WO2000019457A1

WO2000019457A1 - Three phase shell type toroidal high power static electromagnetic device

Info

Publication number: WO2000019457A1
Application number: PCT/IB1998/001668
Authority: WO
Inventors: Christian Sasse; Jan Karlsson; Pan Min
Original assignee: Abb Ab
Priority date: 1998-09-29
Filing date: 1998-09-29
Publication date: 2000-04-06
Also published as: AU9554298A

Abstract

A core-less high voltage static induction device has a winding in the form of a flexible cable with at least one current-carrying conductor and a magnetically permeable, electric field confining over surrounding the conductor. The cable forms at least one uninterrupted turn in the winding. A flux bearing member establishes a flux path around the windings, and a region of relatively low reluctance forming a portion of the flux path surrounding a major portion of the winding and a region of relatively high reluctance completing the flux path around the winding. At least one cooling channel in heat exchange relation with the cable.

Description

THREE PHASE SHELL TYPE TOROIDAL HIGH POWER

STATIC ELECTROMAGNETIC DEVICE

BACKGROUND OF THE INVENTION

The present invention relates to a three phase shell type toroidal high power static

electromagnetic device, and in particular to a high power transformer, reactor, inductance, or

regulator. As used herein the high power devices include those having a rated power ranging

from a few hundred kVA up to more than 1000 MVA with a rated voltage ranging from 3-4

kV and up to very high transmission voltages, 400 kV to 800 kV or higher.

In the transmission and distribution of electric energy, various known static inductive

devices such as transformers, reactors, regulators and the like are used. The purpose of such

devices is to allow exchange or control of electric energy in and between two or more electric

systems. Such devices belong to an electrical product group known as static inductive

devices. Energy transfer or control is achieved by electromagnetic induction. There are a

great number of textbooks, patents and articles which describe the theory, operation and

manufacture of such devices and associated systems, and a detailed discussion is not

necessary.

Conventional electric high voltage control is generally achieved in core type devices

by having one or more windings wound on one or more legs of a so called core. In shell type

devices a rectangular coil and rectangular core limbs are employed. Known devices use

complex methods and expensive materials to produce efficient and low loss components. Said device uses complex and expensive schemes to cover the windings and protect against

overloads. It is desirable to manufacture a simplified shell type toroidal high power inductive

device employing an exterior shell which is efficient, has a relatively low operating

temperature and which may employ simplified covering techniques.

SUMMARY OF THE INVENTION

The invention provides a high power static electromagnetic or induction device with a

rated power ranging from a few hundred kVA up to over 1000 MVA with a rated voltage

ranging from 3-4 kV and up to very high transmission voltages, such as 400 kV to 800 kV or

higher, and which does not entail the disadvantages, problems and limitations which are

associated with the prior art power devices.

The invention is based on the discovery that each phase of a device employs a cable

surrounded by a shell having a region of relatively low reluctance surrounding a major

portion of the cable forming a gap at a region of relatively high reluctance formed in the gap.

In Transformers and multiphase devices an exterior shell surrounds each of the enclosed

windings. Certain exemplary embodiments employ a simplified cooling arrangement.

In a particular embodiment, the invention comprises a high power static induction

device having a winding in the form of a cable wound as a toroid having a flux bearing path

for each phase surrounding the cable. A plurality of such phases are surrounded by an outer

flux bearing path. Each of the windings is formed of one or more current carrying conductors

surrounded by a magnetically permeable, electric field confining insulating cover.

In another exemplary embodiment, the cover comprises a solid insulation surrounded by an outer and an inner potential-equalizing layer being partially conductive or having

semiconducting properties. The electric conductor is located within the inner layer. As a

result the electric field is confined within the winding. The electric conductor, according to

the invention, is arranged so that it has conducting contact with the inner semiconducting

layer. As a result no harmful potential differences arise in the boundary layer between the

innermost part of the solid insulation and the surrounding inner semiconductor along the

length of the conductor.

