GB2107938A

GB2107938A - Rotor for a turbo-generator

Info

Publication number: GB2107938A
Application number: GB08136457A
Authority: GB
Inventors: Tage Persson
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1981-10-15
Filing date: 1981-12-03
Publication date: 1983-05-05
Also published as: FR2514964A1; FR2514964B1; SE428076B; CH657726A5; JPS5872352A; GB2107938B; SE8106100L

Abstract

Generator rotor (1) for a turbo- generator, in which the rotor winding is fed via two feeding conductors, which are each arranged in a bored channel (8, 9) in the rotor body (2). The two channels (8, 9) diverge in relation to one another and each channel is bored in part in an axial shaft portion (4) of the rotor body and in part in the slotted rotor portion of the rotor body. A second axial shaft portion (5) supports a connector (7) for the turbine (not shown). <IMAGE>

Description

SPECIFICATION Rotor for a turbo-generator Technical Field The present invention relates to the generator rotor of a turbo-generator of at least 20 MVA, comprising a rotor body of magnetic material and a rotor winding supported by said rotor body, said rotor body comprising a circular-cylindrical portion which is provided with a plurality of axially extending winding slots, as well as first and second shaft portions, extending from opposite ends of said cylindrical portion, feeding conductors for the exciting current of the rotor winding being arranged in two conductor channels bored in said rotor body, said channels traversing at least a part of said first shaft portion. A rotor of this kind is disclosed in U.S. Patent Specification 3,131,321.

Background Art In a known generator rotor, each of the two feeding conductors, connected to the rotor winding, has a portion disposed parallel to the axial center line of the rotor and adjacent thereto, which portion is arranged in direct electncal connection with a first radially directed portion, which is located in a radially directed bore. From this radial portion the electric connection continues in the form of an axially extending conductor, embedded in the rotor shaft, which finally continues as a second radially outwardlydirected conductor portion which is connected to a point in that part of the rotor winding which is surrounded by a winding capsule.When the rotor speed increases from zero to its maximum value, the diameter of the winding capsule will increase considerably, for example by 5 mm, under the influence of centrifugal forces, and it may be assumed that the above-mentioned second radial conductor portion, similar to corresponding conductor portions of other known rotors, is connected to the rotor winding via a flexible conductor element. This flexible element is also stressed by movements of a relatively small amplitude but of a high frequency, namely movements substantially caused by deflection of said first shaft portion, i.e. in the shaft portion which is not connected to the driving turbine.

It has proved to be very difficult to achieve a sufficiently reliable, flexible connection between the rotor winding and the current feeding system of the rotor winding, and it has often been found that fatigue breakdown has taken place in the above-mentioned flexible conductor element after some time in operation. In the case where the fatigue failure is a complete breakage of the flexible conductor element, an arc arises which can easily result in harmful heating of the winding capsule, which in turn may cause very serious damage.

There have also been examples where the provision of radial conductor channels in the rotor shaft have resulted in shaft fracture.

By using a rotor design according to the invention, the above-mentioned drawbacks are avoided.

Statement of Invention According to the invention there is provided a generator rotor for a turbo-generator of at least 20 MVA, comprising a rotor body of magnetic material having a substantially circular-cylindrical portion with a plurality of axially extending winding slots formed therein, a rotor winding with parts thereof located in said winding slots, a first shaft portion extending from one end of said substantially circular-cylindrical portion, a second shaft portion extending from the opposite end of said substantially circular-cylindrical portion, a turbine connecting means on said second shaft portion, two conductor channels bored in said rotor body and extending at least in part along said first shaft portion, and two feeding conductors for the exciting current of said rotor winding, one disposed in each of said channels, which is characterised in that said conductor channels extend through at least part of said substantially circular-cylindrical portion while diverging in the direction towards said second shaft portion.

