
short-time-delayed short-
circuit protection
Use for time selectivi-
ty. Time delay of t
sd
can be definite-time
or inverse-time in
relation to I²t
For example, at t
sd
= 0.4 s
(constant): Tripping after 400 m
for short-circuit values above
8000 A and below a value of I
i
I
I
i
Current setting value of the
instantaneous short-circuit
protection
I
i
= 1.5 … 15 x I
n
Limitation of the
short-circuit range in
which the impermis-
sibly high current has
to be interrupted as
quickly as possible
I
sd
= 12 x I
n
= 12000 A
(at I
n
= 1000 A)
Range of the instantaneous trip-
ping on short-circuits as of
12000 A
G I
g
Current setting value of the
ground-fault protection
Line protection
On ground-fault current
as of 0.1 x I
n
= 100 A
(at I
n
= 1000 A)
Tripping, for example, after a time
of t
g
= 0.1 s