According to an exemplary embodiment of the invention, the device has a flux

bearing region in the form of a toroidal shell surrounding each winding. The shell is in the

form of multiple alternating layers of magnetically permeable material and insulation. The

shell has a gap which extends around a central axis of the toroid. The gap is formed of a high

reluctance material including air.

Certain exemplary embodiments employ structures which have cooling channels

within which the windings are located. One such structure employs radial cooling channels

with a concentric winding support structure. Another embodiment employs an air cooled

device having horizontal or transverse winding supports. Yet another embodiment employs a

water or liquid cooled hollow toroidal structure with transverse winding supports

The invention employs windings having a solid insulation and semiconducting layers

which exhibit similar thermal properties to the solid insulation as regards the coefficient of

thermal expansion. The semiconducting layers may be integrated with the solid insulation so

that these layers and the adjoining insulation exhibit similar thermal properties to ensure good contact independently of the variations in temperature which arise in the line at different

loads. At temperature gradients the insulating layer and semiconducting layers form a

monolithic cover, and defects caused by different temperature expansion in the insulation and

the surrounding layers do not arise.

The electric load on the material is reduced because the semiconducting layers form

equipotential surfaces and the electric field in the insulating part is distributed nearly

uniformly over the thickness of the insulation.

In an exemplary embodiment, a transformer according to the invention employs a

plurality of adjacent windings arranged as coaxially around a central axis perpendicular to the

plane of each coil. Each winding has one or more turns and a high resistance outer shell

forming a flux bearing region surrounding a major portion of the turns. Each cover has a

region of relatively high reluctance in the gap and thereby forming at least one continuous

turn or flux bearing region around a central axis of each winding.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings,

wherein

Fig. 1 shows the electric field distribution around a winding of a conventional

inductive device such as a power transformer or reactor;

Fig. 2 shows an embodiment of a winding in the form of a cable in a high power

inductive device according to the invention;

Fig. 3 A shows a schematic cross-sectional illustration of a generalized three phased power transformer employing laminated exterior shell type flux bearing region according to

the invention;

Figs. 3B and 3C are enlarged fragmentary details of the flux bearing region shown in

Fig. 3A;

Fig. 4 is a respective illustration of a three phase transformer according to the

invention;

Fig. 5 is an enlarged fragmentary sectional detail of the transformer of Fig. 4;

Figs. 6A, 6B, 6C are illustrations of a multiphase toroidal inductive device employing

radial cooling channels and concentric winding supports shown respectively in perspective,

end and fragmentary sectional views;

Figs. 7A and 7B are illustrations of a toroidal inductive device employing traverse

cooling channels shown respectively in perspective and end views; and

Fig. 8 A, 8B and 8C are illustrations of a multiphase toroidal inductive device having

transverse fluid cooling channels shown respectively in perspective, end and enlarged

fragmentary sectional views.

DESCRIPTION OF THE INVENTION

The inventive concept which forms the basis of the present invention is applicable to

various static inductive devices including, power transformers, reactors and regulators. As is

known, the devices herein may be designed as single-phase and three-phase systems.

Fig. 1 shows a simplified and fundamental view of the electric field distribution

around a winding of a conventional static induction device such as a power transformer/reactor 1, including a winding 2 and a core 3. Equipotential lines 4 show where

the electric field has the same magnitude. The lower part of the winding is assumed to be at

earth potential. The core 3 has a window 5 and carries a flux φ.

The potential distribution determines the composition of the insulation system since it

is necessary to have sufficient insulation both between adjacent turns of the winding and

between each turn and earth. In Fig. 1 the upper part of the winding is subjected to the

highest dielectric stress. The design and location of a winding relative to the core are in this

way determined substantially by the electric field distribution in the core window 5.

Fig. 2 shows an example of an exemplary cable 6 which may be used in windings

which are included in high power inductive devices according to the invention. Such a cable

6 comprises at least one conductor 7 including a number of strands 7A with a covering 8

surrounding the conductor. The covering 8 includes an inner semiconducting layer 9

disposed around the strands 7A. Outside of this inner semiconducting layer is the main

insulation layer 10 of the cable in the form of a solid insulation, and surrounding this solid

insulation is an outer semiconducting layer 11. The cable 6 may be provided with other

additional layers for special purposes, for example for preventing too high electric stresses on

other regions of the device. In the exemplary embodiment, the majority of the strands 7A of

the conductor 7 are mutually insulated. However, one or two strands may be formed without

insulation so as to be in conductive contact with the inner semi-conducting layer 9.

