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Functions
Current
Transformer
Saturation
Circuit Breaker
Status
6-22
The current ratio may also be calculated from the desired reach of the parallel line
compensation and vice versa. The following applies (refer to Figure 6-12):
x l ⁄
I
E
--------
----------------- -
=
or
2 x l ⁄
I
–
EP
The 7SA6 contains a saturation detector which largely eliminates the measuring errors
resulting from the saturation of the current transformers. The threshold above which it
picks up can be set in address 1140A I-CTsat. Thres.. This is the current level
above which saturation may be present. The setting ∞ disables the saturation detec-
tor. This setting can only be modified with DIGSI
current transformer saturation is expected, the following equation may be used as a
thumb rule for this setting:
Setting value I-CTsat. Thres.
where
P
+
P
N
i
n' = n ·
------------------ -
= actual overcurrent factor (accuracy limit factor)
P'
+
P
i
P
= rated burden of the current transformer [VA]
N
P
= internal burden of the current transformer [VA]
i
P' = actual connected burden (protection device + connection cable)
ω = 2πf = system frequency
τ
= system time constant
N
In order to function optimally, several protection and supplementary functions require
information regarding the state of the circuit breaker. The device contains a circuit
breaker state recognition function which processes the status of the circuit breaker
auxiliary contacts as well as recognising switching operations, close and open, by
processing of measured values (refer also to Section 6.22).
In address 1130A the remaining current PoleOpenCurrent, which will definitely not
be exceeded when the circuit breaker pole is open, is set. If parasitic currents (e.g.
through induction) can be excluded when the circuit breaker is open, this setting may
be very sensitive. Otherwise this setting must be increased correspondingly. In most
cases the preset value is sufficient. This setting can only be modified with DIGSI
under "Additional Settings".
The remaining voltage PoleOpenVoltage which will definitely not be exceeded
when the circuit breaker pole is open, is set in address 1131A. Voltage transformers
are presumed to be on the line side. The setting should not be too sensitive because
of possible parasitic voltages (e.g. due to capacitive coupling). It must in any event be
set below the smallest phase-earth voltage which may be expected during normal op-
eration. The preset value is usually sufficient. This setting can only be modified with
®
DIGSI
4 under "Additional Settings".
The switch-on-to-fault action (seal-in) time SI Time all Cl. (address 1132A) de-
termines the action time of the protection functions enabled during energization of the
line (e.g. fast tripping high-current stage). This time is started by the internal circuit
breaker switching detection when it recognizes energization of the line or by the circuit
breaker auxiliary contacts and a binary input of the device to provide information that
the circuit breaker has closed. The time must therefore be greater than the tripping
time of the protection functions plus an additional backup reserve. This setting can
only be modified with DIGSI
x
2
-- -
------------------------ -
=
l
1
-------------- -
1
+
⁄
I
I
E
®
4 under "Additional Settings". If
n'
⋅
------------------- - I
=
ωτ
nom
1
+
N
®
4 under "Additional Settings".
EP
7SA6 Manual
C53000-G1176-C156-2
®
4
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