Abstract:
Brush holder ( 1, 1 ′) for an electrical swivel, wherein the brush holder ( 1, 1 ′) is provided with an electrically conductive body ( 10 ), provided with means ( 11,12 ) for connecting the body ( 10 ) to a feed line ( 30 ) for electrical energy and provided with at least one recess ( 13 ) for receiving a brush ( 40 ) adapted to transfer electrical energy towards a connector ( 20 ), wherein the brush ( 40 ) is connected to the body ( 10 ) by means of a electric wire ( 14 ) for the transfer of electrical energy from the body ( 10 ) towards the brush ( 40 ) and by means of a spring ( 41 ) for allowing the brush ( 40 ) to be pushed out of the recess ( 13 ) and to protrude from the surface ( 80 ) of the body ( 10 ) adapted to face the connector ( 20 ) and for urging the brush ( 40 ) against the connector ( 20 ).

Description:
[0001]    The invention relates to a brush holder for an electrical swivel and more specifically to a box-type brush holder for several brushes for an electrical swivel. 
       INTRODUCTION 
       [0002]    The invention relates to a brush holder, specifically adapted to be used in an electrical swivel. An electrical swivel is used in an off shore installation for the transfer of electricity between a first, geo-stationary element towards a further element which can weathervane around the first element. 
         [0003]    Such an electrical swivel is known, for instance from, U.S. Pat. No. 7,137,822. This document describes a swivel that can be used to transfer electricity produced on a weathervaning FPSO towards a geostationary sub-sea power line. The known swivel comprises at least one connector in the form of a slip ring in combination with a conductor in the form of a brush holder provided with carbon brushes for allowing the transfer of electricity from the conductor towards the connector ring. 
         [0004]      FIG. 1  shows a brush holder  100  for an electrical swivel according to the prior art. The brush holder  100  comprises four brushes in the form of brush blocks  140 , each for the transfer of electrical energy which is fed via feed line  130  towards a connector  120 . 
         [0005]    The brush holder  100  comprises an arm  110  which on both ends is provided with a clamp  111 ,  112 , each with a first  113  and second  114  frame to receive a brush block  140 . Each frame  113 ,  114  is provided with a spring  141  to urge the brush block  140  against the exterior of the connector  120 . 
         [0006]    A first problem that occurs with the brush holder  100  according to  FIG. 1  is the fact that the transfer of electricity from the feed line  130  until the brush block  140  encounters several locations wherein proper electrical contact could proof to be difficult. The feed line is connected by means of fixing means, including a bolt  150 , to a lip  151 . This lip  151  is connected to the arm  110  by means of welds. The presence of the welds is a first potential obstacle for proper transfer of electricity. 
         [0007]    The arm  110  is at its ends connected to the clamps  111 ,  112  by means of further bolts  152 ,  153 . This connection of the arm  110  to the clamps  111 ,  112  is a further potential obstacle for proper transfer of electricity in the direction of the brush blocks  140 . 
         [0008]    A further, related problem is the fact that it is likely to have a difference in the electrical resistance between the arm  110  and the clamp  111  at the one end and the arm and the clamp  112  at the other end. This difference in resistance may lead to unwanted and unequal distribution of electricity in the direction of the brush blocks  140 . 
         [0009]    A further problem related to the use of the brush block  100  is the relative long distance between the brush blocks  140  at opposite ends of the brush holder  100 , as will be explained with reference to  FIGS. 2 and 3 . 
         [0010]      FIG. 2  shows schematically the transfer of electricity from a feed line  130 , via a brush holder  100  towards a connector  120  and an outlet  160 , wherein the brush holder  100  and the connector  120  are in a first position. The feed line  130  will transfer the electricity to the brush holder  100 . The several brushes  140  of the brush holder  100  will contact the connector  120  and transfer the electricity to the connector  120  in order to allow the electricity to be transferred in the direction of the outlet  160 . 
         [0011]    In the position according to  FIG. 2  the electrical resistance of the connector  120  will be similar for electricity which will flow from the brush holder  100  towards the outlet  160  via either path A or path B. 
         [0012]    However, the situation will be very different in the situation shown in  FIG. 3 . According to  FIG. 3  the transfer of electricity from the brush holder  100  to the connector  120  is at a position which will cause the electrical resistance of the path A′ to be much less then the electrical resistance via the path B′. Because of the difference in electrical resistance between the path A′ and B′ in combination with the relative long distance between the brushes  140  at opposite ends of the brush holder  100 , the majority of the electrical energy will be transferred from the brush holder  100  to the connector  120  by means of the brushes  140  which are closest to the outlet  160 . 
         [0013]    This means that the transfer of electricity from the brush holder  100  to the connector will not evenly be distributed over the several brushes  140 , but on the contrary will be concentrated in only few of the brushes  140 . This will lead to local heating of the brushes  140  (also known under the name hot spots) and this may deteriorate the functioning of the device in the long run. 
         [0014]    The object of the invention is to provide a brush holder for an electrical swivel and an electrical swivel provided with such a brush holder which can avoid at least some of the problems related to the installation, use and maintenance of brush holders for electrical swivels according to the prior art. 
