Abstract:
A power operator for switchgear for use in mains power distribution systems such as public medium high voltage distribution systems, where the switchgear comprises a closed cabinet ( 5 ) with an operating shaft protruding therefrom that is rotatable between two positions and has a coupling part. The motor operator includes a housing ( 11, 20, 21, 27 ) which is mountable on an external surface ( 4 ) of the switchgear cabinet ( 5 ), and a rotatable connection shaft connected to an electromechanical linear actuator. The connection shaft has a first coupling part which connects with the coupling part of the switchgear in a longitudinal axial sliding and non-rotational interlocking manner. The housing ( 11, 20, 21, 27 ) is a tube element which is tamper resistant, is relatively easy to seal against dust and moisture, and is inexpensive to manufacture.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a motor operator for opening or closing contacts of a switchgear adapted for use in mains power distribution systems such as public medium high voltage distribution systems. The motor of the operator may be activated either locally or remotely to open or close the contacts of the switchgear. Alternatively, a drive element normally coupling the motor to the contact operating shaft is selectively removable so that a wrench may be used to manually open and close the contacts in case of failure of the motor operator, or as a safety precaution. 
     2. Description of the Prior Art 
     Underground or pole-mounted electrical transmission and distribution systems include a main service line leading from a sub-station with a number of individual distribution lines along the main line connected thereto. It is often the practice, particularly where power is supplied to a user entity such as a discrete residential area, industrial area or shopping area, to provide switchgear in each of the lateral distribution lines connected to the main line in order to enable selective de-energization of the lateral distribution line without the necessity of de-energizing all of the lateral distribution lines. Switchgear conventionally includes electrical, movable contacts which may be opened and closed by maintenance personnel, in case of fault in or maintenance of a distribution line. In a particularly useful type of switchgear, the contacts are mounted under oil or in an inert gas atmosphere. 
     Generally, the contacts of switchgear require snap action opening and closing mechanisms to minimize arcing and assure a positive closing of the contacts. Actuation of the switch operating mechanism has normally been accomplished manually, requiring service personal to locate and travel to the switchgear in question. Recently, there has been increased interest in switch contact actuating mechanisms that are motor operated and can be activated at remote locations as well as manually locally. In some cases motor operators have been installed within the switchgear cabinet itself for powered actuation of the opening and closing mechanism. By design, these motor operators are not suitable for installation on a retrofit basis on an external side of an existing switchgear cabinet. Moreover, most of the available motor gear operators are relatively expensive, both in terms of cost for various components as well as expenses for installation of the same. Furthermore, these motor operators do not readily lend themselves to manual actuation in the event of motor failure or in the event that the operator desires to open the switch contacts by hand. 
     As a consequence of the fact that it is almost impossible to incorporate a motor operator in a switchgear cabinet, there is an increased interest in motor operators that can be mounted externally to the cabinet of the switchgear. In this respect it should be noted that it is not allowed to make any holes in the cabinet or make any weldings, which renders the mounting very difficult. It should also be considered that in most cases the motor operator should not only be weather proof but also secured against unauthorized intrusion. Further, it should be fully operable under all weather conditions and operate in a reliable manner. 
     An example of a motor operator to be mounted externally on a switch gear is dealt with in U.S. Pat. No. 4,804,809. This motor operator may even be mounted as a retrofit unit. The motor operator is composed of an assembly of individual elements mounted in a housing, necessitating a tedious dismounting of the connection between the motor operator and the switchgear for manually operating the switchgear. Further, the motor operator has to be designed for each individual types of switchgear. This renders the motor operator costly. The housing is designed as a regular locker of sheet metal with a door hinged at one side. It should be taken into consideration that the motor operator is located outdoors and subject to dust, rain and snow. The motor operator should operate perfectly under all weather conditions. For safety reasons, the housing should only be accessible to authorized personal and it should be secured against intrusion and vandal proof. In this sense it is fairly easy to get access to a locker. 
