Software-Monitoring; Monitoring Of The External Instrument Transformer Circuits - Siemens siprotec 7SA522 User Manual

Functions
6.16.1.2 Software–Monitoring
Watchdog

6.16.1.3 Monitoring of the External Instrument Transformer Circuits

Current Symmetry
6-218
For the continuous monitoring of the program execution, a time monitoring is incorpo-
rated 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 detect-
ed. This watchdog also initiates a reset of the processor.
If a fault is not removed by the restart of the processors, 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 de-
vice failure state with its normally closed contact.
Interruptions or short circuits in the secondary circuits of the current and voltage trans-
formers, as well as incorrect terminations (important during commissioning) are large-
ly recognized by the device and alarmed. To this end, the measured values are cycli-
cally checked in the background as long as no fault detection is present.
During normal system operation, a certain degree of current symmetry can be as-
sumed. 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
| < %$/ )$&725 ,
|I | / |I
min max
as long as / I
I
max N
is the largest and I
I
max
factor %$/ )$&725 , is a measure of the phase conductor non-symmetry, the
threshold value %$/$1&( , /,0,7 represents the lower limit of the operating range
of this monitoring function (refer to Figure 6-115). Both parameters can be set. The
reset ratio is approx. 97 %.
This failure is alarmed by ")DLO , EDODQFH".
I
min
I
N
76G6I8@ÃDÃGDHDU
Figure 6-115 Current symmetry monitoring
> %$/$1&( , /,0,7 / I
is the smallest of the three phase currents. The symmetry
min
slope:
76GÃA68UPSÃD
I
max
I
N
N
7SA522 Manual
C53000-G1176-C119-2