Circuit breaker comprising a current transformer with a partial air gap

• US 20020121948A1
• Filed: 05/01/2002
• Published: 09/05/2002
• Est. Priority Date: 03/06/2000
• Status: Abandoned Application

• Current Assignee: Alan J. Messerli, Zoltan Giday
• Original Assignee: Alan J. Messerli, Zoltan Giday
• Inventors: Messerli, Alan J., Giday, Zoltan
• Application Number:
  US10/063,511
• Publication Number:
  US 20020121948A1
• Time in Patent Office: Days
• US Class Current: 335/18
• CPC Class Codes: H01F 3/14 Constrictions; Gaps, e.g. air-gaps in magnetic shunt paths H01F3/12
• CPC Class Codes: H01F 38/30 Constructions
• CPC Class Codes: H01H 71/125 characterised by sensing elements, e.g. current transformers for differential protection H01H83/144

Abstract

A circuit breaker assembly having an electronic trip unit used to detect an overcurrent condition in a protected electrical circuit. The electronic trip unit being electrically connected to a current transformer used to sense electrical current and provide operating power to the electronic trip unit. The current transformer comprising a metal core having a top surface and a bottom surface where the difference between the top and bottom surfaces defines a height of the core. The core having a concentrical opening extending through the height so that the distance between an outside point on the concentrical opening and the closest outside point of the core defines a thickness of the core at that point. Passing through the core opening is a primary winding and encircling the thickness of the core is a secondary winding. To optimize usage of the current transformer, a partial air gap is added to the metal core so that the range of operation is maximized while at the same time minimizing the remanence attenuation.

Claims

1. A current sensor for sensing a current in a conductor, comprising:

a toroidal transformer core encircling said conductor;

a secondary winding passing through the toroidal transformer core at least once such that a voltage signal is generated in said secondary winding that is indicative of a current in said conductor;

a sensing circuit electrically connected to said secondary winding for receiving said voltage signal and generating a response that depends upon the magnitude of said voltage signal; and

wherein said core includes a partial air gap comprising a portion of reduced circumferential cross-section area.

2. The current sensor of claim 1 wherein said partial air gap is configured to reduce the remanence attenuation of said toroidal transformer core without reducing the operating range of the current sensor below a selected minimum.

3. The current sensor of claim 1 wherein said partial air gap has a thickness between approximately 0.010 inches and approximately 0.020 inches.

4. The current sensor of claim 3 wherein said partial air gap has a thickness of approximately 0.010 inches.

5. The current sensor of claim 1 wherein said circumferential cross section area of said toroidal transformer core at said partial air gap is reduced by approximately ⅓

to approximately ¾

.

6. The current sensor of claim 5 wherein said circumferential cross section area of said toroidal transformer core at said partial air gap is reduced by approximately ¾

.

7. A current sensor for sensing a current in a conductor, comprising:

transformer for generating a signal indicative of a current in said conductor, said transformer comprising a toroidal core;

means for optimizing the operational dynamic range of the load current and the remanence attenuation; and

means for processing said signal.

8. The current sensor of claim 7 wherein:

said means for optimizing the operational dynamic range of the load current and the remanence attenuation includes a partial air gap in said core.

9. The current sensor of claim 8 wherein said means for processing includes a trip unit configured to trip a circuit breaker when said signal indicates a fault condition.