METHOD AND DEVICE IN MANUFACTURING A TRANSFORMER/REACTOR

PROCEDE ET DISPOSITIF INTERVENANT DANS LA FABRICATION D'UN TRANSFORMATEUR / REACTEUR

English Abstract

Gas or water-cooled transformer/reactor and a method for manufacturing the
same having at least one gas or water-cooled transformer/reactor provided with
winding, the winding comprising a high-voltage cable (111) and at least one
additional member (9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) is wound into
the winding (2, 3, 4) arranged around the legs (22, 23, 24) of the
transformer/reactor.

French Abstract

La présente invention concerne un transformateur / réacteur refroidi par gaz ou eau. L'invention concerne également un procédé de fabrication de ce transformateur / réacteur pourvu d'un enroulement, lequel enroulement comprend un câble haute tension (111), un élément additionnel au moins (9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) étant enroulé dans l'enroulement (2, 3, 4) entourant les jambes (22, 23, 24) du transformateur / réacteur.

Claims

13



CLAIMS

1. Method of manufacturing a gas or water-cooled
transformer/reactor having at least one winding, characterized in
that the winding comprises a high-voltage cable (111) having an
insulated electric conductor comprising at least one live conductor (112),
also comprising a first layer (113) with semiconducting properties arranged
surrounding the live conductor (112), a solid insulating layer (114)
arranged surrounding said first layer (113), and a second layer (115) with
semiconducting properties arranged surrounding the insulating layer (114),
and in that the transformer/reactor is designed with at feast one additional
member (9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) which is wound into the
winding (2, 3, 4) when the high-voltage cable (111) is wound around the
legs (22, 23, 24) of the transformer/reactor.
2. Method as claimed in claim 1, characterized in that
a) a first layer of cable is wound,
b) additional members (9, 11, 12, 13, 14, 50, 55, 60, 65, 70,
75) are wound on or applied,
c) an additional layer of cable is wound, whereupon steps b)
and c) are repeated until the entire coil is fully wound.
3. Method as claimed in claim 1, characterized in that
the high-voltage cable is wound at the same time as the additional
members (9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) are being wound on or
applied.
4. Method as claimed in any of claims 2-3, characterized
in that spacers (10) are placed on the winding before the additional
members (9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) are wound on or
applied.
5. Method as claimed in claim 4, characterized in that
spacers (10) are also placed on the winding after the additional members
(9, 11, 12, 13, 14, 50, 55, 60, 65, 70, 75) have been wound on or applied.




14



6. Method as claimed in any of claims 1-5, characterized
in that a cooling tube (9, 11, 12, 13) is wound as additional member in
the winding.
7. Method as claimed in any of claims 1-5, characterized
in that a single tubular member (50), an earthing member (55), a
stabilizing compound (60), a mechanical stabilizer (65), a
noise-suppressing member (70) or an electric transducer (75) is wound in as
additional member in the winding.
8. Method as claimed in claim 6, characterized in that
water flows through the cooling tube (9, 11, 12, 13).
9. Method as claimed in claim 8, characterized in that
a) a thermally conducting compound (10) is sprayed between
the spaces formed between the turns of the winding after the first layer of
cable has been wound,
b) additional thermally conducting compound (10) is sprayed
onto the cooling tube (9, 11, 12) or insulating tube (14) after the cooling
tube (9, 11, 12) or insulating tube (14) has been wound in the spaces
formed between the winding turns.
10. Method as claimed in claim 8, characterized in that
a) a cooling tube (9, 11, 12) or an insulating tube (14) which
has been extruded or embedded in a thermally conducting compound (10)
is wound onto the cable after the first layer of cable has been wound,
b) the thermally conducting compound (10) is shaped to abut
the cables when the second layer of cable is wound another turn.
11. Gas or water-cooled transformer/reactor (1) having at least one
winding wound around the legs (22, 23, 24) of the transformer/reactor,
characterized in that the winding (2, 3, 4) is performed using
an insulated electric conductor comprising at least one live conductor
(112), also comprising a first layer (113) with semiconducting properties




