ABB RET670 Applications Manual page 689

1MRK504116-UUS C
Application manual
The following conditions in any one of TR8ATCCs (90) in the group will cause mutual
blocking when the circulating current method is used:
• Over-Current
• Total block via settings
• Total block via configuration
• Analog input error
• Automatic block via settings
• Automatic block via configuration
• 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 (90), 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 (90) that receive a
mutual block signal will only set its AUTOBLK output.
Section 3
IED application
683