Improvements in Motor Generator Transformers.
Year: 1895

page_text: Date of Application, 6th June, 1895
Complete Specification Left, 6th Mar., 1896-Accepted, 23rd May, 1896
PROVISIONAL SPECIFICATION.
Improvements in Motor Generator Transformers.
We ALEXANDER BEWICKE BLACKBURN, Chief Engineer of the Electric
Construction Company Limited of Wolverhampton in the County of Stafford,.
and WILFRID L. SPENCE of Dunluce, Tettenhall Road, Wolverhampton,
Civil Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to motor generator transformers and consists in the
combination of partially separated primary and secondary armatures with
independently controlled means of varying the ratio of electro motive force of
the armatures.
According to this invention the armature core is in two portions carried on the
same shaft each portion revolving in its own field and one being usually larger
than the other. The one core (the larger) carries the whole of one winding and a
portion only of the other, the remainder being carried on the other core (the
smaller or regulating core).
The ratio between the primary electro-motive-force and the secondary electro-
motive-force on the one core is a fixed quantity and is unaffected by the speed of
rotation and by variation in the strength of field. The electro-motive-force due to
the secondary core which only carries one winding either primary or secondary
may be varied both by the speed of rotation and by the field strength.
In practice we prefer to place only so much of say the secondary winding on the
main core as will generate the minimum electro-motive-force required, any increase
in electro-motive-force being obtained in part by strengthening the auxiliary field
and the rest by increasing the speed of rotation.
The field coils are advantageously wound each as a shunt across a conveniently
low pressure circuit and series coils for starting may be used if desired. One end
of each coil is connected with one pole (say the positive pole) and the other ends
are connected together through a fixed resistance. The other pole (say the negative
pole) of the circuit is connected to the said resistance in such a manner that it can
be adjusted to simultaneously throw resistance into one field circuit and cut it out
of the other, thus varying the division of electro-motive-force between the two
armatures.
We do not limit ourselves to this particular method of regulation, any means by
which the auxiliary field may be varied at will is suitable but we prefer to
arrange the circuits so that the main field may be varied simultaneously with the
auxiliary field but in reverse way thereto.
Dated this 6th day of June 1805
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.

page_text: improvements in Motor Generator Transformers.
We, ALEXANDER BEWICKE BLACKBURN, Chief Engineer of the Electric
Construction Company Limited of Wolverhampton in the County of Stafford,
and WILFRID L. SPENCE, of Dunluce, Tettenhall Road, Wolverhampton,
Civil 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 :-
This invention relates to motor generator transformers and consists in the
combination of partially separated primary and secondary armatures with
independently controlled means of varying the ratio of electro motive force
which one armature bears to the other armature.
In a motor generator transformer according to this invention the armature core
is in two portions both secured to the same shaft and one usually larger than the
other and which we refer to respectively as the larger core and the smaller core.
The larger core carries the whole of one winding and a portion only of the second
winding, the remainder being carried on the small or regulating core. Each of the
said cores revolves in its own field.
The ratio between the primary electro-motive-force and the secondary electro-
motive-force on the one core is a fixed quantity and is unaffected by the speed of
rotation and by variation in the strength of field. The electro-motive-force due to
the regulating core which only carries one winding (either primary or secondary)
may be varied both by the speed of rotation and by the field strength.
In practice we prefer to place only so much of, say, the secondary winding on
the main core as will generate the minimum electro-motive-force required, any
increase in electro-motive-force being obtained in part by strengthening the
auxiliary field and the rest by increasing the speed of rotation.
Either winding
may however be controlled by the auxiliary field.
The field coils are advantageously wound each as a shunt across a conveniently
low pressure circuit and series coils for starting may be used if desired.
We will now describe our invention more particularly with reference to the
drawings premising that we do not limit ourselves to the precise details shewn.
Figure 1 is a side elevation (part section) of a variable ratio continuous current
transformer constructed and connected according to our invention.
The armature shaft A, carries main and regulating cores, M and R, with
corresponding windings, P and S. The primary winding is carried over both
cores and is connected to its commutator P. C. The secondary winding surrounds
the main core only and is carried out to the commutator, SC. Each armature
rotates in its own independently excited magnetic field marked respectively MF,
and RF.
One method of obtaining the necessary regulation is shown in this figure. The
two field coils M F, and RF, are in series with a fixed resistance, V R, which is
placed between them and are connected with their free ends to the same pole of
the circuit. The other pole is brought by a sliding contact to the resistance V R.
By moving the said sliding contact to the right the regulating or auxiliary
field, RF, is strengthened, and the main field, M F, is weakened.
Movement of
the said sliding contact to the left produces the opposite effect. Thus if the
primary electro-motive-force be supposed constant movement of the said sliding
contact to the left, will raise the secondary pressure, whilst sliding it to the right,
will decrease the said secondary pressure.
We do not limit ourselves to this particular form of regulation as any means by
which the auxiliary field may be manually or equivalently varied at will may be

