Abstract:
A modular, space-efficient support structure mounts multiple electrical devices. The structure is modular to allow for subsequent addition and removal of electrical devices by adding and removing primary structural elements coupled for structural efficiency. The structure is deployable in many locations without reconfiguration and has reduced dependence on local site conditions. The structure uses non-permanent construction methods to facilitate rapid assembly, disassembly, re-deployment and re-use of components. Multiple electrical devices such as transformers are mounted at elevation on device mounting columns. The electrical devices are interconnected to each other in parallel or series with connectors mounted on the top portion of the device to allow maintenance clearance underneath. The arrangement of the electrical devices maximizes the density of the devices while maintaining vertical, lateral and radial safety clearances. The electrical devices are arranged in a symmetrical fashion around the primary structural element for symmetrical load distribution.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/326,240 filed Apr. 22, 2016. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to systems and methods for mounting electrical equipment at an electrical substation. 
         [0004]    2. Prior Art 
         [0005]    An electrical substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from one voltage level to another, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through multiple types of substations with different functions operating at different voltage levels. 
         [0006]    Electrical substations are expensive and time-consuming to deploy. An electrical substation may cost $60 million and take more than 5 years to deploy. The permit approval process may require multiple ecological and safety studies which slow down the overall deployment. An electrical substation usually contains multiple, heavy current and voltage-controlling devices such as transformers, capacitors, switches, etc. Electrical substations employ many different methods for mounting these current-controlling devices. Electrical substations are usually designed for a specific, permanent deployment and cannot easily be disassembled and re-deployed at a second location. 
         [0007]    The current and voltage-controlling devices need to be mounted so they are easy to install and maintain. Each device has specific mounting requirements which include: operating voltage levels, orientation, device spacing and visibility or signal path. Each deployment of the support structure requires a full understanding of the local environmental, seismic and geotechnical conditions. The design of the mounting structure depends on the loads it will experience and the local geotechnical conditions. The soils ability to resist the load often has the greatest effect on the structural solution and selection. 
         [0008]    Using the normal, industry-standard, structural-design practice, each support is designed to meet the unique conditions for the location it will be deployed in. This approach results in structural members, foundation mounting and anchoring conditions that are unique to each location and which cannot be disassembled and redeployed in another location without significant construction and reconfiguration costs. Most of the currently available designs either have a strong dependency on the local soil conditions requiring substantial customization or are structurally inefficient needing expensive and time consuming construction methods. 
         [0009]      FIG. 1  (Prior Art, U.S. Pat. No. 6,215,653) shows a modular substation design that is easy to erect and disassemble. The transformer  23  is mounted on a central section of base  2  and flanked by structures  4  and  5 . The design requires the base of the structure to be tied to all structural elements. In situation where numerous electrical devices need to be installed, the base restricts maintenance access. The beams needed to tie the columns together require steel members that are fairly high, e.g., ˜12″ or more. The beams become physical access barriers for maintenance equipment. Maintenance equipment cannot and should not drive over those structural members after they have been installed. 
         [0010]    The maintenance requirement can be met by vertically mounting the electrical devices at an elevation.  FIG. 2  (Prior Art, U.S. Pat. No. 3,556,310) shows vertical mounting of the electrical devices  13 . However in medium-voltage (MV) and high-voltage (HV) applications, the electrical devices have horizontal spacing requirements that prevent close coupling of the device  13  and the structural members  12 . While  FIG. 5  (Prior Art, U.S. Pat. No. 4,277,639) addresses the use of electrical devices at elevation with the horizontal spacing requirement, it also supports each device with its own independent support. Transformer  1  is supported by insulators  14  and  16 ; and transformer  2  is supported by insulator  24  and  26 . This method leads to a structurally inefficient design when used in a configuration that requires multiple electrical devices. Each structure supports the device and resists the loads independently. 
         [0011]      FIG. 3  (Prior Art, U.S. Pat. No. 4,710,850) and  FIG. 4  (Prior Art, U.S. Pat. No. 4,577,826) show a completely different approach. Both provide electrical isolation in HV and MV applications through the use of an insulated, elevated substation. These implementations require the use of structural insulators as the primary force resisting elements. In  FIG. 3  stories  2 ,  4 ,  6 ,  8 ,  10  and  12  a e led to each other by outdoor-type insulators  27  which are connected to the node elements  24 . In  FIG. 4 , platform  4  is supported by insulator columns  6 . These structural insulators are expensive to use and are designed to meet the specific requirements of the application and location. Using the same structural insulators in a different application requires substantial redesign and cost. 
