CABLE FORERUNNER

Abstract: A cable forerunner for winding a high-voltage cable in an electric machine, wherein one end of the cable forerunner (11) is attached to the end (10) of the cable (1), the cable forerunner (11) is arranged to draw the cable (1) through a first slot (15) arranged in the machine body (8) and also to control the curvature of the cable (1) at its exit from the slot (15) unitl its entry into a second slot (16) arranged in the machine body (8), as well as a procedure and also an electric machine having at least one winding comprising a high-voltage cable wound in accordance with the procedure for winding a high-voltage cable (1) in an electric machine, wherein one end of the cable forerunner (11) is attached to the end of the cable (1), whereafter the cable forerunner (11) is caused to draw the cable (1) through a first slot (15) arranged in the machine body (8) and to control the curvature of the cable (1) at its exit from the slot until its entry into a second slot (16) arranged in the machine body (8).

Description: Cable forerunner TECHNICAL FIELD: The present invention relates to electric machines such as transformers, synchronous machines, normal asynchronous machines as well as dual-fed machines, applications in asynchronous static current converter cascades, outerpole machines and synchronous flow machines as well as alternating current machines intended in the first place as generators in power stations for generating electric power. The invention relates particularly to the winding procedure in such machines. BACKGROUND ART: Conventional machines have been designed for voltages in the range 15-30 kV, and 30 kV has normally been considered to be an upper limit. In the case of generators this normally means that a generator must be connected to the power network via a step-up transformer. The voltage level of the power network can be in the range of approximately 130-400 kV. The present invention is intended to be used with high voltages. In this specification the term "High voltages" means electric voltages exceding 10 kV. Typically, an operating range for a machine wound in accordance with the invention and using a cable forerunner according to the invention may be voltages from 36 kV up to 800 kV. By using high-voltage insulated electric conductors, in the following termed high- voltage cables, with solid insulation similar to that used in cables for transmitting electric power (e.g. XLPE cables) in a rotating electric machine, the voltage of the machine can be increased to such levels that it can be connected directly to the power network without intermediate transformers. The conventional transformer can thus be eliminated. The cable is provided with an outer semi-conducting layer with the help of which its outer potential is defined. The high voltage cables thus enclose the electrical field within the windings. Such an insulated conductor or cable is flexible and it is of a kind which is described more in detail in the PCT applications SE97/00874 and SE97/00875. Additional descriptions of the concerned insulated conductor or cable can be found in the PCT applications SE 97/009001 , SE 97/00902 and SE97/00903. This concept generally implies that the slots in which the cables are arranged in the stator to be deeper than conventional technology (thicker insulation due to higher voltage and more turns in the winding). This entails new problems in winding the high-voltage cable in such machines. Many different methods are available for winding the stator in a rotating electric machine with conventional windings. However, all these methods presume that the windings are stiff and can be inserted without being wound. Further, conventional windings are normally divided into short parts to fit the slots of the stator. These methods cannot be used in the present invention, where the windings consist of high voltage cables of substantial lengths, which have large diameter, high weight per unit length and high flexural rigidity. Further, during the winding process, the outer semiconducting layer of the cable must not be damaged. The difficulties in winding such a cable are thus considerable. OBJECT OF THE INVENTION: The object of the invention is to provide a device and a procedure that enables the winding of a high-voltage cable in an electric machine where the space available for handling the cable is also limited. Advantageous further developments of the invention are indicated in the following description. SUMMARY OF THE INVENTION: The present invention relates to a procedure and a device for winding high-voltage cables in an electric machine, such as the stator winding in a high-voltage alternating current generator. In order to achieve the desired shape, radius, in a flexurally rigid cable in a end winding region in a continuous process when winding the stator for an electric machine, a cable forerunner is used that pulls the cable behind it. This cable forerunner comprises a chain of suitably long rigid or flexible, pliable cylindrical links connected to a jointed coupling at their axial centre. A suitable gap (Δ) is provided between the links in a straight chain at the outer edge of the cylindrical link arms. When the chain is bent the radius is limited to a fixed desired value at which contact occurs between the links at their outer radius. The radius (R) of the cable forerunner (chain) is determined by the gap between the links of the chain, its outer radius and length in accordance with the formula l/2R=Δ/r, which is to be further explained in the following description. As a result of said property the cable forerunner can guide the cable directly through straight slots in the stator and be formed into the desired arc between two slots at the coil end part of the stator. The radius of a bent chain can be varied by varying the gap between links designed in accordance with an embodiment as described below. The invention thus comprises a special cable forerunner designed with a number of links connected by joints, and the distance between the links can be adjusted to define a minimum radius of curvature for the cable forerunner. The cable forerunner is thus rigid at its limit radius but otherwise behaves in substantially the same manner as a rope. BRIEF DESCRIPTION OF THE DRAWINGS : The invention will be described in more detail in the following with reference to the accompanying drawings in which Figure 1 shows a cross section through a high-voltage cable used in the present winding procedure, Figure 2 shows an axial section through a stator being wound in accordance with the invention, Figure 3 shows a section through a cable forerunner according to the invention. Figure 