VCG202/EN M/H11
Technical
The remote selection of AUTO and MANUAL modes can only be made when link [SD1] is
set to ‘1’ or the REMOTE opto-input is energised.
When switched from a locally selected mode to remote, the relay remains in the last
locally selected mode until a new mode is selected remotely. The operating modes of
AUTO and MANUAL are memorised, so that the relay will revert to the last selected
mode following an auxiliary power supply interruption.
Three opto inputs AUTO, MANUAL and REMOTE can be used for local operating mode
selection. AUTO and MANUAL select tap change control in service and REMOTE
enables remote control of AUTO or MANUAL modes.
In ‘MANUAL’ mode, the tap change initiating signal is independent of the voltage at the
remote end and does not take line drop compensation or circulating current
compensation into account. Also, the delay timer is reset instantaneously and runaway
protection is disabled as long as MANUAL mode is selected but all other relay functions
work as normal. If external switching is used to tap the transformer rather than the relay
whilst it is in MANUAL mode then the relay will ignore the start position when it is turned
to AUTO mode thus preventing a runaway alarm.
In ‘MANUAL’ operating mode, three options are available - Block the tap change, Raise
voltage or Lower voltage. After each tap change operation has been signaled the
selection will automatically return to the idle condition.
Two output relay masks for ‘Manual Mode’ and ‘Auto Mode’ are provided to allow an
external indication of the operating mode.
4.6.1 Remote change of operating mode
Either link [SD1] must be set to ‘1’ or the REMOTE input mask must be energised before
the relay will respond to a remote command to change the operating mode. The ‘Mode’
command in the STATUS menu is used to remotely or locally select ‘Manual’ or ‘Auto’
operating modes. The operating mode is remembered when the relay is powered down
and restored on power up. When link SD1=0 the relay will retain its last set operating
mode prior to setting SD1=0. When link [SD1] is set to “0” the operating mode cannot be
changed via the serial port and the mode command will have no effect on the operating
mode in use.
4.6.2 Manual change of operating mode via logic input
The energisation of the opto input allocated with the input mask ‘MANUAL’ will select the
‘Manual’ operating mode. In MANUAL mode, energising either ‘RAISE’ or ‘LOWER’ input
masks will cause the relay to provide an initiating signal to ‘Raise’ or ‘Lower’ to the tap
changer.
4.7 Paralleled transformers
Primary substation transformers are often operated in parallel in order to improve the
security of supply. A common configuration is two transformers positioned adjacently in a
substation and feeding a common busbar. Switching is provided to allow the
transformers to be separated for maintenance purposes but normally the transformers
operate in parallel. Sometimes the two transformers are not alike, sometimes more than
two transformers are paralleled and sometimes transformers several miles apart are
paralleled.
In practice it is often required to operate two or more tap changing transformers
connected in parallel between local busbars.
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