Patent ID: 7307504

Claim:
A current transformer comprising: a generally circular cylindrical current transformer core having a central opening, a height, a width, an inner radius and an outer radius; and a secondary winding disposed about said generally circular cylindrical current transformer core, wherein said generally circular cylindrical current transformer core is formed from a winding of an elongated length of taped steel having a reluctance and a width, wherein the height of said generally circular cylindrical current transformer core corresponds to said width of said elongated length of taped steel, wherein the width of said generally circular cylindrical current transformer core is equal to the difference between said outer radius and said inner radius, wherein an air gap having a reluctance, a width and a depth is disposed in said generally circular cylindrical current transformer core, wherein said depth is along a portion of the height of said generally circular cylindrical current transformer core, wherein the width of said air gap is substantially smaller than both of the height and the width of said generally circular cylindrical current transformer core, wherein the reluctance of said air gap is substantially greater than the reluctance of the taped steel of said generally circular cylindrical current transformer core, and wherein said generally circular cylindrical current transformer core is structured to have a permeability resulting from being annealed at a temperature of about 1450° F. to about 1550° F. for at least about one hour.