Current measuring and magnetic core compensating apparatus and method
First Claim
1. Apparatus for compensating for DC current flowing in a primary winding of a transformer having a secondary winding and a magnetic core with a B-H curve, the DC current having a tendency to supply DC magnetic flux to the core to bias the core so as operating point thereof is displaced from a zero flux position on the B-H curve thereby to cause positive and negative current components in the secondary winding to have different amplitudes and different time durations, the apparatus comprising means responsive to the positive and negative current components for deriving a first signal having a value determined by the average values of the positive current components, a second signal having a value determined by the average values of the negative current components, and a third signal having a value determined by a comparison of the amplitudes of the first and second values to indicate the average values of the positive and negative components, and means for controlling the DC magnetic flux supplied to said core in response to the third signal to overcome the tendency of the core to be biased away from the zero flux position.
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Accused Products
Abstract
DC magnetic flux bias imposed on a magnetic core of a current transformer is compensated in response to an indication of the amplitude and duration of opposite polarity secondary winding current components. In a second embodiment, the magnetic bias is compensated by responding to the integral of the secondary current. The integral of the secondary current is a measure of the magnetic core flux variations. The durations of the positive and negative flux variations are compared.
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Citations
16 Claims
- 1. Apparatus for compensating for DC current flowing in a primary winding of a transformer having a secondary winding and a magnetic core with a B-H curve, the DC current having a tendency to supply DC magnetic flux to the core to bias the core so as operating point thereof is displaced from a zero flux position on the B-H curve thereby to cause positive and negative current components in the secondary winding to have different amplitudes and different time durations, the apparatus comprising means responsive to the positive and negative current components for deriving a first signal having a value determined by the average values of the positive current components, a second signal having a value determined by the average values of the negative current components, and a third signal having a value determined by a comparison of the amplitudes of the first and second values to indicate the average values of the positive and negative components, and means for controlling the DC magnetic flux supplied to said core in response to the third signal to overcome the tendency of the core to be biased away from the zero flux position.
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14. The apparatus of 13 wherein the feedback capacitor is shunted by a stabilizing resistor.
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16. A method of compensating for DC current flowing in a primary winding of a transformer having a secondary winding and a magnetic core with a B-H curve, the DC current having a tendency to supply DC magnetic flux to the core to bias the core so an operating point thereof is displaced from a zero flux position on the B-H curve thereby to cause positive and negative AC current components in the secondary winding to have different amplitudes and different time durations, the method comprising the steps of responding to the positive current components to derive a first indication of the average value of the positive current components, responding to the negative current components to dervie a second indication of the average value of the negative current components, comparing the amplitudes of the first and second indications to derive a third indication for the relative values of the average values of the positive and negative components, and controlling the DC magnetic flux supplied to said core in response to the third indication to overcome the tendency of the core to be biased away from the zero flux position.
Specification