Abstract:
An inverter by pass safety switch for rerouting electrical power either through or around AC variable frequency inverter drives during electrical disturbances, thus allowing a motor to continue operation. The switch works in a mechanical fashion, and comprises a contact block containing electrical contacts and cams operably connected to the contacts and mounted on a shaft that can be turned by an operator. The cams are shaped and mounted on the shaft in such a way to provide a desired switching pattern when the shaft is manually rotated.

Description:
BACKGROUND 
     1. Field of the Invention 
     This patent relates to manually operated electrical switches. More particularly, this patent relates to a manually operated electrical switch that uses a shaft with a plurality of cams operatively connected to electrical contacts to provide the required switching action for rerouting electrical power either through or around AC variable frequency inverter drives. 
     2. Description of the Related Art 
     Inverter drives, or inverters for short, are solid state devices used to vary the speed of common three phase electric motors. Inverters are common in industry and are used in conveyors, fans, cooling towers, extruders, and other applications. However, since inverters are solid state devices, they are vulnerable to lightning strikes, power surges, low voltages, and other disturbances in the electrical line. When disturbances occur, inverter drives can fail. Failure of the inverter drive can stop the motor from operating, thus stopping the application. 
     Several methods have been developed to isolate inverters during electrical disturbances. However, these methods involve expensive and unreliable contactors, relays and timers. 
     The present invention is designed to provide a simple means of isolating an inverter drive during an electrical disturbance to allow a motor to continue at full speed/full power operation until a safe stopping point is reached. This is accomplished by providing an inverter bypass safety switch that can route electrical power through or around an inverter simply by turning a handle on the switch. 
     Thus it is an object of my invention to provide a simple and reliable means for isolating an inverter during electrical disturbances so that the motor can continue at full speed/full power operation until a safe stopping point is reached. 
     Another object of the present invention is to provide a mechanical means for isolating an inverter. The present invention does not require contactors, relays, solenoids, or coils that can consume power, stick, or burn out. 
     Still another object of the present invention is to provide a means for isolating an inverter that uses positive break contacts. Should a contact “weld”, the switch handle cannot be turned. If the switch handle cannot be turned, the contacts cannot transfer. If the switch handle is able to be turned, the contacts transfer. This feature assures the operator that when the switch has been turned the contacts have been transferred. 
     Yet another object of the present invention is to provide a switch having positive removal of the electrical power from the inverter drive. In other words, the switch can be used to disconnect power from both the incoming lines into the inverter and outgoing lines from the inverter. 
     Further and additional objects will become apparent from the description, accompanying drawings, and appended claims. 
     While other less desirable methods have been developed to isolate inverters during electrical disturbances, no prior inverter bypass switch is known that embodies and possesses all the aforementioned characteristics. 
     SUMMARY OF THE INVENTION 
     The present invention is an inverter bypass safety switch comprising a contact block containing a plurality of electrical contacts and a plurality of cams operably connected to the electrical contacts so that rotation of the cams opens or closes the electrical contacts. Each electrical contact comprises two stationary contacts and a moveable contact. The moveable contacts move in response to the movement of the cams. 
     The cams are mounted on a shaft that can be turned by an operator. The cams are shaped to provide a desired switching pattern when the shaft is manually rotated. Although any number of switching patterns may be employed, four are described below: DRIVE, LINE, OFF, and TEST. 
     In the DRIVE position, electrical power is routed through the switch to an inverter drive, from the inverter drive back to the switch and then to a motor. This is the normal position used when providing power to an application. 
     In the LINE position, electrical power is routed from an incoming power source through the switch and directly to the application. This position is used when an operator wants to isolate the inverter drive, such as for repairs or replacement, while not shutting down the application. 
     In the OFF position, electrical power is disconnected from both the inverter drive and the application. This position typically is used when an operator wants to shut down the application. 
     In the TEST position, electrical power is routed from an incoming power source though the switch to an inverter drive, but no power is sent to the application. The TEST position may be used to set up the inverter drive parameters, test the inverter drive function, change settings on the inverter drive, and in any other situation where it is desirable to power the inverter drive but not allow power to the application. 
     Other switching patterns can be made to suit operator requirements. The switch may connected to a fuseblock to protect the motor against short circuits, to a disconnect switch, or to a manual motor starter. 
    
    
     
       THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the inverter bypass safety switch of the present invention. 
         FIG. 2  is a side elevational view of the inverter bypass safety switch of  FIG. 1 , with the base shown in partial cutaway to show the auxiliary contacts. 