     Hence, there is a need for a motor operator which overcomes these and other problems associated with known devices. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a motor operator which is easy to mount and can be mounted on switchgear from various manufactures of switchgear and which to a great extend is none-intrusive and vandal proof. 
     According to the invention this is accomplished in that the housing is made of a tube element with at least one end cover. The wall making up the tube element is by definition dust and moisture proof. It is also non-intrusive as the wall is free from gaps. When closed by end covers, the tube element is, as a whole, weather proof, and by using appropriate means, e.g., burglar-proof screws to secure the end covers to the tube element, it is also, as a whole, non-intrusive. Also, the tube element is rigid and able to resist blows and strokes. As to the manufacturing, a tube element is also advantageous as it can be cut from a length of pipe. 
     In an embodiment the housing is divided in a first sub-housing for a drive unit of the motor operator and a second sub-housing for electrical equipment. As to the manufacturing, this is advantageous as the mechanical parts and the electrical equipment is usually made at different production lines. Also in case of a major overhaul or fault in one of the parts, this could simply be replaced and brought in for service. In case of use of a rechargeable battery package, it is also preferable to divide the housing into a further third sub-housing for a rechargeable battery package. This makes it easy to replace the battery package if needed. A further division into a fourth sub-housing could be beneficial in case of auxiliary equipment to costumers demand such as implementing a location system, e.g., a GPS. 
     Although the cross section of the tube element could have various geometric shapes, it has proven favorable that the tube element has a rectangular or in essential a rectangular cross section. This makes the installation more comfortable, and in case it is divided into sub-housings, the lay-out of these also becomes straightforward. E.g., that the lay-out of the cross section of the second sub-housing is such that the first and the third sub-housing could be arranged on top of the second sub-housing within its perimeter. 
     The housing could be made of various materials, e.g., a heavy duty and weather-resistant plastic; however, metal is preferred, and tube elements of extruded aluminum show good design and constructive qualities. Screw channels, preferably located in the interior of the tube element for mounting purposes is easily made in extruded aluminum tubes and so are longitudinal tracks, preferably dove-tailed shaped tracks on the sides for receiving connection elements, preferably having a dove-tailed shape. 
     In a preferable embodiment the top end cover has a rim running on the exterior surface of the tube-shaped element guiding water away from the contacting surfaces between the tube element and the cover. Further, the end cover preferably has a dome shape, such that water run off. 
     For the purpose of placing sub-housings on top of the second sub-housing, it has a planar top end cover which serves as a base for at least the first sub-housing and the top end cover has an outer shape mating the cross-section of the second sub-housing. 
     As to a bottom end cover, it preferably has an outer shape mating or essentially mating the cross section of the tube element. The edge of the cover might even be withdrawn slightly from the walls of the tube element. This prevents water from running down the wall of the tube element to get caught by the end cover and penetrate the interior; instead, it drips freely off the exterior of the housing. 
     In an embodiment the motor operator comprises a framework for carrying the housing and the framework is designed for fixedly mounting outside the range of the cabinet of the switchgear, preferably mounted on a substructure of the switchgear. Accordingly, the motor operator can be mounted without the necessity of using fastening means on the switchgear housing itself. 
     In an embodiment the framework comprises a vertical beam to which the housing of the motor operator can be mounted. Using a vertical beam means that it is a simple manner to mount the motor operator and it also has the advantage of it being relatively easy to position the motor operator in a correct position to the switch gear. 
     In a further elaboration the vertical beam has one essentially U-shaped mounting bracket by means of which the housing of the motor operator is mounted to the vertical beam. The housing and the U-shaped mounting bracket could be mutually fixed by means of connection elements, preferably having a dove-tailed shape mating longitudinal tracks in the tube element constituting the housing or sub-housing. The first, second and fourth sub-housing are preferably interconnected by means of connection elements. However, as to the third sub-housing, it is preferably attached to the first and second sub-housing by means of screws received in the screw channels. 