         [0012]    Mounting MV and HV electrical devices at elevations provides safe access to the devices for installation, replacement and maintenance. The electrical device spacing clearance distances depend on the voltage levels. The spacing clearance provides electrical insulation and reduces mutual thermal radiation effects. The clearance and spacing requirements of electrical devices lead to tall structures with large foot prints. The larger structures result in longer spans and higher elevations requiring heavier and stronger structural members to resist the forces. The larger members result in higher fabrication and construction costs. Additionally, the larger footprints lead to secondary problems regarding land availability, acquisition, zoning constraints and permit requirements. 
         [0013]    Currently mounting MV and HV devices on elevated structures is limited as in  FIG. 5  (Prior Art, U.S. Pat. No. 4,277,639).  FIG. 5  shows an electrical device centrally mounted on a structure and supported by insulators to achieve the elevation and clearance requirements. The electrical conductors are mounted horizontally and to the mid body of the device. The vertical, wind and earthquake loads on the transformer devices  1  and  2  are transferred to the A-frame structure through the use of insulators,  12 ,  16 ,  24  and  26 . In order to install numerous devices a minimum amount of clearance is required radially from the conductors  4  and  5  to other conductors, structural components or devices on a different phase. While this option is viable for a small number of device deployments, it leads to accessibility and enlarged foot print issues when numerous devices need to be deployed in series or parallel. 
         [0014]    There is a need for an electrical substation support structure that solves the described issues. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The drawings are made to point out and distinguish the invention from the prior art. The objects, features and advantages of the invention are detailed in the description taken together with the drawings. 
           [0016]      FIG. 1  shows a representation of a modular electrical substation from U.S. Pat. No. 6,215,653 (prior art). 
           [0017]      FIG. 2  shows a representation of an elevated structure for mounting electrical devices from U.S. Pat. No. 3,556,310 (prior art). 
           [0018]      FIG. 3  shows a representation of a tower design for high voltage systems from U.S. Pat. No. 4,710,850 (prior art). 
           [0019]      FIG. 4  shows a representation of a stand structure for supporting electrical high voltage equipment from U.S. Pat. No. 4,577,826 (Prior art). 
           [0020]      FIG. 5  shows a representation of a high voltage device suspended by insulators from a structure from U.S. Pat. No. 4,277,639 (prior art). 
           [0021]      FIG. 6  shows an exemplary, modular, space-efficient structure for mounting multiple electrical devices. 
           [0022]      FIG. 7  shows an exemplary foundation connection for the modular, space-efficient structure. 
           [0023]      FIG. 8  shows an example of vertically mounted transformers with an exemplary vertical clearance. 
           [0024]      FIG. 9  shows exemplary beam and column connections. 
           [0025]      FIG. 10 a    shows exemplary Safety Clearance Zones for vertically mounted transformers. 
           [0026]      FIG. 10 b    shows exemplary Safety Clearance Zones for horizontally mounted transformers. 
           [0027]      FIG. 10 c    shows exemplary Vertical Safety Clearance Zones for horizontally mounted transformers. 
           [0028]      FIG. 10 d    shows exemplary Vertical Safety Clearance Zones for stacked horizontally mounted transformers. 
           [0029]      FIG. 11  shows an exemplary, modular, space-efficient electrical substation. 
           [0030]      FIG. 12  illustrates an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    There is a need for an electrical substation support structure supporting multiple heavy electrical devices with a standard, modular approach that speeds the permit approval process; provides easy addition and removal of devices; re-usability with easy assembly, disassembly, and redeployment; easy maintenance access; satisfy different electrical device mounting and clearance requirements; and offer low-cost by being inexpensive to construct, structurally efficient and having a compact footprint. 
         [0032]    The modular, space-efficient structure uses multiple device mounting columns to mount electrical equipment such as transformers or other electrical devices at an elevation. Such electrical devices might be step down transformers and/or other devices for distribution of the power received at a substation for local distribution at one or more lower voltages, though may include current and/or voltage affecting devices for such purposes as lightning and other spike suppression, power factor correction, phase balancing, harmonics suppression, loop current suppression and switching, to name some of the other electrical devices that might be used. The device mounting columns are bolted to (or cast into) a typically concrete foundation. The device mounting columns receive structural support from bolted or welded horizontal beams and reinforcement struts when required. Having a variable number of device mounting columns that can be added or subtracted provides modularity. Using bolted connections (and to a lesser extent welded connections) makes it easy to assemble and disassemble. Welded connections can be pulled apart and the components can usually be re-used. The columns, beams and reinforcement struts are made of light-weight steel making them low-cost and easy to transport. The modular, space-efficient structure uses standard components designed for applicable conditions making it possible to use the same components in different locations with different soil conditions. The modular, space-efficient structure supports multiple electrical devices, such as transformers, mounted radially from the device mounting columns to meet the necessary device clearances. The elevated radial arrangement minimizes the overall substation footprint, allows ease of access for maintenance or installation and provides structural stability by balancing the lateral forces applied to each column. This standard approach to substation construction simplifies the permit approval process reducing the overall deployment schedule and makes it possible to have temporary substation installations. 
