Improvements in Rotary Transformers and Synchronous Motors.
Year: 1899

page_text: Date of Application, 30th May, 1899
Complete Specification Left, 27th Feb., 1900-Accepted, 7th Apr.,
1900
[Communicated from abroad by BENJAMIN GARVER LAMME, of 230, Stratford
Avenue, Pittsburgh, in the County of Allegheny and State of Pennsylvania,
1.S.A., Electrical Engineer.]
Improvements in Rotary Transformers and Synchronous Motors.
I, REGINALD BELFIELD, Electrician. of 32, Victoria Street, Westminster, in
the County of London, England, do hereby declare the nature of this inven-
tion to be as follows:--
My invention relates to rotary transformers and synchronous motors and has
for its object to obviate irregularities in operation due to distortion of the mag-
netic fields of such machines. This distortion is caused by the cross-mag-
netising effect of the current in the armature on the pole tips of the machine
whereby one pole tip becomes strengthened and the other is weakened. The
resultant field is thereby shifted either forward or backward depending on the
action of the current, and the position of the resultant field therefore depends
on the current in the armature of the machine. In the case of a synchronous
motor at no-load there should be very little armature current, and therefore
only a slight distortion of the field; if, however, the rate of alternations applied
are suddenly changed the motor armature will take considerable current, the
resulting field will be shifted and the armature will tend to move into a new
position in this field, consequently the armature will take a current in the
opposite direction for an instant, or if it is receiving current as a motor it
will begin to deliver power for an instant, this distorts the field in the opposite
direction and the armature now tends to swing the other way.
If in the one
case it was slightly accelerating in speed for an instant, it will now slightly
retard so that the armature begins to get into an oscillatory state as regards
speed, varying above and below the normal or synchronous speed. This oscil-
lation may be very small for a time, but under favourable conditions may
increase gradually until it is so violent that the machine is thrown out of step
with the system. The armature current due to the oscillation will be alter-
nately a leading and a lagging current and thereby alternately strengthen and
weaken the field magnetism. In the case of a rotary transformer armature
the ampere turns due to the current supplied are at all loads directly equal
to the ampere turns of the current delivered, consequently there should be
but little distortion. If by any variation the oscillation is started however.
the incoming alternating current represents more ampere turns than the current
delivered, and this will produce distortion as in a synchronous motor, and as
the field alternately strengthens and weakens the electro-motive force will vary.
The variation in distortion of the field may be due to several causes, such as
irregular speed of the generator, difference in the form of the electro-motive
force waves of the generator and the motor or rotary transformer, etc.
According to my present invention, however, I do not deal with these causes,
but I prevent the variation in distortion of the field or reduce it to a com-

page_text: paratively small amount by placing copper shields or plates over or around the
pole tips or edges and copper rings around the ends of the pole pieces. Variation
in distortion of the field at the tips or edges of the pole pieces will cause
secondary currents to flow in such shields and rings which will oppose the
variation in distortion and neutralize its effect.
:-
In the accompanying drawing:-
Figure 1 is an end elevation largely diagrammatic of a rotary transformer
or synchronous motor provided with my improvement, and
Figure 2 is a face view of a field-magnet pole piece provided with a ring
and pair of shields.
The armature of the machine is indicated by a circle at a and may be of
any suitable construction, the pole pieces bare provided with shields as
partially covering or entirely covering, if desired, the face thereof. Each of
the pole pieces is further surrounded near its face by a comparatively heavy
ring of copper. The shields and ring for each pole piece may be stamped
from a single sheet or may be in separate pieces, as desired. Obviously the
ring may be replaced by a closed coil of conducting material.
By the use of my invention the speed of rotary transformers and synchronous
motors is rendered much more uniform and further in the case of rotary
transformers owing to the neutralisation of the magnetising and demagnetising
effects of the armature currents the machine is caused to deliver a smooth
direct current.
1
2011 1
1000
Improvements in Rotary Transformers and Synchronous Motors.
I, REGINALD BELFIELD, Electrician, of Westinghouse Building, Norfolk
Street, Strand, W.C., formerly residing at 32, Victoria Street, Westminster, in
the County of London, England, 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:
The
My invention relates to rotary transformers and synchronous motors and has
for its object to obviate irregularities in operation due to distortion of the mag-
netic fields of such machines. This distortion is caused by the cross-mag-
netising effect of the current in the armature on the pole tips of the machine
whereby one pole tip becomes strengthened and the other is weakened.
resultant field is thereby shifted either forward or backward depending on the
action of the current, and the position of the resultant field therefore depends
on the current in the armature of the machine. In the case of a synchronous
motor at no-load there should be very little armature current, and therefore
only a slight distortion of the field; if, however, the rate of alternations applied
are suddenly changed the motor armature will take considerable current, the
resulting field will be shifted and the armature will tend to move into a new
position in this field, consequently the armature will take a current in the
opposite direction for an instant, or if it is receiving current as a motor it
will begin to deliver power for an instant, this distorts the field in the opposite
direction and the armature now tends to swing the other way. If in the one
case it was slightly accelerating in speed for an instant, it will now slightly
retard so that the armature begins to get into an oscillatory state as regards

page_text: speed, varying above and below the normal or synchronous speed. This oscil-
lation may be very small for a time, but under favourable conditions may
increase gradually until it is so violent that the machine is thrown out of step
with the system. The armature current due to the oscillation will be alter-
nately a leading and a lagging current and thereby alternately strengthen and
weaken the field magnetism. In the case of a rotary transformer armature
the ampere turns due to the current supplied are at all loads directly equal
to the ampere turns of the current delivered, consequently there should be
but little distortion. If by any variation the oscillation is started however,
the incoming alternating current represents more ampere turns than the current
delivered, and this will produce distortion as in a synchronous motor, and as
the field alterately strengthens and weakens the electro-motive force will vary.
The variation in distortion of the field may be due to several causes, such as
irregular speed of the generator, difference in the form of the electro-motive
force waves of the generator and the motor or rotary transformer, etc.
According to my present invention, however, I do not deal with these causes,
but I prevent the variation in distortion of the field or reduce it to a com-
paratively small amount by placing copper shields or plates over or around the
pole tips or edges and copper rings around the ends of the pole pieces. Variation
in distortion of the field at the tips or edges of the pole pieces will cause
secondary currents to flow in such shields and rings which will oppose the
variation in distortion and neutralize its effect.
In the drawing filed with the Provisional Specification
Figure 1 is an end elevation largely diagrammatic of a rotary transformer
or synchronous motor provided with my improvement, and
Figure 2 is a face view of a field-magnet pole piece provided with a ring
and pair of shields.
The armature of the machine is indicated by a circle at a and may be of
any suitable construction, the pole pieces are provided with shields as e
partially covering or entirely covering, if desired, the face thereof. Each of
the pole pieces is further surrounded near its face by a comparatively heavy
ring of copper d. The shields and ring for each pole piece may be stamped
from a single sheet or may be in separate pieces, as desired. Obviously the
ring may be replaced by a closed coil of conducting material.
By the use of my invention the speed of rotary transformers and synchronous
motors is rendered much more uniform and further in the case of rotary
transformers owing to the neutralisation of the magnetising and demagnetising
effects of the armature currents the machine is caused to deliver a smooth
direct current.
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:-
1. A rotary transformer or synchronous motor having the inner ends of its
field magnet pole pieces provided with either conducting shields, or rings, or
both, for the purpose specified.
2. A rotary transformer or synchronous motor constructed substantially as
described with reference to the accompanying drawings for the purpose specified.
Dated the 27th day of Wabruare 1900
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.