Abstract:
An electrical current collector system comprising an electrically conductive slip ring mounted to a rotatable shaft and a fixed conducting ring assembly forming a partially enclosed AC high voltage electrical current conductive ring channel in which slip ring contacting members are mounted. A compartment at ground potential at least partially encloses the slip ring and the fixed conducting ring assembly. A source directs a fluid into the compartment so that the fluid travels through into the conductive ring channel to perform at least one of cooling and cleaning of the slip ring contacting members. A hollow conically shaped insulator has a frustum with a narrower cross-sectional opening connected to the conductive ring channel and a larger diameter cross-sectional portion passing through and connected to the compartment for exhausting the fluid from the current conductive ring channel.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an electrical current collector for a high voltage rotating machines and, in particular, relates to an insulator and filter used for cleaning and cooling the current collector.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are systems, such as, for example, synchronous motors and generators, which supply electrical current to a rotor winding by way of slip rings. The current is typically applied to the slip rings via brushes mounted on a fixed conducting ring. Ordinarily the slip rings are at low voltage, however, the slip rings may be used in high voltage applications.  
           [0003]    A slip ring assembly for use in high voltage machines and applications is disclosed in U.S. Pat. No. 6,465,926 issued Oct. 15, 2002 to Rehder et al entitled Cleaning/Cooling of High Power Rotary Current Collection System. This patent discloses an electrical current collector system that includes for each phase a fixed conducting ring; brushes; an electrically conductive slip ring; and a slip ring support assembly. Cooling air is circulated through the collector system for high voltage rotating machines and is exhausted from collector housing through a cylindrically shaped exhaust passageway and filtering device. This passageway also includes the bus bar that feeds power to and from the fixed conducting ring. Typically, the cooling air stream passes over the brushes in the collector system and in so doing the cooling air moves and carries carbon particles or dust produced as a result of brush wear out through the exhaust duct passageway in the bus bar. This passageway, however, is limited in cross-sectional area due to the primary purpose of the bus bar to carry current. Hence the air flow is limited. Any build up of carbon particles can result in shorting of the windings of the machine if not properly removed from the air flow.  
           [0004]    Accordingly, there is a need in high voltage collector systems for rotating machines and transformers to have an exhaust passageway that provides an insulated exhaust passageway between the high voltage environment of the collector system and the ground potential beyond the exhaust passageway that allows collector cooling air to pass through the exhaust passageway unimpeded and without the exhaust passageway being prone to creep buildup of carbon particles along its inner surfaces. Further, there is a need to filter the collector cooling air after it passes through the exhaust passageway.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention relates to an electrical current collector system comprising an electrically conductive slip ring mounted to a rotatable shaft and a fixed conducting ring assembly forming a partially enclosed AC high voltage electrical current conductive ring channel in which slip ring contacting members are mounted. A compartment at ground potential at least partially encloses the slip ring and the fixed conducting ring assembly. A source directs a fluid into the compartment so that the fluid travels through into the conductive ring channel to perform at least one of cooling and cleaning of the slip ring contacting members. A hollow conically shaped insulator has a frustum with a narrower cross-sectional opening connected to the conductive ring channel and a larger diameter cross-sectional portion passing through and connected to the compartment for exhausting the fluid from the current conductive ring channel.  
           [0006]    The present invention may include a collection chamber mounted to the compartment outer wall and surrounding a portion of the insulator that extends beyond the compartment. The collection chamber has a filter spaced from and across the outlet port of the insulator for filtering particles from the fluid as the fluid passes through the filter.  
           [0007]    The conical shape of the hollow insulator has an electric field profile where equipotential lines tangent to the flow of fluid through the insulator increase in distance between the lines. The conical shape of the insulator exaggerates the stress distribution of the electric potential field so as to be favourable to the carbon particles passing therethrough so that the particles do not move into contact with the inner side wall of the insulator. As a result, carbon particles in the fluid have a tendency to move along a central portion of the insulator spaced from the inside walls of the insulator. This inhibits creepage build-up of carbon particles on the inside surface walls of the insulator which could result in shorting conditions for the rotor assembly. Also, the size of the insulator is governed by the amount of fluid flow needed to cool and clean the electrical current collector system.  