       SHORT DESCRIPTION OF THE INVENTION 
       [0015]    According to a first aspect of the invention, the invention relates to a brush holder for an electrical swivel, wherein the brush holder is provided with an electrically conductive body, provided with means for connecting the body to a feed line for electrical energy and provided with at least one recess for receiving a brush adapted to transfer electrical energy towards a connector, wherein the brush is connected to the body by means of an electric wire for the transfer of electrical energy from the body towards the brush and by means of a spring for allowing the brush to be pushed out of the recess and to protrude from the surface of the body adapted to face the connector and for urging the brush against the connector. 
         [0016]    In the present text the wording ‘electrical swivel’ is used for a device provided with a at least one combination of a brush holder, provided with at least one brush and a connector in the form of a connector ring to which the brush is connected, wherein the electrical swivel is used to transfer electricity from a stationary feed line towards a stationary brush holder and via the at least one brush of the brush holder towards a connector ring and outlet for electrical energy connected to the connector ring, wherein the connector ring is adapted to rotate with respect to the brush holder. 
         [0017]    According to the invention several brushes will be encapsulated close together in a cassette or housing. This enables a much more compact swivel design with fewer components. 
         [0018]    The brush holder according to the invention will allow a safer design and use, with less danger of short circuits, easier installation, change out and maintenance due to a modular structure and the device will avoid sparks and hot spots within the electrical swivel. 
         [0019]    According to a preferred embodiment of the invention the at least one brush has the form of a brush block. 
         [0020]    According to a preferred embodiment of the invention the brush holder is provided with a series of brushes, wherein the brushes are positioned in order to allow the protruding surfaces of the brushes to contact a connector in the form of a ring. 
         [0021]    According to a preferred embodiment of the invention the brush holder is provided with a cover for covering the recesses the brushes received in the recesses. 
         [0022]    According to a preferred embodiment of the invention the brush holder comprises a first series of brushes positioned above a second series of brushes. 
         [0023]    According to a preferred embodiment, the brush holder comprises a temperature prop adapted to give, in real time, the brush temperature during operation. 
         [0024]    According to a preferred embodiment, the temperature prop has the form of an optical temperature prop. 
         [0025]    According to a second aspect of the invention, the invention relates to an electrical swivel provided with the brush holder according to the invention. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be better understood after the following description with reference to the accompanying drawings wherein: 
           [0027]      FIG. 1  shows a brush holder for an electrical swivel according to the prior art; 
           [0028]      FIG. 2  shows schematically the transfer of electricity from a brush holder according to the prior art to a connector in a first position; 
           [0029]      FIG. 3  shows schematically the transfer of electricity from a brush holder according to the prior art to a connector in a second position; 
           [0030]      FIG. 4  shows in a top view the brush holder according to the invention, without the cover to show the interior; 
           [0031]      FIG. 5  shows the brush holder according to the invention, with the cover; 
           [0032]      FIGS. 6   a ,  6   b , and  6   c  schematically show three different embodiments for the brush holder according to the present invention, and 
           [0033]      FIG. 7  shows a second embodiment of the brush holder according to the invention 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]      FIG. 4  shows in a top view a first embodiment of a brush holder  1  according to the invention, without the cover to show the interior of the brush holder  1 . The brush holder  1  is adapted to transfer electricity from a feed line  30  towards a connector  20 . The connector  20  normally has the form of a ring. In  FIG. 3  only a small portion of the ring forming the connector  20  is shown. 
         [0035]    The brush holder  1  is provided with a body  10  from electrical conductive material, such as copper. The body  10  could be formed from a massive copper plate. 
         [0036]    The body  10  of the brush holder  1  is provided with integral connecting means in the form of an opening  11  for receiving the feed line  30 . Proper electrical contact is obtained by urging the body  10  and the feed line  30  to each other by means of bolt  12 . 
         [0037]    The body  10  is provided with a series of recesses  13 , each adapted to receive a brush in the form of a brush block  40 . According to embodiment of  FIG. 4 , seven recesses  13  are shown, which are adapted to receive seven brush blocks  40 . 
         [0038]    In order to connect the brush blocks  40  to the body  10 , shunts  14  are used. For optimal electrical contact, each brush block  40  is connected by means of four shunts  14  to the body  10 . In  FIG. 3  per brush block  40 , only two shunts  14  are clearly visible. 
         [0039]    The brush blocks  40  are also connected to the body  10  by means of springs  41 . These springs  41  are used to allow the brushes  40  to protrude from the surface  80  of the body  10  which is adapted to face the connector  20  and to urge the brushes  40  against the exterior of the connector  20  in order to assure proper electrical contact between the brushes  40  and the connector  20 . 
