Abstract:
An improved cable system and method for an electricity generating windmill having a base formed from a plurality of stacked base sections is provided. Each base section includes a bundle of both power and control cables which are alignable with one another when the base sections are stacked and assembled. Mating electrical connectors which may be easily interlocked are provided at the ends of the power and control cables, and in the terminals of the generator and inverter of the windmill. In the preferred embodiment, bayonet-type connectors are used to provide a secure, interlocking coupling between adjacent cable ends with a minimum amount of twisting motion between the cables, which are necessarily of heavy gauge to conduct the current produced by the generator. The system greatly facilitates installation of the cable system as well as repair or replacement of damaged or worn cables during the lifetime of the windmill.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to electrical cable systems, and is specifically concerned with an improved power cable system for an electricity generating windmill.  
       BACKGROUND OF THE INVENTION  
       [0002]     While windmills per se have been in existence for over one thousand years, electricity generating windmills capable of producing power on the order of several megawatts are a relatively recent development. The general structure of such a modern, power generating windmill is illustrated in  FIGS. 1A and 1B . Such a windmill  1  generally comprises a support base  3  having a head assembly  5  oscillatingly mounted to the top end of the base  3 . The head assembly  5  includes a DC generator  6  having a rotor  7  surrounded by a stator  8  and a power outlet terminal  9 . A wind-operated blade assembly  10  is connected to the rotor  7  of the generator  6  via a gear train  11 .  
         [0003]     The support base  3  is formed from a plurality of stacked and joined base sections  12   a - 12   d . An inverter circuit  14  is disposed in the interior of the support base  3  at the bottom thereof. The inverter circuit  14  includes an inlet terminal  16  for receiving the direct current produced by the generator  6 , and a control power terminal  18  for distributing alternating current that has been converted from direct current produced from the generator  6  to various control systems (not shown) located in the head assembly  5  (i.e., an oscillating movement motor for moving the head assembly  5 , a brake for governing the maximum speed of the blade assembly  10 , and a mechanism for changing the pitch of the blades of the assembly  10 ).  
         [0004]     In order to conduct the direct current produced by the generator  6  to the to the inverter circuit  14 , it is necessary to provide a plurality of power cables between these two components. In the prior art, after the support base  3  had been assembled, fourteen 3.0 cm diameter power cables were hoisted up through the interior of the base, strapped together into a bundle, and secured to the inner walls of the base sections  12   a - 12   d . These cables were hard-wired between the generator  6  and the inverter circuit  14 . A section of these cables was allowed to hang between the generator  6  and the inner wall of the support base  3  in order to form a festoon or drip loop. The function of the drip loop was to absorb the tortional forces exerted on to the power cables when the head assembly oscillated relative to the support base  3  in response to changes in wind direction. These tortional forces are substantial, given the necessary 3.0 cm diameter of the power cables, which must carry 600 volts and 600 amps apiece, and the oscillatory range of the head assembly  5 , which can rotate 540° in both the left and right directions. However, in view of the long length of the power cables necessary to span the 60-100 meter height of the support base  3  of such windmills, it proved prohibitively difficult and dangerous to the construction crew to hoist and mount such heavy cables into the configuration indicated in  FIG. 1B .  
         [0005]     Consequently, an alternative method of construction was developed. In this alternative method, fourteen cables having diameters on the order of 3.0 cm were cut into lengths corresponding to each length of the stacked sections forming the support base, and bundled together. One bundle of power cables was then mounted onto the inner walls of each base section  12   a - 12   d  along a common axis prior to the assembly of the support base  3 . The insulation was removed at both ends of each of the power cable bundles prior to the stacking of the base sections  12   a - 12   d . After the base sections  12   a - 12   d  were stacked and attached together to form the support base  3 , adjacent ends of the axially aligned power cable bundles were spliced together by a workman operating a pneumatic splicing machine. An elastomeric sleeve was then heat shrunk or cold shrunk around each splice in order to prevent short circuiting between adjacent power cables.  
