Functions
6-2557SA6 Manual
C53000-G1176-C133-1
6.19.1.2 Software–Monitoring
Watchdog For the continuous monitoring of the program execution, a time monitoring is
incorporated in the hardware (hardware watchdog). The watchdog expires and resets
the processor system causing a complete reboot if the processor fails or when a
program loses synchronism.
A further software–watchdog ensures that errors in the program execution are
detected. This watchdog also initiates a reset of the processor.
If a fault is not removed by the restart of the processor system, a new restart is
attempted. Following three failed restarts within 30 s the protection takes itself out of
service and the red LED “ERROR” is illuminated. The device ready relay resets and
alarms the device failure state with its normally closed contact.
6.19.1.3 Monitoring of the External Instrument Transformer Circuits
Interruptions or short circuits in the secondary circuits of the current and voltage
transformers, as well as incorrect terminations (important during commissioning) are
largely recognized by the device and alarmed. 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, a certain degree of current symmetry can be
assumed. This symmetry is checked in the device by means of a magnitude
monitoring. The smallest phase current is compared with the largest. Non-symmetry
is detected when
|I
min
| / |I
max
|<%$/)$&725,
as long as I
max
/ I
N
> %$/$1&(,/,0,7 / I
N
I
max
is the largest and I
min
is the smallest of the three phase currents. The symmetry
factor %$/)$&725, is a measure of the phase conductor non-symmetry, the
threshold value %$/$1&(,/,0,7 represents the lower limit of the operating range
of this monitoring function (refer to Figure 6-131). Both parameters can be set. The
reset ratio is approx. 97 %.
This failure is alarmed by “)DLO,EDODQFH”.
Figure 6-131 Current symmetry monitoring
I
min
I
N
slope:
I
max
I
N
%$/$1&(,/,0,7
%$/)$&725,
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