Improvements in Alternating Electric Current Transformers.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 15th Sept., 1900
COMPLETE SPECIFICATION.
Improvements in Alternating Electric Current Transformers.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of
this invention (which has been communicated to us from abroad by Augustine
R. Everest, residing at Lynn, in the County of Essex, State of Massachusetts,
United States of America, Electrical Engineer,) and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement:
-
The present invention relates to alternating electric current transformers for
changing currents of constant potential to currents of constant volume, or the
reverse, and has reference more especially to that type of transformer in which
relatively movable coils are employed.
This invention is chiefly valuable however in connection with transformers of
the type above mentioned, and we use it in this relation for the purpose of
obtaining better regulation. It has been observed that in constant-current trans-
formers such as already referred to, the secondary current at small loads, when
the coils of the transformer are separated from each other, is larger than at
full load when the coils of the transformer are close together. In these trans-
formers, as is well understood, the force of repulsion between the currents in the
primary and secondary coils is opposed by a suitably applied force, the value of
which serve to determine the current at which the coils will separate or move
apart from each other. With every decrease of load in the secondary circuit
there is a tendency toward increase of current and a consequent increase in the
force of repulsion between the primary and secondary coils. The coils therefore
move away from each other, and more leakage flux is created between the coils
than when in the original position. The secondary electro-motive force is thus
decreased, thus tending to decrease the current to its proper value. As above
noted, however, we have observed that the load curve of the transformer is not
a straight line, but shows a larger current at small loads than at full load. In
order to compensate for this defect we provide a device, such for example as a
variable counterweight, of such a nature as to decrease the force urging the coils
together, the more the coils are separated. The decreased force of repulsion
between the coils when they are widely separated is thus opposed by a corre-
spondingly decreased force ürging the coils together. Under these conditions
a given increase in secondary current will produce an increased displacement
of the coils and consequent decrease in electro-motive force sufficient to cut down
the current to its original value.
Our invention will be more readily understood by reference to the following
description and accompanying drawings, while its scope will be clearly and
particularly pointed out in the appended claims.
The drawing illustrates our invention as applied to an alternating current
transformer. The core of the transformer is here shown as of rectangular form,
with a main core or bar 1 connected to end pieces secured within the castings 2
and 3 Bars 4 and 5 are arranged parallel to the bar 1, with their ends like-
wise secured in the end pieces in the castings 2, 3. Clamping bolts 6 engage

page_text: lugs 7 on corresponding ends of the end pieces 2, 3, and serve to clamp the parts
of the transformer together. Primary and secondary coils are illustrated at 8
and 9, and both coils are arranged to embrace the bar 1 of the transformer core.
The coil 9 is preferably stationary, and is arranged so as to rest on the lower
cross-piece of the transformer core. The coil 8 is moved relatively to the coil 9,
and is suspended from one end 12 of an oscillating lever, by means of the looped
cord 10 and suspending cord 11. So far as the principal of the invention is
concerned, it is immaterial which of the coils 8 and 9 is the primary and which
the secondary.
The oscillating lever 13 is mounted on knife-edges 14 carried by a fork shaped
bracket 15 secured to the cross bar or casting 2 of the transformer frame, or
otherwise suitably supported. The other end 16 of the oscillating lever carries
a device similar in form to a cam, the same being pivoted to the end of the
lever at 17. A bolt 18, the head of which is, not shown, passes through the
end 16 of the oscillating lever and through a slot 19 in the cam 20, the slot
being curved along ares arranged radially with the bolt 17 as a centre. By
moving the cam 20 so that the clamping bolt 18 is secured in different positions
in the slot 19, it will be observed that the end 21 of the cam may be moved
toward or away from the fulcrum of axis or oscillation of the lever. The hori-
zontal projections of different points in the winding or cam surface 22 of the
cam 20 are thus shifted relatively to the axis of oscillation of the lever 13.
A cord 23 is connected to the winding surface 22 at a point indicated approxi-
mately at 24 and to the lower end of the cord a weight 25 of suitable value is
secured.
The cord 11 which carries the coil 8, engages a winding surface 26 of cylindrical
shape with its axis coincident with the axis of oscillation of the lever 13, to
which the winding surface is fixed. Whatever therefore be the position assumed
by the lever, the lever arm supporting the weight of the coil 8 remains the same.
Such however is not the case with respect to the lever arm formed by the
weight 25 dragging downward upon the cord 23, passing over the winding
surface 22. Owing to the eccentricity of this winding surface the lever arm or
moment about the axis of the lever is greater when the arm 16 is depressed than
when it is raised in the position illustrated.
The weight 25 is so chosen as partially, but not wholly, to counter-balance the
weight of the coil 8. Owing to the change in the lever arms above mentioned it
will be seen that when the coils are close together, the unbalanced weight of the
coil 8 is greater than when the coils are separated from each other.
In describing the operation of our invention it is unnecessary to set forth the
mode of action of a constant-current transformer of the type illustrated, since
the same is well understood in the art.
Concerning the application of our improvement to this type of transformer, we
may state that the decrease in repulsion of the two coils when they are separated
from each other over that which takes place when they are close together, is
probably due to the fact that the reluctance of the magnetic circuit for the
leakage lines of force which return through each coil without threading through
the other, is greater when the coils are separated than when they are close
together. This increase in magnetic reluctance is however small and varies with
the particular type of transformer employed. It will of course be obvious from
what has been said, that the load curve of the transformer instead of being
made a straight horizontal line may be given any other form by suitably changing
the law of the counter balance. Whether or not this be the reason for the
variation in the force of repulsion between the coils, the fact remains that much
variation exists, and that a device constructed as described, for opposing to the
force of repulsion a force which varies with the load, serves to bring the current
in the secondary circuit to the same value, whatever be the relative positions of
the coils, thus establishing the utility of our invention regardless of its theory of
operation.