         [0006]     While such a cable system was a vast improvement over the previous “hoist and mount” system, the applicant has observed a number of problems and shortcomings associated with it. First of all, the splicing operation has proven to be difficult and time consuming. It requires a skilled worker to be harnessed and pulled up into the appropriate locations and to operate a pneumatic splicing machine which squeezes aluminum cups around the bare, exposed ends of cables of adjacent power cable bundles. Such splicing machines weight on the order of 18 kilograms, and are difficult and time consuming to apply to a dense configuration of relatively stiff cable ends while suspended in midair. After the aluminum cups have been crimped and placed, insulating sleeves must be manually heat or cold shrunk over each new splice. The entire installation operation takes upwards of ninety hours to complete. Secondly, the resulting splices have proved to have an unacceptably high failure rate, despite the fact that the splicing machine squeezes the aluminum cups over the bare ends of adjacent cables at pressure of over 10,000 psi, and despite the diligence of skilled workers in applying insulating sleeves over the resulting splice. The constant tortional forces applied to the cable bundle connected directly to the generator, and thermal differential expansion and contraction due to ambient temperature changes, the constant vibration that the splices or subjected to due to ordinary operating conditions and to inclement weather, sometimes causes gaps to form in the spliced joints. Also, water can gradually accumulate in crevices formed by improperly applied insulating sleeves. The combination of such gaps and/or moisture has led to arcing severe enough to set fire to the insulation surrounding the cables. Finally, when such accidents have occurred, the hard-wired characteristics that such splices give to the power cable system have made it difficult and time consuming to replace sections of burned power cables.  
         [0007]     Clearly, what is needed is a power cable system for an electricity generating windmill that is easier and faster to install, and which provides more reliable connections between the power cables than the crimp-type splices used in the prior art. Ideally, such a cable system would be better able to accommodate, at its upper section, the tortional forces constantly applied to it by reason of the oscillatory movement of the head assembly of the generator. It would also be desirable if such a system allowed damaged or worn cables to be removed and replaced easily and quickly without the need for large amounts of skilled labor.  
       SUMMARY OF THE INVENTION  
       [0008]     The invention is an improved cable system and method for an electricity generating windmill of a type having a base formed from a plurality of stacked base sections, wherein first and second base sections have first and second groups of power cables for conducting electricity generated by the windmill, and wherein ends of one group of power cables are adjacent to ends of another group of power cables or to a terminal of a generator or an inverter when the base sections are stacked and assembled. The improvement of the invention comprises mounting electrical connectors on the adjacent ends of different groups of power cables that detachably couple to one another to form either electrical connector assemblies between power cables, or between a bundle of power cables and the terminal of a generator or an inverter.  
         [0009]     The electrical connectors forming the electrical connector assemblies may be detachably coupled by a mechanical interference coupling, such as a bayonet-type coupling that interlocks the connectors together when they are mated and twisted relative to one another. Preferably, when bayonet-type couplings are used, they are capable of interlocking when mated and twisted no more than 45° relative to one another to minimize the amount of tortional force necessary to interlock the power cables together. A ratchet lock is preferably provided in the bayonet-type coupling for preventing the coupling from being detached after the electrical connectors forming the assemblies are interlocked.  
         [0010]     Whether the mechanical interference coupling takes the form of a bayonet-type coupling or not, it is preferably that the coupling allows done electrical connector to rotate at least 20° with respect to the connector it is coupled to in response to tortional forces applied to the cable. Such a feature advantageously allows the electrical connector assembly to accommodate, in a stress-reducing fashion, the tortional forces which are applied in particular to the upper portion of the power cables joining the generator to the first bundle of power cables located at the top of the base.  
         [0011]     The power cables are preferably formed from a spirally-wound bundle of conductive wires, such as copper, covered by a flexible, elastomeric electrical insulator. To render the cables less more accommodating to the tortional forces which are applied to them during the oscillation of the head assembly of the windmill, the individual wires forming the conductive portion of the cable are all preferably helically wound in a same direction, i.e. either all left handed or all right handed. Such a structure enhances the ability of the cable to comply with torsional forces with reduced stress on the electrical connector assemblies.  