Brief Description of Drawings The invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which: Figures 1, 2, 3 and 4 show four different embodiments of a rotor according to the invention in highly simplified form, Figure 5 shows a side view of part of the rotor schematically shown in Figure 1, without the rotor winding and its associated winding capsule, Figure 6 shows the rotor of Figure 5 in an end view perpendicular to the plane VI--VI of Figure 5, Figure 7a shows a section along the line VIl-VIl of Figure 1, Figure 7b shows a section through a second embodiment of rotor also in section along the line VIl-VIl of Figure 1, Figure 8 shows a part of the rotor shown in Figure 1 in partial axial section along the line VIll-VIll in Figure 7a, Figure 9 shows a partial section along the line IX-IX of Figure 8, a cylindrical sectional surface which is coaxial with the air gap surface being extending in one plane, and Figures 10, 11 and 12 each shows a partial rotor cross-section along, respectively, the lines X-X, Xl-Xl and Xll-Xll in Figure 8.

Figures 1, 5, 6, 7a and B to 12 refer to a first embodiment of a rotor according to the invention.

Description of Preferred Embodiments In Figures 1 to 4 of the drawings, the numerals 1, 1', 1" and 1"' designate four different embodiments of a rotor according to the invention. In all cases the rotor has a rotor body of solid steel which comprises a substantially circular-cylindrical portion 2, 2', 2" and 2"', respectively, which is provided with a plurality of winding slots axially extending along the entire length of this portion. A first shaft portion 4 and 4', 4", 4"', respectively, and a second shaft portion 5, which constitute integrated parts of said rotor body, extend from one end each of said cylindrical portion, said second shaft portion being provided with a flange 7 for connection to a turbine. The coil ends (not shown) of the rotor are surrounded at each rotor end by a winding capsule 6, which is shrunk onto said cylindrical portion.

In the following text, the rotor shown in Figures 1,5,6,7a,8,9,10,11and12willfirstbe described in greater detail. The rotor 1 receives exciting current from a supply unit (not shown) which is either mechanically connected to the shaft portion 4, and can thus feed the current directly to the rotor winding, or does not turn with the shaft portion 4 and feeds the said current via slip rings (not shown) arranged on the said shaft portion. The exciting current is supplied to the rotor winding via two feeding conductors 8 and 9, which traverse the entire shaft portion 4 as well as the entire cylindrical rotor portion 2 and which are electrically connected to the ends of the rotor winding coils which are located at the end of the portion 2 which is adjacent to the shaft portion 5.

Each of the feeding conductors 8 and 9 is electrically insulated and arranged in a straight conductor channel 10 and 11, respectively, bored in the rotor body. These channels are located on opposite sides of a central bore 26, which comprises a supply conduit and a return conduit (not shown) for cooling water flowing through the conductors of the rotor winding. The two conductor channels mutually diverge in the direction towards the shaft portion 5. The projections of the channels in an axial plane intersect each other at an angle of at least 70, preferably at least 100, if the axial plane is selected to maximize the said angle of intersection.The part of the cylindrical portion 2 of the rotor body which is traversed by the diverging conductor channels 10 and 11, has an axial extension which preferably constitutes between 20 and 70% of the total length of the portion 2.

The rotor 1 is provided with twelve winding slots 1 3 and with six auxiliary slots in the form of equalizing slots 14, which are arranged in a known manner to reduce the difference between different moments of inertia of the rotor cross-section and thus to avoid dangerous resonance frequencies of the rotor during operation. The slots 13 and 14 all have the same slot width and each is provided with a slot wedge consisting of a plurality of partial wedges 1 5 arranged axially one after the other.

The bored conductor channels 10 and 11 each open into a different equalizing slot 14 and the two slots are located diametrically or almost diametrically, opposite each other. The feeding conductors 8 and 9, in the respective channels 10, 11 continue into the respective equalizing slot 14.

The part of each feeding conductor which is located in an equalizing slot is, along a predominant part of its length in the slot, constructed in the same way as the part of the feeding conductor located in the bored channel, that is to say, it has a circular cross-section (see Figure 12) with two cooling water tubes 1 6 squeezed between two conductor halves, and with a surrounding electrically insulating layer 1 7. In the slot 14, the circular conductor portion is clamped between an inner filling body 18 and an outer filling body 19 by means of a pressure device, known per se, which consists of a flattened metallic tube 20 filled with epoxy resin which has been allowed to solidify under a pressure of at least 100 bar.The two filling bodies 18 and 19 are made of solid steel, the inner body 18 being magnetic and the outer body 19 being nonmagnetic. Four of the six equalizing slots 14 are made in a conventional manner with an unchanged slot depth along the entire slot length and filled with filling bodies of iron. The remaining two equalizing slots 14 which house the feeding conductors, are made with reduced slox deDth along a minor portion of the slot length, namely on both sides of the point where the bored conductor channel 10 or 11 opens out into the slot.