15



arranged surrounding the live conductor, a solid insulating layer (114)
arranged surrounding said first layer (113), and a second layer (115) with
semiconducting properties arranged surrounding the insulating layer (114))
and in that the device comprises at least one additional member (9, 11,
12, 13, 14, 50, 55, 60, 65, 70, 75) wound into the winding (2, 3, 4).
12. Transformer/reactor as claimed in claim 11,
characterized in that the high-voltage cable (111) is cylindrical
in shape.
13. Transformer/reactor as claimed in any of claims 11-12,
characterized in that at least one additional member (9, 11,
12, 13, 14, 50, 55, 60, 65, 70, 75) is placed in the space (8) formed
between each cable (111) during the winding procedure.
14. Transformer/reactor as claimed in any of claims 11-12,
characterized in that the additional member consists of at
least one cooling tube (9, 11, 12, 14) placed in a space (8) formed
between each cable (111) during the winding procedure, the space (8) that
remains between the cooling tubes (9, 11, 12, 14) and the cables being
filled with a thermally conducting compound (10).
15. Transformer/reactor as claimed in claim 14,
characterized in that a cooling tube (9) with circular cross
section is placed in the space (8).
16. Transformer/reactor as claimed in claim 14,
characterized in that a cooling tube (11) with quadratic cross
section is placed in the space (8).
17. Transformer/reactor as claimed in claim 14,
characterized in that a quadratic cooling tube (12) with
concave sides is placed in the space (8).




16



18. Transformer/reactor as claimed in claim 14,
characterized in that the cooling tube (13) is surrounded by
an insert tube containing filler (10).
19. Transformer/reactor as claimed in any of claims 11-12,
characterized in that the additional member consists of a
single tubular member (50), an earthing member (55), a stabilizing
compound (60), a mechanical stabilizer (65), a noise-suppressing member
(70) or an electric transducer (75) in a space (8) between each cable
(111), the space (8) that remains between the additional member (50, 55,
60, 65, 70, 75) and the cables being filled with a thermally conducting
compound (10).
20. Transformer/reactor as claimed in any of claims 14-19,
characterized in that the thermally conducting compound (10)
has low viscosity at high shear rate and is in paste form at rest.
21. Transformer/reactor as claimed in claim 20,
characterized in that the thermally conducting compound (10)
consists of a one or two-component curing silicon rubber provided with a
heat-conducting filler.
22. Transformer/reactor as claimed in any of claims 14-21,
characterized in that the filler consists of either aluminium
oxide, boron nitride or silicon carbide.
23. Transformer/reactor as claimed in any of claims 14-18 or 20-22,
characterized in that the cooling tube (13) is made of dielectric
material such as polyethylene, polypropene, polybutene, polyvinylidene
fluoride, polytetrafluoroethylene or filled and reinforced elastomers.
24. Transformer/reactor as claimed in any of claims 14-18 or 20-23,
characterized in that the cooling tube (13) is manufactured
from high-density polyethylene (HDPE).



17



25. Transformer/reactor as claimed in any of claims 14-18 or 20-24,
characterized in that the cooling tube (13) is manufactured
from cross-linked polyethylene (XLPE).
26. Transformer/reactor as claimed in any of claims 11-25,
characterized in that the high-voltage cable (111) is of a type
comprising a conductor with a plurality of strand parts (112), a
semiconducting layer (113) surrounding the conductor, an insulating layer
(114) surrounding the inner semiconducting layer, and an outer
semiconducting layer (115) surrounding the insulating layer.
27. Transformer/reactor as claimed in claim 26,
characterized in that the high-voltage cable (111) has a
diameter in the range of 20-250 mm and a conducting area in the range of
40-3000 mm2.
28. Transformer/reactor as claimed in any of claims 11-27,
characterized in that the insulated conductor or high-voltage
cable (111) is flexible.
29. Transformer/reactor as claimed in claim 28,
characterized in that the layers (113, 114, 115) are arranged
to adhere to each other even when the insulated conductor or high-voltage
cable (111) is bent.
30. Transformer/reactor as claimed in any of claims 11-29,
characterized in that at least two adjacent layers (113, 114,
115) of the winding have coefficients of thermal expansion of substantially
the same magnitude.
31. Transformer/reactor as claimed in any of claims 14-30,
characterized in that all coolant, in the form of gas or liquid,
designed to cooling the transformer/reactor is arranged to flow through the
cooling tube (13).




