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16.8
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
DNP3 Communication
DNP3 in the Relay
NOTE:
Because unsolicited
messaging only operates properly in
some situations, for maximum
performance and minimum risk of
configuration problems, SEL
recommends the polled report-by-
exception access method.
In both the unsolicited report-by-exception and quiescent polling methods shown
in
, you must make a selection for the PUNSOL setting. This setting
enables or disables unsolicited data reporting when you turn the relay on. If your
master can send the DNP3 message to enable unsolicited reporting from the
relay, you should set PUNSOL to No.
NOTE:
The DNP3 LAN/WAN settings
have names similar to the serial port
settings above, but include the session
number n as a suffix ranging from 1 to
6 (for example, CLASSB1, UNSOL1,
PUNSOL1). All settings with the same
numerical suffix comprise the
complete DNP3 LAN/WAN session
configuration.
While automatic unsolicited data transmission on power-up is convenient, prob-
lems can result if your master is not prepared to start receiving data immediately
when you turn on the relay. If the master does not acknowledge the unsolicited
data with an application confirm, the relay will resend the data until it is acknowl-
edged. On a large system, or in systems where the processing power of the master
is limited, you may have problems when several outstations simultaneously begin
sending data and waiting for acknowledgment messages.
Collision Avoidance
If your application requires unsolicited reporting from multiple devices on a sin-
gle (serial) network medium, you must select a half-duplex medium or a medium
that supports carrier detection to avoid data collisions. EIA-485 two-wire net-
works are half-duplex. EIA-485 four-wire networks do not provide carrier detec-
tion.
The relay uses application confirmation messages to guarantee delivery of unso-
licited event data before erasing the local event data buffer. Data collisions are
typically resolved when messages are repeated until confirmed.
The relay pauses for a random delay between the settings MAXDLY and
MINDLY when it detects a carrier through data on the receive line or the CTS
pin. If you use the settings of 0.10 seconds for MAXDLY and 0.05 seconds for
MINDLY, the relay will insert a random delay of 50 to 100 ms (milliseconds)
between the end of carrier detection and the start of data transmission.
Transmission Control
If you use a media transceiver (for example, EIA-232 to EIA-485) or a radio sys-
tem for your serial DNP3 network, you may need to adjust data transmission
properties. Use the PREDLY and POSTDLY settings to provide a delay between
RTS signal control and data transmission. For example, an EIA-485 transceiver
typically requires 10–20 ms to change from receive to transmit. If you set the pre-
delay to 30 ms, you will avoid data loss resulting from data transmission begin-
ning at the same time as RTS signal assertion.
Table 16.6
DNP3 Access Methods
Access Method
Master Polling
Relay Settings
Polled static
Class 0
Set ECLASSB, ECLASSC, ECLASSA,
ECLASSV to OFF, UNSOL to N.
Polled report-by-
exception
Class 0 occasionally, Class 1,
2, 3 frequently
Set ECLASSB, ECLASSC,
ECLASSA, ECLASSV to the desired
event class, UNSOL to N.
Unsolicited report-
by-exception
Class 0 occasionally, optional
Class 1, 2, 3 less frequently,
mainly relies on unsolicited
messages
Set ECLASSB, ECLASSC,
ECLASSA, ECLASSV to the desired
event class, set UNSOL to Y and PUN-
SOL to Y or N.
Quiescent
Class 0, 1, 2, 3 never, relies
completely on unsolicited
messages
Set ECLASSB, ECLASSC, ECLASSA,
ECLASSV to the desired event class, set
UNSOL and PUNSOL to Y.
Summary of Contents for SEL-421-4
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