[0001] The present invention relates to a wound electrical component comprising a yoke having
an aperture through which a coil passes.
[0002] Microwave ovens usually use a magnetron to generate microwave for cooking food. Magnetrons
require high voltages and microwave ovens therefore include high voltage transformers
to provide the required high voltages.
[0003] Figures 1 and 2 show a typical high voltage transformer for powering the magnetron
of a microwave oven. The high voltage transformer has an E-shaped core 1 and an I-shaped
core 3 which joined together.
[0004] The E-shaped core 1 is formed with two channels. A primary coil 5 is wound from wire
5a, and is inserted to the channels of the E-shaped core 1. A filament coil 7 is wound
from wire 7a, and is inserted into the channels of the E-shaped core 1 above the primary
coil 5. Pass cores 9 are inserted into the channels of the E-shaped core 1 above the
filament coil 7. Finally, a secondary coil 11 is inserted into the channels of the
E-shaped core 1 above the pass core 9.
[0005] Strips of insulation paper P are wound around the primary coil 5, the filament coil
7, the pass cores 9 and the secondary coil 11, to electrically insulated the coils
5, 7, 9 from the cores 1, 3. A sheet S of insulating material, for example mica, is
disposed between the primary coil 5 and the paper wrapped therearound.
[0006] A terminal plate 14 provided with a terminal 13 is fixed by adhesive tape T to one
end of the primary coil 5. Similarly, a terminal plate 14 provided with a terminal
13 is fixed by adhesive tape T to one end of the secondary coil 11.
[0007] The manufacture process of a typical high voltage transformer for a microwave oven
will now be described.
[0008] The primary coil 5 is wound using wire 5a. A mica sheet S is then wound around the
winding of the primary coil 5 and paper P is in turn wound over the mica sheet S.
The terminal plate 14 is then fixed to the coil 5 using adhesive tape T. The completed
primary coil 5 is then slipped over the middle arm of the E-shaped core 1 and pushed
down to sit at the bottom of the channels in the core 1.
[0009] The filament coil 7 is wound and then wrapped in insulation paper P. The assembled
filament coil 7 is slipped over the middle arm of the E-shaped core 1 and pushed down
to rest on top of the primary coil 5. The pass cores 9 are wrapped with insulation
paper P and positioned on the filament coil 7.
[0010] The secondary coil 11 is wound and then wrapped in insulation paper P. The terminal
plate 14 is fixed to one end of the secondary coil 11 using adhesive tape T. The assembled
secondary coil 11 is then slipped over the middle arm of the E-shaped core 1 and pushed
down to rest on top of the pass cores 9.
[0011] Once the coils 5, 7, 11 have all been mounted to the E-shaped core 1, the arms of
the E-shaped core 1 are bridged with the I-shaped core 3. The I-shaped core 3 is welded
to the free ends of the arms of the E-shaped core 1 to form the transformer's yoke.
[0012] When the yoke has been completed, the high voltage transformer is inserted into an
impregnation tank containing an impregnating material. The impregnating material impregnates
the transformer and protects it from rust and reduces the noise produced in use. The
transformer then is dried and used.
[0013] A problem with the afore-mentioned transformer is that insulation paper P must be
manually wound around the coils and the pass core and then fixed with adhesive tape.
Furthermore, it is desirable that the step of winding the mica sheet about the primary
coil be avoided to simplify manufacture.
[0014] It is an aim of the present invention to ameliorate the afore-mentioned problems.
[0015] A wound electrical component according to the present invention is characterised
in that an insulating liner is provided in the aperture between the coil and the yoke.
It will be appreciated that the use of the liner reduces the amount of insulation
paper required and that it is a simpler process to insert a liner than wrap a coil
with paper as required by the prior art.
[0016] Although, the present invention arose in the field of transformers microwave ovens,
it will be appreciated that the present invention may be usefully employed in other
fields; indeed wherever sheets of insulation material have been wrapped around coils
to insulate the coils from the yoke. However, the present invention is particularly
useful in respect of components adapted for operation with voltages greater than or
equal to 300V, i.e. high voltages and greater.
[0017] A wound electrical component consist of one coil, for example a choke or an autotransformer.
However. the present invention can be usefully applied to components having a further
coil passing through the aperture, for instance a transformer.
