GB274199A - Improvements in and relating to dynamo-electric machines and other electrical apparatus having slots containing conductors - Google Patents

Abstract

274,199. Parsons, Sir C. A., Rosen, J., and Horsley, W. D. April 16, 1926. Transformers.-In slot-wound transformers, or other electrical apparatus having conductors of different voltages arranged side by side in slots, extra insulation is provided for the higher voltage conductors and to accommodate this, the relation between the cross-sectional dimensions of the slot and the conductors is graded at different places in the slot. Metal sheaths may be placed around some of the conductors to equalize the potential drop across the insulation. Fig. 3 shows a slot containing three conductors B, C, D at the bottom, middle and top of the slot and respectively at high, intermediate and low voltage. The section of the conductor B is such as to allow a maximum thickness H of insulation around it. Similarly, the sections of the conductors C, D which are equal in area to that of B, are shallower than that of the conductor B and broader in such proportion as to leave room for insulation thicknesses J, K suitable to their respective voltages. In place of varying sections for the conductors and a constant slot width, a constant section may be employed. The invention may also be applied to tapering or other non-rectangular slots. For circular slots, the conductors B, C, D may be of the sections shown in Fig. 5. Fig. 4 shows the use of metal sheaths L, M, as described in Specification 237,960, for equalizing the potential gradient across the insulation, the sheath L, which is integral or in operative contact with the middle-voltage conductor C being arranged to enclose the insulation around the high-voltage conductor B and the sheath M being similarly disposed with respect to the insulation and the low-voltage conductor D. In place of being U-shaped with overlapping edges, as shown, the sheaths may be applied in the form of tape. The conductors with their graded insulation and sheaths may form a composite bar carried from slot to slot over the end of the core and two or more such bars may be laid in the slot to give a multiple-layer winding. The conductors may be subdivided into strands which are transposed for the reduction of losses or their cross-sectional areas may be so altered as to reduce the losses.