222 Electrical Power Systems Technology
120-volt AC source, which produces the primary magnetic flux. The sec-
ondary has two step-down windings and one step-up winding. Between
points 1 and 2, a voltage of 5-volts AC could be supplied. Between point 5
and point 6, 30-volts AC may be obtained, and between points 3 and 4, a
voltage of 360-volts AC can be supplied to a load. This type of transformer
is used for the power supply of various types of electronic equipment and
instruments.
Figure 8-11. Transformer with multiple secondary windingsAutotransformers
Another specialized type of transformer is the autotransformer, shown
in Figure 8-12. The autotransformer has only one winding, with a common
connection between the primary and secondary. The principle of opera-
tion of the autotransformer is similar to that of other transformers. Both
the step-up and step-down types are shown in Figure 8-12. Another type of
control device is a variable autotransformer, in which the winding tap may
be adjusted along the entire length of the winding to provide a variable
AC voltage to a load.
Figure 8-12. Autotransformers: (A) Step-up type, (B) Step-down type