[0018] Conveniently, the yoke comprises an E-shaped member and an bar-shaped member linking
the arms of the E-shaped member, the or each coil being arranged around the central
arm of the E-shaped member and an insulating liner being provided in each aperture
between a coil and the yoke.
[0019] Since, adhesive tape is no longer required for fixing insulating paper to coils.
It is desirable that the use of adhesive tape be avoided altogether. Accordingly,
a terminal for connecting a coil to a lead may be fixed to the yoke. An alternative
is to mount a terminal to a liner.
[0020] Embodiments of the present invention will now be described, by way of example, with
reference to the accompanying drawings, in which:
Figure 1 shows a prior art high voltage transformer;
Figure 2 is a sectional view of the transformer of Figure 1;
Figure 3 shows a first embodiment of a transformer according to the present invention;
Figure 4 shows a second embodiment of a transformer according to the present invention;
and
Figure 5 is a sectional view of the transformer of Figure 4.
[0021] Referring to Figure 3, those elements of the high voltage transformer shown that
are common to both the present embodiment and the prior art described above have same
reference signs and will not be described again. The high voltage transformer comprises
an E-shaped core 1 and an I-shaped core 3 which are joined to form a yoke.
[0022] First and second liners 20 of insulating material are received within each channel
in the E-shaped core 1. A primary coil 5, wound from wire 5a, is inserted into the
channels of the E-shaped core 1 such that the liners 20 are between the primary coil
5 and the E-shaped core 1. A filament coil 7 is similarly inserted into the channels
and rests on the primary coil 5. Pass cores 9 are inserted into respective channels
and rest on the filament coil 7 and are separated from the E-shaped core 1 by the
liners 20. A secondary coil 11 is inserted the channels of the E-shaped core 1 and
rests on the pass cores 9. The secondary coil 11 is also insulated from the E-shaped
core 1 by the liners 20.
[0023] Strips of insulation paper P are used to insulated the primary and filament coils
5, 7 from each other, to insulate the pass cores 9 from the secondary and filament
coils 11, 7 and to insulate the secondary coil 11 from the I-shaped core 3. Only the
filament coil 7 has strips of paper wrapped completely around and through its centre.
[0024] Screw holes 1a, 3a are provided in faces of the "upright" of the E-shaped core 1
and the parallel face of the I-shaped core 3 respectively. The screw holes 1a, 3a
receive screws 25 to fix terminal plates 23 to respective cores 1, 3.
[0025] The terminal plates 23 are formed with steps to bring their terminals 21 away from
the cores 1, 3.
[0026] The liners 20 and the terminal plates 23 are moulded from polyphenylene sulphide
or polybutylene terephthalate. The primary coil 5 is installed without first being
wound with the insulation paper P thereby reducing the number of steps in the manufacturing
process.
[0027] Referring to Figures 4 and 5, a second embodiment of a transformer according to the
present invention differs from the first embodiment, described above, in the form
of the liners 30 and the use of some paper insulation on the primary coil 5.
[0028] The liners 30 are generally L-shaped and line the floors and outer walls of the channels
in the E-shaped core 1. The liners 30 are provided with flanges 30a to which terminals
32 are fixed with screws 31. This avoids the need to screw terminal plates to the
cores 1, 3.
[0029] Insulator paper P is used on the primary winding to insulate it from the central
arm of the E-shaped core 1 and from the filament winding 7, on the filament winding
7 to insulate it from the central arm of the E-shaped core 1, the primary winding
5 and the pass cores 9, on the pass cores 9 to insulate them from the secondary winding
11, and on the secondary winding to insulate it from the central arm of the E-shaped
core 1 and the I-shaped core 3. It should be noted that only the filament coil 7 is
completely wrapped with paper.
[0030] The liners 30 are moulded from polyphenylene sulphide or polybutylene terephthalate.
[0031] A method of assembling the transformer shown in Figure 3 will now be described.
[0032] The liners 20 are inserted into the channels of the E-shaped core 1. The primary
coil 5 is formed with the wire 5a and is slipped over the central arm of the E-shaped
core 1 and pushed to the bottom of the channels, without the primary coil 5 being
wound with paper or a mica sheet.