18



32. Transformer/reactor as claimed in any of claims 11-31,
characterized in that the winding is flexible and comprises an
electrically conducting core surrounded by an inner semiconducting layer,
an insulating layer of solid material surrounding the inner semiconducting
layer, and an outer semiconducting layer surrounding the insulating layer,
which layers adhere to each other.
33. Transformer/reactor as claimed in any of claims 11-32,
characterized in that said layers are of materials having such
elasticity and such relation between their coefficients of thermal expansion
that the fluctuations in volume in the layers caused by temperature
fluctuations during operation can be absorbed by the elasticity of the
materials so that the layers retain their adhesion to each other at the
temperature fluctuations occurring during operation.
34. Transformer/reactor as claimed in any of claims 11-33,
characterized in that the materials in said layers have high
elasticity, preferably with an E-modulus of less than 500 MPa, more
preferably less than 200 MPa.
35. Transformer/reactor as claimed in any of claims 11-34,
characterized in that the coefficients of thermal expansion of
the materials in said layers are of substantially the same magnitude.
36. Transformer/reactor as claimed in any of claims 11-35,
characterized in that the adhesion between the layers is of at
least the same order of magnitude as in the weakest of the materials.
37. Transformer/reactor as claimed in any of claims 11-36,
characterized in that each semiconducting layer essentially
constitutes an equipotential surface.

Description

CA 02276397 1999-06-29
WO 98/34241 PCT/SE98/00177
METHOD AND DEVICE 1N MANUFACTURING A TRANSFORMER!
REACTOR
TECHNICAL FIELD:
The present invention relates to a gas or preferably water-cooled, cable-
wound power transformer and to a process for manufacturing such a
cable-wound power transformer in the voltage range up to 400 kV.
BACKGROUND ART:
Modern power transformers are usually oil-cooled. The core, consisting of
a number of core legs joined by yokes, and the windings (primary,
secondary, control), are immersed in a closed container filled with oil.
Heat generated in coils and core is removed by the oil circulating internally
through coils and core, which transfers the heat to the surrounding air via
the walls of the container. The oil circulation may either be forced, the oil
being pumped around, or it may be natural, produced by temperature
differences in the oil. The circulating oil is cooled externally by
arrangements for air-cooling or water-cooling. External air-cooling may be
either forced or through natural convection. Besides its role as conveyor
of heat, the oil also has an insulating function in oil-cooled transformers
for
high voltage.
Dry transformers are usually air-cooled. They are usually cooled through
natural convection since today's dry transformers are used at low power
loads. The present technology relates to axial cooling ducts produced by
means of a pleated winding as described in GB 1,147,049, axial ducts for
cooling windings embedded in casting resin as described in
EP 83107410.9, and the use of cross-current fans at peak loads as
described in SE 7303919-0.
The cooling requirement is greater for a cable-wound power transformer.
Forced convection is necessary to satisfy the cooling requirement in all the
windings. Natural convection is not sufficient to cool the cable windings.
A short transport route for the heat to the coolant is important and also


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2
that it is efficiently transferred to the coolant. It is therefore important
that
all windings are in direct contact with sufficient quantities of coolant.
Through DE-A1-2854520, for instance, a resin-embedded coil with highly
flexible plaited cable is known, particularly a commutation coil for a
rectifier
assembly, provided with wound cooling ducts. However, it is not only a
question of taking into consideration a transformed reactor provided with
high-voltage cable with its particular eiectric/magnetic problems.
According to US 5 036 165 a conductor is known having insulation
provided with an inner and an outer layer of semiconducting pyrolized
glassfiber. It is also known to provide conductors in a dynamo-electric
machine with such insulation, e.g. as described in US 5 066 881 where a
semi-conducting pyrolized glassfiber layer is in contact with both the
parallel rods forming the conductor and the insulation in the stator slot is
surrounded by an outer layer of semiconducting pyrolized glassfiber. The
pyrolized glassfiber material is described as suitable since it retains its
resistivity even after impregnating treatment.
OBJECT OF THE INVENTION:
The object of the invention is to provide a transformer/reactor with a
winding procedure whereby additional members are included in the
winding in one or more of the spaces formed between each turn of the
winding. The additional members are selected as required and may be
cooling tubes for gas or liquid, empty tubes which can be used as desired,
earthing arrangements, stabilizing compounds, mechanical stabilizers,
noise-suppressing members or transducers of various types.
Another object of the invention is to provide a transformer of the type
described in the introduction which will enable gas or preferably water-
cooling of a cable-wound power transformer. The invention aims at
cooling each turn in the windings, the coolant being correctly distributed to
satisfy the various cooling requirements of the windings.
_.____~ T _


