TRANSFORMER FOR AN INVERTER SYSTEM AND AN INVERTER SYSTEM COMPRISING THE TRANSFORMER

• US 20140268968A1
• Filed: 07/04/2012
• Published: 09/18/2014
• Est. Priority Date: 07/08/2011
• Status: Active Grant

• Current Assignee: Teledyne UK Limited (Teledyne Technologies Incorporated)
• Original Assignee: e2v Technologies UK Ltd (Teledyne Technologies Incorporated)
• Inventors: Richardson, Robert
• Granted Patent: US 9,607,756 B2
• Time in Patent Office: Days
• US Class Current: 363/140
• CPC Class Codes: H01F 27/36 Electric or magnetic shields or screens movable for varying inductance H01F21/10
• CPC Class Codes: H01F 27/363 made of electrically conductive material
• CPC Class Codes: H01F 27/42 Circuits specially adapted for the purpose of modifying, or compensating for, electric characteristics of transformers, reactors, or choke coils circuits for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output H02P13/00; impedance networks H03H
• CPC Class Codes: H02M 7/44 by static converters

Abstract

A transformer comprises a primary winding 231; a secondary winding 233; a first electrostatic screen 234 located between the primary winding and the secondary winding and most proximate to the primary winding means; and a second electrostatic screen 235 located between the primary winding and the secondary winding means and most proximate to the secondary winding means. The first electrostatic screen is electrically connectable to a power supply electrically connectable to the primary winding and the second electrostatic screen is electrically connectable to a load electrically connectable to the secondary winding. The invention also includes an inverter system including the transformer.

Claims

1. A transformer comprising:

primary winding means;

secondary winding means;

first electrostatic screen means located between the primary winding means and the secondary winding means and most proximate to the primary winding means; and

second electrostatic screen means located between the primary winding means and the secondary winding means and most proximate to the secondary winding means, wherein the first electrostatic screen means is electrically connectable directly by a first lossy impedance to a power supply electrically connectable to the primary winding means and the second electrostatic screen means is electrically connectable directly by a second lossy impedance to a load electrically connectable to the secondary winding means.

2. A transformer as claimed in claim 1, further comprising at least one rectifying means connected across the secondary winding means wherein the second electrostatic screen means is electrically connectable to the at least one rectifying means.

3. A transformer as claimed in claim 1, wherein the first electrostatic screen means is connectable to the power supply via a first lossy impedance and the second electrostatic screen means is connectable to the load or the at least one rectifying means, respectively, via a second lossy impedance.

4. A transformer as claimed in claim 1, wherein:

the secondary winding means comprises a plurality of coaxially arranged toroidal closed magnetic circuit means connected in series on a common axis within an enclosure means;

the primary winding means comprises a plurality of turns including electrically conducting members passing axially through the toroidal closed magnetic circuit means electrically connected respectively to electrically conducting strip line means located on outer faces of walls of the enclosure means to form a continuous electrical conductor, and

the first and second electrostatic screen means, located between the primary winding means and the secondary winding means, are provided by layered members comprising an insulating support layer sandwiched between first and second electrically conducting layers.

5. A transformer as claimed in claim 4, wherein the first electrostatic screen means comprises an inner electrically conducting layer of a tubular first layered member located between the electrically conducting members forming a portion of the primary winding means passing axially through the toroidal closed magnetic circuit means and the toroidal closed magnetic circuit means forming the secondary winding means and outer electrically conducting layers of respective planar layered members located on inner faces of the enclosure means opposed to the outer faces along which the electrically conducting strip line means forming a further portion of the primary winding means are located.

6. A transformer as claimed in claim 5, wherein the second electrostatic screen means comprises an outer electrically conducting layer of the tubular first layered member and inner electrically conducting layers of the respective planar layered members.

7. A transformer as claimed in claim 4, wherein the tubular layered member comprises a first longitudinal slit in the first electrically conducting layer and a second longitudinal slit in the second electrically conducting layer to minimise eddy currents in the tubular layered member.

8. A transformer as claimed in claim 7, wherein the first longitudinal slit is circumferentially offset from the second longitudinal slit.

9. A transformer as claimed in claim 4, wherein the electrically conducting members forming a first portion of the primary winding are mutually spaced apart such that cross-sections of the electrically conducting members lie substantially on a circumference of a circle on a transverse cross-section of the enclosure means.

10. A transformer as claimed in claim 4, wherein the electrically conducting members forming a first portion of the primary winding are at least one of tubes, rods and strip conductors.

11. A transformer as claimed in claim 10, wherein the electrically conducting members forming the first portion of the primary winding are tubes with a wall thickness comparable to a skin depth of the electric current carried thereby at an operating frequency of the transformer.