4 shows a detail from Figure 3. DESCRIPTION OF THE INVENTION: Figure 1 shows a cross-sectional view of a high-voltage cable 1 to be wound in accordance with the present invention. The high-voltage cable 1 comprises a number of strand parts 2 made of copper (Cu), for instance, and having circular cross section. These strand parts 2 are arranged in the middle of the high- voltage cable 1. The conductor area is between 30 and 3000 square mm. Around the strand parts 2 is a first semiconducting layer 3. Around the first semiconducting layer 3 is an insulating layer 4, e.g. XLPE insulation. Around the insulating layer 4 is a second semiconducting layer 5. The outer cable diameter is between 20 and 350 mm. Thus the concept "high-voltage cable" in the present application thus need not include the metal screen and the outer protective sheath that normally surround such a cable for power distribution. Figure 1 also shows a guide roller acting as first or second guide means 6a, 6b. which may be coated with rubber or a rubberlike material, journalled or fixed on a shaft 7 in contact with the outer semiconducting layer 5 of the high-voltage cable 1 in order to rotationallv absorb flexural moment applied to the high-voltage cable as this is pulled or fed in its axial direction. Figure 2 shows an axial section through a machine body 8 which in the Figure consists of a stator in a rotating electric machine being wound with its stator winding 9 in the form of a high-voltage cable as described above. A cable forerunner 11 is connected to the end 10 of the cable with the help of a connector 12 in the form of a clamp connection, for instance. The other end of the cable forerunner is provided with a traction member 13 with a wire 14 attached. By means of the wire 14, therefore, the cable can thus be drawn in and out through a first slot 15 arranged in the machine body 8, and on into a second slot 16, out through this and so on. The cable forerunner 11 is formed from a number of rigid, sleevelike, cylindrical links 17 connected together by joints 18. The joint may be in the form of a ball and socket joint or a joint for moving around only one axis. The material in the cable forerunner is preferably plastic and/or aluminium. The diameter of the cable forerunner is slightly less than the diameter of the cable. To facilitate shaping the unyielding cable to the desired curve, guide members 6a, 6b are placed at outgoing and ingoing slots as first guide members 6a and second guide members 6b, see Figure 2. These rollers, preferably made of steel and coated with rubber, are arranged to absorb forces from the flexural moment M R which is required to bend the cable, enabling normal forces between cable and slot to be reduced. The guide members 6a, 6b may be passive or provided with a drive means feeding the cable at the desired speed and with the direction of rotation indicated by the arrows in Figure 2. In this embodiment the radius can be adjusted by establishing different entry and exit speeds for the control members 6a. 6b, The guide members are thus attached temporarily to the stator in order to absorb torque and to prevent the cable from being damaged against the slot. The rollers can be placed at several slots, about 15, in order to draw cable lengths of up to 100 m simultaneously. The rollers may be driven by a motor to feed the cable instead of or as well as the wire. The rollers may also be in the form of cylinders extending along the entire length of the stator. Figure 3 shows a detail of an advantageous embodiment of the cable forerunner 1 1 revealing that each joint 18 comprises a left part 19 connected to one end of a link 17 and a right part 20 connected to the other end of an adjacent link. Thus these parts together form an intermediate joint 18. Each link is provided with a left part 19 at one end and a right part 20 at the other end. At least the left part 19 or the right part 20 of each link 17 is secured in a spacer 21 axially movable in the link 17. The embodiment according to Figure 3 shows both a left part 19 and a right part 20, each secured in such a spacer. In the embodiment shown each spacer 21 is screwed into one end of the link so that the spacer of the left part 19 has a left- hand thread and the spacer of the right part 20 has a right-hand thread. This implies that turning the links 17 relative to the joints 18 will alter the distance between each link 17. The operating principle is thus the same as for a screw shackle on a yacht. In order to facilitate this relative movement between links and joints, each link is provided with a locking element 22 which connects the two joint parts 19, 20 of the link. This locking element may, as shown in this embodiment, be in the form of a cotter pressed into the spacer 21. Turning of the links relatve to the joints may be performed by providing the whole cable forerunner with a rubber sheath which is shrunk on and fixes the movement of the links relative to each other and, by turning the joints relative to the rubber sheath and thus the links, with the aid of a turning device, not shown. An alternative embodiment is for one or more of the joints to be fixed by means of a radial blocking device running through them, while the axial distance between the links is adjusted by turning respective links. The geometry of the cable forerunner according to Figures 2 and 3 is: 1 / 2R = Δ / r where: 1 = the distance between the two joints of a link (sleeve), R = the limit radius of the cable forerunner Δ = the gap between link and joint. r = the radius of a link (sleeve) Example: 1=100 mm. r=30 mm. R=500. which gives Δ=3 mm. Thus the left-hand and right-hand threads at the ends of a link thus cause rotation of the outer cylindrical sleeve relative to its joint attachment to effect an alteration of the distance " 1" between the sleeve joints and the gap * ' Δ" between the link and the joint. Turning at a single point furthest out at the ends of the cable forerunner results in adjustment of all the sleeve lengths. The sleeves should in this case be coherent from the turning point of view. A turning can be achieved by a motor, e.g. via an elastic, rubberlike, plastic hose shrunk onto the cable forerunner along its entire length, as indicated above. Figure 4 shows a detail of the contact between two adjacent links when the cable forerunner has been curved to its defined minimum radius of curvature, i.e. when the links 17 establish contact at a point or along a surface at both their end peripheries 23. The cylindrical ends of the links 17 are shown rounded off in the Figure but may also be provided with a number of peripherally arranged surfaces to allow a higher surface pressure.