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3
The invention also aims at eliminating the use of oil-cooling in power
transformers and thus achieving internal cooling which results in lower
weight and higher filling factor, and consequently lower costs.
SUMMARY OF THE INVENTION:
The objects mentioned above are achieved by the method and device
according to the invention having the features defined in the appended
claims.
The present invention relates to a transformer or a reactor comprising a
transformer core wound with cable) arranged so that the winding is
provided with a cooling duct between each cable turn. The cooling duct is
also arranged to transport water to cool all winding turns in the
transformer.
In the device according to the invention the windings are preferably of a
type corresponding to cables with solid extruded insulation used nowadays
for power distribution, e.g. XLPE cables or cables with EPR insulation.
Such a cable comprises an inner conductor composed of one or more
strand parts, an inner semiconducting layer surrounding the conductor, a
solid insulating layer surrounding the inner semiconducting layer, and an
outer semiconducting layer surrounding the insulating layer. Such cables
are flexible, which is an essential property in this context since the
technology for the device according to the invention is based primarily on
a winding system in which the winding is performed with conductors which
are bent during assembly. A XLPE cable normally has a flexibility cor-
sponding. to a radius of curvature of approximately 20 cm for a cable
mm in diameter and a radius of curvature of approximately 65 cm for a
cable 80 mm in diameter. In this application the term "flexible" thus refers
30 to a winding flexible down to a radius of curvature in the order of four
times
the cable diameter, preferably 8-12 times the cable diameter.
The winding should be constructed so that it can retain its properties even
when it is bent and when it is subjected to thermal stress during operation.
It is extremely important in this context that the layers retain their
adhesion
to each other. The material properties of the layers, particularly their


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4
elasticity and their relative coefficients of thermal expansion are decisive
here. In a XLPE cable) for instance, the insulating layer is of cross-linked
low-density polyethylene and the semiconducting layer is of polyethylene
with soot and metal particles mixed in. Fluctuations in volume as a result
of temperature fluctuations are absorbed entirely as changes in radius in
the cable and, thanks to the comparatively slight difference in the
coefficients of thermal expansion in relation to the elasticity of these
materials, the radial expansion will be able to occur without the layers
loosening from each other.
The material combinations stated above should be considered only as
examples. Other combinations fulfilling the conditions specified and also
the condition of being semiconducting, i.e. having resistivity within the
range of 10-1-106 ohm-cm, e.g. 1-500 ohm-cm, or 10-200 ohm-cm,
I S naturally also fall within the scope of the invention.
The insulating layer may consist, for example, of a solid thermoplastic
material such as low-density polyethylene (LDPE), high-density
polyethylene (HDPE), polypropylene (PP), polybutylene (PB), polymethyl
pentane (PMP), cross-linked materials such as cross-linked polyethylene
(XLPE), or rubber such as ethylene propylene rubber (EPR) or silicon
rubber.
The inner and outer semiconducting layers may be of the same basic
material but with particles of conducting material such as soot or metal
powder mixed in.
The mechanical properties of these materials, particularly their coefficients
of thermal expansion, are affected relatively little by whether soot or metal
powder is mixed in or not - at least in the proportions required to achieve
the conductivity necessary according to the invention. The insulating layer
and the semiconducting layers thus have substantially the same
coefficients of thermal expansion.
___ ._____~..~.~_ _.._ ._~.~._~.~._.._ ..~.____ __. ~_. T