           [0008]    In one example deployment, the present invention is utilized in a rotating transformer system wherein the electrical current collector system applies current to a rotor assembly having rotor windings which rotate about the rotatable shaft, and wherein a stator has stator windings, and a motor is provided for rotating the rotor assembly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    For a better understanding of the nature and objects of the present invention reference may be had to the accompanying diagrammatic drawings in which:  
         [0010]    [0010]FIG. 1 is a side sectional view of a prior art rotating transformer system.  
         [0011]    [0011]FIG. 2 is a top sectional view of the rotating transformer system showing the conical shaped insulator of the present invention;  
         [0012]    [0012]FIG. 3 is an enlarged sectional view showing a gap between a U-shaped ring structure and a slip ring and includes a cross-sectional view of the conical shaped insulator of the present invention; and,  
         [0013]    [0013]FIG. 4 is a partial half view of the insulator showing the equipotential electric field lines passing through the insulator of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    [0014]FIG. 1 shows a rotary transformer system  20  as disclosed in U.S. Pat. No. 6,465,926 issued Oct. 15, 2002 to Rehder et al, which is incorporated herein by reference in its entirety, which includes both a rotor assembly  22  and a stator  24 . The rotor assembly  22  includes a rotor cage section  26 , slip rings (also known as collector rings and generally depicted by reference numeral  27 ), and a rotatable shaft  28 . Rotor assembly  22  is rotatable about an axis RX of its rotatable shaft  28  in both a clockwise direction and a counter-clockwise direction. Rotation of rotor assembly  22  is effected by a drive motor  30 .  
         [0015]    The rotary transformer system  20  is employed in a high voltage, high current environment having alternating voltages and current. In this example of deployment, rotary transformer system  20  is connected to transfer electrical power between a first electrical system (e.g., first electrical grid) and a second electrical system (e.g., second electrical grid). In such deployment, one of the rotor assembly  22  and the stator  24  is connected (e.g., by three phase lines) to the first electrical system, and the other is connected to the second electrical system. The drive motor  30  rotates the rotor assembly  22  in response to a drive signal generated by an unillustrated control system. The first and second electrical systems may have a differing electrical characteristic (e.g., frequency or phase). The control system can bi-directionally operate the rotary transformer system  20  at a variable speed for transferring power from the first electrical system to the second electrical system or vice versa (i.e., from the second electrical system to the first electrical system).  
         [0016]    A collector system  40  positioned at the top of rotor assembly  22  comprises the slip rings  27 ; a slip ring support assembly  42 ; and, fixed conducting ring assembly  44 . In view of its example deployment in a three phase system, the collector system  40  has three slip rings  27 A,  27 B, and  27 C (any one of which is generically referred to as slip ring  27 ) and three corresponding fixed conducting ring assemblies  44  (any one of which is generically referred to as fixed conducting ring assembly  44 ). Three-phase lines leading from one of the connected electrical systems are connected to respective ones of fixed conducting ring assemblies  44  of collector system  40  of rotor assembly  22 . Other three-phase lines connect the other electrical system to stator  24 . In the illustrated example embodiment, the slip rings  27  are 17 KV rated rings.  
         [0017]    The collector system  40  can be situated in a compartment  56  of housing  50 , in the manner shown in FIG. 1. The compartment  56  is subdivided into three air-sealed subcompartments  57 A- 57 C. These subcompartments are preferably phase isolated from each other and may alternatively be phase segregated. The collector system  40 , which is used to interface electrically with rotor assembly  22 , has structure essentially residing on three distinct planes, herein referred to as phase planes. In the situation depicted in FIG. 1 in which rotary transformer system  20  is vertically mounted, the three phase planes of collector system  40  are substantially horizontal planes. In a first or uppermost such phase plane, depicted by broken line  58 A, both slip ring  27 A and fixed conducting ring assembly  44 A reside within subcompartment  57 A. Similarly, in a second or middle phase plane  58 B both slip ring  27 B and fixed conducting ring assembly  44 B reside within subcompartment  57 B; and in a third or lowermost phase plane  58 C both slip ring  27 C and fixed conducting ring assembly  44 C reside within subcompartment  57 C.  
         [0018]    A slip ring support assembly  42  is provided for each phase plane  58  of collector system  40 . With respect to a representative one of the phase planes  58 , FIG. 2 shows slip ring support assembly  42  as comprising plural post insulators  102  mounted discretely at selected intervals about the outer circumference of rotatable shaft  28 . As an example, FIG. 2 shows six post insulators  102  arranged about axis RX. Each of the post insulators  102  extend essentially radially from periphery of rotatable shaft  28  and have an attachment/adjustment assembly  106  surmounted thereon.  
