Observe that this parameter must be set to Off for the “own” transformer. (for
transformer with identity T1 parameter T1RXOP must be set to Off, and so on.
Blocking
Blocking conditions
The purpose of blocking is to prevent the tap changer from operating under conditions
that can damage it, or otherwise when the conditions are such that power system
related limits would be exceeded or when, for example the conditions for automatic
control are not met.
For the Automatic voltage control for tap changer function, TR1ATCC for single
control and TR8ATCC for parallel control, three types of blocking are used:
Partial Block: Prevents operation of the tap changer only in one direction (only
URAISE or ULOWER command is blocked) in manual and automatic control mode.
Auto Block: Prevents automatic voltage regulation, but the tap changer can still be
controlled manually.
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 59.
Table 59: 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
If the busbar voltage U
B
(not the compensated load point
voltage UVL) exceeds
Umax
(see figure 282), an alarm will
be initiated or further URAISE commands will be blocked. If
permitted by setting in PST configuration, Fast Step Down
(FSD) of the tap changer will be initiated in order to re-enter
the voltage into the range
Umin
< U
B
<
Umax
. The FSD
function is blocked when the lowest voltage tap position is
reached. The time delay for the FSD function is separately
set. The output UHIGH will be activated as long as the
voltage is above
Umax
.
UVPartBk
(automatically
reset)
Alarm
Auto&Man Block
If the busbar voltage U
B
(not the compensated load point
voltage U
L
) is between
Ublock
and
Umin
(see figure282), an
alarm will be initiated or further ULOWER commands will be
blocked. The output ULOW will be activated.
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.
Table continues on next page
1MRK 502 071-UEN - Section 15
Control
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 571
Application manual
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