R.8.9
Date Code 20111215 Reference Manual SEL-421 Relay
IEC 61850 Communications
IEC 61850 Operation
Time Stamps and
Quality
In addition to the various data values, the two attributes quality and t (time
stamp) are available at any time. The timestamp is determined when data or
quality change is detected. A change in the quality attribute can also be used to
issue an internal event.
The timestamp is applied to all data and quality attributes (Boolean, Bstrings,
Analogs, etc.) in the same fashion when a data or quality change is detected.
However, there is a difference in how the change is detected between the
different attribute types. For points that are assigned as SER points, i.e., listed
in the SER dataset, the change is detected as the receipt of an SER record
(which contains the SER timestamp) from the relay to the card. For all other
Booleans or Bstrings, the change is detected via the scanner, which compares
the last state against the previous state to detect the change. For analogs, the
scanner looks at the amount of change relative to the deadband configured for
the point to indicate a change and apply the timestamp. In all cases, these
timestamps are used for the reporting model.
The SEL-421 has predetermined LN data attributes that are available with
SER quality timestamps. These data attributes are listed in the SER dataset in
the default relay ICD file. Modifications to this dataset do not modify which
data attributes have SER quality timestamps. If your application requires SER
quality timestamps on data attributes not in this dataset, contact SEL for
possible modification to your relay default configuration.
LN data attributes listed in the SER dataset have SER accurate timestamps of
1 ms for data change events. All other LN data attributes are scanned on a
1/2-second interval for data change and have 1/2-second timestamp accuracy.
The SEL-421 uses GOOSE quality attributes to indicate the quality of the data
in its transmitted GOOSE messages. Under normal conditions, all attributes
are zero, indicating good quality data. Figure 8.3 shows the GOOSE quality
attributes available to devices that subscribe to GOOSE messages from
SEL-421 datasets that contain them. Internal status indicators provide the
information necessary for the device to set these attributes. For example, if the
device becomes disabled, as shown via status indications (e.g., an internal
self-test failure), the SEL-421 will set the Validity attribute to invalid and the
Failure attribute to TRUE. Note that the SEL-421 does not set any of the other
quality attributes. These attributes will always indicate FALSE (0). See the
ACSELERATOR Architect online help for additional information on GOOSE
Quality attributes.
Figure 8.3 GOOSE Quality
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