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ELECTRICAL APPARATUS

will become necessary, to suit the conditions of service, such as
the double squirrel-cage induction motor in ship propulsion and
similar uses, the various types of concatenation of induction
machines with synchronous and commutating machines, etc.

256. In general, a new design or new type of machine or
apparatus has economically no right of existence, if it is only
just as good as the existing one.

A new type, which offers only a slight advantage in efficiency,
size, cost of production or operation, etc., over the existing type,
is economically preferable only, if it can entirely supersede the
existing type; but if its advantage is limited to certain applica-
tions, very often, even usually, the new type is economically
inferior, since the disadvantage of'producing and operating two
different types of apparatus may be greater than the advantage
of the new type. Thus a standard type is economically superior
and preferable to a special one, even if the latter has some small
superiority, unless, and until, the industry has extended so far,
that both types can find such Extensive application as to justify
the existence of two standard types. This, for instance, was the
reason which retarded the introduction of the three-phase trans-
former: its advantage was not sufficient to justify the dupli-
cation of standards, until three-phase systems had become very
numerous and widespread.

In other words, the advantage offered by a new type of appara-
tus over existing standard types, must be very material, to
economically justify its industrial development.

The error most frequently made in modern engineering is not
the imdue adherence to standards, but is the reverse. The
undue preference of special apparatus, sizes, methods, etc.,
where standards would be almost as good in their characteristics,
and therefore would be economically preferable. It is the most
serious economic mistake, to use anything special, where standard
can be made to serve satisfactorily, and this mistake is the most
frequent in modern electrical engineering, due to the innate
individualism of the engineers.

257. However, while existing standard types of apparatus are
economically preferable wherever they can be used, it is obvious
that with the rapid expansion of the industry, new types of
apparatus will be developed, introduced and become standard,
to meet new conditions, and for this reason, as stated above, a
knowledge of the entire known field of apparatus is necessary
to the engineer.

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