Software Monitoring; Monitoring Of The External Transformer Circuits - Siemens SIPROTEC 4 7SJ61 Manual

[7sj6x-stromsummenueberw-20070315, 1, en_US]
Figure 2-44
AD Transformer Monitoring
The digitized sampled values are being monitored in respect of their plausibility. If the result is not plausible,
message 181 Error A/D-conv. is issued. The protection is blocked, thus preventing unwanted operation.
Furthermore, a fault record is generated for recording of the internal fault.
2.8.1.3

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 discov-
ered. 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 unsuc-
cessful 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.
2.8.1.4

Monitoring of the External 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
measured values in the device checks this balance. The smallest phase current is compared to the largest
phase current. Asymmetry is detected if | Ιmin | / | Ιmax | < BAL. FACTOR I as long as Ιmax > BALANCE I
LIMIT is valid.
SIPROTEC 4, 7SJ61, Manual
C53000-G1140-C210-6, Edition 05.2016
Logic Diagram of the fast current sum monitoring
Functions
2.8 Monitoring Functions
123