Arc limiting device using the skin effect in ferro-magnetic materials

• US 5,978,446 A
• Filed: 02/03/1998
• Issued: 11/02/1999
• Est. Priority Date: 02/03/1998
• Status: Expired due to Fees

• Current Assignee: Picker International, Inc. (Marconi Holdings Company Limited)
• Original Assignee: Picker International, Inc. (Marconi Holdings Company Limited)
• Inventors: Resnick, Theodore A.
• Primary Examiner(s): Porta, David P.
• Assistant Examiner(s): Schwartz, Michael J.
• Application Number:
  US09/017,380
• Time in Patent Office: 637 Days
• Field of Search: 378/105, 378/107, 378/109, 323/108, 323/109, 333/204, 209/7
• US Class Current: 378/105
• CPC Class Codes: H02H 9/02 responsive to excess current current limitation for voltage regulators G05F1/573; disconnection after limiting H02H3/025
• CPC Class Codes: H05G 1/54 Protecting or lifetime predictionoverload protection combined with control H05G1/46

Abstract

A high voltage power supply includes a high voltage high frequency generator (10) having outputs (12, 14). An arc limiting device (20) is connected in series to the outputs (12, 14) of the generator (10). The arc limiting device (20) includes two coils (22, 24) of a wound length of wire (50) that exhibit a skin effect. The skin effect forces higher frequency current components to flow at a surface of the wire (50) through a limited skin layer portion (62) of a cross section of the wire (50). In one preferred embodiment, the arc limiting device (20) is connected via high voltage cables (32, 34) with an x-ray tube (40). Suitable material for the wire (50) includes those materials with high permeability to resistivity ratios, for example iron, purified iron, 78 permalloy, 4-97 permalloy, mu metal, or supermalloy.

Claims

1. A high voltage power supply comprising:

a high voltage high frequency generator including an output; and

,

an arc limiting device connected in series to the output of the generator, said arc limiting device having at least one coil which includes;

a wound length of ferro-magnetic wire that exhibits a skin effect, forcing higher frequency current components to flow at a surface of the wire through a limited portion of a cross section of the wire.

2. The high voltage power supply of claim 1, wherein the wire is constructed of a metal with a ratio of permeability to resistivity higher or equal to 500 where the permeability is measured in Gauss/Oersted and the resistivity is measured in microhm-cm.

3. The high voltage power supply of claim 1, wherein the wire is a material selected from the group consisting of iron, purified iron, 78 permalloy, 4-97 permalloy, mu metal, and supermalloy.

4. An arc limiting device for a high voltage, high frequency power supply including a positive output terminal and a negative output terminal, the arc limiting device including:

at least two coils of ferro-magnetic wire attached in series with the positive and negative output terminals respectively such that during an arc event components of electrical current having higher frequencies are restricted to flow along an outer skin of the ferro-magnetic wire with energy from the electrical current being absorbed thereby.

5. The arc limiting device of claim 4, wherein the ferro-magnetic wire is coated with a magnet wire varnish.

6. The arc limiting device of claim 5, wherein the wire is constructed of a material with a ratio of permeability to resistivity higher or equal to 500 where the permeability is measured in Gauss/Oersted and the resistivity is measured in microhm-cm.

7. The arc limiting device of claim 4, wherein ends of the coils are connected to an anode and a cathode of an x-ray tube, respectively, by high voltage cables.

8. In an x-ray generator including a high voltage power supply connected via an arc limiter and high voltage cables to an x-ray tube, the arc limiter comprising:

a wound length of iron wire, such that higher frequency components of electrical current flow along an outer skin of the iron wire.

9. The arc limiter of claim 8, wherein the wound length of iron wire forms a helical coil.

10. The arc limiter of claim 8, wherein the wound length of iron wire forms multiple pancake coils around a ferrite core.

11. The arc limiter of claim 8 further including additional lengths of iron wire wound into coils.

12. The arc limiter of claim 11 wherein the iron wire coils are arranged in one of a parallel manner, a series manner, and a combination of parallel and series manners.

13. A method of suppressing arcs in the generation of x-rays comprising:

(a) generating an electrical current;

(b) directing the electrical current through a coil of ferro-magnetic metal;

(c) forcing higher frequency components of the electrical current to flow at a surface of the ferro-magnetic metal through a limited skin layer of the ferro-magnetic metal; and

,

(d) applying the electrical current to an x-ray tube.

15. The method of claim 13, wherein in step (c) the method further includes:

absorbing energy from the higher frequency components of the electrical current in the skin layer.

16. The method of claim 13, wherein in steps (b) and (c) the method further includes:

converting and storing excess electrical energy in a magnetic field.

14. A method of suppressing arcs in the generation of x-rays comprising:

(a) generating an electrical current which has desirable lower frequency components and undesirable higher frequency components;

(b) directing the electrical current to a coil of ferrous wire;

(c) preferentially attenuating the higher frequency current components more strongly than the lower frequency current components by forcing the higher frequency components of the electrical current to flow through a limited skin layer of the ferrous wire saturating the skin layer causing the skin layer to become more resistive while passing the lower frequency components below the skin layer of the ferrous wire without saturation; and

,

(d) applying the electrical current with attenuated higher frequency components to an x-ray tube.

17. A line filter for reducing noise in an electrical power transmission line comprising:

at least one coil attached along the electrical power transmission line, the coil including a wound length of ferro-magnetic wire that exhibits a skin effect, such that higher frequency components of electrical current flowing therethrough are forced to flow along a surface of the wire through a limited portion of a cross section of the wire.

18. The line filter of claim 17, wherein the wire is constructed of a metal with a ratio of permeability to resistivity higher or equal to 500 where the permeability is measured in Gauss/Oersted and the resistivity is measured in microhm-cm.

19. The line filter of claim 17, wherein the line filter includes multiple coils attached in one of a parallel manner, a series manner, and a combination of parallel and series manners.