At that end of the slotted rotor portion 2, from which the shaft portion 5 extends, the filling bodies 1 8 and 1 9 are substantially replaced by a filling in the form of a stack of laminations 21 (see Figure 11) consisting of a plurality of electrically insulating laminations of glass-fiber laminate, and (see Figure 10) by a bundle 22 of short copper bars of the same cross-sectional dimensions as the current-carrying copper bars employed in the winding slots 13, and the feeding conductor 8 now has a rectangular cross-section with approximately the same width as these copper bars.With the aid of a T-shaped electrical connecting member 23 (see Figure 9) the rectangular portion of the current feedingconductor 8, axially outside the slotted rotor portion, is connected to two conductors, 24 and 25, respectively, included in the rotor winding, the connecting member providing cooling water channels communicating with the cooling channels in the conductors 24 and 25. The directions of flow of the cooling water are indicated by arrows in Figure 9. The dash dotted line P-P in this Figure indicates the middle of a pole. The conductor 24 is never current-carrying; it has only a strictly hydraulic task. The conductor 25 constitutes one end of a coil group, in which all six rotor coils are series-connected to one another and connected to the current feeding conductors 8 and 9, the feeding conductor 9 being arranged in another of the equalizing slots 14 and connected to the rotor winding in the same way as described above for the feeding conductor 8.

Since the feeding conductors 8 and 9 are clamped in their slots in the same way as the axially extending parts of the rotor winding, they will participate in the oscillations of the rotor body in the same way as said parts, so that these oscillations will not result in significant fluctuating deformations of the feeding conductors of the connecting members 23 arranged between the said feeding conductors and the rotor winding.

The bundle 22 consisting of short copper bars may be replaced by a filling body of a different kind, but the bundle illustrated in Figures 8 and 10 is considered to give a better result since, with the help of such a bundle, conditions are obtained which show great similarity to those which exist in the winding slots 13.

According to Figure 8 the rectangular part of the feeding conductor 8 and its transition from the circular part are arranged in the stack of laminations 21 and formed with a double bend. It is also possible, however, to make the conductor portion, located in the slot 14, completely straight.

If it is desired for some reason to make the rotor 1 without axially extending auxiliary or equalizing slots, it is possible -- as shown in Figure 7b - instead of the above-described conductor channels 10 and 11 bored in the rotor body, to use bored conductor channels 10' and 1 1', which have approximately the same length as the channels 10 and 11 and which each opens out into a winding slot 13, the two winding slots being substantially diametrically arranged with respect to each other. Both in the case shown in Figure 7a and in the case shown in Figure 7b, the bored conductor channels are disposed in such a manner that the distance between them has its minimum value in the part of the shaft portion 4 surrounded by a rotor bearing.This is preferred since it reduces the risk that magnetic fluxes generated by the feeding conductors will give rise to detrimental induced electric currents in the bearing.

In the rotor 1' shown in Figure 2, the feeding conductors 8' and 9' are arranged in bored conductor channels which extend throughout the shaft portion 4' and throughout the slotted rotor portion 2'. This involves a complication in so far as the bored holes are longer, but on the other hand, the demands for precision in the machining are reduced over those existing in the embodiment shown in Figure 1, since each bored conductor channel no longer has to open out into a slot.

The embodiment shown in Figure 3 differs from that shown in Figure 1 in that the projections of the bored conductor channels in an axial plane do not intersect one another. In the same way the embodiment shown in Figure 4 differs from that shown in Figure 2. It will also be noted that the length of the diverging part of the conductor channels is greater in the Figure 3 embodiment than in the Figure 1 embodiment.

In addition to the embodiments shovvn in the drawings, the invention also includes rotors in which the conductors arranged in the channels 10 and 11, after having opened out into corresponding axially extending slots, extend along these in a direction which is opposite to that shown in Figure 8, the conductors being connected to the rotor winding approximately as shown in Figure 8 but at the end of the rotor from which the shaft portion 4 projects.

