RU2174277C2 - Ac machine winding bar - Google Patents

Abstract

FIELD: electrical engineering; medium- and heavy-power machines such as turbogenerators and waterwheel generators. SUBSTANCE: winding bars are assembled of set of electrically insulated partial stranded conductors. Partial conductors on both sections of end clips and on active-part section are stranded together. Novelty is that partial conductors on both sections of end clips are stranded at angle of 60-120 deg. and on active-part section they are under- stranded, that is, uniformly stranded at angle smaller than 360 deg., or else vacant length is provided in middle M of active part where they are not stranded while beyond this section active-part partial conductors are stranded uniformly at 180 deg. Proposed design provides for actually complete equalization of fields in end windings thereby ensuring suppression of loop currents. EFFECT: improved smoothing of temperature field in bar conductors. 4 cl, 8 dwg

Description

 The invention relates to a shorted at the ends of the winding rod of AC machines with extended equalization of fields according to the restrictive part of paragraph 1 of the claims.

 The invention provides a reference to the prior art described, for example, in the Federal Republic of Germany patent N 1488769.

 The stator windings of high-power AC machines typically consist of a plurality of partial conductors isolated from each other and twisted together by the Rebel principle, short-circuited at both ends (see Herstelling der Wicklungen elektrischer Maschinen ", Springer-Verlag Wien, New York, 1973, pp. 69-83, in particular Fig. 19 on p. 79).

The classic Rebel bar has 360 ^o twist in the groove part. In end clamps, partial conductors run in parallel, i.e. not twisted. However, it was soon discovered that, also outside the groove, the rods are exposed to alternating fields passing through the end clamps from the wide side (transverse components) and from the narrow side (radial components).

To prevent additional losses due to the stator end field, the end clamps are divided into partial conductors isolated from each other. However, losses still occur due to the so-called loop currents closing through the connecting sleeve at the ends of the rod. For this reason, a number of special twists have been proposed relating both to the groove or active part of the rod, and to its part with end clamps. G. Najdhefer gives in his title book in Section 3.3 "Roebelstabe mit erweiteryem Feldausgleich" an almost complete overview of the various possibilities for achieving advanced field equalization and thereby eliminating large temperature differences, as well as local overheating inside the rod. A particularly economical solution is twisting at 90 ^o / 360 ^o / 90 ^o , i.e. the partial conductors in both end clamps are twisted 90 ^° , respectively, the partial conductors of the active part are 360 ^° twisted (see ibid., Fig. 24 on page 74 or the FRG patent, N 1488769).

Since machines with a short length of the active part, such as hydrogenerators, the total length of the machine increases due to twisting in the end clamps and the support of far-reaching end clamps is very difficult, in the ISSM-93 conference report "Proceedings of the International Symposium on Salient-Pole- Machines, 10-12.10.93, WUHAN, China, pp. 384-389, in a report by Su Shanchun et al. "A new transposition technique of stator bars of the hydrogenerator" a completely new way for advanced field equalization, namely the so-called undersampling ("non-360 ^o transposition" or "incomplete transposition") or the so-called empty length ( "transposition with a void") in the active part in combination with non-twisted parts of the end clamps. Due to each of the two "special twists", a noticeable decrease in loop currents is achieved, and they, according to the conclusions of the conference report, should sharply reduce the temperature differences inside the rod.

 Based on the described prior art, the basis of the invention is the creation of a twisted rod of the stator winding with advanced equalization of fields, which provides even more suppression of loop currents and thereby smoothing the temperature profile in the conductive rod.

This problem is solved according to the invention due to the fact that the partial conductors on both segments of the end clamps have a twist of 60-120 ^o , and on the segment of the active part provides undercuts, i.e. the twisting on the segment of the active part is made uniform and less than 360 ^o , or with a full twist of 360 ^o on the segment of the active part in the middle of the active part an empty length is provided, i.e. non-twisted segment, while twisting on a segment of the active part outside this non-twisted segment is made in the form of a uniform twisting of 180 ^o .

The general use of partial technical solutions according to the Federal Republic of Germany patent N 1488769 (special twisting 90 ^o / 360 ^o / 90 ^o ) and undercuts / empty lengths on the segment of the active part according to the report of Su Shanchun et al. In the mentioned publication leads to the creation of a conductive rod that provides completely predictable, almost complete suppression of loop currents, thereby achieving a repeated smoothing of the temperature profile in the conductive rod.

 The invention can be applied to all medium and high power machines, for example, turbo or hydro generators.

 The invention is explained in more detail below using the drawing and embodiments.

The drawing shows:
FIG. 1 is a schematic top view of a well-known Rebel bar with extended equalization of fields and with a twist of 90 ^o / 360 ^o / 90 ^o ;
FIG. 2 is a diagram of Rebel rods with different twists to explain the effect of their own field, namely for a Rebel rod with a known twist of 90 ^o / 360 ^o / 90 ^o (Fig. 2a), with an empty length (Fig. 2b) and with under-twist (Fig. . 2c);
FIG. 3 is a diagram of Rebel rods with different twisting to explain the effect of an extraneous field, namely for a Rebel rod with a known twist of 90 ^o / 360 ^o / 90 ^o (Fig. 3a), with an empty length (Fig. 3b) and with under-twisting (Fig. . 3c);
FIG. 4 - schematically half of the under-twisted rod with five partial conductors per column with a twist of 324 ^o .