     In a preferred embodiment the framework comprises a lateral beam to which the vertical beam can be fixed. The lateral beam can be exploited to mount the housings of two motor operators side by side. The vertical beam can be fixed to the lateral beam in that the lateral beam has a longitudinal track for receiving a retaining plate to which the vertical beam can be fixed by screws. This makes it easy to adjust the position of the housings of the motor operator in sideward direction. 
     The framework could be mounted to a substructure of the switchgear or the framework could be designed to be fixedly mounted in the ground in front of the switchgear. Both solutions have their own advantages. 
     As to the lateral beam, this can be mounted on a substructure in various ways; however, mounting brackets are preferred as they are simple and easy to adjust. The substructure could be furnished with a pair of prongs for receiving the mounting brackets, which are of the clamping type with a hole for the prongs. 
     In general, the cabinet of a switchgear has a roofing made of metal sheet with a descending edge. In an embodiment this is exploited to attach the upper part of the housing of the motor operator to the switchgear by means of a mounting bracket which could be fixed to the descending edge of the roof of the switchgear. This stabilizes the vertical beam carrying the motor operator and thus a vertical beam with lower rigidity could be exploited. 
     Many switchgears comprise two individual sets of contacts. According to the invention in order to operate such type of switchgear, the motor operator comprises two first sub-housings for respective drive units for operating two individual operating shafts of the switch gear and one second sub-housing for common electrical equiment and possibly one third sub-housing for a common rechargeable battery package. 
     An embodiment of the invention will be described in the following with reference to the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE EMBODIMENTS 
         FIG. 1  is a perspective view of a switchgear seen from the front furnished with a motor operator, 
         FIG. 2  is a view of the individual sub-housings of the motor operator, 
         FIG. 3  is a view of longitudinal a section of cross the drive unit of the motor operator, 
         FIG. 4  is a cross section of the tube elements of the sub-housings of the motor operator, 
         FIG. 5  is a front perspective view of a framework for mounting the motor operator, 
         FIG. 6  is a perspective view of the control unit seen from below and furnished with a shield for the a cables, 
         FIG. 7  is a perspective view of another type of a switchgear seen from the front and furnished with a motor operator, and 
         FIG. 8  is a longitudinal section cross in another embodiment of the drive unit of the motor operator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is shows a switchgear  1  with to sets of electric contacts operated by a rotary shaft ending in dogs  2 , 3  at the front side  4  of the cabinet  5  of the switchgear. The electric contacts are controlled by a motor operator with respective drive units  6 , 7 . Further the motor operator comprises a control unit  8  and a rechargeable battery package  9 , which is common for the two drive units  6 , 7 . According to customer&#39;s demand, there could be a separate modem unit  10 , such as PAKNET(™ to Vodafone). 
     The drive unit  6  comprises a first sub-housing  11  for the mechanical parts including an electric motor. Specifically the drive unit comprises a electro-mechanical linear actuator  12  operating a rotatable connection shaft with a coupling part  13  engaging the operating shaft  2  of the switchgear. The sub-housing  11  is an extruded aluminum tube element having an in essential rectangular cross section. The ends of the tube element are closed with a top end cover  14  and a bottom end cover  15 . The covers are secured with screws received in longitudinal screw channels  16  in the interior of the tube element  11 . On the outside of the tube element  11  are dovetailed grooves  17  for mounting purposes to be explained in the following. The end covers are of die-cast aluminum, and between the covers  14 ,  15  and the tube-element a sealing arranged. The top end cover  14  is generally dome-shaped, such that water by gravity will run off. Further, the top end cover  14  has a rim  18  running on the exterior of the tube element guiding water away from the dividing line between the top end cover and the tube element. As it appears from  FIG. 3 , the edge  19  of the bottom end cover  15  is retracted a small distance from the outer wall of the tube element  11  so that water will drip off from the outer edge of the tube element. 
     The drive unit  7  is identical to the drive unit  6 . It should be noted that  FIG. 1  the top end covers are removed from the drive units  6 , 7 . 
