GB2037091A - Stator winding bar for alternating current dynamoelectric machine - Google Patents

Abstract

A stator winding bar for an alternating current dynamoelectric machine comprises insulated conductors 1-20 extending along the length of the bar, arranged in two rows, 1-10 and 11-20, and transposed in the slot portion of the bar, pairs of adjacent conductors 1/2, 5/6 etc within the same row being transposed together. <IMAGE>

Description

SPECIFICATION Stator winding bar for alternating current dynamoelectric machine The present invention relates to dynamoelectric machines, and more particularly to winding bars for stators of alternating current dynamoelectric machines.

The invention can most advantageously be used in large low-speed dynamoelectric machines such as hydroelectric generators.

According to the invention, a stator winding bar for an alternating current dynamoelectric machine comprises insulated conductors extending along the length of the bar, arranged in two rows, and transposed in the slot portion of the bar, pairs of adjacent conductors in the same row being transposed together.

The advantages of the present invention are as follows: In the first place, the simultaneous transposition of two adjacent conductors within one row enables the transposition step to be doubled, thus permitting transposition through 540 electrical degrees for stator windings of low-speed dynamoelectric machines with relatively short cores, where it would be practically impossible to transpose one conductor at a time on account of an extremely small transposition step required. As a result of transposition of the bar conductors through 540 electrical degrees on a two-at-a-time basis, the additional losses and hot spots due to circulating currents in the bar are minimized, and the efficiency of the dynamoelectric machine is improved.

Secondly, a greater conductor transposition step facilitates manufacture of the bars and improves performance of the stator winding.

And finally, in dynamoelectric machines with very short stator cores, in which a coiltype stator winding is commonly used, it is found possible to employ a bar-type winding using the proposed bar structure wherein joint transposition of two adjacent conductors within one row, through 360 electrical degrees, is provided.

The invention is further illustrated by a detailed description of its embodiment with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of the end portion of a bar of an alternating current dynamoelectric machine stator winding, according to the invention; Figure 2 is the bar of Fig. 1, with the insulation stripped, looking at the broad side of the bar; Figure 3 is the bar of Fig. 1, with the insulation stripped, looking at the narrow side of the bar.

The stator winding bar of an alternating current dynamoelectric machine, in accordance with the invention, is rectangular in cross section and includes twenty conductor strands, or individual conductors, 1, 2, 3 through 20 (Fig. 1) extending along the length of the bar and arranged in two vertical rows across the height of the bar, with an insulating strip 21 inserted between the two rows, each row being made up of ten, i.e. an even number of conductors. On the outside the bar is enclosed by an insulating shell 22.

In the following discussion, for the sake of convenience, the vertical rows will be referred to as left and right, according to Fig. 1. The conductors 1 through 20 are transposed in a slot portion 23 of the bar, i.e. their position is changed within the length of the bar across the height thereof, with the conductors shifted from the left row to the right row, and conversely; the pairs of each two adjacent conductors, such as the conductors 1 and 2, within the same row being transposed together.

Fig. 2 and Fig. 3 show an embodiment of the proposed bar with the conductors 1 through 20 transposed 540 electrical degrees.

Fig. 2 is a view of an uninsulated bar looking at its broad side, whereas Fig. 3 is a view of the narrow side of the same.

For better illustration of the subject of the invention, Fig. 2 and Fig. 3 show not all the conductors 1 through 20 of the bar, but only some of them selected at random out of the total number of the conductors.

The process of transposition of the conductors 1 through 20 by 540 electrical degrees will now be described.

The length "L" of the slot portion 23 of the bar is speculatively broken down into three sections l" 12 and 13. The length of each of the sections 1, and 13 is one-quarter of the length "L" of the slot portion 23 of the bar, while the length of the section 12 is half the length "L' of the slot portion 23.

The conductors 1 and 2 which are at the top of the left row in an end portion 24 at one end of the bar, at the start of tranposition, are shifted together, by bending off, to positions in the right row occupied by the conductors 11, 1 2 (Fig. 1) prior to tranposition, the conductor 1 taking the place of the conductor 11 and the conductor 2 taking the place of the conductor 1 2. The conductors 11 and 12, in turn, are shifted down to the positions previously oocupied by the conductors 1 3 and 14, respectively, which are likewise transferred to the positions of the conductors 1 5 and 16, respectively, etc.

The conductors 19, 20 which are at the bottom of the right row in the end portion 24 (Fig. 2) at the same end of the bar, at the start of transposition, are shifted together, by bending off, to the positions in the left row occupied, prior to transposition, by the conductors 9 and 10 (Fig. 1), which, in turn, are shifted up to the positions of the conductors 7 and 8, respectively, etc. until the conductors 3 and 4 have taken the positions vacated by the conductors 1 and 2, respectively.

