Total Block: Prevents any tap changer operation independently of the control
mode (automatic as well as manual).
Setting parameters for blocking that can be set in TR1ATCC or TR8ATCC under
general settings in PST/local HMI are listed in table
27.
Table 27: Blocking settings
Setting Values (Range) Description
OCBk
(automatically
reset)
Alarm
Auto Block
Auto&Man Block
When any one of the three HV currents exceeds the
preset value
IBlock
, TR1ATCC or TR8ATCC will be
temporarily totally blocked. The outputs IBLK and
TOTBLK or AUTOBLK will be activated depending on the
actual parameter setting.
OVPartBk
(automatically
reset)
Alarm
Auto&Man Block
UVPartBk
(automatically
reset)
Alarm
Auto&Man Block
UVBk
(automatically
reset)
Alarm
Auto Block
Auto&Man Block
If the busbar voltage U
B
falls below
Ublock
this blocking
condition is active. It is recommended to block automatic
control in this situation and allow manual control. This is
because the situation normally would correspond to a
disconnected transformer and then it should be allowed to
operate the tap changer before reconnecting the
transformer. The outputs UBLK and TOTBLK or
AUTOBLK will be activated depending on the actual
parameter setting.
RevActPartBk(auto
matically reset)
Alarm
Auto Block
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 URAISE 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 or
TR8ATCC temporarily.
Requirements for this blocking are:
• The load current must exceed the set value
RevActLim
• After an URAISE command, the measured busbar
voltage shall have a lower value than its previous
value
• The second requirement has to be fulfilled for two
consecutive URAISE commands
If all three requirements are fulfilled, TR1ATCC or
TR8ATCC automatic control will be blocked for raise
commands for a period of time given by the setting
parameter
tRevAct
and the output signal REVACBLK will
be set. The reversed action feature can be turned off/on
with the setting parameter
OperationRA
.
Table continues on next page
1MRK 504 169-UEN A Section 11
Control
Transformer protection RET650 2.2 IEC 215
Application manual
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