2 Functions
316
7SA522 Manual
C53000-G1176-C155-3
This malfunction is signaled as ´)DLOΣ83K(µ (FNo. 165).
Note
Voltage sum monitoring can operate properly only when an externally formed open
delta voltage is connected to the residual voltage input of the relay.
2.19.1.2 Software Monitoring
Watchdog For continuous monitoring of the program sequences, a time monitor is provided in the
hardware (watchdog for hardware) that expires upon failure of the processor or an in-
ternal 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. 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 (“life contact”).
2.19.1.3 External Transformer Circuits
Interruptions or short circuits in the secondary circuits of the current transformers or
voltage transformers, as well as faults in the connections (important for commission-
ing!), are detected and reported by the device. The measured quantities are periodi-
cally checked in the background for this purpose, as long as no system fault is present.
Current
Symme try
During normal system operation (i.e. the absence of a short-circuit fault), symmetry
among the input currents is expected. The symmetry is monitored in the device with a
magnitude comparison. The smallest phase current is compared to the largest phase
current. Asymmetry is recognized if:
| I
min
| / | I
max
| < %$/)$&725, as long as I
max
/ I
N
> %$/$1&(,/,0,7 / I
N
Thereby I
max
is the largest of the three phase currents and I
min
the smallest. The sym-
metry factor %$/)$&725, represents the allowable asymmetry of the phase cur-
rents while the limit value %$/$1&(,/,0,7 is the lower limit of the operating range
of this monitoring (see Figure 2-139). Both parameters can be set. The dropout ratio
is about 97%.
After a settable time (5-100 s) this malfunction is signaled as ´)DLO,EDODQFHµ
(FNo. 163).
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