If it is not possible to use horizontal communication between the IEDs 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 tap position inputs 1…3
(TR1_TAP_POS..TR3_TAP_POS) 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 six seconds.