ABB REU 610 Technical Reference Manual page 84

REU 610
84
Voltage Relay
Technical Reference Manual
Event buffer overflow
DNP 3.0 event buffer overflow is indicated with the internal indication IIN2.3, as
defined by the standard. IIN2.3 can also indicate event buffer overflow in the
internal communication between the DNP3.0 module and the main CPU module of
the relay. In this case, the relay automatically activates and resets the IIN2.3 bit.
As events have been lost in both cases, the DNP 3.0 master should perform an
integrity scan after the IIN2.3 bit has been reset.
DNP counters and frozen counters
DNP counters in use have a corresponding frozen counter. The frozen counters in
object group 21 have the same DNP point index as the ordinary DNP counters.
Further, frozen counters can only be read as static objects, and frozen counter events
(object group 23) are not supported.
Collision avoidance and detection
The relay supports both collision avoidance and detection. Collision detection can
be enabled or disabled with SPA parameter 503V235. Collision avoidance occurs
before message transmission. When preparing to transmit and the link is busy, the
relay first waits until the link becomes idle. After this, a backoff time starts. When
the backoff time elapses, the relay checks the link again. If the link is not busy, the
relay starts the transmission. The backoff time is calculated as follows:
backoff time = silent interval + random delay
The silent interval is set with SPA parameter 503V232 and the maximum random
delay with SPA parameters 503V233 (the width of a single time slot in
milliseconds) and 503V234 (the maximum number of time slots). By setting the
time-slot width to 10 milliseconds and the maximum number of time slots to 10, for
instance, the maximum random delay is 100 milliseconds.
In a network consisting of several slaves, the priority between the
devices are defined with SPA parameters 503V233 and 503V234. A
device with shorter silent interval and maximum random delay has
higher sending priority than a device with longer silent interval and
maximum random delay.
Collision detection is always active during transmission (provided that it has been
enabled). While sending a message, the relay supervises collisions on the link. If a
collision is detected, the transmission is immediately cancelled. After this, the relay
tries to transmit the message again, using collision avoidance before sending the
message.
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