Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1917-02-10
FIELDS AND FIELD WINDINGS FOR GENERATORS
AND FOR MOTORS ARE DESCRIBED BY EXPERTS
tBy Special Permission From Motor
Age.l

loops OF wire all Of the time excepl
when the two commutator segments
TO which loop is connected are In
contact with q brush or brushes OF
the same polarity. One OF the sim.
plest forms OF colored circuit winding
is shown In Fig. /, which consists OF q
wire ring with four coils wound about
II and interconnected by means OF
four commutator, segments, as shown
in the figure. For convenience in re-
ferring TO these coils they are desig.
mated as A. B, G and d. The two
coils A and B are short circuited by
the two brushes vhen they are In
the position shown In the figure. An
instant later, however, coil A Is in
series with Coil b on the right side
and coil G Is In series with coil ID
on the left side, and this connection
remains until coils b and d are short
circuited by the brushes. An instant
later coll d Is. in series with coil A
en- the right side and coil B Is In
series with coil G. on the left side.
II IL apparent that the coils oppo.
I site each other are short circuited by
the brushes at the same time that
they are symmetricaIly arranged, as
In this case. and as one coil leaves
the right circuit and enters the left
circuit at the lower brush, while there
10 q coil leaving the left circuit and
entering the right circuit at the upper
brush. With this arrangement OF com.
mutator segments and coils all of
the coils are In circuit with the ex.
ternal circuit all Of the time, except
when they are short circuited by the
brushes. II the position Of the
brushes on the commutator is such
that the coils are moving parallel to
the magnetic field when the coils are
short circuited there VIII be no cleo
trical pressure induced In the coils,
and as result the electrical pressure
between the brushes is not decreased
by short circuiting the coils.
Pressure IN Coils
The electrical pressure In all Of
the coils on the right side Of q verti-
cal line through the brushes will be
in the opposite direction to the electri-
cal pressure In the coils on the left
side Of the vertical line through the
brushes. The electrical pressures in
the coils on the right and left sides OF
the vertical line act oppositely to
each other, Just g The electrical pres.
sures of Two bdtt6fies connected In
parallel act opposite with respect to
each other 1ut they act h The same
direction with respect TO the external
circuit.
The movement Of the coils across
the magnetic field inst before they are
short circuited is II the opposite direc-
ton to their movement across the
magnetic. field after they have been
short circuited. This results in the
electrical pressure induced In the coils
before they are short circuited acting
around the coil IN the opposite direc-
ton to that IN which the electrical
pressure induced IN the coil after II
has been short circuited acts. In
other words, the electrical pressure
induced In the coil reverses in direc.
ton while the coil Is short circuited.
The total electrical pressure be-
tween the brushes at any instant will
be equal to the sum OF the electrical
pressure induced in the coils connect
ed In series between the brushes.
When the coils are symmetrieally
placed, as shown In Fg.s1. the varia-
tion In the electrical pressure be-
tween the brushes win correspond to
the variation IN the total pressure
Of the coils connected IN series be-
tween the brushes. Thus the electri-
cal pressure induced In the coil A
with respect to the external circuit
may be represented by q curve SINH
lar to the one marked A In Fig. 2.
Both parts Of the curve are drawn
above the horizontal line, as the con-
nection Of the coil with respect to the
external circuit changes when the coil
passes the position Of short circuit or
the position where the induced cleo
trical pressure reverses In direction.
The electrical pressure induced in the
coil d with respect to the external
circuit may be represented by q sec
0nd curve ID. The electrical pressure
In A il q maximum when the electri.
cal pressure In d is zero and the
electrical pressure in d is a maxi
mum when the electrical pressure in
A Is zero.
The electrical pressure between the
brushes at any instant win be equal to
the sum OF the pressures induced In
the two coils connected In series at
that instant, and IL may be represent
ed by third curve whose height above.
the horizontal is equal to the sum Of
the height Of the two curves A and ID.
This third curve Is shown heavy. From
an inspection Of Fig. II Is seen that
there are four loops to the shaded