         [0033]      FIG. 6  shows an exemplary, modular, space-efficient structure for mounting electrical devices in areas with seismic activity or high winds. The primary load bearing sections  100  and  250  are connected with zero or more expansion sections  200  connected in the middle. Expansion sections  200  are added or removed to match the number of required electrical devices. In this example structure, primary load bearing section  100 , expansion section  200  and primary load bearing section  250  are bolted to one or more concrete foundation blocks. The primary load bearing section  100  consists of device mounting columns,  101 ,  102 ,  103  and load bearing columns  104 ,  105 , and  106  that provide structural support and vertical support for electrical device mounting. The columns are tied together in a grid fashion with horizontal beams  108 - 114  and column cross-beams  115 - 116 . Connections from beams to columns are shop fabricated bolted connections designed to act as a rigid moment resisting connections. Reinforcement struts  117 ,  118  and their equivalent mounted between the beams and the columns supplement the moment resisting connections and provide additional moment resistance as required. 
         [0034]    In this example the load bearing columns  104 ,  105 ,  106 ,  251 ,  252  and  253  provide structural support for the frame and do not support electrical device mounting. The device mounting columns  101 ,  102  and  103  provide electrical device mounting. Load bearing columns  104 ,  105 ,  106 ,  251 ,  252  and  253  are bolted and/or cast into the foundation like the device mounting columns  101 ,  102  and  103 . Expansion device mounting columns  201 ,  202  and  203  of expansion section  200  provide additional electrical device mounting capability. Expansion section  200  provides additional structural resistance through expansion horizontal beams  204 ,  205 , and  206 . The connections between primary load bearing section  100 , expansion section  200  and primary load bearing section  250  are also moment resisting bolted connections with expansion reinforcement struts  209  and  210  to provide additional structural support. 
         [0035]    The electrical devices ( 303  shown in  FIG. 8 ) are mounted on device mounting columns corresponding to any of device mounting columns  101 ,  102  and  103  and connected to different phases of the power grid using an electrical conductor ( 315  of  FIG. 10 a   ). Each primary load bearing section  100  and expansion section  200  has three vertical columns because the power grid has different electrical conductors for each of its three different phases. In the embodiments disclosed herein, an even number of electrical devices are supported, though that is not a limitation of the invention, as in any embodiments shown herein, an odd number of devices and supporting insulators could be used. 
         [0036]      FIG. 6  provides a specific embodiment well-suited to environments with potentially high horizontal stresses caused by seismic activity, winds, soil conditions or other factors. Many other embodiments are possible. In a second embodiment the device mounting columns are anchored by being embedded in concrete as steel piles. In an environment with lower horizontal stresses the reinforcement struts  117  and  118  and expansion reinforcement struts  209  and  210  can be omitted and the column to beam connections need not be rigid moment resisting connections using shop fabricated bolted connections. In an environment with even lower horizontal stresses, the horizontal beams  108 - 114 , column cross-beams  115 - 116  and expansion horizontal beams  204 - 208  can be omitted altogether. 
         [0037]    The modular, space-efficient structure has to fit within the designated property area. Primary load bearing section  100  and expansion section  200  may have a different number of device mounting columns if that is necessary to fit within the designated property area. In one example, primary load bearing section  100  and expansion section  200  have six electrical device mounting columns each where the electrical devices attached to the first 3 columns have electrical connections to the electrical devices attached to the second 3 columns. 
         [0038]    Under difficult environment conditions, primary load bearing section  100  and expansion section  200  may have more structural support columns and/or fewer electrical device mounting columns. 
         [0039]      FIG. 7  shows an exemplary foundation connection for the modular, space-efficient structure. Each vertical column has column anchor flange  300  and is connected to the foundation  398  using multiple column anchor bolts  399 . In one embodiment the size of the column anchor flange  300 , number of bolt holes, length of column anchor bolts  399  and material choice are designed to meet applicable design conditions. In another embodiment the modular, space-efficient structure is constructed from a small number of component choices. In this embodiment the structure designer can select from a small number of possible columns of different types, beams of different types, connections of different types and bolts of different types to meet different requirements. The different column types will have different material, different flanges and different numbers of bolt holes. The vertical column may optionally be embedded in the concrete foundation  398  as shown in  FIG. 7 . Embedding the vertical column in the concrete foundation makes it more difficult to re-use the vertical column but the vertical column can be sawn off at the base or dug out of the concrete. When the vertical column is embedded in the concrete foundation the column anchor flange  300  is optional. 
         [0040]    Table 1 summarizes the components shown in  FIGS. 6 and 7 . 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 FIG. Label: 
                 Description 
               
