Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to leakage reactance
transformers, particularly those suitable for use in
supplying electric arc welding currents or in other
situations where current control is required.
At the present time, there are basically two
distinct types of leakage reactance welding transformers.
These are commonly referred to as the moving coil type
and the moving shunt type.
The moving coil transformer has a fixed secondary
winding and a primary winding coil mounted for movement
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along the centre legs of the transformer core towards
and away from the fixed secondary. By positioning the
movable coil at maximum spacing from the secondary, the
leakage reactance of the transformer is at a maximum and
; 15 the volt/amp (V/A) output is a-t a minimum. When the coils
are broug~tclose together, the leakage reactance is
' minimised and the V/A output is at a maximum.
The rate of increase of leakage reactance with
respect to distance between the windings is not linear but
2C logarithmic and so in order to achieve a reasonable
variation-in the V/A output between the minimum and
maximum values, the transformer core must be made with a
long leg length. This results in high transformer costs.
The moving shunt transformer includes a steel
shunt movably mounted on a frame located between the primary
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and secondary windings ancl capable of movement into
and out of the space between the windings. The
positioning of the shunt bet~een the windings increases
the leakage reactance and provides minimum V/A output
determined by the size o the shunt and the sum of the
air gaps between the shunt and the core. Maximum V~A
output is achieved by fully withdrawing the shunt but
because the windings must be spaced for the shunt the
maximum that can be achieved is limited.
When design requirements dictate a low V/A
requirement or a large min/max ratio then the size of the
shunt must be increased and the air gaps decreased thus
increasing the magnetic forces on the shunt. This increases
the need for precision s~ides to accurately guIde the
shunt frame between the windings. As the slides wear,
jamming and other problems occur and complex arrangements
are required to overcome this problem.
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A number of different transformer constructions
in which the moving coil an~ shunt functions are combined,
are described in the patent literature- for example,
British Patents 227,360 Schrodder, 642,326 National Cylinder
-~ Gas Company, 764,699 Metropolitan Vickers Electrical Company
~, Limited and 1,162,972 The English Electric Company Limited,
,- U.S. Patent 2,572,455 Dunn and French Patents 1,014,815
and 1,463,203 Testuz. However, each suffers from the
disadvantage that it is not suficiently
simple to manufacture to be a commercially
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attractive alternative to the transformers described above.
In one aspect therefore, the invention provides
in a transformer suitable for supplying electrical arc
welding current comprising a magnetic core formed of a
stack of laminated core material and having a closed flux
path, primary and secondary windings having axial ends on
said core, one of said windings being stationary and the
other being movable relative to the stationary wlnding ~`
to vary the current output of the transformer, and a mag-
10 netic shunt means adapted for movement from a :Eirst posi-
: tion in which it contributes to the leakage reac~ance of
` the transformer, to a second position in which it contributes
` substantially no leakage reactance, at least that portion
of said core between the primary and secondary windings being
;: arcuate and said movable winding being arcuatel~ ~ovable
along said portion, said shunt means being movable with said
movable winding, such that when said movable winding is
most remote from the other winding, said shunt means is in
: its first position, and when said movable winding is in close
proximity to the other winding, the shunt ~eans is in its : .:
second position, the impr~vement comprising a keyhole-shaped ::
opening in said core, said opening defining an arcuate por~
tion and two spaced legs extending therefrom with a gap
between said legs, a keeper secured to the free ends of
said legs to close the flux path, the stationary winding ~ .
surrounding one of said legs and being free of penetration
by said keeper, the movable winding surrounding said arcuate .
portion, said magnetic shunt means substantially bridging
said gap between said legs when in said first position,
wherein most of the surface area of an axial end of the .::. .
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movable winding is in overlapping face-to-face relationship .
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with most of the surface area of an axial end of the stat-
ionary winding when the windings are brought into close
proximity, and said windings cannot be placed in con-
; centric relationship.
In its most preferred form the magnetic core isformed with a substantially circular aperture substantially
concentric with said arcuate portion, and rectangular open-
ing communicating with said aperture to create said legs
on either side thereof, said sh~lt being located within
said aperture and bridging the opening therein in said
first position. Thus, the core may be regarded as having a
"key-hole" window therein.
