Measurement and control of magnetomotive force in current transformers and other magnetic bodies
First Claim
1. A method for measuring a magnetomotive force experienced by a magnetic body;
- said magnetic body having a nonlinear permeability;
said method comprising the steps of;
(a) provide a first winding magnetically coupled to said magnetic body;
(b) provide an excitation means for causing a magnetic flux in said magnetic body to oscillate at a predetermined frequency;
said excitation means connected to said first winding;
the operation of said excitation means resulting in an exciting current flowing in said first winding and an excitation voltage induced in said first winding;
said exciting current oscillating at said predetermined frequency;
said excitation voltage oscillating at said predetermined frequency;
said exciting current having a first waveform, and said excitation voltage having a second waveform;
a difference of symmetry between said first waveform and said second waveform being dependent on the magnitude and polarity of said magnetomotive force and on said nonlinear permeability;
(c) utilizing predetermined symmetry relationships, determine said magnetomotive force from characteristics of one or both of said first waveform and said second waveform.
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Abstract
A magnetic body having nonlinear permeability is influenced by a magnetomotive force, the magnitude of which is to be measured or controlled. An electric energy source is connected to a winding that is magnetically coupled to the magnetic body. The electric energy source generates an oscillating output so as to cause the magnetic flux within the magnetic body to oscillate at a predetermined frequency. The oscillating flux is associated with an exciting current and excitation voltage, both oscillating at the predetermined frequency. The nonlinear permeability of the magnetic body causes the waveform of the exciting current to have different symmetry than the waveform of the excitation voltage. The difference of symmetry is indicative of the polarity and average value of magnetomotive force experienced by the magnetic body. The difference in symmetry is used to measure the average magnetomotive force experienced by the magnetic body. Alternatively the difference in symmetry may be used as an input to a control system that controls the average magnetomotive force experienced by the magnetic body. When applied to current transformers, the invention enables ordinary current transformers to operate with a-c and d-c primary currents while coupling very little noise to the primary circuit.
62 Citations
40 Claims
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1. A method for measuring a magnetomotive force experienced by a magnetic body;
- said magnetic body having a nonlinear permeability;
said method comprising the steps of;(a) provide a first winding magnetically coupled to said magnetic body; (b) provide an excitation means for causing a magnetic flux in said magnetic body to oscillate at a predetermined frequency;
said excitation means connected to said first winding;
the operation of said excitation means resulting in an exciting current flowing in said first winding and an excitation voltage induced in said first winding;
said exciting current oscillating at said predetermined frequency;
said excitation voltage oscillating at said predetermined frequency;
said exciting current having a first waveform, and said excitation voltage having a second waveform;
a difference of symmetry between said first waveform and said second waveform being dependent on the magnitude and polarity of said magnetomotive force and on said nonlinear permeability;(c) utilizing predetermined symmetry relationships, determine said magnetomotive force from characteristics of one or both of said first waveform and said second waveform. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
- said magnetic body having a nonlinear permeability;
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17. Apparatus for measuring a magnetomotive force experienced by a magnetic body;
- said magnetic body having a nonlinear permeability;
said apparatus comprising;(a) a first winding magnetically coupled to said magnetic body; (b) an excitation means for causing a magnetic flux in said magnetic body to oscillate at a predetermined frequency without causing saturation of said magnetic body;
said excitation means connected to said first winding;
the operation of said excitation means resulting in an exciting current flowing in said first winding and an excitation voltage induced in said first winding;
said exciting current oscillating at said predetermined frequency;
said excitation voltage oscillating at said predetermined frequency;
said exciting current having a first waveform, and said excitation voltage having a second waveform;
a difference of symmetry between said first waveform and said second waveform being dependent on the magnitude and polarity of said magnetomotive force and on said nonlinear permeability;(c) a sensing means for sensing one or both of said first waveform and said second waveform; (d) a calculating means for calculating said magnetomotive force from said difference of symmetry;
said calculating means utilizing one or more known relationships between said difference of symmetry and said magnetomotive force to calculate said magnetomotive force. - View Dependent Claims (18, 19, 20, 21)
- said magnetic body having a nonlinear permeability;
