Improvements in Dynamo-electric Machines and Motors.
Year: 1889

page_text: Date of Application, 26th Feb., 1889
Complete Specification Left, 26th Nov., 1889-Accepted, 26th Feb.,
1890
REVIVAL DI MULTITUATION.
Improvements in Dynamo-electric Machines and Motors.
I, JAMES SWINBURNE, of 49 Queen's Road, Wimbledon, Surrey, Electrical
Engineer, do hereby declare the nature of this invention to be as follows:-
Alternating motors, as at present designed are either special machines, or machines
resembling alternating current dynamos. My invention refers to the latter class.
At present the usual way of running such machines as motors, is to design them so
that they are kept in step with the generators by their self induction, which is a
wasteful way of working. According to my invention an alternating current motor
is designed so that at any instant its back electromotive force is just less than the
electromotive force on its terminals by enough to cause the armature current needed
to give the power.
At no load such a motor should give a back electromotive force which at any
instant is almost exactly equal to the terminal electromotive force. At full load
the field is weakened enough to let the necessary current pass.
The motor is self exciting, and is so arranged that the least lagging weakens the
field so that more power is spent on it, & vice versa. The field is excited from the
main circuit by means of a commutator. This arrangement provides a motor which
will start itself, though it does not run well till it gets up to speed; in fact it sparks
badly on starting. When at full speed, such a motor would have an intermittent
field excitation, & this would give rise to waste of power. A second coil is therefore
wound on the field magnets, & this is shortcircuited to act as an equaliser. A
third coil is often added, especially in large machines. This is excited by means of
a lagging transformer whose secondary current is a quarter of a period behind the
primary electromotive force. Two or more transformers may be used to get this
effect. Instead of this arrangement, a coil or set of coils may be wound on the
armature to give a current a quarter of a period behind the other for exciting. This
arrangement is also useful in making self exciting alternating current generators, as
in most types the second set of coils can be wound in what now are waste spaces.
In direct current dynamo armatures for very large currents there is often con-
siderable difficulty in avoiding heating of the conductors. To obviate this I wind the.
armature with one circuit which goes round the armature more than once. This
arrangement admits of the use of smaller conductors, and also of a large number of
commutator sections; but the first of these advantages is the greatest, & is the
main object of the invention. This winding is applicable to Gramme or drum
armatures.
To avoid lead of brushes, and the consequent opposing armature current turns I
use what I call reversing pole pieces or reversing magnets. In one form the reversing
pole piece consists of a soft iron extension from the yoke of the magnet to the
uncovered part of the armature, and in another of an attachment to the corner of the
pole piece. Both these forms have been described in former specifications of mine,
but an application made specially for them was dropped, so I cannot now claim them,
I have since found that the reversing pole piece need not be the whole length of the
armature, so that by making short the magnetic leakage can be greatly lessened.
Instead of winding all the necessary wire on the reversing pole, when attached to the
yoke, the effect is produced partly by winding all the series wire on one limb of the
magnet.
Instead of acting on the conductor on the armature the conductors leading to the
commutator, may have an electromotive force induced in them. A sort of subsidiary..
armature, consisting of a ring of wires or discs is placed inside the connections to the
commutator, so that the commutator connections lie on its periphery. A little field

page_text: magnet is arranged so that the connections come under it so as to have the necessary
electromotive force induced at the right time or place. The connections are made
very thin just where the little armature comes, so that the field magnet can be brought
very close to it.
As the electricity only flows through each thinned place for a very
short time, there is no heating. The little field magnet is wound with series coils.
Dated this 23rd day of February 1889.
I, JAMES SWINBURNE, of 49 Queen's Road, Wimbledon, Surrey, 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 refers to direct and to alternating current dynamos and motors. To
avoid lead of brushes in dynamos and motors, and the consequent back ampère turns,
I use reversing magnets.