         FIG. 3  is a cross sectional view of the inverter bypass safety switch, taken along line  3 — 3  of FIG.  2 . 
         FIG. 4  is a cross sectional view of the inverter bypass safety switch, taken along line  3 — 3  of  FIG. 2 , the cam having been rotated approximately 60 degrees in a counterclockwise direction from the orientation shown in FIG.  3 . 
         FIG. 5  is a perspective view of the inverter bypass safety switch of  FIG. 1  enclosed in an enclosure. 
         FIG. 6  is a schematic diagram of the inverter bypass safety switch showing the switch in the DRIVE mode. 
         FIG. 7  is a schematic diagram of the inverter bypass safety switch showing the switch in the LINE mode. 
         FIG. 8  is a schematic diagram of the inverter bypass safety switch showing the switch in the OFF mode. 
         FIG. 9  is a schematic diagram of the inverter bypass safety switch showing the switch in the TEST mode. 
         FIG. 10A  is a front and side view of one embodiment of a handle assembly for the inverter bypass safety switch, referred to herein as the “Selector Style”. 
         FIG. 10B  is a front and side view of a second embodiment of a handle assembly for the inverter bypass safety switch, referred to herein as the “Lockout Style”. 
         FIG. 10C  is a front and side view of a third embodiment of a handle assembly for the inverter bypass safety switch, referred to herein as the “Panel Mount Style”. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the drawings, there is shown in  FIGS. 1  to  4  one embodiment of an inverter bypass safety switch  10  according to the present invention. The switch  10  comprises a base  12 , a contact block  14  mounted on the base  12  and divided into sections  16 , electrical contacts  18  located within the sections  16 , cams  20  operatively connected to the electrical contacts  18 , and a shaft  22  connecting all of the cams  20  together. A handle assembly  24  ( FIGS. 10A ,  10 B and  10 C) attached to the shaft  22  is manipulated by an operator to turn the shaft, thereby selecting a desired operating mode. An enclosure or housing  26  (shown in  FIG. 5 ) allows for easy mounting of the switch  10  on a wall. 
     The contact block  14  may include up to nine power contacts and two auxiliary contacts. The power contacts direct the incoming power either to and from the inverter drive, or directly to the motor, bypassing the inverter. The auxiliary contacts may be used to control a drive control circuit, send signals to a PLC, pilot light, or other device. 
     In the illustrated embodiment, the five sections  16  above the base  12  contain the nine power contacts, and the section  16  below the base  12  contains the two auxiliary contacts. As shown in  FIGS. 3 and 4 , a cam  20  located within each section operates the electrical contacts  18 . 
     Preferably, the contacts  18  are double make/break contacts. That is, each contact  18  has a moving contact  28  and a pair of stationary contacts  30 . In the preferred embodiment, each moving contact  28  comprises a copper bar  32  with silver cadmium oxide contact points  34  on each end. The silver cadmium oxide contact points  34  carry the amp switching load. Each moving contact  28  is held in a follower  36  which is keyed into the housing  38  of the switch  10 . The follower  36  is acted upon by the shaft-mounted cam  20 . 
     Preferably, two stationary contacts  30  are located on either side of each moveable contact  28  and are be made of the same materials as the moveable contacts  28 . The stationary contacts  30  are keyed into the housing or body  38  of the switch  10 , and are connected to electrical terminals  31  for fastening external body wires to the switch  10 . Some of the electrical terminals  31  are connected by electrically conductive bridges  33  to other terminals in the same section  16  of an adjacent section  16 . 
     Each cam  20  has a profile cut into the cam  20  that determines the switching pattern. The profile may include low sections  21  and/or high sections  23 . Each follower  36  is connected to a spring  40  that biases the moveable and stationary contacts  28 ,  30  in a closed (together) position when the cam  20  is rotated such that a low section  21  of the cam profile faces the follower  36 . The moveable and stationary contacts  28 ,  30  are mechanically opened when the cam  20  is rotated to a high section  23  of the cam profile. Opening the contacts  18  does not require use of the spring  40 . 
     The shaft  22  connects all the cams  20  together, and is itself connected to an operating handle  42 . The operating handle  42  can be turned by the operator. The operating handle  42  is part of the handle assembly  24 . 
     By varying the shape of the cams  20  and the orientation of the cams  20  into the shaft  22 , various switching patterns can be achieved. Four different switching patterns or positions shall now be described. 
