Method of operation7SV512
V1
40
C53000---G1176---C91
D Formation of the modulus for the program
memory (EPROM) and comparison of it with a
reference program modulus stored there,
D Formation of the modulus of the values stored
in the parameter store (EEPROM) then com-
paring itwith the newly determined modulus af-
ter each parameter assignment process.
4.5.4.2 Software monitoring
For continuous monitoring of the program se-
quences, awatchdog timer is provided which willre-
set the processor in the event ofprocessor failure or
if a program falls out of step. Further, internal plausi-
bility checks ensure that any fault in processing of
the programs, caused byinterference, willberecog-
nized. Suchfaults lead toreset and restart ofthepro-
cessor system.
If such a fault is not eliminated by restarting, further
restarts are initiated. If the fault is still present after
three restart attempts within 30 s the protective sys-
tem will switch itself out of service and indicate this
condition by drop-off of the availability relay, thus in-
dicating ”equipment fault” and simultaneously the
LED ”Blocked” comes on.
4.5.4.3 Monitoring of external measuring
transformer circuits
To detect interruptions or short circuits in the exter-
nal measuring transformer circuits or faults in the
connections (an important commissioning aid) the
measured values are checked at cyclic intervals, as
long as no pick-up condition exists:
--- Current symmetry
In healthy operation it can be expected that the
currents will be approximately symmetrical. The
following applies:
|I
min
| / |I
max
| < SYM.Fact.I
if
I
max
/ I
N
> SYM.Ithres / I
N
I
max
is always the largest of the three phase cur-
rents and I
min
always the smallest. The symmetry
factor SYM.Fact.I represents the magnitude of
asymmetry of the phase currents, and the thresh-
old SYM.Ithres is the lower limit of the processing
area ofthis monitoring function (see Figure 4.21).
Both parameters can be set (see Section 6.3.6).
SYM.Ithres
Slope:
SYM.Fact.I
I
min
I
max
I
max
I
N
Figure 4.21 Current symmetry monitoring
Table 4.1 gives a survey of all the functions of the
measured value monitoring system.
< SYM.Fact.I
and |I
max
| > SYM.Ithres
|I
max
|
|I
min
|
Relay failures in the signal acquisition circuits
delayed alarm ”Failure I”,
optionally blocking
1. Plausibility check of currents
|i
L1
+ i
L2
+ i
L3
+ k
I
x i
E
| ²
SUM.Ithres x I
N
+ SUM.Fact.I x I
max
2. Current unbalance
i
L1
, i
L2
, i
L3
, i
E
Single, or phase-to-phase short circuits or broken
conductors in the c.t. circuits i
L1
, i
L2
, i
L3
or
Unbalanced load
delayed alarm ”Failure Isymm”
Monitoring Failure covered, reaction
Bolted figures are setting values.
Table 4.1 Summary of measuring circuit monitoring
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