to the TCO input. If the signal is active (=TRUE) for more than 15 seconds after the
control pulse has been deactivated, an alarm is generated (
Chapter 9.10.5.11 Alarm
indication
). If the TCO input is not connected, no alarm is generated.
The control operation is disabled when the TCO input signal is active, unless no tap
changer stuck is detected (
Chapter 9.10.5.11 Alarm indication
). Thus, the controller
cannot send new pulses to the tap changer when this is already operating because
tap changers are typically immune to new pulses when they operate. Furthermore,
because the pulses are omitted, the tap changer pulse counter of the controller is
not incremented.
The commands are not tolerated during an active pulse. Therefore the command
pulse length (setting
LTC pulse time
) has to be carefully selected, although an
active TCO input is used internally to prevent new commands from reaching the tap
changer.
To be more certain that no new pulses are sent when the tap changer is in
operation, the tap changer operating signal can be connected to the LTC_BLOCK
input. In this case, external blocking is achieved when an automatic pulse is sent to
the operating tap changer. By default, the external LTC_BLOCK has no effect when
the active operation mode is set to "Manual" or "Parallel manual".
The status of the TCO input can be read from the TCO input data.
9.10.5.10 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 limits. The
BLK_STATUS monitored data 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
started due to a timer elapse or a local command. This is to avoid unnecessary event
sending.
The BLK_STATUS monitored data is also packed. It contains information about the
blocking status as bit-coded output. The block status output does not indicate
the actual blocking but indicates if the coming command is successful. The
actual blocking is indicated by the corresponding output (BLKD_I_LOD, BLKD_U_UN,
RNBK_U_OV, BLKD_LTCBLK, BLKD_I_CIR, BLK_RAISE and BLK_LOWER) values.
Table
1574
illustrates the meaning of different monitored data values. For example, block
status value 9 indicates that there are conditional circulating current and load
current blockings (8 + 1 = 9) indicated. By default, the status is “0”.
Table 1574: Bit-coded block status and the meaning of different bits
Bit Active value Blocking reason
6 (msb) 64 Lowest position reached
5 32 Highest position reached
4 16 External LTC_BLOCK
3 8 High circuit current
2 4 Overvoltage - Runback raise voltage
1 2 Undervoltage - Block lower voltage
0 (lsb) 1 Overcurrent - Load current
Control functions 1MRS759142 F
1716 REX640
Technical Manual
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