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EP 0 153 808 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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20.04.1988 Bulletin 1988/16 |
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Date of filing: 24.01.1985 |
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Transformers
Transformatoren
Transformateurs
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Designated Contracting States: |
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AT BE CH DE FR IT LI LU NL SE |
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Priority: |
07.02.1984 GB 8403155
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Date of publication of application: |
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04.09.1985 Bulletin 1985/36 |
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Proprietor: THE MARCONI COMPANY LIMITED |
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Stanmore
Middlesex HA7 4LY (GB) |
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Inventor: |
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- Richardson, Robert
Chelmsford
Essex (GB)
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Representative: Hoste, Colin Francis et al |
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The General Electric Company p.l.c.
GEC Patent Department
Waterhouse Lane Chelmsford, Essex CM1 2QX Chelmsford, Essex CM1 2QX (GB) |
(56) |
References cited: :
EP-A- 0 033 441 GB-A- 2 004 421
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DE-B- 2 233 501 GB-A- 2 103 885
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] This invention relates to transformers which are particularly suitable for use in
pulse circuits in which a high current pulse at relatively low voltage is converted
into a very high voltage pulse.
[0002] A transformer of this kind can be used in a pulse circuit to provide the operating
power for a high power oscillator, such as a magnetron, which forms part of a radar
transmitter. Such a pulse circuit is sometimes termed a radar pulse modulator. A radar
transmitter can transmit pulses having a very low mark-to-space ratio; that is to
say, transmitted short pulses are spaced apart in time by relatively long intervals
during which echoes of the pulses are returned by intercepted targets to a radar receiver.
The useful range of a radar is related to the power transmitted during the short pulse
periods and it is therefore very important to maximise the power of these pulses,
whilst ensuring that the pulses turn on and off cleanly without the generation of
excessive noise. Following the turn off, or decay, of a transmitted short pulse, the
receiver of the radar is enabled so that it can detect weak radar echoes. It is clearly
important to ensure that the trailing edges of the transmitted short pulses decay
very rapidly and cleanly so that they do not mask echoes received after only a very
short delay from targets at close range.
[0003] These requirements impose stringent demands on the pulse transformer itself as it
may be required to convert an input pulse of only a few hundred volts to an output
pulse voltage of up to 30 kV or even higher, whilst handling a peak pulse power of
the order of two megawatts.
[0004] The present invention seeks to provide an improved transformer which is suitable
for use in a pulse circuit.
[0005] According to one aspect of this invention, a transformer includes a transformer core
material shaped to constitute a closed magnetic loop; a toroidal secondary winding
wound around said core material so as to magnetically couple therewith; a primary
winding part of which comprises a central rigid conductor which is encircled by the
core material; characterised by including a saturable reactor core in the form of
a hollow cylinder encircling said central rigid conductor and which is also encircled
by said core material whereby the primary winding is operative to couple magnetically
with the saturable reactor.
[0006] By forming the saturable reactor core within the transformer so that the primary
winding also forms part of the saturable reactor, the overall inductance can be kept
to a very low value.
[0007] In a high power pulse transformer, the structures can be physically very large, and
the primary currents can also be large, and by combining the transformer function
and the saturable reactor function into a physically integrated unit, the overall
cost and weight can be reduced whilst the electrical performance is much improved.
[0008] The invention is further described by way of example with reference to the accompanying
drawings, in which:
[0009] Figure 1 is a simplified circuit diagram illustrating the function of the transformer
and saturable reactor,
[0010] Figure 2 is a section view showing construction of the transformer incorporating
the saturable reactor.
[0011] Referring to Figure 1 there is shown therein a high voltage transformer 1 which is
adapted to convert a relatively low voltage pulse generated by a pulse forming network
2 into a very high voltage pulse and to make it available at output terminals 3 and
4. The pulse forming network 2 consists of a distributed inductive and capacitance
circuit as diagrammatically illustrated. Networks of this kind are well known and
it is not thought necessary to describe it in further detail. The network 2 is periodically
charged from a low voltage d.c. power supply present at terminals 5 and 6. When the
network is fully charged, the switch 7 is closed thereby permitting the network to
rapidly discharge via a saturable reactor 8 and the primary winding 9 of the transformer
1.