         [0040]    This force could be in the range of 50-60 Newton, preferably 53 Newton. 
         [0041]    The body  10  is provided with two further openings  15 , to receive fixing notches  50 . The brush block  1  is fixed at an appropriate distance with respect to the connector  20  by fixing the body  10  on the two notches  50  by means of bolts  16 . 
         [0042]    When installing the brush holder  1  the gap between the connector ring  20  and the brush holder  1  is typically in the range of a comfortable 8 mm. This allows the assembly to be easy and without the need of very high precision. The advantage hereof is cost saving. 
         [0043]    Once the brush block  1  is properly fixed next to the connector  20  the electrical energy can by transferred towards the connector  20 : from the feed line  30  towards the body  10 ; from the body  10 , via the shunts  14  towards the brush blocks  40 ; and from the brush blocks  40 , which are biased by means of the springs  41 , towards the connector  20 . 
         [0044]    The brush holder  1  according to  FIG. 4  will be fixed in a certain position. The connector  20  will rotatably fixed in order to allow the surface of the connector  20  to move with respect to the brushes  40 . If the connector moves in a clockwise direction (see  FIG. 4 ) the brush blocks  40  will be pushed against the wall of the recesses  13  at the left hand side (see  FIG. 4 ). If the connector  20  is rotated to move in the opposite direction, similarly the brush blocks  40  will be urged against the opposite walls of the recesses  13 . The walls of the recesses  13  can help to transfer electricity towards the brush blocks  40 . 
         [0045]    The brush holder  1  according to  FIG. 4  has a limited number of components. The main components are the body  10 , the brushes  40  and the shunts  14  and the springs  41  to connect the two together. 
         [0046]    The brush holder  1  according to  FIG. 4  is very compact. The design of the brush holder  1  allows the brush holder  1  to have a large number of brush blocks  40  properly positioned in the device while having limited outside dimensions. The distance between the brush blocks  40  near the first extremity  17  of the brush holder  1  (left hand side of  FIG. 4 ) and the brush  40  near the second extremity  18  of the brush holder  1  (right hand side of  FIG. 4 ) is relatively limited. That means that the difference between the electrical resistance for the transfer of electricity transferred by the brush block  40  near the first extremity  17  and the brush block  40  near the second extremity  18  is also very limited. This allows the transfer of electricity to be evenly distributed over the different brush blocks  40 . 
         [0047]    In other words, the amperage distribution is homogeneous due to the compactness of the brush holder  1 . The brush holder  1  allows more surfaces of the brushes  40  to be in contact in a shorter area of the connector  2 , then the devices according to the prior art (see  FIG. 1 ). This will allow one supply entrance for electrical energy and this will give more possibilities to increase the number of paths inside an electrical swivel. 
         [0048]    Moreover, the brush holder  1  gives more short circuit acceptance due to the increasing surface of the brush holder section. The constant force of the brushes  40  on the connector  20  is guaranteed; even during high short circuit level which will generate high temperature, shocks, and mechanical deformations. 
         [0049]    The design of brush holder  1  according to  FIG. 4  is applicable to both a Low Voltage (600 A) swivel and High Voltage swivel. 
         [0050]      FIG. 5  shows the brush holder  1  according to  FIG. 4 , provided with a cover  70 .  FIG. 5  clearly shows that the brush holder  1  according to the invention provides a very smooth design having a structure in the form of a module or cassette. This module encapsulates all the brush blocks  40  and strap- or shunt connections. The cassette&#39;s smooth design assurances less electro field effect due to high voltage, and no arcing. 
         [0051]    The module also provides advantages when assembling the electrical swivel. The module can be put into place in one single operation. The module can be filled with oil in order to allow the device to be insulated in oil during operation. Also in case of maintenance, the module can be removed and replaced in a very time efficient manner. The device  1  guarantees the encapsulation of all components and will avoid looses of parts during a possible violent external short circuit fault. 
         [0052]    One of the other advantages of having a very compact brush holder is the fact that more rings can be stacked in an electrical swivel, offering more paths in lower height. That means that it is possible to install more connectors  20  due to the compactness of the brush holder  20 . 
         [0053]    In  FIGS. 6   a ,  6   b , and  6   c  schematically three different embodiments for the brush holder according to the present invention are shown. 
         [0054]    According to  FIG. 6   a  the brush holder  1  comprises three brushes  40 . 
         [0055]    According to  FIG. 6   b  the brush holder  1  comprises seven brushes  40 . This embodiment corresponds with the embodiment according to  FIGS. 4 and 5 . 
         [0056]    According to  FIG. 6   c  the brush holder  1  comprises fourteen brushes  40 . In order to keep the brush holder compact, the second layer of brushes  40  is positioned above a first layer of brushes  40 . 
         [0057]    Other alternatives are possible, wherein for instance three or more layers of brushes are used. 
       Examples 
       [0058]    The brush holder  1  according to the invention could be used in the following versions: 
         [0000]    I: A Brush Holder Having 7 Block Brushes (See  FIG. 6   b ) 
       Characteristics: 
       [0000]    
       
