Transformer/reactor

• US 6,940,380 B1
• Filed: 05/27/1997
• Issued: 09/06/2005
• Est. Priority Date: 05/29/1996
• Status: Expired due to Fees

• Current Assignee: GD Searle LLC (Pfizer Inc.)
• Original Assignee: ABB AB (ABB Limited)
• Inventors: Leijon, Mats
• Primary Examiner(s): Nguyen, Tuyen T
• Application Number:
  US08/973,210
• Time in Patent Office: 3,024 Days
• Field of Search: 174DIG 13-DIG 33, 336/60, 336/59, 336/61, 310/45, 148/269
• US Class Current: 336/60
• CPC Class Codes: H01F 2027/329 Insulation with semiconducting layer, e.g. to reduce corona effect
• CPC Class Codes: H01F 2029/143 with control winding for generating magnetic bias
• CPC Class Codes: H01F 27/288 Shielding
• CPC Class Codes: H01F 27/323 Insulation between winding turns, between winding layers
• CPC Class Codes: H01F 27/34 Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
• CPC Class Codes: H01F 29/14 with variable magnetic bias amplitude modulation by means of variable impedance element H03C1/08 ; magnetic amplifiers H03F; circuits for automatic telephonic communication H04M3/00
• CPC Class Codes: H01F 3/10 Composite arrangements of magnetic circuits
• CPC Class Codes: H01F 3/14 Constrictions; Gaps, e.g. air-gaps in magnetic shunt paths H01F3/12
• CPC Class Codes: H02H 3/025 Disconnection after limiting, e.g. when limiting is not sufficient or for facilitating disconnection
• CPC Class Codes: H02K 15/00 Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
• CPC Class Codes: H02K 15/12 Impregnating, heating or drying of windings, stators, rotors or machines
• CPC Class Codes: H02K 2203/15 Machines characterised by cable windings, e.g. high-voltage cables, ribbon cables
• CPC Class Codes: H02K 3/14 with transposed conductors, e.g. twisted conductors
• CPC Class Codes: H02K 3/28 Layout of windings or of connections between windings windings for pole-changing H02K17/06, H02K17/14, H02K19/12, H02K19/32
• CPC Class Codes: H02K 3/40 for high voltage, e.g. affording protection against corona discharges
• CPC Class Codes: H02K 3/48 in slots
• CPC Class Codes: H02K 9/19 for machines with closed casing and closed-circuit cooling using a liquid cooling medium, e.g. oil
• CPC Class Codes: Y10S 174/13 High voltage cable, e.g. above 10kv, corona prevention
• CPC Class Codes: Y10S 174/14 having a particular cable application, e.g. winding
• CPC Class Codes: Y10S 174/20 Stator
• CPC Class Codes: Y10S 174/24 : in an inductive device, e.g. reactor, electromagnet
• CPC Class Codes: Y10S 174/25 : Transformer
• CPC Class Codes: Y10S 174/26 : having a plural-layer insulation system

Abstract

The present invention relates to a power transformer/reactor (14, 15, 16) for high voltages, comprising at least one winding having at least one current-carrying conductor. The winding comprises a solid insulation (7) surrounded by outer and inner layers (8,6) serving for equalization of potential and having semiconducting properties. The layers (6,8) and the insulation (7) adhere along essentially the whole of its contact surfaces. Said conductor is arranged interiorly of the inner semiconducting layer (6). The outer layer (8) is connected to ground or otherwise relatively low potential. Said solid insulation in the windings constitute substantially the total electrical insulation in the power transformer/reactor.

Claims

1. A power transformer/reactor having at least one winding, comprising a flexible cable having a current-carrying conductor including a plurality of insulated strands and at least one uninsulated strand;

and an insulation system including a first layer having semiconducting properties surrounding the conductor and being in contact therewith;

a solid insulating layer surrounding the first layer; and

a second layer with semiconducting properties surrounding the insulating layer.

2. A power transformer/reactor according to claim 1, wherein the first layer is at substantially the same potential as the conductor.

3. A power transformer/reactor according to claim 1, wherein the second layer comprises an equipotential surface surrounding the conductor.

