Siemens Siprotec 7UM611 Manual page 168

2 Functions
Note
Voltage sum monitoring is only effective if an external displacement voltage is con-
nected at the displacement voltage measuring input and this is also notified via the pa-
rameter 223 UE CONNECTION to the device.
Voltage sum monitoring can operate properly only if the adaptation factor Uph /
Udelta at address 225 has been correctly configured (see Section 2.3.1).
Figure 2-63
Software Monitorings
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 inter-
nal 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 discovered. This also initiates a restart of the processor system.
To the extent such a malfunction is not cleared by the restart, an additional restart
attempt is begun. After three unsuccessful restarts within a 30 second window of time,
the device automatically removes itself from service and the red "Fault" LED lights up.
The operational readiness relay ("Life contact") opens and issues an indication (alter-
natively as NO or NC contact).
Monitoring External Transformer Circuits
Interruptions or short circuits in the secondary circuits of the current and voltage trans-
formers, as well as faults in the connections (important for commissioning!), are de-
tected and reported by the device. The measured quantities are cyclically checked in
the background for this purpose, as long as no system fault is present.
Current Symmetry During normal system operation a certain degree of symmetry of the currents is ex-
pected. The symmetry is monitored in the device by magnitude comparison. The
smallest phase current is compared to the largest phase current. Asymmetry is recog-
nised if
| I
168
Voltage Sum Monitoring
| < BAL. FACTOR I as long as I
| / | I
min max
> BALANCE I LIMIT / I
/ I
max N
C53000-G1176-C127-3
N
7UM61 Manual