         [0019]    Each of the fixed conducting ring assemblies  44  have brush assemblies  70  mounted thereon angularity about rotatable shaft  28  at intervals. Electrical current is transferred between the brushes of the brush assemblies  70  and the respective slip rings  27 , and hence between the rotor assembly  22  and the electrical system connected to the fixed conducting ring assembly  44 . The electricity travels between the slip rings  27  and the windings of the rotor assembly  22  over bus conductors  80 . There is a bus conductor  80  for each of the three phases, e.g., bus conductors  80 A,  80 B, and  80 C, only bus conductor  80 C being shown in FIG. 1. Each of the bus conductors  80  extends through a respective one of three phase isolated bus ducts  82  (only bus duct  82  being shown in FIG. 1).  
         [0020]    Referring to FIG. 2, each fixed conducting ring assembly  44  comprises a U-shaped ring structure mounted on ring support insulation post and a ring support shelf (not shown). The ring support shelf serves to form a partition or grounded metal sheet between the subcompartments  57  of compartment  56 . Reference may be made to the aforementioned U.S. Pat. No. 6,465,926 for a more detailed description of the insulation posts and support shelf.  
         [0021]    The U-shaped ring structure  200  has a top conductive ring plate  200 T, a bottom conductive ring plate  200 B, and a covering wall  200 W attached thereto. A conductive ring channel  220  is formed in the interior of U-shaped ring structure  44 , e.g., between top conductive ring plate  200 T and a bottom conductive ring plate  200 B.  
         [0022]    The fixed conducting ring assemblies  44  of each phase plane have brush assemblies  70  situated and mounted thereon in the manner shown, e.g., in FIG. 2 and FIG. 3. The brush assemblies  70  are positioned at angular locations about rotatable shaft  28  in the manner shown in FIG. 3. In the example illustrated embodiment, each U-shaped ring structure  44  has eighty six brush assemblies  70  provided thereon in forty three pairs, with forty three brush assemblies  70  being suspended from beneath the top conductive ring plate  200 T and another forty three brush assemblies  70  being mounted on bottom conductive ring plate  200 B.  
         [0023]    An example pair of brush assemblies  70  employed by rotary transformer system  20  is illustrated in FIG. 3. Each brush assembly  70  comprises a carbon brush  240  and a brush holder  242 . The brush holders  242  are suspended from top conductive ring plate  200 T and mounted on bottom conductive ring plate  200 B by bolts and washers. An insulation board (not shown) is interposed between the brush holder  242  and the ring plates  200 T,  200 B. Electrically conducting leads (e.g., copper braids)  250  emanate from the rear end of the carbon brushes  240 , and terminate at a quick disconnect terminal  252  which is electrically conductivity mounted by fasteners in one of the ring plates  200 T,  200 B. Each brush assembly  70  includes negator spring assemblies  256  for exerting an essentially constant biasing force on the carbon brushes  240  toward slip ring  27 . Reference may be made to the aforementioned U.S. Pat. No. 6,465,926 for a more detailed description of the fixed conducting ring and brush assemblies.  
         [0024]    As shown in FIG. 2, each U-shaped ring structure  200  has an electrically conductive bus bar  260  extending radially therefrom. Bus bar  260  passes through and is insulated from compartment wall  56 . At its distal end remote from U-shaped ring structure  200 , the bus bar  260  has a bus connector  262  provided thereon. Each bus bar  260  has a duct  350  which is provided with a plug  351  welded therein so as to prevent air flow along the bus duct  350 . This prevents any coolant air carrying carbon particles from flowing along the bus bar  260 .  
         [0025]    Referring to FIGS. 2 and 3 a hollow conically shaped insulator  400  is shown extending from the wall  200 W of the conductive ring channel  44 . The hollow insulator  400  is connected to the compartment  56  by a flange  410  that has bolts  424  passing therethrough. The hollow conical shaped insulator  400  has a frustum shape  414  that extends between the fixed conducting ring  44  and the compartment wall  56 . The frustum  414  has a series of ribs  432  that provide increased electrical creepage length to the insulator and the O-ring  423  allows for any expansion between dissimilar materials of the insulator  400  and the fixed conducting ring  44 . As best seen in FIG. 3, the fixed conducting ring  44  has an opening  49  in wall  200 W and is provided with an annular flange  422  comprising a copper material. The insulator  400  has a narrower end or opening  418  inserted into the annular flange  422  and held in place within the copper flange  422  by the O-ring  423 . This attachment allows for some slippage or between the insulator  400  and the conductive ring  44  due to dissimilar rates of thermal expansion of these parts. It should be understood that the insulator  400  comprises a cycloaliphatic epoxy or may comprise any other form of suitable electrical insulation made from a polymeric epoxy or ceramic such as porcelain.  