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Ethylene-vinyl-acetate copolymers/nitrile rubber, butylymp polyethylene,
ethylene-butyl-acrylate-copolymers and ethylene-ethyl-acrylate copoly-
mers may also constitute suitable polymers for the semiconducting layers.
5 Even when different types of material are used as base in the various
layers, it is desirable for their coefficients of thermal expansion to be
substantially the same. This is the case with the combination of the
materials listed above.
The materials listed above have relatively good elasticity, with an E-
moduius of E<500 MPa, preferably <200 MPa. The elasticity is sufficient
for any minor differences between the coefficients of thermal expansion
for the materials in the layers to be absorbed in the radial direction of the
elasticity so that no cracks or other damage appear and so that the layers
are not released from each other. The material in the layers is elastic, and
the adhesion between the layers is at least of the same magnitude as the
weakest of the materials.
The conductivity of the two semiconducting layers is sufficient to
substantially equalize the potential along each layer. The conductivity of
the outer semiconducting layer is sufficiently large to contain the electrical
field in the cable, but sufficiently small not to give rise to signifiicant
losses
due to currents induced in the longitudinal direction of the layer.
Thus, each of the two semiconducting layers essentially constitutes one
equipotential surface, and these layers will substantially enclose the
electrical field between them.
There is, of course, nothing to prevent one or more additional
semiconducting layers being arranged in the insulating layer.
The cooling tubes according to the invention consist of electrically
insulating material, e.g. cross-linked polyethylene in the form of circular
"XLPE tubes" which are alternated with the cables so that the heat is
transferred from the cables to the cooling tubes primarily through heat
conduction. The use of polymer tube material avoids problems with


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6
induced voltages and eddy-currents in the tubes. Besides which, polymer
tubes are considerably more flexible than metal tubes. Neither need
polymer tubes have circular cross section but may have quadratic or some
other cross section which means that they take up the entire space
between the four adjacent cables. To enable each cooling tube or hose to
be led in and led out in each cable layer, each cable layer is wound
separately and is spliced and connected in series afterwards. The space
between cables and cooling tubes is also filled with a thermally conducting
compound.
The transformer core according to the invention can be cooled with either
gas or liquid, e.g. with air from a fan and/or with water circulating in the
cooling blocks provided with cooling ducts. Another possible coolant is
helium.
The invention also relates to a method of manufacturing a cable-wound
transformer/reactor, and a transformerlreactor manufactured in
accordance with the method, wherein additional members consisting of
transducers of various types, cooling tubes, earthing devices, stabilizing
compounds, mechanical stabilizers, noise-suppressing members or empty
tubes may be wound into the winding coil when the cable is wound around
the legs of the transformer/reactor. The empty tubes may be provided
with control or measuring windings, additional magnetic material, extra
windings, etc. During winding of these empty tubes they may be provided
with pulling wires.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described in more detail with reference to the
accompanying drawings.
Figure 1 shows, schematically and partly in section, a three-phase
power transformer according to the invention.
Figure 2 shows schematically a section through a coil with iron core
comprising four embodiments 2a, 2b, 2c, 2d, according to the
present invention.
r. ......... ......._....."_...___.... .. T ....,.........~................. .
. ..._..._,_..~~. .._ ......


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Figure 3 shows schematically a section through a coil with iron core
comprising additional embodiments 3a, 3b, 3c, 3d, 3e, 3f,
according to the present invention.
DESCRIPTION OF THE INVENTION:
Figure 1 shows a power transformer 1 provided with three winding coils 2,
3, 4, each comprising a low-voltage winding 6 and a high-voltage winding
5. The winding coils 2, 3, 4 are wound around legs 22, 23, 24)
respectively, of an iron core where the legs are joined on each side of the
coils by an upper and a lower yoke 7, 8 in the iron core. The legs 22, 23,
24 and the yoke 7, 8 thus form the total iron core of the transformer 1.
Figure 2 shows a cross-sectional view of part of a power transformer
wound with high-voltage cables 111 for use as transformer winding in
accordance with the present invention. The high-voltage cable 111
comprises a number of strands 112 of copper (Cu), for instance, having
circular cross section. These strands 112 are arranged in the middle of
the high-voltage cable 111. Around the strands 112 is a first semi-
conducting layer 113. Around the first semi-conducting layer 113 is an
insulating layer 114, e.g. XLPE insulation. Around the insulating layer 114
is a second semi-conducting layer 115. Thus the concept "high-voltage
cable" in the present application does not include the outer sheath that
normally surrounds such cables for power distribution. The high-voltage
cable 111 is wound around a leg 24 which is joined to the other legs in the
transformer by a yoke 7.
When the high-voltage cable is wound with the cable straight, as shown in
the embodiment according to Figure 2, a space 8 is formed between the
cables, this space being defined by the cylindrical sheath surfaces, i.e. the
second semi-conducting layer 115, of the four adjacent cables 111. The
space 8 is provided with cooling ducts for coolant in liquid phase, suitably
water, which ducts may be designed in any of the four ways shown in the
Figure.