The Rebel rod in FIG. 1 consists of partial conductors 1 electrically isolated from each other, electrically and mechanically connected at the ends by rings 2, 3. It consists of two segments 4, 5 of end clamps in the left and right frontal parts of the winding and segment 6 of the active part. The latter is completely located in the grooves (not shown) in the package 7 of the stator iron (active part) of the electric machine. Both segments 4, 5 of the end clamps are twisted each by 90 ^o , and the segment 6 of the active part is 360 ^o .

The schematic diagram of FIG. 2a and 3a for a Rebel rod with a twist of 90 ^° / 360 ^° / 90 ^° in FIG. 1 shows the arrangement of five in this example, partial conductors af and gl on each column of partial conductors on the left segment 4 of the end clamp, on the segment 6 of the active part and on the right segment 5 of the end clamp. It is clearly seen how the individual conductors in the segment 6 of the active part in the groove each occupy their own position (360 ^° twist), while on the ends of the end clamps they are twisted by 90 ^o . The partial conductor d on both segments 4, 5 of the end clamps is generally positioned the longest in the direction of the rotor R. Other partial conductors are positioned with a shorter length in the direction of the rotor R. As follows from the known action of the electromagnetic field on the piece of end clamps of an untwisted rod, the partial conductor d loaded with the greatest current, and the rest is correspondingly less. To understand the invention, it is sufficient to state that when twisting through 90 ^o / 360 ^o / 90 ^{o, the} intrinsic field of the frontal part of the winding is fully compensated, while its extraneous field is only partially equalized (see the aforementioned publication, in particular, p. 74, Fig. 24 and related text on page 75).

An invention can help here. If on twisted segments 4, 5 of the end clamps at 90 ^{° of the} conductive rod, form a segment 6 of the active part with under-twist, i.e. with a twist of less than 360 ^o , or in the middle of the active part, provide an empty length (non-twisted segment) with a twist of 360 ^o outside the empty length, then those partial conductors that allow high currents to pass are left longer at the bottom of the groove. Then they give current to partial conductors closer to the groove opening, i.e. located closer to the rotor R. These, however, are those conductors that pass less current. Thus, an almost completely uniform current distribution in the conductive rod is achieved.

Both options — empty length and under-twist — are shown schematically in both diagrams in FIG. 2b, 3b and in FIG. 2c, 3c in comparison with the well-known Rebel bar with a 90 ^° / 360 ^° / 90 ^° twist in FIG. 2a, 3a, wherein FIG. 2a, 2b, 2c relate to the case of the own field, and FIG. 3a, 3b, 3c - for the case of an extraneous field. The diagrams are based on the image of Rebel rods accepted in the literature, which is also used, for example, in the German patent N 1488769 cited above. Thus, solid lines passing from left to top and to right down indicate partial conductors that are viewed from the side of a two-plane rod (Fig. . 1) on its front side. Dashed lines indicate tracks on the back side, i.e. in the second plane of partial conductors. Next, in FIG. 2a-2c show the corresponding characteristic B _{E of the} own field B _FE on the segment in the active part and the own field B _WK in the frontal part of the winding along the height of the rod. The minus and plus in the circle indicate the sign of the elementary stress loops induced in the partial surfaces, taking into account the direction of rotation of the surface contours, as well as the direction of the flow passing through them. The surfaces indicated in FIG. 2a, 3a with a question mark in a circle, symbolize the uncompensated part at the untwisted transition from the segment 6 of the active part to the segments 4, 5 of the end clamps. In FIG. 3a-3c show the position of the twelve partial conductors a-1 at the ends of the rod.

 Before explaining the invention in more detail, the following field cases should be explained.

As can be seen from the rod with a twist of 90 ^o / 360 ^o / 90 ^o in FIG. 3a, in the case of an extraneous field, the loopback (question mark in a double circle) remains uncompensated. This uncompensated part creates loop currents distributed along the height of the rod sinusoidally (asymmetrically). The purpose of the empty length / undercuts on the segment of the active part is to equalize this remainder. As explained below, this adjustment succeeds when an unbalanced part (indicated by the “+” in a double circle) is created that counteracts the unequal part in segments 4 and 5 of the end clamp (indicated by a “-” in a double circle). It should be noted here that this mechanism only works when the field of the frontal part of the winding in place of the rod and the groove field in the segment of the active part are approximately equal phase. This is the case when, as is well known, current is displaced in one direction (radially inward) on the segment of the active part and on the segments d of the end clamps, which is explained by equiphase fields. Relatively large unbalanced loop parts in the frontal part of the winding can be compensated by relatively small response loops on a segment of the active part, since the transverse groove field is much stronger.