The invention also consists of a method of manufacturing
a transformer comprising the steps of forming an opening
in a stack of laminations to form a magnetic core, mounting
primary and secondary windings on said core with one wind-
ing being movable towards and away from the other winding ;~
along an arcuate portion of said core, mounting magnetic
shunt means within said opening to be movable with said
one winding such that when said movable winding is most
` remote from the other winding said shunt means is in a
first position in which it contributes to the leakage
reactance of the transformer and when said movable winding -
is close to the other winding said shunt means is in a
second position in which it contributes substantially as
leakage reactance , characterized in that said opening is
formed to define said arcuate portion and two spaced legs, i~
securing a keeper to the free ends of said legs to close
the flux path of said core, said magnetic shunt means being
formed from that portion of the laminations removed to
form the arcuate portion of said opening and substantially
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bridging the gap between said legs in said first position.
In order that the invention may be more readily
understood, two embodiments of the invention will now be
described with reference to the accompanying drawings in
which :
igure 1 is a front elevation of a transformer
~: assembly embodying the invention;
Figure 2 is a side elevation of the assembly of
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.` 10 Figure 3 is a perspective view of the transformer
core;
Figure 4 is a front view of the transformer housing;
. Figure 5 is a front view of modifications including ..
a double core transformer according to the invention;
Figure 6 is a perspective view of the core used in
the embodiment of Figure 5, and ;
Figure 7 is a plan view of one preferred form of : :
! lamination configuration. ;
Referring firstly to Figures 1 to 3, the transformer
: 20 includes a steel core 1 formed from a stack of steel sheet
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; laminations which are cut in the coniguration sh~wn
in Figure 3 by punching or any other suitable means.
The stack of steel sheets is held together by clips 2
secured in slots S formed in the edges of the sheets.
It will be noted that the basic core element is of square
configuration with one corner C of the square rounded and
having a centrally position 'key-hole' K cut therethrough.
The magnetic circuit of the core 1 is completed by a laminated
` steel keeper A of rectangular configuration which is welded
to thè side of the core element through which the 'key-hole'
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K opens. The keeper A is cut from the 'key-hole'cut out
from the core 1 and comprises that portion between the legs
of the core 1 extended to a position adjacent the periphery
of the circular portion of the 'key-hole' configuration.
l 15 The core 1 is suitably mounted on a base 3 on which the
i casing 4 (Figure 4) for the transformer is secured.
Prior to the securement of keeper A to the core 1,
a secondary winding coil 5 is positioned around one leg of
the core 1. The coil 5 is formed around brackets 6 by
means of which the coil 5 is secured to the base 3. The
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coil 5 is formed from an aluminium strip insulated by
Nomex paper or any other suitable combination. Leads 7
are provided for connection to output terminals 8 (Figure 4).
Also prior to securement of the keeper A to the
core 1, a primary winding coil 9 wound from glass covered
aluminium wire or other suitable material on three suitably
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insulated support brackets 10 is positioned on the
core and secured to a supporting frame 11 of the
configur~tion shown by bolts 12 passing through the
brackets 10 as shown. The frame 11 is in turn pivotally
mounted on brackets 13 extending on either side of the
core 1 and rigidly secured thereto by a cross bar 14.
The bearings supporting frame 11 are preferably tapered
to reduce transmission of vibrations. The frame 11 has
extension lugs 15 extending downwardly and inwardly
towards the core 1 and through which bo]ts 16 pass for
securing a clamping bracket 17 adapted to hold a laminated
steel shunt 18. The shunt 18 comprises one of the sectors
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~` remaining in the 'key-hole' cut out after the keeper A has
been cut therefrom so its lower end matches exactly the
curvature of the central opening of the 'key-hole' K. Thus,
the use of this sector as the shunt 18 not only ensures
matching curvature of the shunt 18 and the 'key-hole' K
whereby pivotal movement is facilitated but also utilizes
, the material cut out from the core 1 whereby the economics
of manufacture are improved... The dimensions of the shunt
18 are such as to bridge the gap between the legs of the
core 1 and form a flux path between the legs. The shunt 18
is of course electrically insulated from the frame 11 bolts 16
and bracket 17 by suitable insulating washers and bushes.
It will be evident from the above that the primary
~ winding coil 9 and the steel shunt 18 are supported by a
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common frame 11 with the shunt 18 at about 180 to
the coil 9, the common frame 11 being pivotally mounted
on brackets 13. Thus, when the coil 9 is moved arcuately
from the position shown in Figure 1 to a position adjacent
the secondary coil, the shunt 18 will be moved through
the same angle to a position wherein it is remote rom the
gap between the legs of the core 1.
In this way, the transformer embodying the
~` invention effectively combines the moving coil and moving
shunt features of the prior art devices. In th~ position
shown in~Figure 1, the coil 9 is remote from the coil 5
while the shunt is in the most effective position to
maximise the additional leakage reactance introduced by
the shunt and minimum V/A output is achieved. Maximum V/A
output is achieved when the coil 9 is fully pivoted to a
position adjacent secondary winding coil 5 and since the
shunt is completely removed from the gap it contributes
j effectively no leakage reactance to the magnetic circuit.
