US 6,479,976 B1 · Method and apparatus for accurate measurement of pulsed electric currents utilizing ordinary current transformers

Abstract

A voltage source connected in the secondary circuit of a current transformer is controlled so as to provide a secondary current that is accurately and continuously proportional to a primary current that is either pulsed d-c electric current or pulsed a-c electric current. Similar to U.S. Pat. No. 6,180,697, the voltage source is controlled so as to compensate for the voltage drop caused by secondary current flowing through secondary circuit impedances, thereby reducing the effective burden of the secondary circuit. However, to prevent the accumulation of error when measuring pulsed currents that are not symmetrical, the present invention turns the burden-reducing compensation off whenever secondary current is near zero amperes, thereby providing for the decay of current error and magnetic flux, so that current error remains very small and the current transformer does not saturate. The primary application is thought to be in the accurate measurement and control of pulsed electric current utilizing an ordinary current transformer to provide isolation from the primary circuit.

Claims23

Dependent claims

A method for continuously providing a secondary electric current that is approximately proportional to a primary electric current;

said primary electric current periodically having a magnitude of approximately zero amps for nonzero periods of time;
said primary electric current flowing in a conductor configured as a primary winding of a current transformer, said secondary electric current flowing in a secondary winding of said current transformer;
said primary winding and said secondary winding being magnetically coupled;
a controllable voltage device being connected in series with said secondary winding;
said voltage device producing an output voltage affecting the rate that magnetic flux builds up within said current transformer;
the build-up of said magnetic flux in said current transformer being associated with a secondary electric current error;
said method comprising controlling said voltage device so that
(a) whenever the magnitude of said secondary electric current is greater than a predetermined value said output voltage reduces the rate that said magnetic flux builds up in said current transformer;
and
(b) whenever the magnitude of said secondary electric current is less than said predetermined value said output voltage is controlled so that said secondary electric current error decays while the magnitude of said primary current is approximately zero amps.

7 more elements

Apparatus for producing a secondary electric current that is approximately proportional to a primary electric current;

said primary electric current periodically having a magnitude of approximately zero amps for nonzero periods of time;
said apparatus comprising
(a) a first winding conducting said primary electric current;
(b) a second winding conducting said secondary electric current;
(c) a magnetic coupling means for providing magnetic coupling between said first winding and said second winding, a build-up of magnetic flux in said magnetic coupling means being associated with secondary electric current error;
(d) a controllable voltage device connected to said second winding and producing an output voltage which affects a rate that said magnetic flux builds up;
and
(e) a suitable control means for controlling said voltage device;
said control means controlling said voltage device so that whenever the magnitude of said secondary electric current is greater than a predetermined value said output voltage reduces the rate that said magnetic flux builds up in said magnetic coupling means, and whenever the magnitude of said secondary electric current is less than said predetermined value said output voltage is controlled so that said secondary electric current error decays while the magnitude of said primary current is approximately zero amps.

6 more elements

Dependencies are inferred from the claim text.

Method and apparatus for accurate measurement of pulsed electric currents utilizing ordinary current transformers

Life of this patent

Method and apparatus for accurate measurement of pulsed electric currents utilizing ordinary current transformers

Life of this patent

Abstract

Claims23