In the case of the own field in FIG. 2a-2c, it can be seen that for a rod with a twist of 90 ^° / 360 ^° / 90 ^{°, the} loops are fully compensated. Only non-twisted parts of the rod, for example, on the segment of the active part, create residual stresses for loop currents. The empty length 8 in the segment in the active part creates loop voltages that form loop currents distributed cosine (symmetrically) with respect to the height of the rod. The effect of the untwisted parts of the rod of the frontal part of the winding directly at the output of the active part was enhanced. In contrast, undershot on the segment of the active part causes the opposite. Uncompensated parts in the frontal part of the winding are opposite the uncompensated part in the segment of the active part and mutually compensate each other, and this compensation does not occur at 100%, and undercuts in the segment of the active part are oriented to compensate for the extraneous field of the frontal part of the winding. It may seem that thanks to the invention, improvement is achieved in one place (extraneous field) and deterioration in the other (own field). In fact, this is so. If we consider both of these facts together, then on the whole there is an improvement, in particular, with undercounting.

The conductive rod in FIG. 2b and 3b has an empty length 8 in the middle M of the active part, i.e. untwisted segment. On this segment, the partial conductors a-1 are drawn in parallel. Outside this zone 8, to the left and to the right of the empty length, the twist is 180 ^o, respectively. The axial length l _{V of} this empty length 8 depends, to a first approximation, on the offset value l _{WK of the} frontal part of the winding. Using modern methods of calculation can have a specific machine relatively accurately determine the length of the blank, but as a rough value can, however, indicate that the value of the length l _V blank 8 should be 5-10%, maximum 15% of the l _WK to achieve substantially full (expanded) equalization of fields in the frontal part of the winding. As a second approximate value for calculating the empty length 8 of the turbogenerators, it can be indicated that it can be up to 10% of the length l _{FE of the} active part.

The conductive rod in FIG. 2c and 3c has a non-twist on the segment 6 of the active part, that is, a twist deviating downward from the usual twisting by 360 ^° . In the depicted in FIG. 4 conductive rods with respectively five partial conductors twist is 9/10 from 360 ^o , i.e. 324 ^o , and undershot, respectively, 36 ^o , which for such a rod is at the same time a minimal undershot.

Real Rebel rods have a much larger number of partial conductors, which is usually 80-120 per rod. Thus, for a rod with an n-th number of partial conductors and 360 ^o twist in the segment of the active part, the minimum under-twist U = 360 ^o / n is about 4.5 ^o with 80 partial conductors and 3 ^o with 120 partial conductors per rod.

Similarly to the calculation of the empty length, the degree of under-twisting as a first approximation also depends on the departure of the frontal part of the winding. The larger this offset, the stronger the influence of the end field in the frontal part of the winding and, accordingly, the higher the degree of under-twist on the segment of the active part. As with the calculation of the empty length, here, using modern calculation methods for a particular machine, you can relatively accurately determine the degree of under-twisting, however, as a guide value, it should be in angular degrees 10-15 ^o to achieve almost complete (expanded) equalization of the fields in the frontal part windings.

The above reasoning always proceeded from twisting on segments of end clamps at 90 ^o . Extensive calculations showed that even with deviations of ± 30 ^o , i.e. twisting 60-120 ^o on the segments of 4.5 end clamps, in combination with empty lengths or under-twisting on the segment 6 of the active part, almost complete equalization of the fields in the frontal part of the winding is achieved.

 In principle, it is possible to produce rods which, with the indicated twist, also have under-twist in addition to the empty length on the segment of the end clamps. It is difficult to make such conductive rods, but for special cases this is quite acceptable.

Designation List
1 - partial conductor
2, 3 - rings
4 - the left segment of the end clamp
5 - the right segment of the end clamp
6 - segment of the active part
7 - active part (stator iron packet)
8 - empty length
l _FE is the length of the active part
L _{WK -} departure of the frontal part of the winding
L _V - empty length
M - the middle of the active part
n is the number of partial conductors per column
R - rotor
al - designations of partial conductors in diagrams
U - undercuts, measured in angular degrees

Claims (4)

1. The core of the winding of alternating current machines, short-circuited at the ends, with expanded field equalization, made of a plurality of partial conductors (1) electrically isolated from each other, twisted according to the Rebel principle, and partial conductors as on both segments (4, 5) of the end clamps , and on the segment (6) of the active part are twisted together, characterized in that the partial conductors (1) on both segments of the end clamps have a twist of 60 - 120 ^o , and on the segment (6) of the active part there is under-twisting, that is, twisting on segment (6 ) the active part is made uniform and less than 360 ^o , or on the segment (6) of the active part in the middle (M) of the active part, an empty length (8) is provided, that is, an untwisted segment, while twisting on the segment (6) of the active part is outside this untwisted segment (8) is made in the form of a uniform twist 180 ^o . 2. The rod according to claim 1, characterized in that the axial length (l _v ) of the empty length (8) is about 10% of the magnitude (l _wk ) of the departure of the frontal part of the winding. 3. The core according to claim 1, characterized in that on the segment (6) of the active part, the undercuts, measured in angular degrees, are 10 - 15 ^o . 4. The rod according to claim 1, characterized in that the partial conductors (1) on both segments (4, 5) of the end clamps have a twist of 90 ^o .

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