         [0012]     Each of the electrical connector assemblies includes a water proof sleeve preferably formed from first and second mating sleeves circumscribing the two electrical connectors forming the assembly. These sleeves preferably detachably join in a water tight seal. To minimize the possibility of water incursion, each of the mating sleeves are preferably integrally formed on one end from the same insulation material circumscribing the helically wound wire conductors of the cable. The integrally formed end of each of the sleeves may include a stress relief portion for relieving bending stress on the wire conductors within the cable.  
         [0013]     The cable system further includes first and second groups of control cables for supplying power to control systems of the electrical generator which are likewise formed into bundles and mounted along the inside walls of the base sections forming the support base of the windmill. Adjacent ends of the control cable bundles also preferably include electrical connectors that are detachably connectable to form electrical connector assemblies. Waterproof sealing structures are also included in these electrical connectors to prevent arcing and corrosion.  
         [0014]     In the method of the invention, adjacent ends of bundles of power cables and control cables that have been previously mounted along the inside walls of the base sections of a windmill support base are provided with mateable electrical connectors prior to the stacking and joining of the base sections. After the base sections forming the support base have been stacked and assembled, the connectors of adjacent power and control cables are mated to form secure electrical connections between the cables. Additionally, the terminals of both the generator and the inverter circuit are likewise provided with connectors which mate with connectors provided on the ends of the power and control cables adjacent to these terminals.  
         [0015]     The invention advantageously reduces the time of installation of the windmill cable system from ninety hours to approximately four hours. The resulting connections formed by the electrical connector assemblies are more secure, reliable, and accommodating of tortional forces applied to the upper ends of these cables as a result of the relative movement of the oscillating head assembly, and the support base. The use of a locking bayonet-type coupling between the electrical connectors provides good electrical contact, and a robust mechanical joint capable of easily withstanding the tensile force generated by the weight of the cables in the drip loop near the top of the support base. Additionally, a bayonet-type coupling requires very little movement along the axis of the cable in order for the mating connectors to be joined, which is particularly advantageous in an environment where the cables themselves are fixed to the support base and hence not axially moveable except at their free ends. Finally, the mating, water proof sleeves that are integrally formed at one end from the same insulation surrounding the cables greatly reduces the possibility of water incursion within the connections. This combination of features greatly reduces the probability of arcing, fire, and cable failure. In the event that one or more cables need to be replaced, the cable system of the invention greatly facilitates a replacement or repair operation. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]      FIGS. 1A and 1B  are a front and side cross-sectional view of an electricity generating windmill incorporating the cable system of the invention;  
         [0017]      FIG. 2  is an enlargement of the circled portion of  FIG. 1B , illustrating how the cable system of the invention electrically and mechanically couples the free ends of two adjacent power cable bundles;  
         [0018]      FIGS. 3A and 3B  are a side, cross-sectional view and a front view of one of the female connectors used to interconnect two power cables;  
         [0019]      FIGS. 4A and 4B  are a side, cross-sectional view and a front view of one of the male connectors used to interconnect two power cables, and  
         [0020]      FIG. 5A  is a side view of male and female connectors used to interconnect two adjacent control cable bundles, while  FIGS. 5B and 5C  are front views of the female and male connectors, respectively. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     With reference now to  FIGS. 1A and 1B , wherein like numerals designate like components throughout all the several figures, the electricity generating windmill  1  that the cable system of the invention is applicable generally to includes a support base  3  having a head assembly  5  oscillatorily mounted at the top thereof.  
         [0022]     The head assembly  5  houses a DC generator  6  having a rotor  7  and stator  8 , as well as power outlet terminal  9 . The head assembly  5  further includes a blade assembly  10  driven by ambient wind. A gear train  11  couples the output shaft of the blade assembly  10  to the input shaft of the DC generator  6 .  