page_text: employed but it is preferable to be able to vary in the reverse way, though not
necessarily to the same extent, the main field as well as the auxiliary field.
Figure 2 shews another method in which the auxiliary field alone is variable.
The parts are marked with the same letters as are used to denote the same parts
in Figure 1. A double pole reversing switch DPRS, is shown, but this, while
largely increasing the range of control, is not essential, nor is reversal of the
auxiliary field in all cases desirable, involving in certain cases a rise in speed and
a reduction of efficiency.
Obviously, a certain amount of regulation is also possible by varying the strength
of the main field while keeping constant the strength of the auxiliary field. But in
general the reverse of this is the more convenient.
Transformers built in this way may be used with advantage as motors in long
distance transmission work at high pressure. The secondary armature winding in
this case may either be cut down in capacity to act merely as a means of excitation
for the main field, or the machine may be used as an ordinary transformer for
lighting and other purposes simultaneously with its use as a motor; the auxiliary
field affording facilities for speed regulation or for variation of the electro-motive-
force as the case may be.
When used as a balancing machine in the generating station of a three wire
system of distribution, the variable ratio transformer permits of all the generators
being wound and connected for the double voltage. An excess of load on either
side of the circuit can be compensated by increasing the pressure on that side,
while correspondingly lowering it on the other side.
A form of armature for the application of our improvements to a combined
motor alternator for converting alternating into continuous currents, and con-
versely, is shewn in Figure 3. In the particular case illustrated the fields would
be of the multipolar type. The alternator coils A, are overlaid on a direct
current armature, B, so as to keep the two circuits quite distinct. The former are
connected to the collecting rings, R, and the latter, which is alone controlled by
the auxiliary field, is connected to the commutator C.
Figures 4 and 5 relate to the rectifier type of rotary converter in which the
armature winding, W, is common to both continuous and alternating circuits,
connections being made between the collector rings and suitable points of the
direct current winding for the alternate current supply.
The auxiliary winding is shewn in Figure 4 on the continuous current side ;
the coil sections S, being separately coupled in series with the commutator
connections C.
In Figure (which is marked with similar reference letters) the auxiliary
winding is on the alternate current side interposed between the collector rings, and
the points of juncture with the direct current winding.
In those cases where the alternator portion of this combination has to run in
parallel with other machines, the arrangement must be a synchronous one with
invariable speed, hence it does not offer quite the same flexibility as does the
continuous current transformer running under wide ranges of speed.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
:-
1. A motor generator transformer with main and auxiliary armature cores and
magnetic fields arranged and wound to afford means for varying the transforming
ratio by manual or equivalent regulation, all substantially as and for the purposes
hereinbefore described.
2. A rectifying motor generator transformer with main and auxiliary armature
cores and magnetic fields arranged and wound to afford means for varying the
transforming ratio by manual or equivalent regulation all substantially as and for
the purposes herein before described.
3. In a motor generator transformer the arrangement of primary and secondary

page_text: armature windings with two separate armature cores carried on the same shaft and
having one winding (either primary or secondary) common to both, and the other
winding peculiar to one core alone the two armatures revolving in separate
magnetic fields in combination with an adjustable manual switch and regulating
resistance, or equivalent means in such a manner that the relative excitation of
the two fields may be varied independently of the current strength in either
primary or secondary armature, all substantially as and for the purposes
herein before described.
4. In a motor generator transformer the arrangement of primary and secondary
armature windings with two separate armature cores carried on the same shaft and
having one winding, (either primary or secondary) common to both, and the other
winding peculiar to one core alone, the two armatures revolving in separate
magnetic fields in combination with an adjustable manual switch, regulating
resistance and current reverser, or equivalent means in such a manner that the
relative excitation of the two fields both in magnitude and direction, may be varied
independently of the current strength in either primary or secondary armature, all
substantially as and for the purpose herein before described.
5. In a rectifying motor generator transformer the arrangement of an armature
winding with two separate armature cores on the same shaft and having one circuit
(either primary or secondary) common to both, and the other circuit peculiar to
one core alone, the two armatures revolving in separate magnetic fields in combina-
tion with an adjustable manual switch and regulating resistance, or equivalent
means in such a manner that the relative excitation of the two fields may be varied
independently of the current strength in either primary or secondary armature, all
substantially as and for the purposes herein before described.
6. In a rectifying motor generator transformer the arrangement of an armature
winding with two separate armature cores carried on the same shaft and having
one circuit, either primary or secondary, common to both, and the other circuit
peculiar to one core alone, the two armatures revolving in separate fields in com-
bination with an adjustable manual switch, regulating resistance and current
reverser, or equivalent means in such a manner that the relative excitation of the
two fields both in magnitude and direction may be varied independently of the
current strength in either primary or secondary armature, all substantially as and
for the purposes hereinbefore described.
7. Variable ratio rotary motor generator transformers arranged and operated
substantially as and for the purposes herein before described, and illustrated in the
accompanying drawings.
Dated this 6th day of March 1896
JOHNSONS & 'WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.