ABB RED615 Technical Manual page 744

Section 9
Control functions
738
The values for the FLLWx_CTL command are 1=Lower follower x and 2=Raise
follower x. Consequently, the values for the TAPCHG_FLLW command are
1=Lower and 2=Raise.
If several regulators are to act as masters (one at a time), their outputs also have to
be routed to the inputs of 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. To implement this setting, a group changing has to be planned.
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 the
horizontal GOOSE communication or TPOSSLTC.
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.
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 master/follower mode. First, the master gives a control
command to its own transformer, that is, it is echoed to the followers (the follower
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 modes 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 is. 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 the follower has Lower block tap higher than Raise block
tap, the corresponding TAPCHG_FLLW included control signals should be
connected crosswise. This requires an extra logic where dual-point command bits
have to be converted, that is, 0=>0, [01]=1=>[10]=2 and [10]=2=>[01]=1.
M/F is the only parallel mode which has an out-of-step functionality. In the MCC
and NRP operation modes, the circulating current is minimized, which most
probably means different tap positions in the parallel transformers. Moreover, these
modes allow different ratings and step voltages for the parallel transformers.
1YHT530004D05 D
615 series
Technical Manual