The length of the section "t" (Fig. 2) within which each pair of adjacent conductors such as the conductors 3 and 4 disposed in the same vertical row is shifted so that it occupies the position previously occupied at the start of tranposition, by an adjacent pair of conductors such as 1 and 2 in the same row, is called the transposition step which is equal to the ratio L/n for pairwise transposition of the conductors by 540 electrical degrees on the sections I, and 13, and to the ratio 2L/n for the case of the section 12, where "L" is the length of the slot portion 23 of the bar and "n" is the number of conductors in the bar.

Thus, within a single step of transposition, all the conductors from 1 to 20 (Fig. 1) are shifted in pairs "around a circle" (for the case in hand, clockwise), each pair of conductors adjacent to one another in the row e.g. 3 and 4, 5 and 6, etc., taking the position previously occupied by a preceding pair of conductors, e.g. 1 and 2, 3 and 4, etc., respectively, the conductor 3 being shifted to the position of the conductor 1 and the conductor 4 to the position of the conductor 2.

Further, as shown in Figs. 2, 3 the conductors 1 and 2 remain, within the section I,, in the right row, gradually changing their positions over the height of the bar. At the end of the section I,, these conductors occupy the bottom position in the right row and are then transferred together, by bending, to the positions in the left row which are occupied by the conductors 9 and 1 0, respectively, in Fig.

1.

Within the section 12, the conductors 1 and 2 are also gradually shifted along the height of the bar and returned to the original position which they had occupied at the start of transposition, i.e. to the top of the left row.

Within the section 13, the transposition of the conductors 1 and 2 is performed similarly to that on the section I,, as hereinabove described, and in an end portion 25 at the other end of the bar, these conductors are found to be at bottom right.

The transposition of the remaining conductors 3 through 20 in each vertical row is carried out in a similar manner.

Thus, each pair of adjacent conductors 1 through 20 in either row successively occupies all the positions across the height of the bar in both of the conductor rows, making one and half revolutions with respect to its original position.

In case the stator core is too short to allow pairwise transposition of the conductors adjacent each other within one row through 540 electrical degrees, on account of its being not feasible to provide the transposition step required, these conductors can be transposed through 360 electrical degrees. For the case in question, the transposition of each pair of conductors will be equivalent to that shown in Figs. 2 and 3 for the sections 1, and 12, except that the sections 1, and 12 will be of the same length equal to half the length "L" of the slot portion 23 of the bar, as well as of the same transposition step equal to 2L/n.

As the dynamoelectric machine is operated, the e.m.f.s induced in each pair of the conductors 1 through 20 of the bar are equal in magnitude and no circulating currents exist between individual pairs of the conductors 1 through 20. Yet because of simultaneous transposition of two conductors within each pair of conductors 1 through 20, the e.m.f.

arising from transverse magnetic flux in the slot portion 23 of the bar proves to be uncancelled, which leads to circulating currents flowing between the two conductors of each pair of conductors 1 through 20. As shown by investigations, however, with a sufficiently large number of individual conductors in the bar amounting to several dozens of them, the additional losses due to these circulating currents are substantially below the additional losses capable of being compensated as a result of substitution of pairwise transposition of the conductors within one row through 540 electrical degrees for the conventional procedure of transposing one conductor at a time through 360 electrical degrees.In some instances, e.g. with very short stator cores (about 1 m long), the pairwise transposition of adjacent-in-row conductors actually permits the use of the bar-type winding rather than the coil type. Now it will be noted that no transposition of individual conductors is employed in the turns of the coil-type windings and consequently, the circulating currents between the conductors of one single turn are invariably present. The number of conductors in each turn of the coil generally exceeding four, the losses due to these circulating currents are substantially greater than those produced as a result of introducing transposition of conductors in bar-type windings on a pairwise basis.

To summarize, for low-speed dynamoelectric machines, the present invention provides a satisfactory trade off between the requirement that the additional losses due to circulating currents in the stator winding be minimized and the need to obtain a technically feasible step of transposition of the bar conductors.

Claims (3)

1. A stator winding bar of an alternating current dynamoelectric machine, comprising insulated conductors extending along the length of the bar, arranged in two rows, and transposed in the slot portion of the bar, pairs of adjacent conductors within the same row being transposed together.

2. A stator winding bar of an alternating current dynamoelectric machine, substantially as hereinbefore described with reference to the accompanying drawings.

3. An alternating current dynamoelectric machine incorporating a stator winding bar as claimed in claim 1 or 2.