4. A power transformer/reactor according to claim 1, wherein the second layer is connectable to earth potential.

5. A power transformer/reactor according to claim 1, wherein the first and second semiconducting layers and the insulating layer have substantially the same coefficient of thermal expansion such that, upon a thermal movement in the winding, defects, cracks or the like do not arise in the boundary layer between the semiconducting layers and the insulating part.

6. A power transformer/reactor according to claim 1, wherein the first and second layers have respective contact surfaces secured to corresponding surfaces of the adjacent insulating layer each of the semiconducting layers is secured to the adjacent solid insulating layer along essentially the whole contact surface.

7. A power transformer/reactor according to claim 1, 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.

8. A power transformer/reactor according to claim 1, wherein at least one of the first and second layers and the solid insulation comprise polymeric materials.

9. A power transformer/reactor according to claim 1, wherein the winding is free of partial discharge.

10. A power transformer/reactor according to claim 1, wherein the solid insulation comprises an extrusion.

11. A power transformer/reactor according to claim 1, wherein the cable is substantially void free.

12. A power transformer/reactor according to claim 1, wherein the power transformer/reactor comprises a core of magnetic material.

13. A power transformer/reactor according to claim 1, wherein the power transformer/reactor comprises an iron core including core limbs and yokes.

14. A power transformer/reactor according to claim 1 wherein the power transformer/reactor is air wound and formed without an iron core.

15. A power transformer/reactor according to claim 1, further comprising at least two galvanically separated concentrically wound windings.

16. A power transformer/reactor according to claim 1, wherein the power transformer/reactor is connectable to a plurality of voltage levels.

17. A power transformer/reactor according to claim 1, wherein the windings include terminals in the form of power cable terminations.

18. A power transformer/reactor or according to claim 1, wherein the insulation layer is formed of a solid electrical insulation, substantially all of the electrical insulation in the transformer/reactor is enclosed between the conductor and the second layer of the windings.

19. A power transformer/reactor according to claim 1, wherein the cables includes means for sustaining a high voltage at transmission levels of at least one of greater than 10 kV.

20. A power transformer/reactor according to claim 1, wherein the transformer/reactor is designed for a power range in excess of 0.5 MVA.

21. A power transformer/reactor according to claim 1, wherein the power transformer/reactor includes cooling means comprising at least one of liquid and gas at earth potential.

22. A method for electric field control in a power transformer/reactor comprising the steps of:

forming a magnetic field generating circuit having at least one winding in the form of a flexible cable having at least one electrical conductor and insulation system surrounding the conductor;

forming the conductor with a plurality of insulated conductive strands and at least one uninsulated conductive strand;

forming the insulation system of an inner semiconducting layer contacting the conductor, a solid insulation surrounding the inner layer; and

an outer layer surrounding the solid insulation being connected to ground or otherwise 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.

23. A method according to claim 22, wherein the winding of the transformer/reactor is assembled on-site.

24. A method according to claim 22, further comprising connecting the outer layer to near ground potential.

25. A high voltage electric machine comprising at least one of a transformer and reactor including a winding in the form of a flexible cable including at least one current-carrying conductor comprising a plurality of insulated strands and at least one uninsulated strand;

and a magnetically permeable, electric field confining cover surrounding the conductor, said cable forming at least one uninterrupted turn in the corresponding winding of said machine; and

wherein the cover comprises an insulating surrounding the conductor and an outer layer surrounding the insulating system including an inner semiconducting layer in contact with the conductor, and a solid insulation layer, surrounding the inner layer an an layer having a conductivity sufficient to establish an equipoential surface surrounding the conductor.

26. The machine of claim 25, wherein the insulation system is substantially void free.

27. The machine of claim 25, wherein the inner layer, the outer layer and the solid insulation layer have substantially the same temperature coefficient of expansion.

28. The machine of claim 25, wherein the winding is operable free of partial discharge.

29. The machine of claim 25, wherein the winding comprises multiple uninterrupted turns.

30. The machine of claim 25, wherein the cable comprises a transmission line.