ABB Relion 670 Series Applications Manual page 422

Section 15
Control
• Under-Voltage
• Command error
• Position indication error
• Tap changer error
• Reversed Action
• Circulating current
• Communication error
Master-follower method
When the master is blocked, the followers will not tap by themselves and there is consequently
no need for further mutual blocking. On the other hand, when a follower is blocked there is a
need to send a mutual blocking signal to the master. This will prevent a situation where the
rest of the group otherwise would be able to tap away from the blocked individual, and that
way cause high circulating currents.
Thus, when a follower is blocked, it broadcasts a mutual block on the horizontal
communication. The master picks up this message, and blocks its automatic operation as well.
Besides the conditions listed above for mutual blocking with the circulating current method,
the following blocking conditions in any of the followers will also cause mutual blocking:
• Master-follower out of position
• Master-follower error (No master/More than one master)
General
It should be noted that partial blocking will not cause mutual blocking.
TR8ATCC, which is the "source" of the mutual blocking will set its AUTOBLK output as well as
the output which corresponds to the actual blocking condition for example, IBLK for over-
current blocking. The other TR8ATCCs that receive a mutual block signal will only set its
AUTOBLK output.
The mutual blocking remains until TR8ATCC that dispatched the mutual block signal is de-
blocked. Another way to release the mutual blocking is to force TR8ATCC, which caused mutual
blocking to Single mode operation. This is done by activating the binary input SNGLMODE on
TR8ATCC function block or by setting the parameter
local HMI or PST.
TR8ATCC function can be forced to single mode at any time. It will then behave exactly the
same way as described in section
that horizontal communication messages are still sent and received, but the received
messages are ignored. TR8ATCC is at the same time also automatically excluded from the
parallel group.
Disabling of blockings in special situations
When the Automatic voltage control for tap changer TR1ATCC for single controland TR8ATCC
for parallel control, function block is connected to read back information (tap position value
and tap changer in progress signal) it may sometimes be difficult to find timing data to be set
in TR1ATCCor TR8ATCC for proper operation. Especially at commissioning of for example,
older transformers the sensors can be worn and the contacts maybe bouncing etc. Before the
right timing data is set it may then happen that TR1ATCCor TR8ATCC becomes totally blocked
or blocked in auto mode because of incorrect settings. In this situation, it is recommended to
temporarily set these types of blockings to alarm instead until the commissioning of all main
items are working as expected.
Tap Changer position measurement and monitoring
416
"Automatic voltage control for a single
© Copyright 2017 Hitachi Power Grids. All rights reserved
OperationPAR to Off from the built-in
transformer", except
1MRK 511 401-UEN Rev. K
SEMOD159053-329 v5
SEMOD159053-337 v2
Bay control REC670
Application manual