         [0023]     The support base  3  is formed from a plurality of stacked base sections  12   a - 12   d . An inverter circuit  14  is disposed in the interior of the support base  3  at its bottom. The inverter circuit  14  includes an inlet terminal  16  for receiving direct current produced by the generator  6  and converting it into alternating current. The inverter circuit  14  further includes a control power outlet terminal  18  for powering the various control systems located in the head assembly  5  (i.e. oscillating motor control, blade pitch, cooling systems, and blade assembly braking system). Finally, inverter circuit  14  includes a power outlet terminal  19  for connecting the alternating current output of the windmill  1  to a power grid system.  
         [0024]     The cable system  21  of the invention includes a plurality of cable bundles  24   a - 24   e  connected to the base sections  12   a - 12   d  of the support base  3  along a common longitudinal axis as is illustrated in  FIG. 1B . While the power cable bundles  24   a - 24   e  are generally the same lengths as their respective support base sections  12   a - 12   d , the first cable bundle  24   a  is relatively short, traversing only the distance between bundle  24   b  and inlet terminal  16  of the inverter circuit  14 , while power cable bundle  24   e  is relatively longer than the rest, due to the doubling up of the power cables necessary to form the festoon or drip loop  25 . A PVC sheath  26  surrounds part of the cable bundle  24  immediately under the DC generator  6  forming the drip loop  25  as shown. While the support base  3  of  FIGS. 1A and 1B  is shown as being formed from only four base sections  12   a - 12   d , both the number and the height of these base sections may vary as the overall height of the support base  3  varies anywhere between 60 and 100 meters.  
         [0025]     The cable system  21  of the invention further includes a plurality of control cable bundles  28   a - 28   e  arranged in the same mutually aligned configuration as the previously discussed power cable bundles  24   a - 24   e . The overall function of the control cable bundles  28   a - 28   e  is to conduct power from the terminal  18  of the inverter circuit  14  to the power inlet terminal  30  located at the bottom of the head assembly  5  in order to power the various control systems of the head assembly  5 . However, because the amount of power required for these control systems is far less than the power generated by the DC generator  6 , the cables forming the control cable bundles  28   a - 28   e  are substantially smaller in diameter than the cables forming the power cable bundles  24   a - 24   e.    
         [0026]     With reference now to  FIG. 2 , each of the power cable bundles  24   a - 24   e  is held together by the combination of a shallow, U-shaped tray  32  and cross brackets  33 . The tray  32  receives, for example, three layers of four cables (of which only the outer layer is shown for simplicity). The brackets  33  retain the power cables in the tray by compression such that the weight of the power cables is born by the tray  32 . The tray  32  is in turn secured via mounting plates  35  to the inner wall  38  of the support base  3 . The free ends of the power cables forming the power cable bundles  24   a - 24   e  terminate in either male  40  or female  42  connectors. A sufficient amount of loose length  44  is provided between the male and female connectors  40 ,  42  and the last cross bracket  33  so as to allow the person assembling the cable system  21  a sufficient amount of play between adjacent cable ends to mate and twist the male and female connectors  40 ,  42  together into a connector assembly. For cables having a diameter of approximately 3 cm, the loose length  44  is approximately one-half meter. Such a length allows the workman assembling the cable system  21  to easily align, insert and twist each of the male and female connectors 45° with respect to one another in order to mechanically and electrically secure them together via bayonet-type coupling mechanism described hereinafter.  
         [0027]     With reference now to  FIGS. 3A and 3B , the female connectors  42  each include a crimp tube  48  at their back ends for receiving one end of the copper cable  45  within each of the power cables. Advantageously, the copper cable  45  is formed from a plurality of helically wound copper wires, all of which are twisted in the same direction (i.e., either a right hand or left hand helical twist). By contrast, copper cables of the prior art generally have overlapping layers alternately helically wound in right hand and left hand directions. While such alternate twisting of the wires may impart certain advantages to copper cables used in other contexts, the inventors have found that when all of the wires forming the copper cable  49  are helically twisted in either a left hand or right hand orientation, the resistance to tortional forces on the resulting power cables is substantially reduced, thereby lowering both the tortional resistance and stresses of the power cables forming the upper most cable bundle  24   e  which are periodically twisted in one direction or the other as the head assembly  5  oscillates relative to the support base  3 .  
