Software Monitoring; Monitoring Of The Transformer Circuits - Siemens siprotec SJ62 User Manual

Scanning

2.11.1.3 Software Monitoring

Watchdog
Offset Monitoring

2.11.1.4 Monitoring of the Transformer Circuits

Measurement Value
Acquisition – Cur-
rents
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Scanning and the synchronization between the internal buffer components are con-
stantly monitored. If any deviations cannot be removed by renewed synchronization,
then the processor system is restarted.
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 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 unsuccessful restarts within a 30 second window of time, the device
automatically removes itself from service and the red „Error" LED lights up. The readi-
ness relay drops out and indicates „device malfunction" with its normally closed con-
tact.
This monitoring function checks all ring buffer data channels for corrupt offset replica-
tion of the analog/digital transformers and the analog input paths using offset filters.
The eventual 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 indication is
issued (191 „Error Offset") that is part of the warn group annunciation (annunci-
ation 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 annunci-
ation continuously occurs.
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.
Up to four input currents are measured by the device. If the three phase currents and
the ground fault current from the current transformer star point or a separated ground
current transformer of the line to be protected are connected to the device, their digi-
tised sum must be zero. Faults in the current circuit are recognised if
= | i + i + i + k · i
I
F A B C I
The factor k takes into account a possible difference in the neutral current transformer
I
(e.g. toroidal current transformer see addresses 217, 218, 204 and 205):
ratio I
N
Σ I THRESHOLD and Σ I FACTOR are programmable settings. The component Σ I
FACTOR · Imax takes into account the permissible current proportional ratio errors of
the input transformer which are particularly prevalent during large short-circuit cur-
rents (Figure 2-58). The dropout ratio is about 97 %. This malfunction is reported as
„Failure Σ I".
| > Σ I THRESHOLD · I
N
2.11 Monitoring Functions
+ Σ I FACTOR · I
Nom max
186