[0012] As the switch 7 is typically a solid state thyristor it can take a finite time to
change from a fully non-conductive state to a fully conductive state, and if appreciable
current were allowed to flow through it during this impedance transition phase a great
deal of power would be dissipated within the switch itself. It is to prevent this
happening that the saturable reactor 8 is provided. As is well known, a saturable
reactor initially behaves as an inductance and therefore controls the rate at which
the build-up of discharge current can occur, but the magnetic core of the saturable
reactor rapidly saturates and then behaves as a very low value inductance, and exhibits
a very low impedance.
[0013] Typically, the power handling capacity of the transformer is very large. Although
the pulse forming network can take a relatively long time to become fully charged,
and therefore to store a predetermined amount of energy, its discharge will occur
extremely rapidly so that the peak power transferred by the transformer is correspondingly
great. Typically, the primary winding 9 of the transformer 1 is only a single turn
although in practice it may consist of two or more turns. The secondary winding 20
has a very large number of turns to provide the required step-up voltage. In order
to obtain a rapid discharge of the pulse forming network 2 once the switch 7 has become
fully conductive, it is important to minimise the inductance of the discharge path.
It has proved very difficult to achieve this in a satisfactory manner. In practice,
output terminal 3 is connected to a high frequency oscillator such as a magnetron,
which generates bursts of oscillations during the time that the high voltage pulses
are applied to it.
[0014] Referring to Figure 2, there is shown in more detail the pulse transformer which
incorporates the saturable reactor as an integral part of it. This figure shows a
section view taken through the central axis of the transformer. The low voltage high
current discharge path is represented by the opposite conductive faces 10 and 11 of
a double- sided printed circuit board 12. This board 12 is held in contact with the
housing of the transformer 1. The primary winding of the transformer consists of those
portions of the conductive sheets 10 and 11 which are adjacent to the transformer,
a solid conductive central boss 13, a stud 24 which connects the sheet 10 to the boss
13, a conductive plate 14, and a plurality of conductive studs 15 arranged on a circle
around the central boss 13 which make contact with the plate 14 and the sheet 11.
The central portion of the sheet 11 is removed, so as not to contact the boss 13.
Alternatively, the studs 15 may be replaced by a cylindrical shell which serves the
same electrical function, but this is less satisfactory.
[0015] The secondary winding 20 of the transformer consists of very many turns of fine wire
wrapped around a transformer core material 21 which is in the form of a circular ring
so that the winding 20 is of a conventional toroidal nature. In practice, the core
material will be mounted in a manner described in our previous UK patent application
8124320, as it is of a relatively delicate mechanical nature. The secondary winding
20 is retained in position by embedding it in a non-conductive resin material 16.
[0016] The magnetic core of the saturable reactor 8 is constituted by a thin sleeve 17 of
a saturable reactor material which closely surrounds the central boss 13. It will
be appreciated that it is entirely surrounded by current flowing in the primary winding
in the same way that the core material 21 of the transformer is surrounded. It therefore
behaves as a saturable reactor in exactly the same way as the conventional series
representation shown in Figure 1.
[0017] As the transformer handles very large currents, it inevitably dissipates a certain
amount of heat and can become fairly hot in operation. In order to transfer the heat
rapidly to a suitable heat sink, an internal metal cylinder 18 is provided in contact
with the resin material 16, but spaced apart from the sleeve 17. Heat can therefore
be extracted via the plate 14 which can be suitably coupled to an external heat sink
system.
[0018] The location of the saturable reactor material in the form of the sleeve 17 makes
it unnecessary to provide an additional winding of the kind usually associated with
a saturable reactor. This enables the inductance of the saturable reactor to be kept
at an extremely low level, so that the pulse from the pulse forming network is not
distorted to any significant extent. The total stray inductance of the transformer
and reactor can be altered by changing the profile of the central boss 13. Thus, in
Figure 2, an annular recess 22 is formed in its outer surface and this has the effect
of increasing the inductance as compared with an unrecessed boss of the same maximum
diameter. It is not necessary that the length of the saturable reactor material sleeve
17 is less than the nominal thickness of the transformer housing, as it can project
from one or both side faces thereof, if it is necessary to accommodate a large volume
of the reactor material.
