Functions
6-149
7SJ63 Manual
C53000-G1140-C120-1
current measured from a separate current transformer. If all four currents inputs are
connected, their digitized sum must be zero.
Faults in the current circuit are recognized if
I
F
=|i
a
+i
b
+i
c
+(k
N
⋅
i
g
)
| >
Σ
,7+5(6+2/'
⋅
I
N
+
Σ
,)$&725
⋅
I
max
The factor k
N
(= address
&71&73K
) takes into account a possible difference
in the neutral current transformer ratio.
Σ
,7+5(6+2/'
and
Σ
,)$&725
are pro-
grammable settings. The component
Σ
,)$&725
⋅
I
max
takes into account the allow-
able error of the input transformer, which can be especially large when high fault cur-
rent levels are present (Figure 6-61). The dropout ratio is about 97%. This malfunction
is reported as “
)DLOXUH
Σ
,
”.
Figure 6-61
Current Sum Monitoring
6.17.1.2 Software Monitoring
Watchdog
For continuous monitoring of the program sequences, a time monitor is provided in the
hardware (hardware watchdog) that runs upon failure of the processor or an internal
program, and causes a complete restart of the processor system.
An additional software watchdog ensures that malfunctions during the processing of
programs are discovered. This also initiates a restart of the processor system.
To the extent such a malfunction is not cleared by the restart, an additional restart at-
tempt is begun. After three unsuccessful restarts within a 30 second window of time,
the device automatically removes itself from service and the red “Error” LED lights up.
The readiness relay opens and indicates “device malfunction” with its normal contact.
Note:
Current sum monitoring is only in effect if the ground current for the line to be protect-
ed is connected.
I
F
I
N
I
max
I
N
Σ
,7+5(6+2/'
Increase:
Σ
,)$&725
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