               
                   
               
             
             
               
                   
                 100 
                 Primary load bearing section 
               
               
                   
                 101-103 
                 Device mounting columns 
               
               
                   
                 104-106 
                 Load bearing columns 
               
               
                   
                 108-114 
                 Horizontal beams 
               
               
                   
                 115-116 
                 Column cross-beams 
               
               
                   
                 117, 118 
                 Reinforcement struts 
               
               
                   
                 200 
                 Expansion section 
               
               
                   
                 201-203 
                 Expansion device mounting columns 
               
               
                   
                 204-208 
                 Expansion horizontal beams 
               
               
                   
                 209, 210 
                 Expansion reinforcement struts 
               
               
                   
                 300 
                 Column Anchor flange 
               
               
                   
                 398 
                 Foundation 
               
               
                   
                 399 
                 Column Anchor bolt 
               
               
                   
                 250 
                 Primary load bearing section 
               
               
                   
                 251-253 
                 Load bearing columns 
               
               
                   
               
             
          
         
       
     
         [0041]    The modular, space-efficient structure supports electrical devices with different mounting orientations and different safety clearances.  FIG. 8  shows an example of vertically mounted transformers with an exemplary vertical clearance.  FIG. 8  shows an electrical device  303  mounted on device mounting column  301 . In this first embodiment of the support structure the electrical device  303  is supported vertically by the device mounting column  301  using a beam and tie assembly,  309  and  312  respectively which may be in the form of a simple truss structure, and vertical apparatus support and electrical insulator  302 . As a truss structure, tie member  312  is always in tension, so can be a beam like member or even a cable or chain (tension resisting only). The electrical device  303  is further insulated from device mounting column  301  using lateral device structural support and electrical insulator  305 . Lateral device structural support and electrical insulator  305  connects to the device mounting column  301  using structural support attachment  313 . Structural support attachment  313  is typically an industry-standard weld or a bolted bracket. In a second embodiment of the support structure, shown later in  FIG. 10 c   , the device is supported directly by the device mounting column  301  through the use of one or more insulators. The device mounting columns,  301 , are themselves supported using support beams and reinforcement struts,  310  and  311  respectively in a grid type. Electrical device  303  has the required minimum vertical safety clearance  308 .  FIG. 8  shows conductor  315  connected to the power grid and to the top of electrical devices  303  allowing unrestricted maintenance access from below. 
         [0042]      FIG. 9  shows exemplary horizontal beam and device mounting column connections via expanded top, front and side views. Table 2 summarizes the components that connect the horizontal beams to a device mounting column. Bent plate  401  is welded to the cross beam and bolted to longitudinal through-plate  402  and transverse through-plate  403 . The transverse through-plate  403  passes through the column supporting cross beam, and is staggered from the longitudinal through plates  402 . Reinforcement strut  408  connects to the device mounting column by welding bent plate  405  to the reinforcement strut and then bolting bent plate  405  to through-plate  407 . Reinforcement strut  408  connects to the horizontal beam by welding bent plate  405  to the reinforcement strut and then bolting bent plate  405  to through-plate  404 . The connection component dimensions including thicknesses, size and shape depend on the electrical devices being mounted. 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 FIG. Label: 
                 Description 
               
