ABB RET670 Applications Manual page 684

Section 3
IED application
678
Setting Values (Range)
RevActPartBk(auto Alarm
matically reset) Auto Block
CmdErrBk Alarm
(manually reset) Auto Block
Auto&Man Block
Table continues on next page
Description
The risk of voltage instability increases as transmission
lines become more heavily loaded in an attempt to
maximize the efficient use of existing generation and
transmission facilities. In the same time lack of reactive
power may move the operation point of the power
network to the lower part of the P-V-curve (unstable part).
Under these conditions, when the voltage starts to drop, it
might happen that an VRAISE command can give
reversed result that is, a lower busbar voltage. Tap
changer operation under voltage instability conditions
makes it more difficult for the power system to recover.
Therefore, it might be desirable to block TR1ATCC (90) or
TR8ATCC (90) temporarily.
Requirements for this blocking are:
• The load current must exceed the set value
RevActLim
• After an VRAISE command, the measured busbar
voltage shall have a lower value than its previous
value
• The second requirement has to be fulfilled for two
consecutive VRAISE commands
If all three requirements are fulfilled, TR1ATCC (90) or
TR8ATCC (90) automatic control will be blocked for raise
commands for a period of time given by the setting
tRevAct and the output signal REVACBLK will
parameter
be set. The reversed action feature can be turned off/on
OperationRA .
with the setting parameter
Typical operating time for a tap changer mechanism is
around 3-8 seconds. Therefore, the function should wait
for a position change before a new command is issued.
The command error signal, CMDERRAL on the
TCMYLTC or TCLYLTC (84) function block, will be set if
the tap changer position does not change one step in the
correct direction within the time given by the setting
tTCTimeout in TCMYLTC or TCLYLTC (84) function
block. The tap changer module TCMYLTC or TCLYLTC
(84) will then indicate the error until a successful
command has been carried out or it has been reset by
changing control mode of TR1ATCC (90) or TR8ATCC
(90) function to Manual and then back to Automatic. The
outputs CMDERRAL on TCMYLTC or TCLYLTC (84) and
TOTBLK or AUTOBLK on TR1ATCC (90) or TR8ATCC
(90) will be activated depending on the actual parameter
setting.
This error condition can be reset by the input RESETERR
on TCMYLTC (84) function block, or alternatively by
changing control mode of TR1ATCC (90) or TR8ATCC
(90) function to Manual and then back to Automatic.
1MRK504116-UUS C
Application manual