1. * GB780079 (A)
Description: GB780079 (A) ? 1957-07-31
Electric transformer
Description of GB780079 (A)
PATENT SPECIFICATION
..... Date of filing Complete Specificat Application Date: Oct. 12,
1954.
Complete Specification Published; tion: Oct. 12, 1955.
No. 29346/54.
: July31, 1957.
Index at acceptance:-Class 38(2), T1F, T7(A4: A5: C5).
International Classification:-H021.
COMPLETE:SPEC!OIFliOATI:ON Electric Transformer 1, FRANZ HIRSCHMANN,,
Of 9,3, 'Highview Road, London, W.d3, a British Subject, do hereby
declare the invention, for which I pray that a patent may be granted
to me, and the mnethod by which it is to be performed, to be
particularly described in and by the following statement:-
The invention relates to electric stray flux transformers with movable
magnetic shunts.
Such transformers are mainly used for 'applications, like arc welding
and arc furnaces, where the short circuit current has to, be not much
higher than the load current at.the normal load voltage, and where
load current and short-circuit current have 'to be adjustable in wide
limits. The movable magnetic shunts are arranged so that a share of
the main flux is diverted to pass through ithem, if the secondary
lcoils of the transformer are loaded.
The size of this share changes with the position of the one or more
movable shunts, according $to their distance from 'the centre of the
main core and the magnetic resistance of the lair gaps between main
core and magnetic shunts.
Stray flux,transformers of the described type tend' to vibrate
heavily, when loaded, unless their components are made and assembled
to very close limits., Such limits are difficult to maintain with
laminated, transformer cores. The excessive vibration causes noise,

2. and sometimes instability of the arc.
Object of the invention is a stray flux transformer which avoids these
faults, and which is built up of a small number ou simple components.
The electric stray flux transformer according to the invention has one
or more movable magnetic shunts which bridge the main transformer core
between primary 'and 'secondary coils, guide rods& mounted' on. the
main core on its side of the planes defined by the air - gaps between
the main core and the movable magnetic shunts, and bearings sliding
along said guide rods, said bearings being mounted on the movable
shunts! and protruding across the air gap ibetween the main core and
the movable shunts.
An example of the invention is shown in the drawings filed with the
Provisional Specification.. Figure 1 is a side view, with part of the
main, core cut away along the line A-A of Figure 2, Figure 2 is 'a top
view of such a stray flux transformer, with part of the main core cut
away along the line B---B of 'Figure 1.
The main core 1 of the transuormer carries primary coils 2 and
secondary coils 3. The main core is bridged between, the primary and
secondary, coils by movable magnetic shunts 4, the position of which
is. altered by spindle 5 and handwheel 6. The spindle 5 consists of
'two parts with left han'd thread and right 'hand thread respectively.
The movable shunts consists of the nuts,7,which are shifted by the
spindle 5, and the laminations 8 held together and attached to the
protruding parts 15 of the nut 7 by screws or rivets 113. The
laminations '8 are built up vertically to the laminations of the main
core 1. Some of ithe laminations 'of the movable 'shunts 'are of
shorter length in, order to fill out that part of 'the width of ithe
air gap which corresponds to the protruding parts '115, and is clamped
by 'the traversing spindle; all laminations are rectangular in shape.
The 'coils spacers 'and supporxts 9 are aattached to the main core 1
by the core clamping bolts '10, and each carry one guide rod, 11; the
bearings 12 are mounted oan, the nuts 17 of the movable shunts 4 by
screws 14 which pass through elongated holes in the bearings 12.. The
bearings 12 will be aloose during assembly, so that they do not
obstruct it; they can be 'adjusted',after rthe 'assembly of the
transformer,has 'been' completed, so that the,gaps against the main
core 1 on 'both 'sides of the movable shunts are,of equal size. The
bearings 'are secured, in the final position, by tapered pins, not
shown in. the drawing. The position of the guide rods lIl can be
adjusted, by moving the coils spacers 9' relative to the main core 1.
Bars '16 connect the guide rods 1,1, and form the bearings for the
spindle 5.
The,core clamping bolts I10 have to be in78S0079 sulated against each
other and against the spindle 5, so as to avoid a short circuit for a

3. part of the main flux. The bolts can be insulated for this purpose
against the metallic coil spacers 9 by insulating washers; the coil
spacer 9 can intead be made of an insulating material. The same result
can be achieved by equipping the bearings 12 and 'the bars 16 with
inserts of an insulating material, preferably a high-polymer plastic
material like nylon. The bearings 12 can be closed, as shown in the
drawing, or slotted, or open and surrounding only part of the
circumference of the guide rods 11, which themselves can be round as
shown or have any other cross section, suitabe for the bearings. The
bearings can be elastically mounted on the nuts, in order to damp any
vibrations.
The guide rods '11 which are mounted outside the area of the movable
shunts and cn the main core side of the planes defined by the air gaps
do not prevent any part of the width of the air gap as measured
between the primary and the secondary coils of one leg from being used
as a conductor of the magnetic flux through the shunts. The width of
the movable shunts as measured between the primary and the secondary
coils of one leg is on the transformer shown in the drawing
substantially filled with laminations, apart from the small gap
between shunts and coils which has to be held for reasons of
electrical insulation. A greater width filled with laminations in the
movable shunts reduces the current at the minimum setting when both
shunts are moved near to each other, and it increases the regulating
range of the transformer; it makes it possible to design the
transformer with a larger air gap between main core and movable
magnetic shunts, thus improving its physical and mechanical stability.
The British Patents Specifications 426,352 and 699,319 describe stray
flux transformers with movable magnetic shunts on which the guide rods
are positioned between the laminations of the movable shunts, in the
air gap or on the movable shunt side of the planes defined by,the air
gaps.
These transformers require for their assembly very accurately made
components, without the possibility of any adjustment after assembly;
the width of the air space between the primary and secondary coils
can, for these transformers only partly be utilised for the conduction
of a stray flux through movable magnetic shunts.
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