In the event that the conductor channels are arranged to open out into a winding slot, for example in the same way as the channels 10' and 11' shown in Figure 7b, the feeding conductors 38 and 39 extending through the channels may be passed along the winding slot in one or the other direction and be connected to the winding in much the same way as the feeding conductor 8 shown in Figure 8, or each of the feeding conductors may be connected to the rotor winding within a corresponding winding slot.

The rotor described with reference to Figures 1, 5, 6, 7a and 8-12 is intended to be cooled by means of direct water cooling. A rotor according to the invention may just as well be made without cooling channels in the rotor winding.

A rotor according to the invention is usually made with at least twenty-four winding slots.

Claims

1. A generator rotor for a turbo-generator comprising a rotor body of magnetic material having a substantially circular-cylindrical portion with a plurality of axially extending winding slots formed therein, a rotor winding with parts thereof located in said winding slots, a first shaft portion extending from one end of said substantially circular-cylindrical portion, a second shaft portion extending from the opposite end of said substantially circularcylindrical portion, a turbine connecting means of said second shaft portion, two conductor channels bored in said rotor body and extending at least in part along said first shaft portion, and two feeding conductors for the exciting current of said rotor winding, one disposed in each of said channels, characterised in that said conductor channels extend through at least part of said substantially circular-cylindrical portion while diverging in the direction towards said second shaft portion.

2. A rotor according to claim 1, in which said feeding conductors are connected to parts of said rotor winding axially outside said winding slots at that end of the substantially circular-cylindrical portion from which said second shaft portion extends.

3. A rotor according to claim 1, in which each conductor channel opens into an axially extending slot formed in said substantially circular-cylindrical portion and provided with a slot wedge, each feeding conductor thus being disposed in part in its respective conductor channel and in part in one such slot.

4. A rotor according to claim 3, in which each feeding conductor is connected to said rotor winding at the end of the substantially circularcylindrical portion from which said first shaft portion extends.

5. A rotor according to claim 3, in which each said slot, into which a conductor channel opens, is a winding slot, the two said winding slots being disposed substantially diametrically with respect to one another in the rotor.

6. A rotor according to claim 3, in which, in addition to the slots in which parts of the rotor winding are located, the substantially circularcylindrical portion of the rotor is provided with two auxiliary slots arranged substantially diametrically with respect to one another, the said conductor channels opening into respective ones of said auxiliary slots.

7. A rotor according to any of claims 1-6, in which the part of said substantially circularcylindrical portion which is traversed by said diverging conductor channels constitutes between 20 and 70% of the total length of said portion.

8. A rotor according to any of claims 1-7, in which the angle of inclination between the projections of the diverging parts of the conductor channels in an axial plane of the rotor selected to maximize the said angle of intersection is at least 70.

9. A rotor according to claim 8, in which the angle of inclination between the projections of the diverging parts of the conductor channels in an axial plane of the rotor selected to maximize the said angle of intersection is at least 100.

1 0. A turbo-generator of at least 20 MVA, comprising a generator having a rotor body of magnetic material having a substantially circularcylindrical portion with a plurality of axially extending winding slots formed therein, a rotor winding with parts thereof located in said winding slots, a first shaft portion extending from one end of said substantially circular-cylindrical portion of the generator rotor, a second shaft portion extending from the opposite end of said substantially circular-cylindrical portion of the generator rotor, a turbine connected to said second shaft portion, two conductor channels bored in said rotor body and extending at least in part along said first shaft portion, and two feeding conductors for the exciting current of said rotor winding, one disposed in each of said channels, said conductor channels extending through at least part of said substantially circular cylindrical portion of the generator rotor while diverging in the direction towards said turbine.

11. A generator rotor for a turbo-generator substantially as hereinbefore described with reference to any of Figures 1-4 of the accompanying drawings.

12. A generator rotor for a turbo-generator substantially as hereinbefore described with reference to, and as illustrated in, Figures 1, 5, 6, 7a and 8-12 or Figures 1 and 7b of the accompanying drawings.