Claims: CLAIMS 1. A procedure for winding a high-voltage cable (1) in an electric machine, characterized in that one end of a cable forerunner (11) is attached to the end of the cable (1), whereafter the cable forerunner (11) is arranged to draw the cable (1) through a first slot (15) in the machine body (8) and arranged to control the curvature of the cable (1) at its exit from the slot until its entry into a second slot (16) arranged in the machine body (8). 2. A procedure as claimed in claim 1. characterized in that the cable forerunner (11) outside the machine body (8) controls the curvature of the cable (1) to a minimum radius of curvature determined by the cable forerunner (11). 3. A procedure as claimed in claim 2, characterized in that the minimum radius of curvature of the cable forerunner (11) is determined by adjusting the distance between links (17) in the cable forerunner (11) which are connected by joints (18). 4. A procedure as claimed in claim 3, characterized in that the minimum radius of curvature of the cable forerunner (11) is set by turning the links (17) relative to the joints (18). 5. A procedure as claimed in any of claims 1-4, characterized in that the cable forerunner (11) is drawn through the slots by a traction member. 6. A procedure as claimed in any of claims 1-4, characterized in that the cable forerunner (11) is drawn through the slots (15, 16) by a feed member. 7. An electric machine having at least one winding comprising a high- voltage cable wound in accordance with the procedure claimed in any of claims 1-6. 8. A cable forerunner for winding a high-voltage cable in an electric machine, characterized in that one end of the cable forerunner ( 11 ) is attached to the end (10) of the cable (1) and that the cable forerunner (11) is arranged to draw the cable (1) through a first slot (15) arranged in the machine body (8) and is arranged to control the curvature of the cable (1) at its exit from the slot (15) until its entry into a second slot (16) arranged in the machine body (8). 9. A cable forerunner as claimed in claim 8, characterized in that it comprises a number of rigid links (17) connected with joints (18). 10. A cable forerunner as claimed in claim 9, characterized in that each link (17) is provided at least at one end with an axially displaceable spacer (21) connected to the joint (18). 11. A cable forerunner as claimed in claim 10, characterized in that the spacer (21 ) is connected to the link ( 17) by means of a screw j oint. 12. A cable forerunner as claimed in claim 11, characterized in that each link (17) is provided at both ends with an axially displaceable spacer, each spacer being connected to the link (17) by a screw joint, one screw joint of the link (17) having a left-hand thread and the other screw joint of the link (17) having a right-hand thread. 13. A cable forerunner as claimed in either of claims 11-12, characterized in that a locking element (22) preventing rotation is arranged between each joint (18). 14. A cable forerunner as claimed in any of claims 11-13, characterized in that a blocking element preventing rotation is arranged to be detachably inserted between each link (17) when setting the gap between the link (17) and joint (18). 15. A cable forerunner as claimed in any of claims 8-14, characterized in that the cable forerunner (11) is arranged to cooperate with guide members (6a, 6b) to facilitate curving the cable (1) to the selected radius of curvature. 16. A cable forerunner as claimed in any of claims 8-15, characterized in that the guide members (6a, 6b) are motor-driven so that they can also draw the cable (1) from the first slot (15) to the second slot (16). 17. A cable forerunner as claimed in any of claims 15-16, characterized in that first guide members (6a) are arranged at the exit from the machine body (8) and that second guide members (6b) are arranged at the entry into the machine body (8) and that one of the guide members (6a.6b) is arranged to be driven with a speed deviating from the speed of the other guide member (6a, 6b).

Inventors: BERGGREN SOEREN, BERGGREN, SOEREN
Applicants: ASEA BROWN BOVERI, BERGGREN SOEREN, ASEA BROWN BOVERI AB, BERGGREN, SOEREN
Application year: 1997
Main classification: H02K15
IPC codes: H02K15