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8
The first embodiment of the transformer, designated 2a, is provided with
cylindrical cooling tubes 9 of cross-finked polyethylene (XLPE tubes),
surrounded by a spacing agent 10 acting as a thermally conducting
compound, which completely fills out the space 8 between the cooling
tube 9 and the cylindrical sheath surfaces of each cable 111.
The second embodiment of the transformer, designated 2b, is provided
with quadratic cooling tubes 11, also made of cross-linked polyethylene
(XLPE tubes) and surrounded by a spacing agent 10 acting as a thermally
conducting compound. The spacing agent 10 completely fills out the
space 8 between the cooling tube 11 and each cable 111. The quadratic
shape of the cooling tube 11 allows greater utilization of the space 8 for
cooling purposes.
1 S The third embodiment of the transformer, designated 2c, is provided with
concave quadratic cooling tubes 12, the sides having the same curved
shape as the cylindrical cables. This shape further minimizes the
remaining space between cooling tube 12 and cable in comparison with
the second embodiment. In this embodiment also the cooling tubes 12
are made of cross-linked polyethylene (XLPE tubes), here too surrounded
by a spacing agent 10 acting as a thermally conducting compound which
completely fills out the space 8 between the cooling tube 12 and each
cable 111.
In all three embodiments described above coolant in the form of cooling
water flows in respective cooling tubes 9, 11) 12. However) a gaseous
coolant such as helium is also possible. Other types of liquid coolants in
the tubes are also possible.
The fourth embodiment of the transformer, designated 2d, is provided with
cylindrical XLPE tubes 13 running in pairs inside a quadratic insert tube 14
of cross-linked polyethylene (XLPE tubes), the XLPE tubes 13 being
surrounded by spacing agent 10 inside the insert tube 14, said insert tube
14 also being surrounded by spacing agent 10 which completely fills the
space 8 between the cooling tube 9 and each cable 111. The spacing
_ _._._...._ T . _._....~_.._. ~_.._.


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9
agent 10 acts as a thermally conducting compound both inside and
outside the insert tube 14.
The thermally conducting compound in the form of spacing agent in all the
S embodiments described consists of one or two-component curing silicon
rubber filled with heat-conducting filler such as aluminium oxide. In
uncured state the material is given such rheological properties that it is
liquid at high shear rates (pumpable) and is in paste form at rest.
In a first procedure according to the invention the compound is first
sprayed onto the cables, after which the cooling tube 9, 11, 12 or the
insert tube 14 is placed in the groove formed between winding turns of the
cable. Fresh compound is sprayed onto the cooling tube 9, 11, 12 or the
insert 14 and another turn of cable is wound, and so on. The winding
1 S drum rotates during winding, but it may stand still without the spacing
agent 10 running off.
In a second procedure according to the invention a curing silicon rubber
compound is cast or extruded as spacing agent around the cooling tube 9,
11, 12 or the insert 14. In cured state the compound has such a
consistency (similar to modelling clay) that it is moulded to fill out the
remaining space between the cables during winding.
According to Figure 2) furthermore, the iron core is provided with a yoke 7
and a leg 24, the yoke being provided with a longitudinal cooling channel
15.
The cooling requirement is different for the windings and the flow of liquid
in the various cooling tubes is thus also different. A higher flow is
generally required in the tubes situated close to the low-voltage winding
than in the tubes situated close to the high-voltage winding. In order to
achieve the correct flow distribution the tubes may have different
diameters or be connected in different series and parallel combinations.
Polymer cooling tubes can be manufactured from many materials, such as
polyethylene, polypropene, polybutene) polyvinylidene fluoride,


