ELECTRICAL CURRENT TRANSDUCER WITH ELECTROSTATIC SHIELD

• US 20160154026A1
• Filed: 11/03/2015
• Published: 06/02/2016
• Est. Priority Date: 11/28/2014
• Status: Active Grant

• Current Assignee: LEM International SA (LEM Holding SA)
• Original Assignee: Lem Intellectual Property SA (LEM Holding SA)
• Inventors: Claeys, St?phane
• Granted Patent: US 9,846,179 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 15/183 using transformers with a magnetic core
• CPC Class Codes: G01R 15/185 with compensation or feedback windings or interacting coils, e.g. 0-flux sensors using galvano-magnetic field sensors G01R15/20; conversion of DC into AC using transductors G01R19/20
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: H01F 2038/305 with toroidal magnetic core
• CPC Class Codes: H01F 27/02 Casings
• 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 38/30 Constructions

Abstract

Electrical current transducer to measure the current flowing in a primary conductor, the transducer including an outer casing, a magnetic core comprising a magnetic circuit gap, a magnetic field detector comprising a sensing portion positioned in the magnetic circuit gap, an insulating core housing, a secondary coil formed from a wire wound around a coil support portion of the insulating core housing, and an electrostatic shield. The electrostatic shield is positioned between secondary coil and a radially inner wall portion of the outer casing, the radially inner wall portion defining a passage configured to receive said primary conductor therethrough. The electrostatic shield comprises a skirt portion formed by a plurality of flexible strips extending axially from an edge of the shield, the flexible strips configured to elastically bias against a base wall portion of the outer casing.

Claims

1. Electrical current transducer to measure the current flowing in a primary conductor, the transducer including an outer casing, a magnetic core comprising a magnetic circuit gap, a magnetic field detector comprising a sensing portion positioned in the magnetic circuit gap, an insulating core housing, a secondary coil formed from a wire wound around a coil support portion of the insulating core housing, and an electrostatic shield positioned between secondary coil and a radially inner wall portion of the outer casing, the radially inner wall portion defining a passage configured to receive the primary conductor therethrough, wherein the electrostatic shield comprises a skirt portion formed by a plurality of flexible strips extending axially from an edge of the shield, the flexible strips configured to elastically bias against a base wall portion of the outer casing.

2. Current transducer according to claim 1, wherein the strips are separated by slits, and wherein juxtaposed strips and slits are substantially evenly distributed around a circumference of the shield.

3. Current transducer according to claim 1, wherein the electrostatic shield is formed from a thin flexible sheet, selected from a group consisting of stamped sheet metal and metallized flexible substrate, folded into a shape configured to surround the primary conductor passage.

4. Current transducer according to claim 1, wherein the electrostatic shield comprises a securing mechanism configured to hold the shield in a closed bent configuration prior to mounting on to the core housing.

5. Current transducer according to claim 1, wherein the electrostatic shield comprises locking orifices cooperating with screen fixing protrusions of the core housing to position and hold the electrostatic shield to the core housing during manufacturing assembly.

6. Current transducer according to claim 5, wherein the locking orifices comprise a wide portion and a narrow portion, and the screen fixing protrusions comprise a profile having a wide head portion and narrow stem portion, whereby the wide head portion is insertable through the wide portion of the locking orifice, and the narrow stem portion is slidable into the narrow portion of the locking orifice.

7. Current transducer according to claim 6, wherein the narrow portion of the locking orifice is oriented towards the skirt portion relative to the wide portion, such that the spring biasing force acting on the shield when assembled in the casing tends to confirm the locking of the electrostatic shield to the core housing.

8. Current transducer according to claim 1, wherein the insulating core housing comprises a coil terminal connection portion, the coil support portion, and at least one circuit board support portion.

9. Current transducer according to claim 8, wherein the coil support portion has a generally U-shaped cross-sectional profile comprising a base wall, a radially inner wall extending from the base wall and a radially outer wall extending from the base wall, the radially inner and outer walls having a height configured such that open end edges thereof extend slightly beyond an axial thickness of the magnetic core including any manufacturing tolerances such that the open end edges are folded inwards around corners of the magnetic core by the coil wound around the magnetic core housing.

10. Current transducer according to claim 8, wherein the coil support portion comprises core latching elements in the form of latching shoulders configured to allow the core to be axially inserted in the core housing and to hold the core within the core housing during assembly.

11. Current transducer according to claim 8, wherein the coil support portion of the core housing comprises wire anti-slip elements configured to prevent slipping of a first winding layer of the secondary coil on the core housing during the winding process.

12. Current transducer according to claim 8, wherein the core housing comprises deflector ribs arranged in corners joining the coil support portion to the coil terminal connection portion and circuit board support portion, the deflector ribs configured to avoid a build-up of windings adjacent side walls of the coil support portion and the coil terminal connection portion.

13. Current transducer according to claim 8, wherein the coil terminal connection portion comprises a magnetic sensor receiving cavity for lodging the magnetic field detector therein.

14. Current transducer according to claim 8, wherein the coil terminal connection portion comprises a circuit board resting edge and a circuit board latching element that extends over an edge of the circuit board, and wherein the circuit board support portion comprises a circuit board resting edge and a circuit board latching element configured to extend over an edge of a circuit board, to secure the magnetic core, core housing and secondary winding assembly to the circuit board.

15. Current transducer according to claim 1, wherein the core housing is a single molded part.