` Since the transformer embodying the invention
: 20 incorporates substantial leakage reactance due to the
spacing of the coils in the position shown in the dr~wing,
the size of the shunt 18 is relatively much smaller and
the air gaps greater than in the prior a`rt moving shunt
design. Thus the usually mandatory requirements of the
moving shunt design are avoided and a greatly simplified
design is permitted.
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; One particularly preferred lamination
; shape is shown in Figure 7. The lamination has a
central cut-out M for the keeper A and a circular
- cut-out N which in turn defines the sector O to be
used as the shunt 18. It will be seen that the
cut-out M has one portion P of one side extending at
an angle to the remainder of the side. This increases
the size of sector O to therefore increase the volume
of metal included in the shunt 18 so that the low-curren~ .`
~,10 Qutput is improved. The remaining smaller sectors are
wasted.
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It will be apparent from the drawing that
the amount of steel used in the embodiment described
is substantially less than for the moving coil device
and approximately the same as for the moving shunt
design. Thus, in view of the simple nature of the design,
a greater min/max V/A output ratio can be achieved for
a lower cost. By using the section cut from the core 1
to form both the keeper A and the shunt 18, a particularly
efficient commercial transformer can be manufactured
which'avoids all of the disadvantages inherent in the
prior art combined moving coil/shunt arrangements
rsferred to above. The described arrangments solve the
problems associated with the manufacture of a pivoted
mov.ing coil/shunt transformer and which are largely ignored
by the prior art such as French Patent 1,463,203.
It will be appreciated that the roles played by
the windings 5 and 9 may be reversed, i.e., winding 5 may
operate as the primary while winding g is the secondary.
As shown in Figure 5, the transformer
described above is enclosed in a suitable casing 4 having
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a front panel B formed with an arcuate slot C through
which a threaded operating knob D passes for engagement
with a boss 19 (Figures 1 and 2) on the supporting frame
11. Thus, arcuate movement of the knob D moves the primary
winding coil 9 an* the shunt 18 as described to adjust the
V/A output of the transformer. The knob D may be ~ixed
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in any desired position by screwing the knob into
engagement with the front panel B. A nylon or like
washer (not shown) is positioned between the panel B
and the knob D for smooth operation.
; 5 Alternatively, the knob D may be internally
threaded to engage a bolt passing through an arcuate
; slot (not shown)in the rear panel of the casing 4,
through holes in the frame 11 and projecting through the
slot C in the front panel B. This arrangement has the
adva~tage that the front and rear panels may be identical.
In a further alternative, the manual arrangements
- described above may be replaced by a winder operating a lead
screw adapted to move the frame 11 between its extreme
operating positions.
In the alternative form shown in Figures 5 and 6,
the magnetic core of the transformer is extended by joining
two cores similar to 1 described above interleaved together
as shown in Figure 6 and held together by nylon rivets 20.
Alternatively, the ends of laminations in each core may be
welded together in some suitable manner either with or
without interleaving as shown. A single winding 5 is
positioned around one leg of the composite core and two
windings 9 and steel shunts 18 are arranged as in the
first embodiment of the respective core components 1~
~he arrangement works in the same manner as before only
the two windings 9 are connected in parallel to constitute
the secondary winding of the transformer and both are moved
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towards winding 5, which is the primary in this case,
when additional V/A output is required. If desired,
the two support frames for cores 9 and shunts 18 may be
interconnected by a suitable linkage (not shown) so that
they move in union. Howeverj separate movement provides
for a greater V/A range and allows individual outputs
to be derived ~rom each sécondary so as to provide a dual
operator welder.
By using basically the same core stamping for
both em~ diments a wide range of V/A outputs can be
accommodated at a lower cost.
It will be appreciated that the specific core
conEiguration and other details described above are not
essential to the invention. For example, while the
'key-hole' configuration is preferred for the core window
opening, it may be possible to leave the sector of the
'key-hole' opposite to the sector removed for the shunt 18
intact so that the opening in the core 1 is P-shaped.
However, with khis type of arrangement the coi]. 9 would
need to be enlarged to receive the shunt 18 and a linkage
mechanism interconnecting the coil 9 and shunt 18 would be
required to move the shunt 18 in the opposite direction
to the coil 9. For these reasons this modification may
not be-a commercially attractive proposition although
still technically feasible.
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