A sort of subsidiary armature core consisting of a ring of wires or discs is placed
inside the connections to the commutator, so that the commutator connections be on
its outer surface, or in grooves milled out of the discs. A little field magnet is
arranged so that the connections come under it so as to have the necessary electro-motive
force induced at the right time or place. When the connections lie on the outside of
the reversing armature core they are made very thin, so that the reversing field
magnets may have their pole pieces brought close to the iron of the reversing
armature. As each of the connections has a current for only a very short time each
half revolution, the heating is inappreciable. The reversing magnet is wound in
series with the main circuit; and may be mounted on the bed plate or fixed to the
bearings in any convenient way. The reversing magnets may be moved with the
brushes to regulate the dynamo. If the dynamo is large it may be made to give
constant electromotive force as a generator, or constant speed as a motor when shunt
wound by giving the brushes & reversing magnet the requisite negative or positive
lead.
Alternating current motors, as at present designed, are either special machines or
machines resembling alternating current dynamos. My invention refers to the latter
class. At present the usual way of utilising such machines as motors, is to design
them so that they are kept in step with the generators by their self induction; or, as I
prefer to explain it, by their own unassisted armature reactions which is a wasteful
way of working; because the maximum armature current and back electromotive
force are not at the same times. According to my invention, an alternating current
motor is designed so that at any instant its back electromotive force is just less than
the electromotive force on its terminals by enough to cause the armature current
needed to give the power. At no load such a motor should give a back electromotive
force which at any instant is almost exactly equal to the terminal electromotive force.
At full load the field is weakened enough to let the necessary current pass; so that
the motor does not need to lag much & weaken its field by the reaction of its armature
current.
Two
I produce this effect in several ways. According to one method the motor is self
exciting. The field magnets are excited from a commutator in connection with a
special armature circuit, or, on starting, with the main circuit. After the motor is
started I prefer to excite it from a special armature circuit. To avoid sparking it is
sometimes advisable to have two exciting armature cireuils & two commutators.
field magnet circuits are then arranged so that the alternating currents produced in
them differ in phase by à quarter of a pericd. A closed coil may also be wound on
each of the field magnets so as to prevent any perceptible fluctuation of the excitation.
In most cases this is not necessary. This method of excitation may be used either for
alternating generators or motors.

page_text: In the case of a motor the exciting circuits are so arranged that at no load the field
excitation gives a back electromotive force approximately equal to the electromotive
force in the mains. If it has very nearly the same back electromotive force the motor
at no load becomes cophasedly synchronised and takes just enough current to drive it
& give power for excitation. It is best to allow a margin so that the back electro-
motive force is a little less than the main electromotive force. The motor then leads
a little at no load. This slight lead allows a small armature current to pass which
strengthens the field by reaction. This increases the excitation, as the exciting coils
in the armature come under the influence of the same pole pieces. This increases the
back electromotive force, so that neither the lead nor the armature current becomes
excessive. If too much margin is allowed, the motor will lead too much, & will take
a large current at no load, which is wasteful.
When load is put on, the motor begins to lag. The armature current then reacts
on the fields and weakens them; this weakens the field excitation, as the exciting coils
are influenced by the same field magnets, & the field can thus be weakened enough
without much lag. The field excitation should be so designed that the iron is not
highly magnetised. On the other hand it must not be too sensitive.
Though in my provisional specification I proposed to use a double field circuit,
as just described, I now prefer to use a single field circuit connected with the double
armature exciting circuit. The two armature circuits are then coupled up to a
commutator as in an ordinary closed or open armature circuit direct current machine.
The field excitation is then still affected by the main armature current's reaction on
the field magnets.
The field excitation may be lessened more directly at full load by passing the
main current of the motor round the field magnets, after commutation. This
arrangement can be employed when the machine is separately excited. This main
or series demagnetising current may be taken round the field maguets of the exciter
instead of round the alternator field magnets; but I prefer to act on the alternator
magnets.
0
All these methods depend for their final adjustment on the lagging of the motor
as the load increases, but instead of being considerable, the lag is small, because
the current turns round the field magnets are fewer at full load than at light
loads.
As the problem of running alternators in parallel as generators is akin to that
of running them as motors off parallel supply circuits, machines made according
to my invention are suitable for parallel running generators. For instance, if two
or more self-exciting alternators of the kind described are in parallel, & one falls
behind, or lags a little, its field is at once weakened in a much greater degree than
it would be if the ampère turns on it remained constant.
If the motors with backward mains or demaguetising field circuits in series with the
armature are used as generators the direction of the main currents is reversed, &
they become compound wound alternating current dynamos; & they may be coupled
up to run in parallel like direct current compound wound generators.