12. A transformer as claimed in claim 10, wherein the electrically conducting members forming the first portion of the primary winding are flat strip conductors have a thickness comparable to a skin depth of the electric current carried thereby at an operating frequency of the transformer.

13. A transformer as claimed in claim 4, wherein the electrically conducting members forming the first portion of the primary winding comprise a combination of electrically conducting members connected in parallel, each conducting member with a wall thickness comparable to a skin depth of the electric current carried thereby at an operating frequency of the transformer.

14. A transformer as claimed in claim 4, wherein the electrically conducting strip line means forming a second portion of the primary winding are formed in printed circuit boards located on outer faces of walls of the enclosure means.

15. A transformer as claimed in claim 4, wherein the enclosure means has a substantially rectilinear transverse cross-section and the walls of the enclosure means parallel to a longitudinal axis of the enclosure means are substantially planar.

16. A transformer as claimed in claim 15, wherein the electrically conducting strip line means are located on first, second and third walls of the substantially planar walls of the enclosure means and have a thickness greater than a skin depth at an operating frequency of the transformer.

17. A transformer as claimed in claim 15, wherein a fourth substantially planar wall of the enclosure means comprises a printed circuit board for rectifying means.

18. A transformer as claimed in claim 4, comprising insulating tube means on which the secondary toroidal closed magnetic circuit means are located arranged to provide voltage hold off for the electrically conducting members passing axially through the toroidal closed magnetic circuit means.

19. A transformer as claimed in claim 4, comprising coolant distribution means.

20. A transformer as claimed in claim 19, wherein the coolant distribution means comprises tube means, coaxial with, and of smaller diameter than, core apertures of the toroidal closed magnetic circuit means, the tube means being supplied with bleed hole apertures to direct the coolant towards respective secondary toroids.

21. A transformer as claimed in claim 4, comprising electrically insulating sheet means located between the toroidal closed magnetic circuit means and the planer twin-thin walled members to provide high voltage insulation and minimise a risk of high voltage tracking across a surface of the insulator.

22. A transformer as claimed in claim 4, wherein the individual secondary toroidal closed magnetic circuit means are interconnected such that each secondary toroidal closed magnetic circuit means of the transformer is star connected and provides an input to a two pulse rectifier.

23. A transformer as claimed claim 1, arranged for three-phase current, comprising a first, a second and a third primary winding means and a corresponding first, second and third secondary winding means arranged for the three phases respectively, and a first and second electrostatic screen means between the first primary and secondary winding means, a third and fourth electrostatic screen means between the second primary and secondary winding means and a fifth and sixth electrostatic screen means between the third primary and secondary winding means wherein the first, third and fifth electrostatic screen means are electrically interconnected and the second, fourth and sixth electrostatic screen means are electrically interconnected.

24. An inverter system comprising a transformer as claimed in claim 1.

25. An inverter system as claimed in claim 24, wherein output ports of an inverter are electrically connected to the primary winding means of the transformer and the first electrostatic screen means is electrically connected to an input port of the inverter via a first impedance such that a first stray current flowing through a first stray capacitance between the primary winding means and the first electrostatic screen means flows through the first impedance to the inverter.

26. An inverter system as claimed in claim 25, wherein the first impedance is sufficiently lossy that substantially all of the energy associated with the first stray current is dissipated in the first impedance.

27. An inverter system as claimed in claim 25, wherein output ports of the inverter are electrically connected to the primary winding means via an inductance forming a common mode choke between the inverter and primary winding means.

28. An inverter system as claimed in claim 24, wherein at least one rectifying means is electrically connected across the secondary winding means of the transformer and the second electrostatic screen means is electrically connected to the at least one rectifying means via a second impedance such that a second stray current flowing through a second stray capacitance between the secondary winding means and the second electrostatic screen means flows through the second impedance and the at least one rectifying means.

29. An inverter system as claimed in claim 28, wherein the second impedance is sufficiently lossy that substantially all of the energy associated with the second stray current is dissipated in the second impedance.

30. An inverter system as claimed in claim 24, wherein a monitor resistance is connected in series with a load electrically connectable to the secondary winding of the transformer to monitor a current passing through the load, and at least one of the first and second electrostatic screen means substantially prevents a first stray current which passes thorough a first stray capacitance between the primary winding means and the first electrostatic screen means and a second stray current which passes thorough a second stray capacitance between the secondary winding means and the second electrostatic screen means respectively from also passing through the monitor resistance.

31. A three-phase inverter system, comprising three individual and isolated transformers as claimed in claim 1, wherein the primary winding means of the transformers are delta connected and arranged to be fed from a three-phase inverter.

32. A three-phase inverter system as claimed in claim 31, wherein the secondary toroidal closed magnetic circuit means of the three individual and isolated transformers are interconnected such that each secondary toroidal closed magnetic circuit means of a transformer is star connected and provides an input to a six pulse rectifier.