Technique for calibrating a transformer element

• US 5,453,697 A
• Filed: 09/09/1993
• Issued: 09/26/1995
• Est. Priority Date: 09/09/1993
• Status: Expired due to Term

• Current Assignee: 564935 Ontario Limited
• Original Assignee: Caroma Industries Limited (GWA Group Limited)
• Inventors: Pilkey, Ross M., Schweer, G. Carl
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/118,880
• Time in Patent Office: 747 Days
• Field of Search: 324/546, 324/547, 324/601, 324/537, 364/571.01
• US Class Current: 324/601
• CPC Class Codes: G01R 35/02 of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating
• CPC Class Codes: G01R 35/04 of instruments for measuring time integral of power or current

Abstract

Disclosed herein is a technique for calibrating a transformer element, comprising the steps of providing a transformer element with a primary winding and a secondary winding; providing a memory to store a range of expected values of a power component, each value being representative of a flow of power expected through the secondary winding for a corresponding flow of power through the primary winding; establishing a flow of power at a first level through the primary winding, thereby to establish a corresponding flow of power through the secondary winding; measuring the power component for the flow of power through the secondary winding to obtain a first measurement thereof; comparing the first measurement with a corresponding expected value and calculating a first factor according to the difference there between; and storing the first factor; varying the flow of power in the primary winding to a second level; measuring the power component for the flow of power through the secondary winding to obtain a second measurement thereof; comparing the second measurement with a corresponding expected value and calculating a second factor according to the difference there between; and storing the second factor.

Claims

1. A technique for calibrating a crude toroidal transformer element, comprising the steps of:

providing a crude toroidal transformer element having a ring and a secondary winding wound on said ring;

extending a main through said ring to form a primary winding;

providing a stored range of expected values of a first power component, each value being representative of a flow of power expected through said secondary winding for a corresponding flow of power through said primary winding;

establishing a flow of power at a first level through said primary winding, thereby to establish a corresponding flow of power through said secondary winding;

measuring said first power component for the flow of power through said secondary winding to obtain a first measurement thereof;

calculating a first factor relative to both said first measurement and a corresponding one of said expected values of the first power component;

storing said first factor;

varying incrementally said flow of power through said primary winding to a second level;

measuring said first power component for the flow of power through said secondary winding to obtain a second measurement thereof;

calculating a second factor relative to both said second measurement and a corresponding one of said expected values of the first power component;

storing said second factor;

varying incrementally said flow of power in said primary winding to a number of subsequent power levels;

measuring said first power component for each of said subsequent power levels in said secondary winding to obtain a corresponding number of subsequent measurements;

calculating a set of factors relating each of said subsequent measurements and a corresponding one of said expected values of the first power component;

storing said set of factors;

transferring said first, second and said set of factors to a portable recording medium, wherein said transformer element, together with said first, second and said set of factors, are capable of generating measurements of power with improved accuracy when corrected by said factors.

3. A technique as defined in claim 1 further comprising the step of:

providing a stored range of expected values of a second power component, each value being representative of a flow of power expected through said secondary winding for a corresponding flow of power through said primary winding;

varying incrementally said flow of power in said primary winding to a number of power levels;

measuring said second power component for each of said subsequent power levels in said secondary winding to obtain a corresponding number of subsequent measurements;

calculating another set of factors relating each of said subsequent measurements and a corresponding one of said expected values of the second power component; and

storing said other set of factors.

4. A transformer assembly as defined in claim 3 wherein said second power component is RMS voltage.

5. A technique as defined in claim 1 wherein said first power component is phase angle.

6. A technique as defined in claim 1 wherein said first power component is RMS voltage.

7. A device as defined in claim 5 wherein a resistor element is positioned across said secondary winding, wherein said power component is represented by the voltage across said resistor.

8. A technique as defined in claim 1 wherein:

said step of calculating a first factor includes the step of comparing said first measurement with said corresponding expected value of the first power component; and

said step of calculating a second factor includes the step of comparing said second measurement with said corresponding expected value of the first power components.

9. A technique as defined in claim 8 wherein set of increments has up to about 200 increments.

2. A technique as defined in claim i further comprising the steps of:

applying a resistor element across said secondary winding; and

measuring said first power component for the flow of power through said secondary winding by recording the RMS voltage appearing across said resistor element.

10. A device for calibrating a crude toroidal transformer element, comprising:

a crude toroidal transformer element having a ring and a secondary winding wound on said ring;

said transformer element being further arranged with a main extending through said ring to form a primary winding;

means for establishing a flow of power at successive incremental levels through said primary winding, thereby to establish a corresponding flow of power at successive incremental levels through said secondary winding;

means for measuring a power component for each of said incremental levels of said flow of power through said secondary winding to obtain a first range of incremental measurements thereof;

means for storing a second range of expected values of said power component, each value being representative of an incremental change in the flow of power expected through said secondary winding for a corresponding in cremental change in the flow of power through said primary winding;

means for calculating a set of factors each being relative to one of said incremental measurements in said first range and a corresponding one of said expected values in said second range;

means for storing said set of factors wherein said device is operable to convert said crude transformer element into one which, together with said set of factors, is capable of generating power measurements with improved accuracy when corrected by said factors.

11. A device as defined in claim 10 wherein said means for calculating further includes a comparator for comparing each of said measurements in said second range against a corresponding expected value in said first range.