Abstract:
The present disclosure relates to a stripping tool, a method to strip a conductor bar, and an arrangement for stripping a conductor bar from a slot of a core of an electric machine. The disclosure provides a device and a method to facilitate the removal of a conductor bar out of a slot of an electric machine. A stripping tool for removing a conductor bar out of a slot of a core of an electric machine is described, with a piston and a support to apply the piston to the core, a rope to be wound around the conductor bar, and a puller suitable to move the rope vertically to the core to pull the conductor bar out of the slot by means of the rope. Also disclosed is a method to strip a conductor bar out of a slot of a core of an electric machine.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a stripping tool, a method to strip a conductor bar, and an arrangement for stripping a conductor bar from a slot of a core of an electric machine. 
         [0002]    The electric machine is, in particular, a rotating electric machine such as a synchronous generator to be connected to a gas or steam turbine (turbogenerator) or a synchronous generator to be connected to a hydro turbine (hydro generator) or an asynchronous generator or a synchronous or asynchronous electric motor or also other types of electric machines. 
       BACKGROUND 
       [0003]    Electrically conductive windings are composed to electric coils in electric machines. These coils or windings are made from conductor bars from copper usually. The conductor bars are placed in slots in the core of the rotor or stator of the electric machine. In maintenance and repair of huge electric machines damaged conductor bars of the windings are replaced or repaired. The removal however is complicated as the heavy conductor bars, which are several meters in length, are tightly connected and firmly fixed to the walls of the slots after long term operation. Contaminations in the slot further impede the removal of conductor bars. Commonly, this work is done by workers who cut the conductor bars out of the slots with several tools in a long lasting maintenance effort. 
       BRIEF DESCRIPTION 
       [0004]    It is an object of the invention to provide a device and a method to facilitate the removal of a conductor bar out of a slot of an electric machine. 
         [0005]    This object is solved with the features of a stripping tool, a method to strip a conductor bar, and an arrangement for stripping a conductor bar according to the present disclosure. The described stripping tool, method to strip, and arrangement provide for an easy, cheap, save, and fast solution for stripping a conductor bar from a slot. 
         [0006]    Further examples of the invention are disclosed herein. 
         [0007]    In an example of the invention the puller of the stripping tool is driven by hydraulics or pneumatics. A hydraulic or pneumatic device provides the appropriate lifting or stripping force to the conductor bar. 
         [0008]    In a further example the puller is designed as a massive tube slidable along the piston with a bolt projecting from the puller. The rope is wound around the bolt to pull the conductor bar out of the slot by means of the rope. This structure of a stripping tool enables an easy and reliable removal of a conductor bar from the slot. 
         [0009]    In a further example the stripping tool comprises at least a displacement sensor to determine the position of the conductor bar in the slot. The displacement sensor transfers the data regarding the position of the conductor bar to a controller via a signal line. The controller steers the stripping or pulling force exerted to the conductor bar in dependency of the position of the conductor bar. By this means the stripping force is reduced the more the conductor bar is stripped away from the slot with a maximum force at the start. By this means a secure removal of the conductor bar is guaranteed, a damage to the conductor bar, the slot and the stripping tool is avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Further characteristics and advantages will be more apparent from the description of a non-exclusive embodiment of a stripping tool, a method to strip a conductor bar, and an arrangement to strip a conductor bar illustrated by way of non-limiting example in the accompanying drawings, in which: 
           [0011]      FIG. 1  shows a schematic front view of a stripping tool according to an example of the invention applied to a core of a stator of an electric machine, with a rope wound around a conductor bar housed in a slot of the core; 
           [0012]      FIG. 2  shows a schematic front view similar to  FIG. 1 , with a puller pulled upwards along a piston of the stripping tool and the conductor bar partly pulled out of the slot; and 
           [0013]      FIG. 3  shows a schematic side view of an arrangement for stripping a conductor bar according to an example of the invention with a series of stripping tools surrounded by a frame to support the stripping tools. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0014]    With reference to the figures, these show a stripping tool  1  and an arrangement with a series of stripping tools  1 , wherein like reference numerals designate identical or corresponding parts throughout the several views. 