               
                   
               
             
             
               
                 401 
                 Bent plate welded to cross arm, bolted to through plate 
               
               
                 402 
                 Longitudinal through plates 
               
               
                 403 
                 Transverse through plates 
               
               
                 404 
                 Through plates for reinforcement strut 
               
               
                 405 
                 Bent plate welded to brace, bolted to plates 
               
               
                 406 
                 Transverse knife plate through column supporting cross 
               
               
                   
                 arm, staggered from longitudinal through plates 
               
               
                 407 
                 Through plates for reinforcement strut 
               
               
                 408 
                 Reinforcement strut 
               
               
                   
               
             
          
         
       
     
         [0043]      FIG. 10 a    shows exemplary safety clearance zones for vertically mounted transformers. Electrical devices  303  are mounted on device mounting column  301  using lateral device structural support and electrical insulator  305  which also provides electrical isolation. The primary structural element, device mounting column  301  is symmetrically loaded around the vertical axis to reduce unbalanced loads on the structural element. This in turn reduces the amount of material needed to resist the forces acting on the structure. 
         [0044]    The modular, space-efficient structure uses multiple electrically isolating beams, struts or lateral device structural support and electrical insulators  305  to provide lateral and vertical support. The insulators also provide the lateral distance needed to meet clearance requirements to other devices and device mounting column  301 , beam  309  and support beam  310 . The lateral and vertical insulators are mounted radially on device mounting column  301  with a structural support attachment  313  or equivalent. The lateral device structural support and electrical insulators  305  are arranged to maximize the density of devices in a horizontal plane and reduce the interstitial spacing  306  while maintaining each device&#39;s radial and horizontal spacing clearance  304 , horizontal spacing clearance  307 , and lateral spacing clearance  314 . In order to minimize the interstitial space and maximize the device density, the radial arrangement of the devices is quadrangular, hexagonal, octagonal or any symmetric configuration around their vertical axis. 
         [0045]    The modular, space-efficient structure uses electrical conductors  315  mounted on the upper portion of the electrical device,  303 , to provide access and reduce the clearance requirements to the lower portion of the required minimum vertical safety clearance  308 . The electrical conductors  315  can be single, double or multiple conductors and typically connect to the power grid, and are connected to each electrical device  303  in a series or parallel configuration. 
         [0046]    Table 3 summarizes the components shown in  FIGS. 10 a , 10 b , 10 c  and 10 d   . 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 FIG. Label: 
                 Description 
               
               
                   
               
             
             
               
                 301 
                 Device mounting column 
               
               
                 302 
                 Vertical apparatus support and electrical insulator 
               
               
                 303 
                 Electrical device 
               
               
                 304 
                 Radial and horizontal spacing clearance 
               
               
                 305 
                 Lateral device structural support and electrical insulator 
               
               
                 306 
                 Interstitial spacing 
               
               
                 307 
                 Horizontal spacing clearance 
               
               
                 308 
                 Required minimum vertical safety clearance 
               
               
                 309 
                 Beam 
               
               
                 310 
                 Support beam 
               
               
                 311 
                 Reinforcement strut 
               
               
                 312 
                 Tie member 
               
               
                 313 
                 Structural support attachment 
               
               
                 314 
                 Lateral spacing clearance 
               
               
                 315 
                 Electrical Conductors 
               
               
                 316 
                 Device vertical spacing clearance requirement 
               
               
                   