         [0026]    The inside walls  460  of the insulator  400  diverge convexly at walls  426  located beyond the compartment  56  and flange  424 . The purpose of the divergent wall  460  is twofold. One purpose is to increase the opening surface area  428  throughwhich the fluid exhausting the fixed conductor ring  44  travelling as shown by air path  334 F increases such that air velocity out of opening  428  and into adjacent filter  420  is low enough for the filter to effectively absorb the carbon particles contained within the air flow. The other reason that the walls  460  convexly diverge is to further inhibit creepage build up of carbon particles beyond the influence of the electric field profile (as shown in FIG. 4) between the high voltage connection at copper flange  422  and the ground connection at flange  424  to the compartment  56 . The conical shape of the frustum  414  results in the distance between the equi-potential lines  500  (See FIG. 4) passing through the hollow insulator  400  in the vicinity of the frustum  414  increasing in distance between these lines  500  along the central axis  600 . Consequently, any charged particles or carbon particles capable of being charged by the high voltage within the collector system are influenced by the electrical field profile to flow through the center of the insulator  400  and not flow adjacent the internal walls of the insulator  400 .  
         [0027]    [0027]FIGS. 2 and 3 further show a collection chamber  430  which comprises a rectangular shaped chamber having side walls  431  and flanges  429  mounted by bolts  434  to the compartment wall  56 . It should be understood that for higher current ratings, the chamber  430  may be cylindrical in shape. The side walls  431  is provided with an inturned flange  442  bolted thereto. Flange  442  has filter  420  mounted and supported therefrom. The filter is a conventional industrial filter for carbon dust so as to eliminate carbon dust having particle size of less than about 1 micron. As a result, the use of the filter and the insulator provides an effective manner for allowing the fluid to escape along path  334 G thereby permitting for a cooling of the fixed conductive ring and at the same time eliminating or removing the carbon particles by the filter  420  from the fluid stream  334 F.  
         [0028]    It should be understood that the shape of the insulator  400  provides significant advantage over merely the use of a hollow insulator. Due to the electric field profile between the fixed conductive ring operating at a high voltage potential and the ground potential of the casing  56 , the shape of the hollow insulator  400  inhibits any carbon particles from depositing and forming a creep layer along the inside surface walls of the insulator  400 . This thereby inhibits the carbon particles from creating shorting conditions along the inside walls of the insulator.  
         [0029]    Since rotary transformer system  20  is operating at a high voltage, it must be enclosed. The enclosures for rotary transformer system  20 , including compartment  56  of housing  50 , are described above. However, in the enclosure dust produced from the wearing of the carbon brushes  240  can accumulate inside the enclosures and contaminate insulation surfaces, such as the post insulators  102 . Therefore, in accordance with one aspect of rotary transformer system  20 , a cooling/cleaning fluid (e.g., air) is introduced and the flow of this cooling/cleaning fluid is controlled to carry the brush dust away from the post insulators  102 . Moreover, the air flow gap  48  between slip ring  27  and fixed conducting ring assembly  44  plays a part in the cleaning and cooling of rotary transformer system  20 . The cooling/cleaning fluid passes through the air flow gap  48 , past the contact points of carbon brushes  240 , and then along a semicircular envelope toward the exhaust insulator  400 . The moving cooling/cleaning fluid provides a means of carrying away heat from the carbon brushes  240  and the fixed conducting ring assembly  44 , reducing the temperature rise due to electrical losses and mechanical friction.  