From the point of view of geometrical dimension, the cables 6 in Fig. 2 will generally

have a conductor area which is between about 30 and 3000 mm² and an outer cable diameter which is between about 20 and 250 mm.

In the embodiment illustrated, the outer semiconducting layer 11 exhibits such

electrical properties that potential equalization along the conductor is achieved. The

semiconducting layer does not, however, exhibit such conductivity properties that the induce

current causes an unwanted thermal load. Further, the conductive properties of the layer 11

are sufficient result in that an equipotential surface. Exemplary thereof, the resistivity, p, of

the semiconducting layer 11 generally exhibits a minimum value, pmin = 1 Ωcm, and a

maximum value, pmax = 100 kΩcm, and, in addition, the resistance of the semiconducting

layer per unit of length in the axial extent, R, of the cable generally exhibits a minimum value

R_min = 50 Ω/m and a maximum value R_max = 50 MΩ/m.

The inner semiconducting layer 9 exhibits sufficient electrical conductivity in order

for it to function in a potential-equalizing manner and hence equalizing with respect to the

electric field outside the inner layer. In this connection, the inner layer has such properties

that any irregularities in the surface of the conductor are equalized, and the inner layer forms

an equipotential surface with a high surface finish at the boundary layer with the solid

insulation. The layer may, as such, be formed with a varying thickness but to ensure an even

surface with respect to the conductor and the solid insulation, its thickness is generally

between 0.5 and 1 mm. However, the inner layer 9 does not exhibit such a great conductivity

that it contributes to induce voltages. Exemplary thereof, for the inner semiconducting layer,

thus, Pmin = 10^"6 Ωcm, R_min = 50 μΩ/m and, in a corresponding way, Pmax = 100 kΩcm,

R_max = 5 MΩ/m. Fig. 3 A shows, in a schematic cross-section, a high power inductive device in the

form of a three phase external shell type transformer 12 in accordance with the present

invention. The transformer 12 comprises three windings 13-1, 13-2, and 13-3, one for each

phase, each formed of multiple turns of the cable 6 in Fig. 2. Each winding 13-1, 13-2, and

13-3 has a corresponding flux bearing shell 15-1, 15-2, and 15-3 including a region of

relatively low reluctance 16 and a region of high reluctance 18. It should be understood that

the suffixes herein designate the position of the corresponding element, and are otherwise not

used when the position is not relevant to the discussion.

The region of low reluctance 16 may comprise a high resistance metal, and the region

of high reluctance may comprise a non-magnetic dielectric. In the arrangement illustrated,

the region of low reluctance 16 may further comprise insulated layers of a conductor 24 and

an insulator or dielectric 26 formed in the gap 22 as shown in Fig. 3B. The region of

relatively low reluctance surrounds a major portion of the winding and has endpoints 20 in

relatively close proximity which form a gap 22 therebetween as shown in Fig. 3A. The

region of high reluctance 18 is formed in the gap 22 and may comprise air, but in the

exemplary embodiment comprises a solid dielectric or a number of layers of dielectric 28 as

shown in the enlargement of Fig. 3B.

The transformer 12 has an outer flux bearing region 30 which may be similarly

formed with respective relatively high and low reluctance regions 32 and 34 in the same way

as described with respect to regions 16 and 18 respectively. Figs. 4 and 5 illustrate an

exemplary embodiment of a toroidal transformer 40 comprising three windings 41-1, 42-1, and 42-3 having central axis 44-1, 44-2, and 44-3 forming vertices of an equilateral triangle

46. Each winding 42 has one or more turns of the insulated cable as shown in Fig. 2 and may

be provided with a power cable termination or coupler 43

Each cable is formed with conductors and an insulated cover as described above.