page_text: Although unessential features of our invention, we may mention that a trans-
former of the type shown in the drawings is preferably enclosed in an iron casing
which may be filled with oil or other material for insulating the parts of the
transformer. With this arrangement the transformer is generally secured to
the casing such as illustrated at 27, by means of brackets 28. The casing 27 is
referably formed of sheet iron and is riveted or otherwise secured to the cast
base plate 29. A block of wood 30 rests on the top of the cast base plate 29,
and if desired may carry the weight of the transformer itself.
Having now particularly described and ascertained the nature of our .said
invention (as communicated to us from abroad) and in what manner the same
is to be performed, we declare that what we claim is:-
1 The method which consists in allowing the force of repulsion between
currents flowing in opposite directions in two coils to cause a relative motion
between the coils and opposing the force of repulsion by a variable force less than
proportional to the displacement of the coils from each other.
2- The method which consists in allowing the force of repulsion between
currents flowing in opposite directions in a plurality of coils to cause a relative
motion between the coils and opposing the force of repulsion by a force which
decreases as the coils separate.
3-The method of shaping the load curve of a constant current transformer
with relatively movable coils which consists in opposing to the force of repulsion
between currents in the coils, a force which is less at some given load than at a
higher load.
4-The method of producing a constant current in the secondary of a trans-
former which consists in allowing the force of repulsion between the currents
in the primary and secondary coils to cause a relative motion between said coils,
and opposing the force of repulsion by a force which decreases as the load
decreases.
5-The method of producing a constant current in the secondary of a trans-
former, which consists in allowing the force of repulsion between the currents
in the primary and secondary coils to cause a relative motion between said
coils, and opposing the force of repulsion by a force which is less at some given
load than at a higher load.
6 The combination of relatively fixed and movable coils, one of which is
attached by suitable means to one end of an oscillating lever, and means for
applying to the lever a turning moment which decreases as the coils separate.
7-The combination of relatively fixed and movable coils, one of which is
attached by suitable means to one end of an oscillating lever, means for applying
to a lever a turning moment, and means for varying the turning moment corre-
sponding to a given relative position of the coils.
8-The combination of relatively fixed and movable coils, one of which is
attached by suitable means to one end of an oscillating lever, a device adjustably
secured to the opposite end of the lever, and having a curved winding surface, the
centers of curvature of parts of which are non-co-incident with the axis of
oscillation of the lever.
9 The combination of relatively fixed and movable coils, one of which is
attached by suitable means to one end of an oscillating lever, a device carried
by the opposite end of the lever, and having a curved winding surface, and means
for shifting the centers of curvature of the winding surface relatively to the
axis of oscillation of the lever.
10 In an alternating current transformer the combination of primary and
secondary coils, means for allowing the force of repulsion between the currents
in the coils to cause a relative motion between the coils, and means for opposing
the force of repulsion by a force which decreases as the load decreases.
11 In an alternating current transformer the combination of primary and
secondary coils, means for allowing the force of repulsion between the current

page_text: 4
in the coils to cause a relative motion between the coils, and means for opposing
the force of repulsion by a force which is less at some given load than at a
higher load.
12 In an alternating-current transformer, the combination of relatively
movable primary and secondary coils, means for opposing to the force of
repulsion between the currents in the coils a force which varies with the load, and
means for varying the rate of variation of the force last mentioned.
13 In an alternating current transformer the combination of relatively
movable primary and secondary coils, and means for opposing to the force of
repulsion between the currents in the coils, a force which varies in such a
manner as to make the current in the secondary coil at full load-equal in value
to the current in the secondary coil when the load is small.
14 The combination of relatively fixed and movable coils, in mutual inductive
relation to each other, an oscillating lever to one end of which one of the coils is
suitably attached, a device having a curved winding surface carried by
the other end of the lever and means for varying the position of the centers of
curvature of parts of said winding surface relatively to the axis of oscillation of
the lever.
THE BRITISH THOMSON-HOUSTON CO. LTD.
J. J. MANHEIM,
A. R. MONKS,
Directors.
ALFRED CLEMENTS,
Assistant Secretary,