Siemens 6MD85, Manual

Page: 533 / 1256

Input Signal: >Threshold sensitive
In order to ensure that the function picks up reliably in all switch positions of the power-supply system (exam-
ples: opposite end of line open, switching onto a ground fault), the setting of the parameter
Threshold
sensitive
can be applied dynamically to all currents – including phase currents – in the presence of ground
faults. For this purpose, the binary signal
>Threshold sensitive
must be activated. This can be done via a
device-internal function for ground-fault detection (if provided in the device), for example, using Overvoltage
protection with zero-sequence voltage. In this case, the pickup of the V0> function must be linked with the
binary signal. Alternatively, the signal can be coupled from a separate device for sensitive ground-fault detec-
tion via a binary input.
Parameter: Circuit-breaker auxiliary contact criterion allowed
•
Recommended setting value
(_:103) CB aux.cont. crit. allowed
=
no
Parameter Value Description
no
If sufficient current flow is ensured under all conditions with the CB closed,
Siemens recommends not to permit the auxiliary contacts as a further crite-
rion for determining the CB position, because measurement based on the
current flow is the most reliable criterion.
w. 'CB pos. closed 3p.'
w. 'CB pos. closed Lx'
(1/3-pole CB)
The auxiliary contacts are permitted as a further criterion in applications
(see the following examples) where the current is no reliable criterion for
determining the circuit-breaker position.
The following applies for the 1/3-pole CB:
If the protection trips phase-selectively, it makes sense to connect also the
auxiliary contacts to the device in a phase-selective way to ensure a pole-
selective detection of the position. To do this, select
w. 'CB pos.
closed Lx'
.
If pole-selective detection is not possible, you must set
w. 'CB pos.
closed 3p.'
. Observe that the CB is detected as open as soon as the 1st
pole has opened.
Parameter:
3I0 criterion
•
Recommended setting value
(_:120) 3I0 criterion
=
Plausibility check
Parameter Value Description
Plausibility check
The ground current serves only for the plausibility check of the phase
currents. The threshold for the ground current uses the value set in the
Threshold sensitive
parameter.
Direct release
The current-flow criterion can be satisfied only by the ground current
without the phase currents exceeding their set threshold value. The
threshold for the ground current uses the value set in the
Threshold 3I0
dir. release
parameter in this case.
i
i
NOTE
With the 1/3-pole circuit breaker, the setting value
Direct release
can cause an unwanted tripping of
the circuit-breaker failure protection in case of a 1-pole tripping of the circuit breaker.
If you have set the
Threshold phase current
to be larger than the maximum usual load current, over-
function due to a false start is impossible. To have a circuit-breaker failure protection function for smaller
ground faults also with this setting, you can set the
3I0 criterion
to
Direct release
and set the
Threshold 3I0 dir. release
to be correspondingly smaller than the
Threshold phase current
.
Parameter:
I2 criterion
•
Recommended setting value
(_:121) I2 criterion
=
Plausibility check
Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
SIPROTEC 5, High-Voltage Bay Controller, Manual 533
C53000-G5040-C015-9, Edition 11.2017