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polytetrafluoroethylene or be filled and reinforced elastomers. Among
these polyethylene with high density, HDPE, is preferred since its thermal
conductivity increases with increased density. If the polyethylene is cross-
linked, which can be achieved by peroxide-splitting, silane cross-linking or
5 radiation cross-linking, its ability to withstand pressure at increased
temperature is increased and at the same time the risk of stress corrosion
disappears.
The tubes must be embedded since the thermal resistance between tube
10 and cables will otherwise be too high. To increase the heat transfer
between tube and winding) the space is filled with a cross-linkable casting
compound. This may consist of a polymer which has low viscosity and
can thus be filled with a high percentage of heat-conducting filler before
being injected into the space where it is converted to a non-liquid
compound by a chemical reaction. Examples of suitable compounds are
acryl, epoxy, unsaturated polyester, polyurethane and silicon) the latter
being preferred since it is non-toxic. Heat-conducting filler may also
comprise oxides of aluminium, magnesium, iron or zinc) nitrides of boron
or aluminium, silicon carbide. A mixture of for instance aluminium oxide
and silicon, i.e. polydimethyl siloxane with vinyl groups which react with
hydrogen polydimethyl siloxane in the presence of a platinum catalyst, is
forced at over-pressure into the space between the XLPE tube and the
winding, after which curing is effected by the hydrogen atoms being added
to the vinyl groups.
Figure 3 shows a corresponding picture to figure 2, but in which the
cooling tubes are combined or replaced by other types of members. The
figure indicates which other members are suitable for being wound to-
gether with the high-voltage cable 111. The high-voltage cable is of the
same shape as those which have been described as embodiments under
figure 2. Also the transformerlreactor core is similar to the one shown in
figure 2.
Figure 3a shows an additional member in the form of an empty tubular
member 50 arranged to be wound in together with the high-voltage cable
111. This tube 50 is also surrounded by a spacer 10 which in this case
___ . ~_ ~ _~__... _.______ ~


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11
may also act as a thermally conducting compound but which may be given
other properties suitable for the additional member. The tube 50 is
intended to enable insertion of various components into the winding, such
as extra windings for control or measurement. In other embodiments
magnetic material may be inserted into the tubes in order to alter the
electrical and/or magnetic properties of the transformerlreactor. It is also
possible to "stitch" in extra windings of the same type as the high-voltage
cable 111 described above. In such a method of inserting a winding, the
tube is lubricated with a suitable agent, e.g. soapy water. To facilitate the
insertion of various components into the tube 50 it is provided with one or
more pulling wires 51.
Another embodiment is illustrated as 3b in the Figure, the additional
member being arranged as an earthing member 55. This is elliptical in the
Figure but may of course have different cross-sectional shape.
According to yet another embodiment illustrated in Figure 3c, the
additional member is in the form of a stabilizing compound fi0 which is
stiffer than the surrounding spacer 10 and has a defined shape even at
room temperature during storage.
Figure 3d shows an embodiment with an additional member in the form of
a mechanical stabilizer 65 which may be produced from a number of
loose, arc-shaped parts or as a wire which can be rolled in.
Figure 3e shows an embodiment with an additional member in the form of
a noise-suppressing member 70 which is star-shaped in order to absorb
mechanical vibrations.
Figure 3f shows an embodiment with an additional member in the form of
an electric transducer 75 which is wound into the winding. The transducer
is also provided with conductors, not shown, for connection to calculation,
evaluation and control equipment.


CA 02276397 1999-06-29
WO 98/34241 PCTISE98/00177
12
The spacer 10 completely fills the space 8 between each additional
member and the surrounding high-voltage cables 111 in all the
embodiments described above.
The invention is not limited to the examples shown. Several modifications
are feasible within the scope of the invention. The cables need not be
symmetrically placed as shown in Figures 2-3, in which case the space
between adjacent windings will have a different appearance and the
additional members must then be adapted to the shape of the space.
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