CURRENT SENSOR

• US 20130027021A1
• Filed: 07/28/2011
• Published: 01/31/2013
• Est. Priority Date: 07/28/2011
• Status: Abandoned Application

• Current Assignee: ABB Incorporated (ABB Limited)
• Original Assignee: ABB Incorporated (ABB Limited)
• Inventors: Gokhale, Kalyan P.
• Application Number:
  US13/192,783
• Publication Number:
  US 20130027021A1
• Time in Patent Office: Days
• US Class Current: 324/117.R
• CPC Class Codes: G01R 15/183 using transformers with a magnetic core
• CPC Class Codes: G01R 19/0015 separating AC and DC

Abstract

A current sensor is provided for measuring DC current in a primary conductor also carrying AC current. The current sensor includes a ferromagnetic core through which the primary conductor may extend. The core has a narrow air gap formed therein and a magnetic flux sensor is disposed in the air gap. A secondary winding is mounted to the core and has an impedance connected therein. The impedance has a value of substantially zero at one or more frequencies of the AC current. The impedance may be a short or an impedance source that includes a capacitor and an inductor.

Claims

1. A current sensor for measuring DC current in a primary conductor also carrying AC current, the current sensor comprising:

a ferromagnetic core through which the primary conductor may extend, the core having an air gap formed therein;

a magnetic flux sensor disposed in the air gap;

a secondary winding mounted to the core, the secondary winding have an impedance connected therein, the impedance having a value of substantially zero at one or more frequencies of the AC current; and

wherein the air gap has a width less than twice the thickness of the magnetic flux sensor.

2. The current sensor of claim 1, wherein the impedance comprises a short in which ends of the secondary winding are connected together.

3. The current sensor of claim 2, wherein the secondary winding has a single turn.

4. The current sensor of claim 1, wherein the air gap has a width less than one and a half times the thickness of the magnetic flux sensor.

5. The current sensor of claim 1, wherein the core comprises a pair of spaced apart legs and a pair of spaced-apart yokes, a first one of the yokes extending across first ends of the legs and a second one of the yokes extending across a second one of the legs, and wherein the air gap is formed in one of the legs.

6. The current sensor of claim 1, wherein the core is toroidal.

7. The current sensor of claim 1, wherein the impedance comprises a circuit having at least one device selected from the group consisting of a resistor, an inductor, a capacitor, an operational amplifier, a transistors and a diode.

8. The current sensor of claim 7, wherein the circuit comprises an inductor and a capacitor.

9. The current sensor of claim 8, wherein the inductor and the capacitor are connected in series.

10. The current sensor of claim 8, wherein the inductor and the capacitor are connected in parallel.

11. The current sensor of claim 1, wherein the magnetic flux sensor is a Hall element.

12. An inverter system for connection by one or more primary conductors to a utility network, the inverter system comprising:

an inverter for connection by the one or more primary conductors to the utility network; and

one or more current sensors for connection to the one or more primary conductors, respectively, each current sensor comprising;

a ferromagnetic core through which one of the primary conductors may extend, the core having an air gap formed therein;

a magnetic flux sensor disposed in the air gap;

a secondary winding mounted to the core, the secondary winding have an impedance connected therein, the impedance having a value of substantially zero at one or more frequencies of the AC current; and

wherein the air gap has a width less than twice the thickness of the magnetic flux sensor.

13. The inverter system of claim 12, further comprising a controller for controlling the operation of the inverter based on the DC current(s) measured by the one or more current sensors.

14. The inverter system of claim 13, wherein the controller is operable to control the inverter such that 0.1 percent or less of the current output from the inverter is DC current.

15. The inverter system of claim 12, wherein the inverter is a three-phase inverter, the one or more primary conductors comprise three primary conductors and the one or more current sensors comprises three current sensors connected to the three primary conductors, respectively.

16. The inverter system of claim 12, wherein the impedance comprises a short in which ends of the secondary winding are connected together.

17. The inverter system of claim 12, wherein the impedance comprises a circuit having at least one device selected from the group consisting of a resistor, an inductor, a capacitor, an operational amplifier, a transistors and a diode.

18. The inverter system of claim 17, wherein the circuit comprises an inductor and a capacitor.

19. The inverter system of claim 18, wherein the inductor and the capacitor are connected in series.

20. The inverter system of claim 18, wherein the inductor and the capacitor are connected in parallel.