CHAPTER XII *~;
FREQUENCY CONVERTER OR GENERAL ALTERNATING-
CURRENT TRANSFORMER
103. In general, an alternating-current transformer consists of £
a magnetic circuit, interlinked with two electric circuits or sets
of electric circuits, the primary circuit, in which power, sup- '
plied by the impressed voltage, is consumed, and the secondary >
circuit, in which a corresponding amount of electric power I
is produced; or in other words, power is transferred through ' I
space, by magnetic energy, from primary to secondary circuit. j|
This power finds its mechanical equivalent in a repulsive thrust li
acting between primary and secondary conductors. Thus, if
the secondary is not held rigidly, with regards to the primary,
it will be repelled and move. This repulsion is used in the
constant-current transformer for regulating the current for
constancy independent of the load. In the induction motor,
this mechanical force is made use of for doing, the work: the
induction motor represents an alternating-current transformer,
in which the secondary is mounted movably with regards to
the primary, in such a manner that, while set in motion, it still
remains in the primary field of force. This requires, that the
induction motor field is not constant in one direction, but that
a magnetic field exists in every direction, in other words that
the magnetic field successively assumes all directions, as a so-
called rotating field.
The induction motor and the stationary transformer thus are
merely two applications of the same structure, the former using
the mechanical thrust, the latter only the electrical power
transfer, and both thus are special cases of what may be called
the " general alternating-current transformer," in which both,
power and mechanical motion, are utilized.
The general alternating-current transformer thus consists of
a magnetic circuit interlinked with two sets of electric circuits,
the primary and the secondary, which are mounted rotatably
with regards to each other. It transforms between primary
electrical and secondary electrical power, and also between