To start an alternating inotor I use one of the methods already mentioned by me
in earlier patent specifications; namely; starting by connecting batteries with the
direct current exciter; starting by turning the alternating current into the exciter,
which has, preferably, in this case, laminated magnets; or starting by connecting the.
armature & field magnets of the motor with the alternating current."
The method I prefer is to shift the brushes of the series circuit on starting, & to
turn on the alternating current gradually. The brushes are shifted back to their
normal position when the motor has attained its normal speed.
When there is no series circuit, & there are two armature exciting circuits, & two
field circuits to correspond, the motor may be started by putting one field circuit with
its commutator in series with the armature circuit, & passing the main alternating
current through. When synchronism is attained, the connections are altered The
necessary connections for such alterations are more easily arranged in machines in
which the field magnets revolve, while the armature is stationary.

page_text: Fig. 1 is a diagram of a reversing armature & maguet attached to an armature &
commutator. A is the armature of the dynamo or motor & E the commutator. B is
the reversing armature core, in the periphery of which the commutator connections
are embedded, & C is one pole of the reversing magnet. A yoke D is shown, but in
practice the vertical parts of the maguet are mounted on the bed plate.
The
brushes make contact at the sides of the commutator so as to touch the sections that
are connected to the armature section whose current is being reversed by the pole
pieces. The main armature is wound in the usual way, but the commutator connections
pass through narrow grooves in the reversing armature B, & then pass in radially to the
commutator in the usual way.
Fig. 2, shews the reversing magnets arranged in another way. They are mounted
on an iron crossbar which is not shown, & which forms the yoke. This crossbar
also carries the brushes, so that the position of reversing magnets & the brushes may
be varied simultaneously the brushes always being under the reversing pole pieces. It
is advisable to allow for a small adjustment of the brushes relatively to the reversing
magnets as well.
Figs. 3. 4 are diagrams showing the commutator sections & connections of alter-
nating current motors according to my invention. is a ring armature. For the
sake of simplicity a two pole machine is taken, though in practice it is better to have
six or more, so that the speed is not too great. H, H, are the active coils or main coils
of the machine. They are connected to collecting rings as usual which are not shown
in the diagrams. I III are the exciting coils of the armature. In Fig. 3 two
commutators are shown, one within the other; they are actually mounted on a hob
side by side, & are of the same diameter. The connections are made, as in many are
machines, by connecting the pairs of brushes in parallel. The insulating spaces may
then be made large, so that each coil is cut out of circuit for a time when it is
giving little or no electromotive force. The brushes & pairs of coils may be connected
in series, as shown in Fig. 3. In that case the insulating gap is small, so that there
is always a circuit through each commutator. Insulating sections may, even in this
case be used to cut the coils out of circuit when not active, but they must, of course,
be connected across. The opposite coils are shown connected in parallel; they may
be coupled in series. The brushes are in connection with the field magnets by the
leads K. L. If the armature is stationary & the field rotates, the brushes are connected
to the armature coils, & the sections of the commutator to the field circuit.
In fig. 4, the exciting coils are connected up as in a Gramme ring. This arrange-
ment demands four brushes & two sections when the armature is stationary & the
field rotates.
Fig. 5. is a diagram of the exciting armature coils in a machine whose armature
is made of flat strip without an iron case. The artist has shown the main coils H. H

page_text: & pole pieces N. S. N. with parallel sides, instead of radial, for the sake of simplicity.
The main armature coils are shown as dotted flat oval coils H H. They are connected
to collecting rings in the usual way, and the connections are not shown. Inside the
main coils, in the space at present generally left vacant, are pairs of exciting coils
shown as full lines, I I. These coils are more clearly distinguished in figures 6 & 7
where the main coils H H are omitted. N, S, N, are diagrammatic representations of
the pole pieces in figs. 5, 6, & 7. The arrows on the pole pieces show the direction
they induce a current when a conductor passes from right to left. The arrows in the
coil circuits show the direction of the induced exciting currents.