     In the DRIVE or normal position, shown schematically in  FIG. 6 , electrical power is routed through the switch  10  to the inverter drive  11 , from the inverter drive  11  back to the switch  10 , then to the motor. In the DRIVE position, full function of the inverter drive is available to the motor at all times. 
     In the LINE or bypass position, shown schematically in  FIG. 7 , electrical power is routed from the incoming power source through the inverter bypass safety switch  10  directly to the motor. Thus power is eliminated from both the input and output side of the inverter drive  11 . In the LINE mode, the inverter drive  11  can be physically removed from service while the motor is left operating at full speed-full voltage. 
     In the OFF position, shown schematically in  FIG. 8 , electrical power is disconnected from both the inverter drive and the motor. 
     The TEST position, shown schematically in  FIG. 9 , electrical power is routed from the incoming power source through the inverter bypass safety switch to the inverter. No power is sent to the application. 
     The inverter bypass safety switch may be configured in either a two position, three position, four position unit, depending on the needs of the user. The two position unit has a DRIVE and a LINE position. The three position unit has DRIVE, LINE, and OFF positions. The four position unit has DRIVE, LINE, OFF and TEST positions. Other switching patterns can be achieved by changing the configuration of the cams. 
     The switch is operated in the following manner. The desired switching pattern is achieved by turning the operating handle  42  to the desired setting. Turning the handle causes the cams  20  to rotate, which acts upon the moveable contacts  28 , either opening or closing the electrical connections between the moveable and stationary contacts. 
     As shown in  FIGS. 10A ,  10 B and  10 C, the handle assembly  24  has at least three embodiments. In the embodiment referred to herein as the “Selector Style” (FIG.  10 A), the handle assembly  24 a comprises a backplate  44 a, an operating handle  42 a mounted to the backplate  44 a, and a gasket (not shown) mounted to the side of the backplate  44 a opposite the handle  42 a. If an electrical disturbance occurs, the operator can turn the handle  42 a from, say, the DRIVE position to the OFF or LINE position and interrupt the flow of electricity through the inverter  10 . 
     The embodiment referred to herein as the “Lockout Style” ( FIG. 10B ) includes all of the features of the Selector Style embodiment, and further comprises holes for mounting padlocks (not shown) to lock the handle  42 b in the LINE, OFF, DRIVE, or TEST positions. In this way, the switch  10  can be locked into a desired position. 
     The embodiment referred to herein as the “Panel Mount” style ( FIG. 10C ) includes all of the features of the Lockout Style embodiment, and further comprises an extension shaft  46 c and an extension shaft coupling  48 c. The extension shaft  46 c and extension shaft coupling  48 c allow the switch  10  to be mounted on the rear panel of the enclosure  26 , as shown in  FIG. 5 , while the handle assembly  24 c is mounted on the front of the enclosure  26 . 
     The unique features of the inverter bypass safety switch  10  include the following. First, unlike conventional switches, the present invention has positive removal of the electrical power from the inverter drive. In other words, the switch  10  can be used to disconnect power from both the incoming lines into the inverter drive  11  and outgoing lines from the inverter drive  11 , as shown in FIG.  7 . 
     Second, the present invention features entirely mechanical operation. That is, the switch  10  does not depend on coils, relays, contactors, or other electromechanical devices to switch power. 
     Third, the present invention features positive break contacts. This means that, should a contact  18  “weld”, the operating handle  42  cannot be turned, thus assuring the operator that when the operating handle  42  has been turned the contacts  18  have been transferred. If the operating handle  42  is able to be turned, the contacts  18  transfer. 
     It is anticipated that the switch  10  may be enclosed in a UL listed nonmetallic enclosure such as the one shown in  FIG. 5  or other enclosure as desired, allowing for easy installation of the switch on a wall. It is also anticipated that the switch  10  may be connected to a fuseblock to protect the motor against short circuits. It is further anticipated that the switch  10  can be enclosed in a nonmetallic enclosure or other enclosure with a disconnect switch, thus combining the features of an inverter bypass switch with a disconnect switch. Finally, it is anticipated that the switch  10  can be used in conjunction with a manual motor starter. The manual motor starter would provide protection against excessive motor current and short circuits. The manual motor starter could be reset like a circuit breaker. 
     Although the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be obvious that certain modifications and alternative embodiments of the invention are contemplated which do not depart from the spirit and scope of the invention as defined by the foregoing teachings and appended claims.