     As to the control unit  8  this is located in a second sub-housing  20  and the rechargeable battery package  9  is located in a third sub-housing  21 . The sub-housing  21  is identical to the sub-housing  11 , the only difference being that the length of the tube element itself is shorter. The second sub-housing  20  for the control unit containing the electrical equipment such as the control equipment is also an extruded aluminum tube element, the cross section of which is shown in  FIG. 4 . This sub-housing  20  also has internal screw channels  22  and external dovetail grooves  23 . The cross section of the tube element of the sub-housing  20  corresponds to the cross section of the tube elements of the first and third sub-housings  11 , 21 . The depth is the same, but the width is twice the width of the tube element of the first and third sub-housings. The tube element of the second sub-housing has a planer top end cover  24  serving as a base for the first and third sub-housings  11 ,  21  arranged on top of the second sub-housing  20 . They could be mutually fixed exploiting the internal screw channels, namely by a long screw extending from the underside of the second sub-housing  20  reaching into the screw channels of the first and third sub-housings  11 ,  21 . The bottom of the tub-element is closed by a bottom end cover  25  with sockets for various electric cable connections, indicated by  26 . In the top end cover  24  are through holes also for electric cable connections to the drive unit  6  and the battery package  9 . 
     As to the separate modem unit  10 , this is located in the fourth sub-housing  27 , also made up of a tube element of extruded aluminum and a top end cover  28  and bottom end cover  29  also of die-cast aluminum. The cross section of the tube element has a depth corresponding to the depth of the other tube elements and has also screw channels  30  and dovetailed tracks  31 . The modem unit  10  could be fixed to the housing of the battery package as indicated in  FIG. 1 . To this end a connection member  32  is used, the connection member  32  having dovetails at either sides mating the dovetailed tracks on the side surfaces of the sub-housings of the battery package and the modem unit. The connection member is fixed by means of screws in the holes indicated. 
     As it appears from  FIG. 1 , the motor operator is mounted on a framework  33  arranged up front of the front surface of the switch gear  1 . Referring to  FIGS. 1 and 5 , the framework comprises a lateral beam  34  which at a rear side facing the front side of the switchgear can be furnished with a pair of mounting brackets  35  by means of which the lateral beam can be mounted on a U-shaped frame  36 . The U-shaped frame  36  is part of the support structure of the switchgear by means of which, it is fixedly mounted in the ground. On the vertical part of the U-shaped frame there is a pair of upright prongs (not shown) for receiving the mounting brackets  35  which is of the clamping type with a hole for the prongs. 
     On its front side, the lateral beam  34  has a C-shaped track  37  for receiving a retaining plate (not shown). The ends of the lateral beam  34  are closed with end plates  38 . A lower end vertical beam  39  can be attached to the lateral beam  34  by means of a pair of screws in the holes  40  received in the retaining plate and thereby fix the vertical beam  39  to the lateral beam  34 . At an upper end of the vertical beam  39  there is by means of screws  41  attached an essentially U-shaped mounting bracket  42 . The central back portion of the mounting bracket  42  has a U-shaped track receiving the vertical beam  39  and supporting it in sideward direction. The U-shaped mounting bracket  42  has a first side wall  44  and a second side wall  45 . The drive unit  6  is placed in the mounting bracket  42  between the two side walls  44 , 45 . However, before doing so a connection element  46 ,  47  having a dovetailed cross section is located in the dovetailed tracks  17  on either side of the housing of the drive unit  6 . The connection elements are fastened by means of a pair of tailstock screws. A screw bolt  49  is placed in the right hand side connection element  47 . In the right side wall  45  of the mounting bracket there is a horizontal slit  50  for receiving the shaft of the screw bolt  49 . Accordingly, when locating the drive unit  6  in the mounting bracket  42  the weight of the drive unit is carried by the screw bolt  49 . In the other side wall  44  there are horizontal longitudinal holes for inserting screw bolts  51 ,  52 , which are screwed into threaded holes in the connection element  46 . Accordingly, the drive unit could be adjusted to and from the back portion of the mounting bracket. Further, the drive unit could be adjusted up and down by loosing the tailstock screws through the horizontal longitudinal holes  53 ,  54 . Accordingly, the position of the drive unit  6  in relation to the connection shaft  2  of the switchgear is easy to adjust as the position of the drive unit  6  could be adjusted laterally as well as horizontally and also to and from the switchgear. 
