JPS5539638A - 3-phase 5-leg type iron core for transformer - Google Patents

Abstract

PURPOSE: To give a fixed relation between the size of the four rectangular hollow portions and the sectional size of a 3-phase 5-leg iron core for raising material yeild and for keeping the magnetic flux of the various portions of said iron core within a fixed limit of density when normal operation is underway and said one-wire earthing is provided.

CONSTITUTION: The length l and width w₁ of rectangular hollow portions, the width w₃ of yokes, the width w₃ of inner legs, the width w₄ of outer legs, and the length L of an iron core are fixed at w₁=w₂, 4l=L, 3w₃+2w₄=L-4w₂. No waste is produced if a silicon steel plate with length L and width 2(1+2w₂) is punched for obtaining rectangular pieces c₁-c₄ and said yokes. On normal operation, the voltages applied on the primary coils of phases are balanced, and no magnetic flux occurs to the no-coil legs N. When U-phase is earthed, however, the magnetic flux of the iron core legs of V- and W-phases become 3^1/2 of that ϕ obtained on normal operation and ϕ×3/2 at said legs N. Since width w₄ is large, however, magnetic flux density does not become so large and is kept within a required limit. Thus, a 5-leg type iron core for transformers which is readily adaptable for the restriction due to the error of transformation ration can be obtained.

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