Patent ID: 6954060

Claim:
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.