     To stabilize the drive unit  6 , the top of it can be furnished with a plate-shaped fixture  55  having an essentially angular shape with a horizontal flange  56  to be placed in a countersinking  57  on top of the top end cover  14 . The leg  56  has a pair of screw holes  58  mating the screws for fastening the top end cover. An upright flange  59  of the fixture  55  is meant to grip around a descending edge  60  of a roofing  61  of the switchgear and thereby resting in the gab between the descending edge  60  of the roofing and the front side of the cabinet of the switch gear. Preferably, the outmost area of the descending edge rests in a groove in the fixture. 
     The other drive unit  7  could be mounted by similar means and in a similar manner as indicated in  FIG. 1 . 
     Needless to say, any necessary apertures and holes can be machined in the tube elements. 
     For completeness reference numeral  13   a  indicates an external operating knob device at the end of coupling part  13  for manually operating the switchgear. The invention allows the existing switchgear handle to be used, as the dog  13   b  has the same shape as on the switchgear. Reference numeral  62  indicates an operating knob device for releasing the thrust rod  63  of the linear actuator from the drive motor when manually operating the switchgear. 
     As it would be apparent from the above, the housing of the motor operator comprises the following five sub-housings, namely the first two sub-housings for the drive units  6 , 7 , the second sub-housing  20  ,of the control unit  8 , a third sub-housing  21  for the rechargeable battery package  9 , and finally the fourth sub-housing  27  for the separate modem unit  10 . 
     To protect the sockets and interconnection cables at the bottom of the control unit  8 , this can be furnished with a U-shaped shield  64  having a cross section coherent with the cross section of the sub-housing of the control unit  8 . Accordingly, the sockets and interconnection cables are located between the shield  64  and the front surface  4  of the switchgear housing. 
     The above description relates to a motor drive for a switch gear where the operating shaft  2 , 3  is rotatable about its longitudinal axis. However, there are also known switchgears where the operating shaft  2   a ,  3   a  can rotate about a transverse axis, c.f.  FIG. 7 . A drive unit  6  for such types of switchgears is shown in  FIG. 8 . For the same parts as in the drive unit shown in  FIG. 3 , the same reference numerals are used. As it can be seen from the drawing an outer tube  65  of the electro-mechanical actuator  12  passes through a hole  66  in the top end cover  67  and is sealed against the rim of the hole. The thrust rod  63  of the linear actuator is connected directly to the operating shaft  67  of the switchgear. 
     In  FIG. 7  it is seen that the individual sub-housings are arranged differently than at the switchgear shown in  FIG. 1 , proving the flexibility of the motor operator according to the invention. The rechargeable battery package  9  is mounted separately on the framework  33   a  and the modem unit  10  is attached to the battery package  9 . Thes drive units  6   a ,  7   a  of the type shown in  FIG. 8  are mounted with a side on the framework  33   a,  i.e, it is arranged perpendicular to the front side  4  of the housing  5  of the switchgear. The control unit  8  is mounted on the bottom end of the drive unit  7   a,  i.e., perpendicular to each other which is possible due to the lay-out of the cross-sections of the housing. Accordingly, it would be understood that the drive unit, the control unit, the rechargeable battery and the modem unit could be mutually interconnected or mounted separately. 
     In the embodiment described above tube elements with a rectangular cross section are indicated, however, it is obvious for a skilled person that other tube elements with a different cross section could be used evidently a tube element with a square cross section. However, also tube elements with different cross sections could be used such as a rectangular combined with a circular cross section.