ABB RELION REX640 Technical Manual page 1558

Section 9
Control functions
1552
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. In
input control or command mode, a regulator acting as a follower, can be set to master
by activating the MSTR_TRIGG input if the Master input enabled setting is activated.
The regulator indicates its master status ("Independent", "Master" or "Follower") by
the TR_STATUS output. 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,
the follower should be manually controlled to the same position as the master. This
can also take place in the M/F mode. First, the master gives its own transformer a
control command which is echoed to the followers (the follower's tap positions have
to be connected). Thereafter, successive control commands to the followers take place
until the master and followers have the same tap positions.
Out-of-step function
The out-of-step function is usually used in the M/F mode only. The out-of-step
function means that the master is able to detect the position values of the followers and
control them to the same position as the master's. In this case, the master assumes that
the followers also have either Raise block tap higher than Lower block tap or Lower
block tap higher than Raise block tap because this defines what is the given command
pulse for a follower. If the master has Raise block tap higher than Lower block tap and
1MRS759142 C
REX640
Technical Manual