[0033] The filament coil 7 is wrapped about with insulation paper P, slipped over the central
arm of the E-shaped core 1 and pushed down to rest on the primary coil 5. The assembled
pass cores 9 are inserted into the channels of the E-shaped core 1 on top of filament
coil 7. The exposed upper parts of the pass cores 9 are covered with insulation paper
P. The secondary coil 11 is slipped over the central arm of the E-shaped core 1 and
brought to rest on the pass core 9. Strips of insulating paper P are then placed on
the secondary coil 11 to insulate it from the I-shaped core 3.
[0034] Once all the coils 5, 7, 11 and the pass cores 9 are in position, the I-shaped core
3 is welded to the E-shaped core 1 to complete the yoke. The assembled transformer
is soaked in impregnating material in a tank and thereafter dried.
[0035] The terminal plates 21 are screwed to the yoke using screws 25 which pass into the
screw holes 1a, 3a.
[0036] In the above assembly process, insulating paper is not wrapped completely around
either the primary or the secondary coils 5, 11 and no mica sheet S is wrapped around
the primary coil 5. Consequently, the manufacturing process is simplified. The terminal
plates 23 are screwed to the cores 1, 3 avoiding the need for adhesive tape.
[0037] A method of assembling the transformer shown in Figure 4 will now be described.
[0038] The primary coil 5 is wound from wire 5a. Insulation paper P is then partially wound
around the turns of the primary coil 5 (see Figure 5). Insulation paper P is wrapped
around the turns of the filament coil 7. A strip of insulating paper P is wrapped
around the top of each of the pass cores 9. Insulation paper P is also partially wrapped
around the secondary coil 11 (see Figure 5). Thereafter, the primary coil 5, the filament
coil 7, the pass cores 9 and the secondary coil 11 are stacked in the liners 30, to
which the terminals 32 have previously been screwed. The liners 30 and stack of coils
are inserted into the E-shaped core 1 over the central arm thereof. The I-shaped core
3 is then welded to the ends of the arms of the E-shaped core 1.
[0039] The assembled transformer is then impregnated with impregnating material in a tank
to prevent rust forming and to reduce noise. The transformer then is dried and used.
[0040] The use of the liners 30 means that a mica sheet need not be wound about the primary
coil 5. Although insulation paper P is still used, it only partially wraps most of
the components thereby simplifying assembly and the cost of the insulation paper P
used.
[0041] Although the preferred embodiments of the present invention have been disclosed for
illustrative purposes, those skilled in the art will appreciate that various modifications,
additions and substitutions are possible.
1. A wound electrical component comprising a yoke (1, 3) having an aperture through which
a coil (5) passes, characterised in that an insulating liner (20;30) is provided in the aperture between the coil and the
yoke.
2. A wound electrical component according to claim 1, adapted for operation with voltages
greater than or equal to 300V.
3. A wound electrical component according to claim 1 or 2, wherein at least one further
coil (7, 11) passes through the aperture.
4. A wound electrical component according to claim 1, 2 or 3, wherein the yoke comprises
an E-shaped member (1) and an bar-shaped member (3) linking the arms of the E-shaped
member, the or each coil (5, 7, 11) being arranged around the central arm of the E-shaped
member and an insulating liner being provided in each aperture between a coil and
the yoke .
5. A wound electrical component according to any preceding claim, wherein a terminal
(21;32) is fixed to the yoke for connecting a coil to a lead.
6. A wound electrical component according to any one of claims 1 to 5, wherein a terminal
(32) is mounted to a liner.
7. A high voltage transformer for a microwave oven comprising an E-shaped core provided
with a channel for piling up a primary coil, a filament coil, a pass core and a secondary
coil sequentially, and an I-shaped core connected to the E-shaped core, characterised
in that bobbins of insulation materials being mounted at each inner wall of the channels
of he E-shaped core, terminal plates being connected at each outside of the E-shaped
core and I-shaped core, terminals being connected to each terminal plate.
8. A high voltage transformer for a microwave oven comprising an E-shaped core provided
with a channel for piling up a primary coil, a filament coil, a pass core and a second
coil sequentially, and an I-shaped core counted to the E-shaped core, characterised
in that the bobbins of insulation materials being mounted at each inner wall of the
channels of the E-shaped core, said bobbins being formed with a terminal fixing part
therein, terminals being connected to the terminal fixing part.