Abstract: A flat, electrically and thermally conductive flat surface group is formed in the common connection region 32 of the secondary coil 13. The flat conductive surface group is directly and mechanically joined to the connecting surfaces of the first conductor plate 42, the second conductor plate 44, and the third conductor plate 46, respectively. The first conductor plate 42, the second conductor plate 44, and the third conductor plate 46 cover the entire common connection region 32. The annular first conductor plate 42 occupies the maximum area. The refrigerant can be circulated in the annular cavity provided inside the first conductor plate 42 to efficiently cool the whole.

Abstract: It is possible to control a welding in a high speed and a high precision large electric current, and consumption electric power is also reduced. In the welding transformer, a loop magnetic core 25, a wound primary coil 12, plural positive side coils 14 and plural negative side coils 16 that are alternately sandwiched between respective gaps 12a of the primary coil 12, are comprised. A coil is fixed on the other surface of a contact base member 62. On the other surface of the contact base member 62, a first connection polar board 44 is electrically connected to a positive side electric conductor 30 through the first connection polar board 44. A negative side coil 16 is electrically connected to a negative side electric conductor 32. The connecting part of the positive side coil 14 and the negative side coil 16 is electrically connected to the third connection polar board 48.

Abstract: It is possible to control a welding in a high speed and a high precision large electric current, and consumption electric power is also reduced. In the welding transformer, a loop magnetic core 25, a wound primary coil 12, plural positive side coils 14 and plural negative side coils 16 that are alternately sandwiched between respective gaps 12a of the primary coil 12, are comprised. A coil is fixed on the other surface of a contact base member 62. On the other surface of the contact base member 62, a first connection polar board 44 is electrically connected to a positive side electric conductor 30 through the first connection polar board 44. A negative side coil 16 is electrically connected to a negative side electric conductor 32. The connecting part of the positive side coil 14 and the negative side coil 16 is electrically connected to the third connection polar board 48.