         [0015]      FIG. 1  shows a schematic front view of a stripping tool  1  according to an example of the invention. The stripping tool  1  comprises a piston  7  and a puller  2  arranged around the piston  7 . The stripping tool  1  has a longitudinal dimension. The piston  7  is designed massive, the puller  2  is designed as a massive tube which is shiftable along the piston  7  to change the length of the stripping tool  1 . A bolt  5  is mounted to the puller  2  and projects perpendicularly from the puller  2 . Around the bolt  5  a rope  6  is strained. This rope  6  can be any tear-resistant thread or strand with a thin diameter to fit into the gap between the slot  11  and the conductor bar  9 . The rope  6  can also be designed as a wire. The stripping tool  1  has a support  8  which comprises an annular shoe  12  to adjoin the core  10  as shown in  FIG. 1 . The core  10  is illustrated in the Figs in a cut front view of a small part of the core  10 . In this perspective the conductor bars  9  project into the image plane. 
         [0016]    The stripping tool  1  is surrounded by the complete stator core  10 . The support  8  of the stripping tool  1  has further a middle section  13  which connects the shoe  12  and the piston  7 . The middle section  13  serves as a support for the piston  7  and as a frame for the rope  6  and stabilizes the stripping tool  1 . The shoe  12  has a shape at the downside which is adjusted to the bending of the core  10  as the inside of the core  10  is concave. When operated an unshiftable connection between the stripping tool  1  and the core  10  is created by means of the shoe  12 . The rope  6  clutched around the bolt  5  at one end is clutched around a conductor bar  9  at the other end which is housed in one of the slots  11  of the core  9 . Therefore, the stripping tool  1  and the conductor bar  9  are bound together with a specific tension to secure the stripping tool  1  to the inner face of the core  10 . To the end of winding the rope  6  around the conductor bar  9  the rope  6  is guided by a connected thin stick which is suitable to pass through the small gap between slot  11  and conductor bar  9  to the bottom of the slot  11 . There, the thin stick unfolds with the rope  6  in a horizontal direction to the other side of the conductor bar  9 . The thin stick with rope  6  is grabbed by a different tool from the other side of the conductor bar  9  and pulled upwards along and around the conductor bar  9  within the small gap, as is shown in  FIG. 1 . 
         [0017]    Shown in  FIG. 1  is the status of stripping a conductor bar  9  before the stripping tool  1  is activated with the stripping tool  1  arranged to the core  10  and the rope  6  wrapped around the conductor bar  9  in the slot  11  as described. Next, the puller  2  is activated by a controller  15  operated by an operator of the stripping tool  1  via a signal line  16 . The controller  15  is part of an assigned computer. Alternatively, the stripping tool  1  is activated by the operator on site directly at the stripping tool  1 . In each case a pneumatic or hydraulic device assigned to the puller  2  or integrated into the stripping tool  1  drives the puller  2 . The pneumatics or hydraulics are suitable to exert a pulling force to the conductor bar  9  sufficient to move the conductor bar  9 . The pulling force causes the puller  2  to move relatively to the piston  7  of the stripping tool  1 . By this the puller  2  with the bolt  5  is shifted in the vertical direction. The rope  6  wound around the bolt  5  and the conductor bar  9  moves the conductor bar  9  in a vertical direction accordingly when the friction force is overcome. This status is shown in  FIG. 2  where the puller  2  is pushed upwards and lifts the conductor bar  9  upwards by a specific extent. 
         [0018]    The stripping tool  1  comprises at least a displacement sensor  14  to determine the position of the conductor bar  9  in the core  10 . The displacement sensor  14  is arranged at the inner wall of the slot  11 . The displacement sensor  14  measures the position of the conductor bar  9  and transfers this information to the connected controller  15 . The displacement sensor  14  can be designed as an optical sensor to gather the information whether the conductor bar  9  captures the space in the slot  11  or not. Other sensor types are useable, e.g. contact sensors sensing the contact between the displacement sensor  14  and the conductor bar  9 . In an example the position of the conductor bar  9  is measured continuously in each slot  11  by means of a series of displacement sensors  14 . 