Each winding is surrounded by a flux bearing region 48-1, 48-2, and 48-3. The entire

structure is likewise surrounded by a outer main or mutual flux bearing region 50. Each of

the windings 42 produce a corresponding flux which is carried by the corresponding flux

bearing region 48 and by the outer flux bearing region 50. As discussed with respect to Figs.

3 A -3C, the various flux bearing regions have relatively low and relatively high reluctance

areas 54 and 56 formed in the manner described hereinabove. In the devices described

herein, the high reluctance region 56 protects the device from excessive magnetic fields

induced by high currents which may be caused by a fault or short. It should be understood

that any one winding, for example, 42-1 could be operated alone as a separate reactor if

desired, and one need only make a single winding with the high and low reluctance cover.

Such an arrangement need not be separately shown in Figs. 4 and 5, but is part of the

invention as exemplified in Figs. 7A and 7B.

Fig. 6A, 6B and 6C are illustrations of an air cooled three phase transformer 60

according to the invention formed with radial channels 62 forming pie shaped phases 64-1,

64-2, and 64-3 each of which has a flux bearing region 66. The transformer also has an outer

flux bearing region 68 surrounding the phases 64. The flux bearing regions have regions of high and low reluctance including a gap similar to the arrangement described above.

Each phase has a corresponding winding 70-1, 70-2, and 70-3 supported in a series of

toroidal concentric ring-like segments 72-1, 72-2, and 72-3. The segments 72 may each be

formed of a pair of closely spaced curved metal sheet elements 74 having welded spacers 76

for supporting the elements in confronting relation as shown. The segments establish cooling

channels 78 therebetween. The channels may be adapted to carry any of a variety of working

or cooling fluids such as air, gas or liquids.

Fig. 7A and 7B illustrate a single phase inductive device 80 having a winding 82

surrounded by a flux bearing number 84 of the type as hereinabove described. In the

arrangement, transverse supports 86 are provided in the form of parallel annular rings

forming a toroidal structure. The supports 86 may be formed of confronting parallel sheets

88 with spacers 90 forming cooling channels 92 for carrying a cooling fluid.

Figs. 8A, 8B and 8C illustrate a three phase transformer formed with three devices 80-

1, 80-2 and 80-3 of the type similar to the arrangement of Fig. 7A-7B, surrounded by a outer

or mutual flux bearing member 96 and forming a fluid cooled three phase transformer

according to the invention.

In accordance with the invention, the various cooling structures herein described may

be coupled to earth or appropriately grounded.

While there have been provided what are considered to be exemplary embodiments of

the invention, it will be apparent to those skilled in the art that various changes and

modifications therein may be made without departing from the invention, and it is intended in the appended claims to cover such changes and modifications as fall within the true spirit and

scope of the invention.

Claims

1 claim:

1. A high voltage static induction device comprising at least one winding formed of a high voltage cable having at least one turn, said cable including at least one current- carrying conductor; a first layer with semiconducting properties surrounding the conductor; a solid insulating layer surrounding the first layer; a second layer with semiconducting properties surrounding the insulating layer; and a flux bearing path for the at least one winding having a first region of relatively low reluctance surrounding a major portion of the winding; and a second region of relatively high reluctance completing the path for surrounding the conductor.

2 A device according to claim 1 wherein the first and second layers are operable at the same potential.

3. A device according to claim 1, wherein the second layer comprises an equipotential

surface surrounding the conductor.

4. A device according to claim 1, wherein the second layer is connectable to earth potential.

5. A device according to claim 1, wherein the first and second layers and the insulating layer

are connected at a boundary therebetween and have substantially the same coefficient of

thermal expansion such that, upon thermal movement, the winding remains substantially free of voids, defects and cracks in the boundary layer between the semiconducting layers and the

insulating layer.

6. A device according to claim 1 , wherein the first and second layers have respective contact

surfaces secured to corresponding surfaces of the adjacent insulating layer and each of the

semiconducting layers is secured to the adjacent solid insulating layer along essentially the

whole contact surface.

