R.6.7
Date Code 20111215 Reference Manual SEL-421 Relay
DNP3 Communications
DNP3 in the SEL-421
With the event class settings ECLASSB, ECLASSC, ECLASSA, and
ECLASSV you can set the event class for binary, counter, analog, and virtual
terminal information. You can use the classes as a simple priority system for
collecting event data. The relay does not treat data of different classes
differently with respect to unsolicited messages, but the relay does allow the
master to perform independent class polls.
NOTE: Most RTUs that act as
substation DNP masters perform an
event poll that collects event data of
all classes simultaneously. Confirm
that the polling configuration of your
master allows independent polling for
each class before implementing
separate classes in the SEL-421.
For event data collection you must also consider and enter appropriate settings
for dead band and scaling operation on analog points shown in Table 6.6. You
can either set and use default dead band and scaling according to data type or
use a custom data map to select dead bands on a point-by-point basis. See
Configurable Data Mapping on page R.6.10 for a discussion of how to set
scaling and dead-band operation on a point-by-point basis.
The settings ANADBA, ANADBV, and ANADBM control default dead-band
operation for the specified data type. Because DNP Objects 30 and 32 use
integer data, you must use scaling to send digits after the decimal point and
avoid rounding to a simple integer value.
With no scaling, the value of 12.632 would be sent as 13. With a scaling
setting of 1, the value transmitted is 126. With a scaling setting of 3, the value
transmitted is 12632. You must make certain that the maximum value does not
exceed 32767 if you are polling the default 16-bit variations for Objects 30
and 32, but you can send some decimal values using this technique. You must
also configure the master to perform the appropriate division on the incoming
value to display it properly.
Set the default analog value scaling with the DECPLA, DECPLV, and
DECPLM settings. Application of event reporting dead bands occurs after
scaling in the DECPLA, DECPLV, and DECPLM. For example, if you set
DECPLA to 2 and ANADBA to 10, a measured current of 10.14 amps would
be scaled to the value 1014 and would have to increase to more than 1024 or
decrease to less than 1004 (a deadband of 0.2 amps) for the relay to report a
new event value.
The relay uses the NUMEVE and AGEEVE settings to decide when to send
unsolicited data to the master. The relay sends an unsolicited report when the
total number of events accumulated in the event buffer reaches NUMEVE.
The relay also sends an unsolicited report if the age of the oldest event in the
buffer exceeds AGEEVE. The SEL-421 has the buffer capacities listed in
Tab le 6.5.
Binary Controls
The SEL-421 provides more than one way to control individual points within
the relay. The relay maps incoming control points either to remote bits within
the relay or to internal command bits that cause circuit breaker operations.
Tab le 6.15 and Table 6.16 list control points and control methods available in
the SEL-421.
Table 6.5 SEL-421 Event Buffer Capacity
Type Maximum Number of Events
Binary 1024
Analog 256
Counters 128
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