LTC_BLOCK input. In this case, the external blocking is achieved when an
automatic pulse is sent to the operating tap changer. The external LTC_BLOCK has
by default no effect when the acting operation mode is set to "Manual".
The status of the TCO input can be read from the TCO input data.
9.5.13 Blocking scheme
The operation of the voltage regulator can be blocked for several reasons. The
purpose of blocking is to prevent the tap changer from operating under conditions
that can damage the tap changer or exceed other power system-related limits. There
is the BLK_STATUS monitored data that does not imply actual blocking but
reveals if the coming command pulse is issued or not. The blocking itself happens
when the corresponding bit in the signal BLK_STATUS is active and the command
pulse is to be started due to a timer elapse or a local command. This is to avoid
unnecessary event sending.
The cross (X) in the table defines when the operation is blocked (if the
corresponding bit is active in BLK_STATUS). For example, an overvoltage
(runback raising voltage) results in blocking only when the acting operation mode
is "Manual" and the manual raising command is to be given.
Table 629: Default blocking schema in OLATCC
Acting
operation
mode
Command Load
current
Block
lowering
voltage
Runback
raising
voltage
High
circulating
current
External
Block
Extreme
positions
Manual Raise X X X
Lower X X
Auto
follower
Raise X X X X
Lower X X X X
Auto
single,
Auto
master,
NRP,
MCC
Raise X X
X
1)
X
X
2)
Lower X X
X
1)
X
X
2)
1) Because the circulating current is only calculated in the NRP and MCC modes, it can have a
blocking effect only in these modes.
2) However, in these cases pure automatic operation notices that the extreme position has already
been reached and there is no need to activate the signal for data set event sending. The automatic
follower case can here be compared to a manual case and an event can be sent, that is, the
corresponding output is activated.
In addition to the default blocking, the Custom Man blocking setting has been
added due to different operation practices considering the manual command
blocking. The setting can be used to adapt blockings considering the manual
overcurrent, undervoltage or external blocking. (The blockings are in the table in
columns Load current, Block lowering voltage and External block for the manual
operating mode.) The default value for the parameter is "OC". This means that the
Section 9 1YHT530004D05 D
Control functions
746 615 series
Technical Manual
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