Siemens SIPROTEC 4 7VK61, Manual

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Software Monitoring
Watchdog
For continuous monitoring of the program sequences, a time monitor is provided in the hardware (watchdog
for hardware) that expires upon failure of the processor or an internal program, and causes a reset of the
processor system with complete restart.
An additional software watchdog ensures that malfunctions during the processing of programs are discov-
ered. This also initiates a restart of the processor system.
If the fault is not eliminated by the restart, a second restart attempt is initiated. If the fault is still present after
three restart attempts within 30 s, the protection system will take itself out of service, and the red LED
“ERROR” lights up. The device ready relay drops out and alarms the device malfunction with its normally closed
contact(“Life-Contact”).
Monitoring External Transformer Circuits
Interruptions or short circuits in the secondary circuits of the current and voltage transformers, as well as
faults in the connections (important for commissioning!), are detected and reported by the device. To this
end, the measured values are cyclically checked in the background as long as no fault detection is present.
Current Symmetry
During normal system operation the currents are assumed to be largely symmetrical. The symmetry is moni-
tored in the device by magnitude comparison. The smallest phase current is compared to the largest phase
current. Asymmetry is recognized if:
|
Ι
min
| / |
Ι
max
| <
BAL. FACTOR I
as long as
Ι
max
>
BALANCE I LIMIT
Ι
max
is the highest,
Ι
min
the lowest of the three phase currents. The symmetry factor
BAL. FACTOR I
(address 2905) represents the allowable asymmetry of the phase currents while the limit value
BALANCE I
LIMIT
(address 2904) is the lower limit of the operating range of this monitoring (see Figure 2-50 ). The
dropout ratio is about 97 %.
After a settable time (5 s -100 s), this malfunction is signaled as
Fail I balance
(No. 163).
[stromsymmetrieueberwachung-020313-kn, 1, en_GB]
Figure 2-50 Current symmetry monitoring
Broken Conductor
A broken wire of the protected line or in the current transformer secondary circuit can be detected, if the
minimum current
PoleOpenCurrent
flows via the feeder. If the minimum phase current is below this limit
while the other phase currents are above this limit, an interruption of this conductor may be assumed. If
2.7.1.2
2.7.1.3
Functions
2.7 Monitoring Functions
SIPROTEC 4, 7VK61, Manual 133
C53000-G1176-C159-5, Edition 05.2018