Software Monitoring; Monitoring Of External Measuring Transformer Circuits - Siemens 7SV512 Instruction Manual

7SV512
V1
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 it with the newly determined modulus af-
ter each parameter assignment process.
4.5.4.2

Software monitoring

For continuous monitoring of the program se-
quences, a watchdog timer is provided which will re-
set the processor in the event of processor failure or
if a program falls out of step. Further, internal plausi-
bility checks ensure that any fault in processing of
the programs, caused by interference, will be recog-
nized. Such faults lead to reset and restart of the pro-
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:
Monitoring
1. Plausibility check of currents
|i + i + i + k
L1 L2 L3 I
SUM.Ithres x I + SUM.Fact.I x I
N
2. Current unbalance
|I |
min
< SYM.Fact.I
|I |
max
and |I | > SYM.Ithres
max
Bolted figures are setting values.
Table 4.1 Summary of measuring circuit monitoring
40
x i | ²
E
max
--- Current symmetry
In healthy operation it can be expected that the
currents will be approximately symmetrical. The
following applies:
|I | / |I
min max
if
/ I > SYM.Ithres / I
I
max N
is always the largest of the three phase cur-
I
max
rents and I always the smallest. The symmetry
min
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 of this monitoring function (see Figure 4.21).
Both parameters can be set (see Section 6.3.6).
I
min
I
max
SYM.Ithres
Figure 4.21 Current symmetry monitoring
Table 4.1 gives a survey of all the functions of the
measured value monitoring system.
Failure covered, reaction
Relay failures in the signal acquisition circuits
i , i , i , i
L1 L2 L3 E
delayed alarm "Failure
optionally blocking
Single, or phase-to-phase short circuits or broken
conductors in the c.t. circuits i
or
Unbalanced load
delayed alarm "Failure Isymm"
Method of operation
| < SYM.Fact.I
N
Slope:
SYM.Fact.I
I
max
I
N
I",
, i , i
L1 L2 L3
C53000---G1176---C91