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2.10.1.3 Software Monitoring
Watchdog
For continuous monitoring of the program sequences, a time monitor is provided in the hardware (hardware
watchdog) that expires upon failure of the processor or an internal program, and causes a complete restart of
the processor system.
An additional software watchdog ensures that malfunctions during the processing of programs are discovered.
This also initiates a restart of the processor system.
If such a malfunction is not cleared by the restart, an additional restart attempt is begun. After three unsuccess-
ful restarts within a 30 second window of time, the device automatically removes itself from service and the red
„Error" LED lights up. The readiness relay drops out and indicates „device malfunction" with its normally closed
contact.
Offset Monitoring
This monitoring function checks all ring buffer data channels for corrupt offset replication of the analog/digital
transformers and the analog input paths using offset filters. Possible offset errors are detected using DC filters,
and the associated sampled values are corrected up to a specific limit. If this limit is exceeded, an indication is
generated (191 „Error Offset") and integrated into the warning group indication (160). As increased offset
values impair the measurements, we recommend sending the device to the OEM plant for corrective action
should this indication persist.
2.10.1.4 Monitoring of the Transformer Circuits
Open circuits or short circuits in the secondary circuits of the current and voltage transformers, as well as faults
in the connections (important during commissioning!), are detected and reported by the device. The measured
quantities are periodically checked in the background for this purpose, as long as no system fault is present.
Current Symmetry
During normal system operation, symmetry among the input currents is expected. The monitoring of the mea-
sured values in the device checks this balance. The smallest phase current is compared to the largest phase
current. Asymmetry is detected if | Imin | / | Imax | < BAL. FACTOR I as long as Imax > BALANCE I LIMIT
is valid.
Thereby Imax is the largest of the three phase currents and Imin the smallest. The symmetry factor BAL.
FACTOR I (address 8105) represents the allowable asymmetry of the phase currents while the limit value
(address 8104) is the lower limit of the operating range of this monitoring (see Figure 2-50). Both parameters
can be set. The dropout ratio is about 97 %.
This failure is thus located below the curve for all values and is reported as „Fail I balance".
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
Functions
2.10 Monitoring Functions
167
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