When joining end faces of a plurality of soft magnetic sheets which are superposed in the sheet thickness direction and which are bent at parts forming corner areas of a core, offset of positions of the end faces from the desired positions is suppressed.

In a region of a window part comprised of a region inside of a first part 110 and second part 120, a third part 130 with a length in a longitudinal direction (X-axial direction) the same as a length in the X-axial direction of the window part at the position where the third part 130 is arranged is arranged so as to contact the region of the inner circumferential surface between the first corner area 101 and third corner area 103.

A core body includes a central iron core, an outer peripheral iron core surrounding the central iron core, and a single hoop material wound body formed by winding a hoop material. At least three iron portions of an outer circumferential surface of the hoop material wound body are bent radially inward thereof. The central iron core includes at least three iron cores, each of which having a cut tip, is made by cutting at least three projection portions of the hoop material wound body. Each of the at least three projection portions is located between the at least three portions.

A wound core (10) is a wound core including a portion in which grain-oriented electrical steel sheets (1) in which planar portions (4) and bent portions (5) are alternately continuous in a longitudinal direction are stacked in a sheet thickness direction and formed by stacking the grain-oriented electrical steel sheets (1) that have been individually bent in layers and assembled into a wound shape, wherein, when an average length of a roughness curve element in a width direction intersecting the longitudinal direction forming a surface of the bent portion (5) of the grain-oriented electrical steel sheet (1) is RSm(b), and an average length of the roughness curve element in the width direction forming a surface of the planar portion 4 of the grain-oriented electrical steel sheet (1) is RSm(s), the relationship of 1.00<RSm(b)/RSm(s)≤5.00 is satisfied.

This wound core is a wound core including: a substantially rectangular wound core main body in a side view in which first planar portions and corner portions are alternately continuous and at least one of two or more bent portions existing in at least one corner portion satisfies Equations (1) to (3) below.

Tave≤40 nm  (1)

(To−Tu)/Tave≤0.50  (2)

Tave(To−Tu)≤240 nm.sup.2  (3)

The present invention allows individual control of an output voltage of a main transformer and an output voltage of a teaser transformer while utilizing output characteristics of the respective transformer when a Scott connected transformer has control equipment arranged on the input side thereof, including first control equipment arranged in one of two phases of the main transformer on the input side in order to control a voltage or a current and second control equipment arranged in one end of a primary coil of the teaser transformer on the input side in order to control a voltage or a current, the control equipment controlling an output voltage of the main transformer and an output voltage of the teaser transformer individually.

A core for a transformer includes a multiplicity of bent metal sheets that are all connected to form a structure which surrounds a core opening and forms the core. The sheet ends of each of the metal sheet do not touch one another within the core. The metal sheets together with the core form at least one air gap at the respective sheet ends within the core or at a periphery of the core. The core is impregnated or coated, at least at the sheet ends of the metal sheets, with a lacquer or coating that contains magnetic particles. The impregnation or coating fills at least the air gaps at the sheet ends of the metal sheets. A method for producing a transformer having a core is also provided.

A grain-oriented electrical steel sheet for a wound transformer core. The steel sheet having a sheet thickness t, where t and an iron loss deterioration ratio obtained by subjecting the steel sheet under elliptic magnetization satisfy the following relations: (i) when t0.20 mm, the iron loss deterioration ratio is 60% or less; (ii) when 0.20 mm<t<0.27 mm, the iron loss deterioration ratio is 55% or less; and (iii) when 0.27 mmt, the iron loss deterioration ratio is 50% or less. The iron loss deterioration ratio is calculated from ((W.sub.AW.sub.B)/W.sub.B)100, where W.sub.A is iron loss under 50 Hz elliptic magnetization of 1.7 T in a rolling direction and 0.6 T in a direction orthogonal to the rolling direction, and W.sub.B is iron loss under 50 Hz alternating magnetization of 1.7 T in the rolling direction.

A grain-oriented electrical steel sheet according to the present invention has a steel sheet surface provided with grooves and includes two or more broken lines including the grooves having a length of 5 to 10 mm on a straight line intersecting a rolling direction on the steel sheet surface. In each of the broken lines including the grooves, the grooves are arranged at equal intervals, and a ratio of the length of the groove to a length of a non-groove is in a range of 1:1 to 1.5:1.

A wound core is formed by laminating a plurality of bent bodies formed from a grain-oriented electrical steel sheet having a coating containing phosphorus formed on a surface, in a sheet thickness direction of the grain-oriented electrical steel sheet, in which the bent body is formed in a rectangular shape by having four flat portions and four corner portions adjacent to the flat portions, the corner portion has a bent region having a total bending angle of approximately 90 in a side view, the number of deformation twins present in the bent region in the side view is five or less per 1 mm of a length of a center line in the bent region in the sheet thickness direction, and the amount of phosphorus eluted from the corner portion in a case of being boiled in water for 30 minutes is 6.0 mg or less per 1 m.sup.2 of a surface area of the corner portion.

The present invention allows individual control of an output voltage of a main transformer and an output voltage of a teaser transformer while utilizing output characteristics of the respective transformer when a Scott connected transformer has control equipment arranged on the input side thereof, including first control equipment arranged in one of two phases of the main transformer on the input side in order to control a voltage or a current and second control equipment arranged in one end of a primary coil of the teaser transformer on the input side in order to control a voltage or a current, the control equipment controlling an output voltage of the main transformer and an output voltage of the teaser transformer individually.