In fig. 5 two pair of coils are shown. Each pair is connected in series. 1, 2
are the ends of one pair, & 3, 4 the ends of the other pair. In an actual machine
instead of two pairs there are two sets of correspondingly situated coils, coupled,
preferably in series. Below the diagrams of the coils in tigs. 5, 6, & 7 are diagrams
of the commutator sections, & the brushes, which are connected with the field magnet
circuit. The numbers on the commutator sections show which ends of the coils I I
are connected to them. In Fig. 5. each set of active coils is in circuit when it has an
electromotive force induced in it, the other set being out of circuit. Fig: 6 is
analogous, roughly, to Fig. 3. There are two commutators & two pair of brushes, &
the sets of coils are in series. For starting the motor the brushes are shifted to the
dotted positions, & the main current is passed through both the field & armature
circuit; and when speed is attained, the connections are altered. Fig. 7 shows an
arrangement somewhat analogous to that of Fig. 4.
Fig. 8 is a diagrammatic view of a dynamo or motor according to my invention.
p is the collector for the main armature current, is the commutator in series with
the armature circuit for weakening the field in the case of a motor, & strengthening
it in the case of a dynamo, y are the terminals of the main or series field coils, is
the commutator in connection with the armature exciting coils, for exciting the field
magnets, and are the terminals of the field circuit connected to it. To start the
machine as a motor the brushes of the series circuit are shifted so that the series wire
magnetises instead of demagnetising. The main current is then turned on through a
safety resistance. When the machine has reached its normal speed the brushes are
shifted to their proper position, & the load is put on.
Fig. 9 is a diagramimatic view of a separately excited alternating motor with
secondary cells for starting it by their action on the exciter. P is the ordinary ring
collector for the main armature current. is the commutator for rectifying the main
armature current before it is. passed round the fields to demagnetise them. y are
terminals connected with the main, series, or demagnetising circuit round the field
magnets, & with the brushes bearing on the commutator 9. The exciter is shown to
the left. Lis one pole piece, M one shunt field coil & N the commutator. There is
no series winding on the exciter. O is a secondary battery, which is in shunt to the
exciter when the armature of the electromagnetic cut out 's is held on. If the motor
is running at its normal speed the exciter charges the batteries when the armature of
the cut out is held on, & also excites the field magnets of the alternator, as the
brushes of the exciter are connected with, which are the terminals of the exciting
coils of the field magnets of the alternator. To start the motor the switches t & u are
opened, J being already open, & the armature of the cut out s is held on.
secondary battery then discharges by three paths in parallel, namely (1) the armature
of the exciter, through the resistance in shunt to t, by the commutator N of the exciter,
& through the cut out magnets; (2) the shunt coils of the exciter, through the
resistance in shunt to w; & (3) through the main exciting coils of the main machine
connected with the terminals. The resistance in shunt to t is to prevent an excessive
armature current when the cells are switched on while the machine is still at rest. The
exciter then acts as a motor & starts & drives the whole machine.
As soon as a
fair speed is attained the switch is closed so that the whole pressure of the cells is
on the exciter armature. The resistance in the exciter's field weakens it so that as a
motor it goes faster & a speed somewhat above the normal is attainable if desired.
When normal speed is attained J is closed & the large machine begins to act as &
The

page_text: 2
motor. w is then closed & the field of the exciter is strengthened so that it becomes
a dynamo. At the instant of reversal of current through s the armature of the cut out
falls off, but is drawn on again by the current passing throughs to the upper terminal z
of the main field magnets. The exciter gradually charges up the cells again. To
stop the motor J is opened. The speed then falls slightly so that the cells can
drive the exciter as a motor again, but the reduction of the current through s releases
the armature of the cut out & disconnects the cells.
Having now particularly described and ascertained the nature of my said inven-
tion, & in what manner the same is to be performed, I declare that what I
claim is
A generator or motor for direct currents having;
1. A reversing armature core with the commutator connections embedded in it.
2. A reversing armature with the commutator connections thin where they pass
through the reversing field.
3. A reversing armature core with each commutator connection passing over the
outside only once, substantially as set forth.
4. Reversing magnets adjustable as to position substantially as described.
A synchronising alternating current motor;
5. In which the current-turns on the field magnets are decreased when the load
increases.
6. Excited from its own armature.
7. A self exciting alternating generator or motor with two or more exciting coils
on the armature giving currents differing in phase, substantially as, and for the
purposes set forth.
Dated this 25th day of November 1880