         [0028]     A female barrel  51  is provided at the front end of the female connector  46 . Barrel  51  includes a rounded cam member  52  that radially extends beyond the inner wall of the barrel  51  as shown. The inner wall of the barrel  51  further includes a plurality of ratchet teeth  53  which extend around the circumference of the barrel  51  for about 30°. The female connector  42  is surrounded by a waterproof sleeve  54  that is integrally formed with the cable insulation  55 . The sleeve  54  includes a hemispherical projection  56  that surrounds the outer end of the barrel  51 , and a tubular protrusion  57  which extends from the front of the hemispherical projection  56 .  
         [0029]     With reference now to  FIGS. 4A and 4B , the male connector  40  likewise includes a crimp tube  60  at its back end for receiving the ends of a copper cable  49  formed from copper wires  50  which are helically wound in a same direction. At its front end, the male connector  40  includes a split male pin  62  which is generally complementary in shape to the inner walls of the barrel  51  of the female connector  42 . The split male pin  62  includes a flattened side  64  for receiving the rounded cam member  52  of the female barrel  51 . A cam groove  66  is provided at the back of the split male pin that accommodates the cam member  62  to create the bayonet locking action when the male pin  62  is inserted into the female barrel  51  and twisted. A ratchet pawl  68  is biased into an engaging position via spring  70  with the previously discussed ratchet teeth  53  on the inner walls of the female barrel  51 . The engagement between the ratchet pawl  68  and the ratchet teeth  53  when the male and female connectors  40  and  42  are mated and twisted prevents the connectors from mechanical disengagement during the operation of the cable system  21 . For disengagement of the male and female connectors  40  and  42 , a pawl retractor  72  is provided. Pawl retractor  72  includes a detent button  74  formed from an elastomeric material which in turn contacts a plunger  76  which is reciprocally movable within a bore  77 . The distal end of the plunger  68  engages a pawl lever  78  which, when depressed, withdraws the ratchet pawl  68  back into a groove in the split male pin, thereby disengaging it from the ratchet teeth  53  of the female barrel  51 . It should be noted that the cam groove  66  extends around the circumference of the back of the split male pin  62  a substantially greater extent than the ratchet teeth on the inner wall of the female barrel  51  (i.e., 120° vs. 30°). Such relative dimensioning allows the split male pin  62  to rotate within the female barrel  51  up to approximately 20° in response to torsional forces applied to the power cables after the ratchet pawl  68  is rotated past al of the ratchet teeth  53 .  
         [0030]     Like the previously described female connector  42 , the male connector  40  likewise includes a waterproof sleeve  80  which is likewise integrally formed with the insulation  81  covering the copper cable  49 . The waterproof sleeve  80  also includes a hemispherical recess  80  which is complementary in shape to the hemispherical projection  56  of the waterproof sleeve  54  of the female connector  42 . This hemispherical recess  82  terminates with a cylindrical recess  84  surrounding the rear of the split male pin  62  which is complementary in shape to the tubular protrusion  57  of the female waterproof sleeve  54 . Both waterproof sleeves  54  and  80  and cable insulations  55  and  81  are preferably formed from a flexible, compliant artificial rubber such as Hypalon.  
         [0031]     It should be noted that the basic design features of the male and female connectors  40 ,  42  do not per se form the invention, being previously disclosed in U.S. Pat. Nos. 3,109,690; 3,226,667 and RE 25,506, the entire specifications of which are hereby expressly incorporated by reference.  
