Improvements in Armatures of Dynamo Electrical Machinery and Electrical Motors.
Year: 1886

page_text: Date of Application, 9th Oct., 1886.
Complete Left, 8th July, 1887.
Complete Accepted, 12th Aug., 1887.
Improvements in Armatures of Dynamo Electrical Machinery and
Electrical Motors.
TROOKES EVELYN BELL CROMPTON of the Arc Works Chelmsford in the County
of Essex Electrical Engineer do hereby declare the nature of this invention to be as
follows:-
My invention relates to armatures for dynamos or motors which have large arma-
ture currents.
The object of the invention is to diminish waste of power and heating which are
generally consequent on large armature currents.
In an armature for large currents it is usual to use rods or bars of copper as
conductors. Whenever such bars are moved so as to pass through a magnetic field
the currents induced on the two sides of each bar being of unequal electromotive
force cause local currents to be induced in the bars themselves, which take power
and convert it into heat, thus causing waste and high armature temperature. It also
weakens the field. To avoid this I do not use broad bars laid flat on the outside of
the armature, but I use instead two or more smaller bars or wires, connected in
parallel at the ends of armature.
In an armature of the cylinder type one bar inside may thus carry the current of
two external bars in parallel. The outside bars are not merely laid side by side, but
are twisted half a turn at or about the middle of their length, so that they cross one
over the other, thus changing places as to the stronger and weaker field, so that each
bar, rod, or wire has the same total electromotive force induced in it.
The conductor on the outside of the armature may, according to my invention be
formed of cable having at least half a turn in the length of the armature. The wires
or strands of the cable need be only very slightly insulated from one another.
The conductor I prefer for large armatures, especially where a section of the
commutator is devoted to each turn of conductor, is formed of two bars or strips of
copper on the outside of the armature, and a single strip of about double the area
in the inside. These strips are laid side by side on the outside of the armature, and
are crossed half way along it by one passing under the other. A groove is cut
in the iron of the armature to allow room for this. The crossing may be done

page_text: without cutting away the armature by flattening the bars or strips where they
cross.
The same method of crossing the bars or strips is applicable to the drum
armature.
In a short cylinder, or ring armature I prefer to use two or more strips both
inside and outside, and arrange two or more turns of double or treble wire per section
of commutator. The crossing need not then be arranged in the middle of the
armature but can be arranged at the end or ends. If the armature has say one
layer on the outside and two inside the crossing takes up no extra space, and the
armature has the same appearance as one wound for twice the electromotive force
and half the current. This winding is suitable also for cylinder armatures of medium
size.

page_text: COMPLETE SPECIFICATION.
Improvements in Armatures of Dynamo Electrical Machinery and
Electrical Motors.
I ROOKES EVELYN BELL CROMPTON of the Arc Works Cholmsford in the County
of Essex, Electrical Engineer do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
My invention relates to armatures for dynamos or motors which have large arma-
ture currents.
The object of the invention is to diminish the waste of power, and the heating which
are generally consequent on large armature currents.
In an armature for large currents it is usual to use single rods or bars of copper
as conductors. Whenever such bars are moved so as to pass through a magnetic
field which is not uniform the electromotive force induced on one side of each bar is
greater than that induced on the other, so that local currents are induced, or the
current density in the bar is not uniform, so that there is waste of power in heat.
Thus in entering a field, or when a bar is passing under the corner of a pole piece
into the magnetic field, there is a greater electromotive force induced in the side of the
bar that enters first, so that the current density on that side is greater. If the machine
is not giving any external current, there is a local current produced along one side
of the bar, and back by the other.
To avoid this effect I dispense with the use of broad bars laid flat on the outside of
the armature using instead two or more smaller bars or wires, connected in parallel
at the ends of the armature. Each group of bars or strips I call a conductor. The
outer bars are not merely laid side by side, but are twisted half a turn at, or
about the middle of their length, so that they cross one over the other thus changing
places as to the stronger and weaker field, so that each bar rod or wire has the same
total electromotive force induced in it.
In an armature of the cylinder type one inside bar may carry the current of two
external bars in parallel.
The conductor on the outside of the armature may, according to my invention be
formed of cable having at least half a turn in the length of the armature.
The wires or strands of the cable need be only very slightly insulated from one
another.
The conductor I prefer for large armatures, especially where a section of the com-
mutator is devoted to each turn of conductor, is formed of two bars or strips of
copper on the outside of the arinature, and in the case of cylinder armatures, a single
strip of about double the area in the inside. These strips are laid side by side on
the outside of the armature, and are crossed half way along it by one passing under
the other. A groove is cut in the iron of the armature to allow room for this. The

page_text: crossing may be arranged without cutting away the armature by flattening the bars
or strips where they cross.
The same method of crossing the bars or strips is applicable to the drum armature.
Figure 1 of the accompanying drawings shews by two half sectional views of two
modified forms of arrangement the portion above the line - representing one
form and that below that line another, the outside conductors b and c. In the
upper half view Figure 1 the conductor is shewn being bent under c. They
are both connected to the inside bar q, the iron of the armature is shown in section
at a a.
Figures 3, 4 and 5 are enlarged views of the crossing of the bars.
In the other view Figure 1 the bars d. e are shewn flattened where they cross, so
that no groove is needed.
Figures 6, 7, and 8 are enlarged views of the crossings of these bars d and e.
In a short cylinder, or ring armature, I prefer to use two or more strips both
inside and outside, and to arrange two or more turns of double or treble wire to
each section of commutator. The crossing need not then be arranged in the middle
of the armature, but can be at the end or ends. Thus, if the armature bas one layer
on the outside and two inside the crossing takes up no extra space, and the arma-
ture has the same appearance when not closely examined, as one wound for twice the
electromotive force and half the current. This winding is suitable also for cylinder
armatures of medium size.
Having now particularly described, and ascertained the nature of my said invention,
and in what manner the same is to be performed, I declare that what I claim is
In an armature for a dynamo electric machine or motor for large currents
1. Forming the active parts of the conductors of wires twisted together as and for
the purposes described.
2. The construction of external conductors formed of two or more bars crossed in
the middle of the armature substantially as and for the purposes described.
3. Constructing each conductor so as to be divided into two or more bars strips or
wires connected at the ends and crossed so that they have equal electromotive forces
induced when passing into or out of the field as and for the purpose set forth.
4. Forming the conductors of two or more bars, strips or wires crossed at the
end or ends of the armature, so that in each section the electromotive force is
approximately the same in all the bars strips or wires as set forth.
Dated the 8th day of July 1887.
WM. BROOKES & SON,
55 & 56, Chancery Lane, London,
Agents for the Applicant.