Method and apparatus for adjusting overload compensation for a watthour meter

• US 5,604,414 A
• Filed: 09/15/1994
• Issued: 02/18/1997
• Est. Priority Date: 09/15/1994
• Status: Expired due to Term

• Current Assignee: Landis+Gyr AG (Landis+Gyr Group AG)
• Original Assignee: Landis & Gyr Energy Management, Inc. (Landis+Gyr Group AG)
• Inventors: Milligan, James W., Voisine, John T.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US08/307,297
• Time in Patent Office: 887 Days
• Field of Search: 318/632, 324/126, 324/127, 324/142, 324/110, 323/357
• US Class Current: 318/632
• CPC Class Codes: G01R 11/21 Compensating for errors caused by damping effects of the current, e.g. adjustment in the overload range

Abstract

An apparatus for electrically setting the overload compensating magnetic reluctance in a single phase induction watthour meter includes a moveable magnetic shunt positioned adjacent the poles of a current core of a current stator circuit. An electrical parameter of the current stator circuit is sensed and changes in this parameter are used to set the air gap between the magnetic shunt and the current core poles. In one embodiment, a programmable controller controls a motor to move the shunt in response to variation of the sensed electrical parameter from a predetermined value. In one method, the sensed electrical parameter is the voltage induced in a first current coil when a second current coil is energized. In other methods, the sensed electrical parameter is the flux induced in the magnetic shunt or the self inductance of a current coil. A further method is to determine the ration of a harmonic voltage to a fundamental voltage which corresponds to the desired degree of magnetic saturation of the overload compensator at the control point.

Claims

1. An apparatus for electrically setting the overload compensation of a current stator circuit for an induction type watthour meter having a current core wound with at least one current coil, and a magnetic shunt positioned adjacent to poles of the current core, comprising:

means for energizing the current stator circuit;

an electrical sensing device for sensing an electrical parameter of the current stator circuit when said current stator circuit is energized, said electrical sensing device producing a sensory signal corresponding to the sensed electrical parameter;

a motor, including a control input, with means for removably attaching to the magnetic shunt, said motor operable to change the position of the magnetic shunt in relation to the poles of the current core in accordance with a control signal supplied at said control input of said motor; and

control means for controlling said motor in response to said sensory signal by calculating a desired position of said magnetic shunt based on said sensory signal, and sending a corresponding control signal to said control input of said motor, whereby said motor positions the magnetic shunt appropriately in response to said control signal.

2. The apparatus of claim 1 wherein said means for energizing is a current source and said electrical sensing device is a voltage sensor, said voltage sensor attached to a current coil to sense induced voltage.

3. The apparatus of claim 1, wherein said electrical sensing device consists of a magnetic induction sensor, said induction sensor being magnetically coupled to said magnetic shunt.

4. A method for electrically setting the overload compensation in a current stator circuit of an induction watthour meter, the method comprising the steps of:

determining an electrical parameter which varies in response to changes in magnetic response of the current stator circuit;

determining a value for said electrical parameter, said value corresponding to appropriate overload compensation of the current stator circuit;

energizing the current stator circuit;

sensing the electrical parameter; and

adjusting the position of an overload compensator by controlling a motor in response to the sensed electrical parameter until said predetermined value for said electrical parameter is sensed, said motor having means for removably attaching to the overload compensator.

5. The method of claim 4 wherein the current stator circuit includes a current core with two poles and the overload compensator is a magnetic shunt which is positioned adjacent to said poles of the current core.

6. The method of claim 4, wherein the desired electrical parameter is a voltage value for a first current coil positioned around the current core, said voltage value corresponding to the desired overload compensating magnetic reluctance.

7. The method of claim 5, in which the desire electrical parameter corresponds to a flux value at a desired magnetic reluctance for the magnetic shunt.

8. The method of claim 4, in which the desired electrical parameter is a ratio of the low frequency harmonic voltage of said current stator circuit to the fundamental voltage of said current stator circuit, said ratio corresponding to a desired magnetic reluctance.

9. The method of claim 7 in which the desired electrical parameter is a ratio of one or more harmonic voltage of said current stator to the fundamental voltage of said current stator, said ratio corresponding to a desired magnetic reluctance.