7. A device according to claim 1, wherein the at least one winding comprises a flexible

transmission line cable.

8. A device according to claim 7, wherein the cable is manufactured with a conductor area

which is between about 30 and 3000 mm² and with an outer cable diameter which is between

about 20 and 250 mm.

9. A device according to claim 1, wherein at least one of the first and second layers and the

solid insulation comprise polymeric materials.

10. A device according to claim 1, wherein the winding is free of partial discharge.

11. A device according to claim 1 , wherein the solid insulation comprises an extrusion.

12. A device according to claim 1, wherein the current-carrying conductor comprises a first

plurality of strands being insulated from each other and a second plurality of strands being

uninsulated in order to secure electric contact with the first semiconducting layer.

13. A device according to claim 1, wherein the cable is substantially void free.

14. A device according to claim 1, wherein the winding comprises a core.

15. A device according to claim 1, wherein the winding is air wound and formed without an

iron core.

16. A device according to claim 1, wherein the at least one winding comprises a plurality of

galvanically separated concentrically wound windings.

17. A device according to claim 1, including means for connecting the at least one winding

to a plurality of voltage levels.

18. A device according to claim 1, wherein the at least one winding includes a power cable

termination.

19. A device according to claim 1, wherein the insulation layer is formed of a solid electrical insulation enclosed between the conductor and the second layer.

20. A device according to claim 1, wherein the cable includes means for sustaining a high

voltage at transmission levels including at least one of greater than lOkV, 36kV, 75.5kV,

400kV and 800kV.

21. A device according to claim 1, being operable in a power range in excess of at least 0.5

MVA and 30 MVA.

22. A device according to claim 1, including cooling means for supporting the winding at

least one of liquid and gas operable at earth potential

23. A device according to claim 22 wherein the cooling means employs a cooling fluid

comprising at least one of liquid and gas operable at earth potential.

24. A device according to claim 22 wherein the cooling means comprises a plurality of heat

conductive supports.

25. A device according to claim 24 wherein the heat conductive support comprises

confronting pairs of sheet elements and spacer means located between the sheet elements

forming fluid carrying channels therein.

26. A device according to claim 25 wherein the sheet elements comprise a plurality of

parallel transverse annular rings.

27. A device according to claim 26 wherein the rings are disposed transverse a central axis of

the winding.

28. A device according to claim 26 wherein the rings are disposed concentrically of a central

axis and of the winding

29. A method for electric field control in a high voltage static induction device comprising

forming a magnetic field generating circuit having at least one winding with at least one

electrical conductor an insulation layer and at least one outer layer externally thereof, wherein

the insulation is formed by a solid insulation material; and surrounding the conductor with a

flux bearing path having a first region of relatively low reluctance surrounding a major

portion of the conductor and a second region of relatively high reluctance completing the

path.

30. A method according to claim 29 further comprising connecting the outer layer to a

relatively low potential and having an electrical conductivity higher than the conductivity of

the insulation but lower than the conductivity of the electrical conductor so as to equalize

potential and cause the electrical field to be substantially enclosed in the winding internally of the outer layer.

31. A method according to claim 29, further comprising connecting the outer layer to near

ground potential.

32. A core-less high voltage static induction device comprising a winding in the form of a

flexible cable including at least one current-carrying conductor and a magnetically permeable,

electric field confining cover surrounding the conductor, said cable forming at least one

uninterrupted turn in the winding of said device; a flux bearing member for establishing a

flux path around the windings, said member having a region of relatively low reluctance

forming a portion of the flux path surrounding a major portion and a region of relatively high

reluctance completing the flux path around the winding; and a at least one cooling channel in

heat exchange relation with the cable.

33. A static power electromagnetic device comprising:

at least one winding for producing a flux when energized comprising at least one

current-carrying conductor and a magnetically permeable, electric field confining, insulating

covering surrounding the conductor; and

a flux bearing shell region surrounding the winding having a region of relatively low

reluctance surrounding a major path of the winding and forming a gap; and;

a region of relatively high reluctance formed in the gap.