         [0030]    Elaborating upon the foregoing, as shown in FIG. 1, rotary transformer system  20  has one or more cooling/cleaning sources, such as ventilation fan  300  and ventilation fan  302 . The ventilation fan  302  has a fan motor  304 , and is connected to apply ventilation fluid, also known as cooling/cleaning fluid (e.g., air), via duct system  308  to the interior of housing  50 , as indicated by fluid flow indication arrows  310 . The ventilation fan  300  is mounted on bracket  320  (attached to housing  50 ), and serves both motor  30  and compartment  56 , including the cooling and cleaning of the slip rings  27  and the fixed conducting ring assemblies  44  with their brush assemblies  70 . The cooling/cleaning fluid (e.g., air) passes from ventilation fan  300  through duct system  328  as shown by fluid flow indication arrows  330 . The duct system  328  has an exit portal or the like for each phase plane  58 , so that for each phase plane  58  the ventilation fluid enters into the interior of the respective subcompartments  56 A,  56 B, and  56 C, as depicted by fluid flow indication arrows  332 A- 332 C in FIG. 1.  
         [0031]    An example path of the cooling/cleaning fluid for a single example phase plane  58  is shown from above rotary transformer system  20  in FIG. 3. In this regard, FIG. 2 shows by fluid flow indication arrow  334 A the cooling/cleaning fluid entering through a portal  336  of duct system  328 . The cooling/cleaning fluid entering the subcompartment  58  is blown toward the center of the hexagonal shaped subcompartment  58 , filling the interior of subcompartment  58  up to rotatable shaft  28 . As such, the entering cooling/cleaning fluid sweeps around each of the post insulators  102 , as indicated by fluid flow indication arrow  334 B in FIG. 2. The cooling/cleaning fluid then flows over the slip ring  27 , as indicated by fluid flow indication arrow  334 C, which cools the slip ring  27 . The cooling/cleaning fluid then enters the air flow gap  48  (depicted in FIG. 3) between the slip ring  27  and fixed conducting ring assembly  44 , as indicated by fluid flow indication arrow  334 C (shown in FIG. 2 but better illustrated in FIG. 3). The air flow gap  48  thus directs the flow of cooling/cleaning fluid across the interface of the carbon brush  240  and slip ring  27 . The cooling/cleaning fluid thereby enters the conductive ring channel  220  in the brush assembly  70  and passes over the brush assembly  70  (depicted by fluid flow indication arrow  334 D in FIG. 3). Once in the conductive ring channel  220 , the cooling/cleaning fluid travels in the conductive ring channel  220  in a semicircular path around the fixed conducting ring assembly  44 , in the manner illustrated by fluid flow indication arrow  334 E (see FIG. 2). Thus, inside fixed conducting ring assembly  44  the cooling/cleaning fluid moves in a semicircular fashion, even when there is no rotation of rotatable shaft  28 . The cooling/cleaning fluid is then exhausted from compartment  58  through an exhaust duct  350 , as illustrated by fluid flow indication arrow  334 F in FIGS. 2 and 3.  
         [0032]    The velocities of the cooling/cleaning fluid is greater within the conductive ring channel  220  of fixed conducting ring assembly  44  than in the spacing interior to slip ring  27 , facilitating pick up of brush dust and the like as the cooling/cleaning fluid moves around the ring shape of the conductor envelope assembly. But even in the space interior to  27 , there is movement of cooling/cleaning fluid past the post insulators  102 , tending to keep them clean.  
         [0033]    Air has been cited above as one example of a suitable cooling/cleaning fluid. Other non-limiting examples of suitable fluid which can serve as the cooling/cleaning fluids are oil, hydrogen gas, and sulfahexaflouride gas (SF6). Usage of SF6 in a closed or sealed system can reduce the size of collector system  40 . SF6 has a higher thermal conductivity and higher dielectric strength than air. With SF6 at one atmosphere pressure, the distance between conductors and ground can be reduced to half the air clearances.  
         [0034]    It should be understood further that ventilation fan  300  and ventilation fan  302  are just examples of sources of the cooling/cleaning fluid. Other sources which can direct the cooling/cleaning fluid into the appropriate compartments are also within the scope of the invention, such as pressurized sources of cooling/cleaning fluid, for example. Further, it is envisaged that the flow of fluid into the conductive ring channel  220  could be introduced by ducting passing through one or more of walls  200 T,  200 B and  200 W in addition to air passing through the air gap  48 .  
         [0035]    As used herein, high voltage” in the rotating machine art is understood to be in a range of 13.8 kV up to at least 26 kV, and can be higher. Low voltage is generally considered to be 4 KV and below; medium voltage is deemed to be 6600 v and 7200 v.  
         [0036]    While the invention has been described in connection with the above described embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.