a-c current transformer functional with a d-c current component present
First Claim
1. An a-c current transformer able to function with a primary electric current having a d-c current component;
- said current transformer comprising a saturable magnetic core and a secondary winding magnetically coupled to said magnetic core;
said primary electric current flowing in a conductor configured as a primary winding of said current transformer;
wherein the improvement is that said magnetic core is optimized to have nonlinear incremental permeance such that(a) said magnetic core operates with high incremental permeance when said d-c current component is not present, thereby providing for current transformer operation with high accuracy when said d-c current component is not present; and
(b) said magnetic core is constructed so that a first part of said magnetic core operates with a high first permeance, and a second part of said magnetic core operates with a second permeance that is lower than said first permeance, thereby causing said magnetic core to have said nonlinear incremental Permeance;
said magnetic core does not saturate when said d-c current component is present; and
(d) said magnetic core operates in a non-saturated manner with reduced incremental permeance when said d-c current component is present, thereby providing current transformer operation with reduced accuracy when said d-c current component is present.
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Abstract
The magnetic core of an a-c current transformer is optimized so that the current transformer is able to function with a primary electric current having a d-c current component. In the preferred embodiment, the magnetic core is optimized to have nonlinear incremental permeance so that the magnetic core operates with high incremental permeance when the d-c current component is not present (thereby providing current transformer operation with relatively high accuracy), and the magnetic core operates in a non-saturated manner with reduced incremental permeance when the d-c current component is present (thereby providing acceptable current transformer operation, but with reduced accuracy). An electronic assist means may be provided for improved current transformer accuracy. An alternate embodiment combines an electronic assist means together with a magnetic core that has low permeance.
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Citations
16 Claims
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1. An a-c current transformer able to function with a primary electric current having a d-c current component;
- said current transformer comprising a saturable magnetic core and a secondary winding magnetically coupled to said magnetic core;
said primary electric current flowing in a conductor configured as a primary winding of said current transformer;
wherein the improvement is that said magnetic core is optimized to have nonlinear incremental permeance such that(a) said magnetic core operates with high incremental permeance when said d-c current component is not present, thereby providing for current transformer operation with high accuracy when said d-c current component is not present; and
(b) said magnetic core is constructed so that a first part of said magnetic core operates with a high first permeance, and a second part of said magnetic core operates with a second permeance that is lower than said first permeance, thereby causing said magnetic core to have said nonlinear incremental Permeance;
said magnetic core does not saturate when said d-c current component is present; and
(d) said magnetic core operates in a non-saturated manner with reduced incremental permeance when said d-c current component is present, thereby providing current transformer operation with reduced accuracy when said d-c current component is present. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- said current transformer comprising a saturable magnetic core and a secondary winding magnetically coupled to said magnetic core;
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10. A method for continuously providing a secondary alternating electric current that is approximately proportional to an alternating current component of a primary electric current;
- said primary electric current subject to also having a d-c current component;
said method, comprising the steps of;(a) providing a current transformer magnetic core having nonlinear permeance such that said magnetic core operates with high incremental permeance when said d-c current component is not present, thereby providing for current transformer operation with high accuracy when said d-c current component is not present; and
said magnetic core operates in a non-saturated manner with reduced incremental permeance when said d-c current component is present, thereby providing current transformer operation with reduced accuracy when said d-c current component is present;
(b) provide a secondary winding wrapped around said magnetic core;
(c) terminate said secondary winding so that said secondary electric current can flow freely;
(d) cause said primary electric current to flow in a conductor configured as a primary winding of said current transformer;
thereby causing said secondary alternating electric current to flow in said secondary winding. - View Dependent Claims (11, 12, 13, 14, 15, 16)
- said primary electric current subject to also having a d-c current component;
Specification