Simple changing of taps during an energized status is
unacceptable due to momentary loss of system load
during the switching operation
(fig. 3). The “make (2)
before break (1) contact concept”, shown in Figure 4,
is therefore the basic design for all OLTCs. The transition
impedance in the form of a resistor or reactor
consists of one or more units that bridge adjacent
taps for the purpose of transferring load from one
tap to the other without interruption or appreciable
change in the load current. At the same time they
limit the circulating current (I C ) for the period when
both taps are used. Normally, reactor-type OLTCs use
the bridging position as a service position and the reactor
is therefore designed for continuous loading