Master/Follower principle M/F
The M/F operation principle is suitable for power transformers with identical
ratings and step voltages. One voltage regulator (master) measures and controls
and the other regulators (followers) follow the master, that is, all the tap changers
connected in parallel are synchronized. This parallel operation is obtained by
connecting the FLLWx_CTL output of the master to the corresponding OLGAPC
function input TR_TAP_FLLW of the followers via horizontal GOOSE communication.
The values for the FLLWx_CTL command are 1=Lower follower x and 2=Raise
follower x. Consequently, the values for OLGAPC function TR_TAP_FLLW command
are 1=Lower and 2=Raise.
If several regulators act as masters (one at a time), their outputs also have to be
routed to the inputs of the other regulators. To start the parallel operation, the
master regulator is set to the "Auto master" mode and the followers to the "Auto
follower" mode. A regulator acting as a follower can be set to master in three ways.
• Activating input MSTR_TRIGG if
Parallel mode
is set to "Input control"
• Activating MstrOp via communication if
Parallel mode
is set to "Command"
• Activating the Master Trig button in the LHMI control dialog for OL5ATCC if
Parallel mode
is set to "Command"
The regulator indicates its master status (“Independent”, “Master” or “Follower”)
by the TR_STATUS monitored data. A parallel regulator, previously acting as master,
receives this signal via the TR_STATUS input of OLGAPC and changes its status to
follower.
Connect the TR_STATUS input to the OLGAPC of the parallel transformer
and route the TR_DAT output from OLGAPC to OL5ATCC TRx_DAT
for proper M/F functionality. If TR_STATUS is left unconnected, that
particular parallel transformer is assumed to not be participating even
though receiving valid tap position information.
To keep all the tap changers in the same position, the master needs to know
the tap positions of the followers. This way, the circulating current is kept at its
minimum. The position values of the followers can be brought to the master either
via horizontal GOOSE communication or TPOSYLTC.
If it is not possible to use horizontal communication between the protection relays
and the position information cannot be wired from the parallel transformers,
the M/F principle can still be used to regulate two or an unlimited number of
transformers in parallel. Since the master cannot detect the tap positions of parallel
transformers, it just activates the lowering and raising outputs for all the followers
when it controls its own tap changer. This is called blind control. In this case, a
number of parallel transformers are regulated as one unit.
The combined data inputs TRx_DAT must be left unconnected for the master to
know that the tap positions of the followers are unknown. The time delay between
successive commands can be set by the
Follower delay time
setting. The default
value is 6 seconds.
When a disconnected transformer is taken into use and the tap position is unknown,
it is recommended that the follower should be manually controlled to the same
position as the master. In the M/F mode, the master gives its own transformer
a control command which is echoed to the followers (the follower's tap positions
must be connected). Thereafter, successive control commands to the followers take
place until the master and followers have the same tap positions.
1MRS759142 F
Control functions
REX640
Technical Manual
1707
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