         
           
             Voltage rating up to 52 kV continuous 
             Amperage rating up to 1000 A continuous 
             Short circuit rating is 20 kA R.M.S.—1 sec—50 kA peak 
             Power rating max per phase is 72 MegaWatts in three-phases 
             Power rating max per phase is 59 MegaWatts in two-phases 
           
         
       
     
         [0064]    II: Brush Holder Having 14 Block Brushes (See  FIG. 6   c ) 
       Characteristics: 
       [0000]    
       
         
           
             Voltage rating up to 52 kV continuous 
             Amperage rating up to 3000 A continuous 
             Short circuit rating is 36 kA R.M.S.—1 sec—90 kA peak 
             Power rating max per phase is 140 MegaWatts in three-phases 
             Power rating max per phase is 117 MegaWatts in two-phases
 
III: Brush Holder Having 3 Block Brushes (See  FIG. 6   a )
 
           
         
       
     
       Characteristics: 
       [0000]    
       
         
           
             Voltage rating up to 52 kV continuous 
             Amperage rating up to 450 A continuous 
             Short circuit rating is 7.5 kA R.M.S.—1 sec—18.75 kA peak 
             Power rating max per phase is 36 MegaWatts in three-phases 
             Power rating max per phase is 29 MegaWatts in two-phases 
           
         
       
     
       Optional Design 
     IV: Brush Holder Having 4 Block Brushes 
     Characteristics: 
       [0000]    
       
         
           
             Voltage rating up to 52 kV continuous 
             Amperage rating up to 600 A continuous 
             Short circuit rating is 10 kA R.M.S.—1 sec—25 kA peak 
             Power rating max per phase is 43 MegaWatts in three-phases 
             Power rating max per phase is 35 MegaWatts in two-phases 
           
         
       
     
         [0080]    In  FIG. 7 , a second embodiment of the brush holder  1 ′ is shown wherein the brush holder  1 ′ is closed off with a cover  70 ′. The brush holder  1 ′, according to  FIG. 7 , is provided with seven brushes  40 . The brush holder  1 ′, according to  FIG. 7 , is also equipped with a temperature prop  50 . This temperature prop is, for instance, an optical temperature prop adapted to give, in real time, of the brush temperature. The addition of this temperature prop  50  is especially important for security reasons during high voltage (for instance in the region of 120 kV to 300 kV) and very high amperage operations. 
         [0081]    The temperature prop  50  can be used for monitoring of the temperature of the brush holder  1 ′ wherein a change in temperature of the brush holder  1 ′ indicates if there is a contact deficiency between brushes  40  and a contact ring  20  with which the brushes  40  are in contact. The presence of a temperature prop will add an additional safety feature to the brush holder  1 ′. 
         [0082]      FIG. 7  also shows the presence of an insulation  51  around the feet line  30  in order to provide additional protection during high voltage and very high amperage operations.