1. A transformer including a transformer core material (21), shaped to constitute
a closed magnetic loop; a toroidal secondary winding (20) wound around said core material
(21), so as to magnetically couple therewith; a primary winding (10, 24, 13, 14, 15,
11), part of which comprises a central rigid conductor (13) which is encircled by
the core material (21); characterised by including a saturable reactor core (17) in
the form of a hollow cylinder encircling said rigid conductor (13) and which is also
encircled by said core material (21), whereby the saturable reactor (17) is operative
to couple magnetically with the primary winding (10, 24, 13, 14, 15, 11) but not the
secondary winding (20).
2. A transformer as claimed in claim 1 and wherein the cylinder is in contact with
the central conductor.
3. A transformer as claimed in claim 2 and wherein the outer surface of the central
conductor is profiled in dependence on the inductance value which the transformer
is required to exhibit.
4. A transformer as claimed in claim 1, 2 and 3 and wherein heat conductive means
are positioned in proximity to the secondary winding so as to extract the heat therefrom.
5. A transformer as claimed in claim 4 and wherein the heat conductive means comprises
a cylinder which is coaxial with said sleeve but is spaced apart therefrom.
1. Transformator mit einem Transformator-Kernmaterial (21), das zur Bildung einer
geschlossenen magnetischen Schleife geformt ist, einer toroidförmigen Sekundärwicklung
(20), die um das Kernmaterial (21) zur magnetischen Kopplung mit diesem gewickelt
ist, einer Primärwicklung (10, 24,13,14, 15, 11), von dem ein Teil einen zentralen
starren Leiter (13) umfaßt, der von dem Kernmaterial (21) umgeben ist, dadurch gekennzeichnet,
daß ein sättigbarer Reaktorkern (17) in Form eines den starren Leiter (13) rings umgebenden
Hohlzylinders enthalten ist, der wiederum rings durch Kernmaterial (21) umgeben ist,
wodurch der sättigbare Reaktor (17) zur magnetischen Kopplung mit der Primärwicklung
(10, 24, 13, 14, 15, 11), jedoch nicht mit der Sekundärwicklung (20) wirksam ist.
2. Transformator nach Anspruch 1 und bi dem der Zylinder mit dem zentralen Leiter
in Berührung ist.
3. Transformator nach Anspruch 2 und bei dem die Außenfläche des zentralen Leiters
in Abhängigkeit von dem Induktanzwert, den der Transformator zu zeigen bestimmt ist,
profiliert ist.
4. Transformator nach Anspruch 1, 2 und 3 und bei dem wärmeleitende Mittel in Nachbarschaft
zur Sekundärwicklung angeordnet sind, um so die Wärme von dieser abzuziehen.
5. Transformator nach Anspruch 4 und bei dem das wärmeleitende Mittel einen Zylinder
umfaßt, der koaxial mit der erwähnten Hülse, jedoch mit Abstand zu dieser angeordnet
ist.
1. Transformateur, contenant un matériau (21) de noyau de transformateur, ayant une
configuration telle qu'il constitue une boucle magnétique fermée, un secondaire toroïdal
(20) enroulé autour du matériau (21) de noyau afin qu'il soit couplé magnétiquement
à lui, et un primaire (10, 24, 13, 14, 15, 11) dont une partie comprend un conducteur
central rigide (13) qui est entouré par le matériau (21) de noyau, caractérisé en
ce qu'il comprend un noyau (17) d'enroulement saturable à réactance sous forme d'un
cylindre creux entourant le conducteur rigide (13) et qui est aussi entouré par le
matériau (21) de noyau, si bien que l'enroulement saturable à réactance (17) assure
le couplage magnétique avec le primaire (10, 24,13, 14, 15, 11) mais non avec le secondaire
(20).
2. Transformateur selon la revendication 1, dans lequel le cylindre est au contact
du conducteur central.
3. Transformateur selon la revendication 2, dans lequel la surface externe du conducteur
central est profilée en fonction de la valeur de l'inductance que doit présenter le
transformateur.
4. Transformateur selon l'une quelconque des revendications 1, 2, et 3, dans lequel
un dispositif conducteur de la chaleur est placé à proximité du secondaire afin qu'il
en extraie de la chaleur.
5. Transformateur selon la revendication 4, dans lequel le dispositif conducteur de
la chaleur est un cylindre coaxial au manchon mais distant de celui-ci.