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22. A method for continuously providing a secondary electric current that is proportional to a primary electric current;
- said primary electric current having a d-c component;
said method comprising the steps of;(a) provide a current transformer and cause said primary electric current to flow in a conductor configured as a primary winding of said current transformer;
said current transformer comprising a magnetic core and a secondary winding magnetically coupled to said magnetic core;
said magnetic core having a nonlinear permeability;
said secondary electric current flowing in said secondary winding;
said secondary electric current being approximately proportional to said primary electric current;
said secondary electric current being proportionally smaller than said primary electric current by a turns ratio of said current transformer;
an induced voltage in said secondary winding being proportional to a rate of change of a magnetic flux in said magnetic core;
a secondary electric current error being proportional to a magnetomotive force acting on said magnetic core, an instantaneous value of said magnetomotive force being equal to an instantaneous difference between said primary electric current multiplied by the number of turns of said primary winding and said secondary electric current multiplied by the number of turns of said secondary winding;
said secondary electric current error comprising a d-c component and an a-c component;
said d-c component herein referred to as a d-c current error, said a-c component herein referred to as an exciting current error;(b) connect a controllable voltage device in series with said secondary winding;
said voltage device providing an output voltage that controls said induced voltage, thereby controlling said rate of change of said magnetic flux;(c) continuously control said voltage device so that said induced voltage oscillates at a predetermined frequency, thereby causing said magnetic flux to oscillate at said predetermined frequency;
said exciting current error thereby also being caused to oscillate at said predetermined frequency;
a dissymmetry of said exciting current error being dependent on the magnitude and polarity of said d-c current error and said nonlinear permeability;(d) continuously detect said dissymmetry; (e) based on characteristics of said dissymmetry, continuously adjust said output voltage so as to minimize said d-c current error, thereby causing said secondary electric current to be approximately proportional to said primary electric current. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
- said primary electric current having a d-c component;
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33. Apparatus for enabling a current transformer to continuously provide a secondary electric current that is proportional to a primary electric current, said primary electric current having a d-c component;
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said current transformer comprising a magnetic core and a secondary winding magnetically coupled to said magnetic core;
said magnetic core having a nonlinear permeability;
said secondary electric current flowing in said secondary winding;
the magnitude of said secondary electric current being approximately proportional to said primary electric current;
said secondary electric current being proportionally smaller than said primary electric current by a turns ratio of said current transformer;
an induced voltage in said secondary winding being proportional to a rate of change of a magnetic flux in said magnetic core;a secondary electric current error being proportional to a magnetomotive force acting on said magnetic core, an instantaneous value of said magnetomotive force being equal to an the instantaneous difference between said primary electric current multiplied by the number of turns of said primary winding and said secondary electric current multiplied by the number of turns of said secondary winding;
said secondary electric current error comprising a d-c component and an a-c component;
said d-c component herein referred to as a d-c current error, said a-c component herein referred to as an exciting current error;said apparatus comprising; (a) a sensing means for sensing said secondary electric current and providing an information signal containing information about said exciting current error; (b) a controllable voltage means for producing an output voltage that controls said induced voltage, thereby controlling said rate of change of said magnetic flux;
said controllable voltage device being connected in series with said secondary winding;(c) a control means for receiving said information signal and controlling said voltage means; said control means controlling said output voltage so that said induced voltage oscillates at a predetermined frequency, thereby causing said magnetic flux to oscillate at said predetermined frequency and causing said exciting current error to oscillate at said predetermined frequency;
a dissymmetry of said exciting current error being dependent on the magnitude and polarity of said d-c current error and said nonlinear permeability;
said control means continuously detecting said dissymmetry, and, based on characteristics of said dissymmetry, continuously adjusting said output voltage so as to minimize said d-c current error, thereby causing said secondary electric current to be approximately proportional to said primary electric current. - View Dependent Claims (34, 35, 36, 37, 38, 39, 40)
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Specification