         [0032]     With reference now to  FIGS. 5A, 5B  and  5 C, the control cable bundles  28   a - 28   e  are formed from a plurality of control cables  88  terminating in male and female connectors  90 ,  92  as shown. Because the load applied to such control cables is far smaller than the load applied to the power cables (i.e., 30 amps vs. 600 amps), the diameter of the control cables  89  is substantially smaller than the diameter of the previously discussed power cables. Accordingly, the weight of the control cables  88  is far less, and so there is no need for the male and female connectors  90 ,  92  to employ the bayonet-type coupling used in conjunction with the power cables. Instead, the male connector  90  includes a plurality of male prongs  94   a ,  94   b ,  94   c  and  94   d , three of which are surrounded by a conically shaped waterproofing sleeve  96 . These sleeves  96  are insertable into cylindrical recesses  98  in the female connectors  92 . The metallic ends of the male prongs  94   a - 94   d  are, of course, receivable within contacting barrels (not shown) in the female connector  92 . Preferably, the female connector  92  is provided with a receptacle cap  100  which can be snapped over the cylindrical recesses  98  in order to prevent water from entering the metallic barrels within the female connector  92 . Although not specifically shown in the drawings, the control cable bundles  28   a - 28   e  are constructed much the same as the previously described power cable bundles  24   a - 24   e , and are secured onto the inner wall  38  of the support base  3  by way of a tray and bracket structure so that the weight of the bundles  28   a - 28   e  is supported along the wall  38 . Typically, each bundle  28   a - 28   e  has only four cables.  
         [0033]     In operation, the individual cables forming both the power cable bundles  24   a - 24   e  and control cable bundles  28   a - 28   e  are manufactured with appropriate male or female connectors on either end. Each cable bundle whether  24   a - 24   e  or  28   a - 28   e  is then mounted within its respective base section  12   a - 12   d  via the previously described tray  32 , brackets  33  and mounting plates  35 . Each of the power cable bundles  24   a - 24   e  and control cable bundles  28   a - 28   e  is mounted along a same longitudinal axis in the base sections  12   a - 12   d  such that when the base sections  12   a - 12   d  are stacked and assembled to one another, the bundles  24   a - 24   e  and  28   a - 28   e  are aligned with one another. The male and female connectors of adjacent cable ends are then secured together to form electrical connector assemblies by mating and twisting with respect to the power cable bundles  24   a - 24   e , and merely by mating in the case of the control cable bundles  28   a - 28   e . The electrical connectors of both the power cable bundles  24   a - 24   e  and control cable bundles  28   a - 28   e  adjacent to the terminals of the generator  6  and inverter circuit  16  are likewise mated to complimentary-shaped electrical connectors located in these terminals. The cable system is then ready for use. In the event that one or more of the cables within the power cable bundles  24   a - 24   e  or control cable bundles  28   a - 28   e  needs to be repaired or replaced, the male and female connectors located on either end of such cables may easily be detached from its mating electrical connector so that the damaged or defective cable may be removed.  
         [0034]     While this invention has been described with respect to a preferred embodiment, various modifications, additions and substitutions may be made without departing from the scope of the invention. For example, while the invention has been described with respect to a wind powered DC generator that utilizes fourteen power cables, it can also apply to wind powered AC generators that utilize any where between 3 and 14 power cables. While a bayonet-type mechanism has been described with respect to the connectors joining the power cable bundles  24   a - 24   e , other types of mechanically interlocking connectors may also be used. While waterproof sleeves are preferred which are integrally molded into the insulation of the cable, any type of sleeve which is merely vulcanized into the insulation, or otherwise sealingly connected to it may also be used. Additionally, a number of different support structures other than the previously described trays and brackets may be used to support the power cable bundles  24   a - 24   e  and control cable bundles  28   a - 28   e . Also, it is possible for a cable bundle to traverse the length of two base sections in the event that such sections are unusually short. All such modifications, variations and additions are encompassed within the scope of the invention, which is limited only by the claims appended hereto and their equivalents.