'(& )( )'& &) ( &!& ")& &$(( $# Ć %&( $# #)" &&#$
4 - 32
Siemens AG ⋅ May 1998
!
The instantaneous values of the measured quantities
are sampled every 1 ms and stored in a cyclic buffer
in the master unit.
D Instantaneous values of the currents in all bays
(per phase)
D Differential and stabilizing currents of all busbar
sections and of the check zone. (per phase)
After starting the fault recording (through a busbar
short-circuit, via binary input or by operation)
), the data are stored from 200 ms before up
to 100 ms after the trip command. The master unit
stores up to two fault records.
This data can be read out locally by means of a PC
and evaluated using the DIGSI software.
Via parameters the mode of release of
the fault record buffer is defined. With "automatic
release" the last fault is recorded and available for
read-out. Each new fault record overwrites the preĆ
vious one.
With "manual release" for the last two faults each
record is stored. The fault record buffer has to be eraĆ
sed and thus "released" for writing new records after
reading out the data.
The release can be effected through the communicaĆ
tion program DIGSI, the integrated keypad
( ) or via binary input.
!
The protection system 7SS52 incorporates compreĆ
hensive self-monitoring functions which cover both
the hardware and the software. This guarantees a
high availability and security against overfunctioning
and underfunctioning as well as low demand on mainĆ
tenance.
"
The complete protection system is cyclicly monitored
from the measuring inputs through the data commuĆ
nication between master unit and bay units up to the
command relay coils.
Monitoring circuits and processors monitor the hardĆ
ware for faults and impermissible conditions. Details
are as follows:
D Auxiliary and reference voltages.
The processor of the bay unit monitors the offset and
reference voltages. The protection is blocked as soon
as impermissible deviations occur; permanent faults
are annunciated.
The DC-DC converter voltages in the master unit and
bay units are also monitored by the converters themĆ
selves and faults are annunciated. Failure or disconĆ
nection of the auxiliary voltage automatically takes the
affected device out of service; this status is annunĆ
ciated via a NC contact. Transient auxiliary voltage
dips of up to 50 ms will not influence the unit.
Failure of the auxiliary voltage in a bay unit results in
blocking of the protection system.
D Measured value monitoring
The analog input circuits of the bay unit are cyclicly
monitored from the input transducers up to the digitiĆ
zation. This is done by forming the current sum and
executing the following plausibility check:
Dāāāi =i
L1
+i
L2
+i
L3
+i
E
S IiI=Ii
L1
I+Ii
L2
I+Ii
L3
I+Ii
E
I
The measured value monitoring picks up if
I Dāāāi I>āāāI>MV-MONIT ( ) and
I Dāāāi I>kxS IiI
k = 0,125 (stabilizing factor)
The pick-up characteristic is shown in figure 4.31.
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