         [0019]    In  FIG. 1  for sake of illustration only one displacement sensor  14  is shown, several further displacement sensors  14  are provided at different areas in the slot  11 . In dependence of the position of the conductor bar  9  and the extent the conductor bar  9  is lifted the force exerted by the stripping tool  1  can be adjusted. The controller  15  steers the stripping tool  1  in this manner. When the conductor bar  9  reaches a position according to  FIG. 2  for example the force exerted via the rope  6  is reduced. At first when the conductor bar  9  is completely housed in the slot  11  the force is high to release the conductor bar  9  from the slot  11  initially. Step by step the force is reduced as the conductor bar  9  is lifted more and more. The pulling force is adjusted in dependency of the position of the conductor bar  9 . Finally, the conductor bar  9  is removed from the slot  11  completely. The conductor bar  9  is then positioned in the support  8  and the puller  2  reaches the highest position. The conductor bar  9  is removed from the stripping tool  1  in a next working step and the conductor bar  9  is released from the rope  6 . 
         [0020]      FIG. 3  shows a schematic side view of an arrangement  20  for stripping a conductor bar  9  according to an example of the invention. The arrangement  20  is deployed at the core  10  of a stator of an electric machine which is shown cut. The arrangement  20  comprises a frame  21  and rods  22  connected to support a series of stripping tools  1  as described above. The frame  21  projects lengthwise through the core  10  and has a pillar  23  on each end which securely rest on the ground. The rods  22  at each end of the frame  21  carry a rail  24  at which the series of stripping tools  1  is fixed. Here, nine stripping tools  1  are comprised by the arrangement  20 . In an embodiment, the arrangement  20  comprises more than five stripping tools  1  and up to twelve stripping tools  1 . The rods  22  have an adjustable height along arms  25  of the frame  21  to properly position the rail  24  with the stripping tools  1  at the slot  11  in the core  10 . The adjustment of the frame  21  at the slot  11  as shown in  FIGS. 1 and 2  is done by the operator or alternatively automatically and controlled by the controller  15 . The installation of the arrangement  20  in the core  10  is done by the operators. The stripping tools  1  are applied along a length of a slot  11  and each rope  6  is wound around the conductor bar  9 . Thus, the ropes  6  enclose the conductor bar  9  at several points. This measure is used to strip a heavy conductor bar  9  with a length of several meters. The lifting and stripping of the conductor bar  9  is performed as described above. The controller  15  is electrically connected to all stripping tools  1  via the signal line  16  and controls the stripping process as well as the force applied to each of the stripping tools  1 . The conductor bar  9  is by these means stripped evenly from the slot  11  to avoid damaging of involved parts and to accelerate the stripping process. 
         [0021]    In particular, the stripping force of all stripping tools  1  along the conductor bar  9  is evenly distributed to prevent deformations of the conductor bar  9 . The conductor bar  9  is not equally bonded in the slot  11  along its length. Therefore, the controller  15  carefully controls the individual stripping tools  1  in a manner that the conductor bar  9  is detached from the slot surface without deformation. Displacement sensors  14  in different parts of the slot  11  make the even removal of the conductor bar  9  along the length of the slot  11  feasible. A signal from a displacement sensor  14  indicating to the controller  15  that the conductor bar  9  has reached a specific position triggers the controller  15  to stop or reduce the stripping force at the corresponding stripping tool  1  acting on this area. The stop or reduction of stripping force is upheld as long as other displacement sensors  14  at other parts of the corresponding slot  11  measure a different height position. When all displacement sensors  14  in the different spots of the slot  11  signal the same position within a specific bandwidth then all stripping tools  1  are activated by the controller  15 . 
         [0022]    All stripping tools  1  exert a stripping force to the conductor bar  9  then at all areas at which the stripping tools  1  are mounted. When one or more displacements sensors  14  signal an overshoot of a threshold value in relation to the other displacement sensors  14  then the assigned stripping tools  1  at these spots are instructed to stop or reduce the stripping force by the controller  15 . With the provision of several displacement sensors  14  assigned to each stripping tool  1  any fine-tuning of the stripping force control is realized. The described automatic control by the controller  15  is predominant against the manual adjustment which is done by several operators. The manual adjustment of the applied force of the individual stripping tools  1  in dependency to each other and in dependency to the extent of removal of the conductor bar  9  in a specific area requires a higher working effort. This manual stripping is done by appearance and manual measurement along the conductor bar  9  to be stripped. 
         [0023]    While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.