Method of manufacturing magnetic cores for power transformers

A method of making transformer core laminates with bent corners from magnetic strip material having a predetermined thickness and power loss in the manufacture of a low-stress polyhedral core for a power transformer comprising the steps of:

• cutting a strip of the magnetic material to a predetermined length corresponding to one-half the length of a single turn of the core and reflecting the position of the turn in the core to form a rectangular half-laminate,
• positioning the half-laminate between a male die and a female die at a bending station,
• moving the male die toward the female die and against the half-laminate so that a first bend in a first corner is made about a predetermined bending line and at a predetermined angle,
• advancing the half-laminate through the bending station to reach a position for the formation of a second corner in the laminate and,
• moving the male die toward the female die and against the half-laminate so that the first bend in the second corner of the laminate is made about a predetermined bending line and at a predetermined angle, and
• during the bending of each corner limiting the zone in each corner where the laminate is subject to plastic deformation to <5 d, where d=lamination thickness, so that the specific power loss in the transformer core will equal that of the magnetic strip material except within said zone, where the power loss is higher due to plastic deformation of the magnetic strip material.

A method of making transformer core laminates with bent corners from magnetic strip material having a predetermined power loss in the manufacture of a low-stress polyhedral core for a power transformer comprising the steps of:

• cutting a strip of the magnetic material to a predetermined length corresponding to one-half the length of a single turn of the core and reflecting the position of the turn in the core to form a rectangular half-laminate,
• positioning the half-laminate between a male die and a female die at a bending station,
• moving the male die toward the female die and against the half-laminate so that a first bend in a first corner is made about a predetermined bending line and at a predetermined angle,
• advancing the half-laminate through the bending station to reach a position for the formation of a second corner in the laminate and,
• moving the male die toward the female die and against the half-laminate so that the first bend in the second corner of the laminate is made about a predetermined bending line and at a predetermined angle, and
• during the bending of each corner limiting the plastic deformation to ±1.5 mm from each bending line so that the specific power loss in the transformer core will equal that of the magnetic strip material except within +1.5 mm from the bending lines, where the power loss is higher due to plastic deformation of the magnetic strip material.