               
             
          
         
       
     
         [0047]      FIG. 10 b    shows a top view with exemplary safety clearance zones for horizontally mounted transformers. Horizontally mounted transformers have a larger footprint as made evident in the top view.  FIG. 10 b    shows electrical device  303  supported by device mounting column  301  and the interstitial spacing  306  and required radial and horizontal spacing clearance  304 , horizontal spacing clearance  307 , and lateral spacing clearance  314 . Minimizing the interstitial spacing  306  gives a greater density of transformers and minimizes the required footprint. The distance between vertical device mounting columns  301  is selected to minimize the interstitial spacing  306 . 
         [0048]      FIG. 10 c    shows a side view with exemplary vertical safety clearance zones for horizontally mounted transformers. Electrical devices  303  are mounted using lateral device structural support and electrical insulator  305  which also provides electrical isolation. The required minimum vertical safety clearance  308  defines the minimum elevation for mounting the transformer.  FIG. 8  shows the first embodiment of the support structure with the electrical device  303  supported vertically by the device mounting column  301  with a lateral device structural support and electrical insulator  305  anchored to a beam and tie assembly,  309  and  312  respectively.  FIG. 10 c    shows a second embodiment of the support structure, the device is supported by the device mounting column  301  through the use of multiple lateral device structural support and electrical insulators  305  connected to structural support attachment  313  without the beam and tie assembly  309  and  312 . 
         [0049]      FIG. 10 d    shows exemplary vertical safety clearance zones for stacked horizontally mounted transformers. In this embodiment the electrical devices  303  are still arranged symmetrical about device mounting column  301  but also stacked vertically to increase the number of transformers mounted in a given footprint. In addition to required minimum vertical safety clearance  308  there is a device vertical spacing clearance requirement  316 . Note that the possibility of stacking of electrical devices is not limited to this embodiment. 
         [0050]    If onsite assembly is to be by way of bolted together assemblies, then the component parts will typically have predrilled, bolt together flanges welded onto the respective component parts as necessary for simple, bolt together assembly at the installation site. With or without flanges, parts to be bolted together would be predrilled, again for simple, bolt together assembly at the installation site. If a welded assembly is to be used at the substation site, then again any welding flanges needed would be pre-mounted (typically welded) onto any component parts as required. In either case, these approaches minimize the expensive on-site labor and other costs. Also, by simply providing the component parts in a limited range of sizes, each selected for assembling substations using equipment of corresponding capacities, and merely replicating structures during onsite assembly as required for the required substation, a highly modular, low cost, and particularly if realized by a bolted together assembly, is readily expandable by merely replicating assembled structures, or can be disassembled for moving, etc. as desired. In addition, the components may be proportioned to meet electrical component spacing requirements and sufficiently elevate the electrical components to allow servicing and/or replacement from below without disturbing other components just for access purposes. 
         [0051]      FIG. 11  shows an exemplary, modular, space-efficient electrical substation. Electrical conductors  315  connect the power grid to multiple electrical devices  303 .  FIG. 12  illustrates an alternate device mounting column  301  extending vertically and anchored at a lower end to a foundation, and alternate electrical device mounting structure, electrical device and insulator support. In particular, the device mounting column is a tapered, tubular structure with eight equally spaced, outward extending arms supporting electrical devices  303 , each on a pair of insulators  302 , the electrical devices having their electrical connections on the sides thereof instead of the top thereof. Like the embodiments of  FIGS. 10 a  and 10 b   , and embodiments like  FIG. 12  can be positioned with minimum spacing by rotating the outward extending arms supporting electrical devices on one mounting column 22.5 degrees with respect to the outward extending arms supporting electrical devices on the adjacent mounting column. 
         [0052]    Thus the present invention has a number of aspects, which aspects may be practiced alone or in various combinations or sub-combinations, as desired. Also while certain preferred embodiments of the present invention have been disclosed and described herein for purposes of exemplary illustration and not for purposes of limitation, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.