The diagram of connections is shown in Fig. 43. This method employs
an auxiliary reactor to assist tap changing. The switches for the taps and that across
the reactor(S) are connected as shown. The reactor has a center tapped winding on
a magnetic core. The two ends of the reactor are connected to the two bus bars to
which tapping switches of odd/even numbered taps are connected. When only one tap
is connected to the reactor the shorting switch S is closed minimizing the drop in the
reactor. The reactor can also be worked with both ends connected to two successive
taps. In that case the switch ’S’ must be kept open. The reactor limits the circulating
current between the taps in such a situation. Thus a four step tapped winding can be
used for getting seven step voltage on the secondary(see the table of switching). The
advantage of this type of tap changer are