Functions
2.5 Monitoring Functions
SIPROTEC, 7RW80, Manual
C53000-G1140-C233-1, Release date 10.2010
69
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.
2.5.1.3
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. Any possible offset errors are detected using DC
voltage filters and the associated samples are corrected up to a specific limit. If this limit is exceeded, an an-
nunciation is issued (191
„Error Offset“
) that is part of the warn group annunciation (annunciation 160).
As increased offset values affect the reliability of measurements taken, we recommend to send the device to
the OEM plant for corrective action if this annunciation continuously occurs.
2.5.1.4
Monitoring of the Transformer Circuits
Interruptions or short-circuits in the secondary circuits of the voltage transformers, as well as faults in the con-
nections ( important for 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.
Voltage Symmetry
During normal system operation, balance among the voltages is expected. Since the phase-to-phase voltages
are insensitive to ground faults, the phase-to-phase voltages are used for balance monitoring. If the device is
connected to the phase-to-ground voltages, then the phase-to-phase voltages are calculated accordingly,
whereas, if the device is connected to phase-to-phase voltages and the displacement voltage V
0
, then the third
phase-to-phase voltage is calculated accordingly. From the phase-to-phase voltages, the device generates the
rectified average values and checks the balance of their absolute values. The smallest phase voltage is com-
pared with the largest phase voltage.
Asymmetry is recognized if
| V
min
| / | V
max
| <
BAL. FACTOR V
as long as | V
max
| >
BALANCE V-LIMIT
. Where V
max
is the highest of the
three voltages and V
min
the smallest. The symmetry factor
BAL. FACTOR V
(address
8103
) represents the
allowable asymmetry of the conductor voltages while the limit value
BALANCE V-LIMIT
(address
8102
) is the
lower limit of the operating range of this monitoring (see Figure 2-13). Both parameters can be set. The dropout
ratio is about 97%.
This fault is signalled after settable delay time with
„Fail V balance“
.
