USRE40161E1 - Cam operated inverter bypass safety switch - Google Patents

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 ofFIG. 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 line3—3 of FIG.2.

FIG. 4 is a cross sectional view of the inverter bypass safety switch, taken along line3—3 ofFIG. 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 ofFIG. 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 inFIGS. 1 to4 one embodiment of an inverterbypass safety switch10 according to the present invention. Theswitch10 comprises abase12, acontact block14 mounted on thebase12 and divided intosections16,electrical contacts18 located within thesections16,cams20 operatively connected to theelectrical contacts18, and ashaft22 connecting all of thecams20 together. A handle assembly24 (FIGS. 10A,10B and10C) attached to theshaft22 is manipulated by an operator to turn the shaft, thereby selecting a desired operating mode. An enclosure or housing26 (shown inFIG. 5) allows for easy mounting of theswitch10 on a wall.

Thecontact block14 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 fivesections16 above the base12 contain the nine power contacts, and thesection16 below the base12 contains the two auxiliary contacts. As shown inFIGS. 3 and 4, acam20 located within each section operates theelectrical contacts18.

Preferably, thecontacts18 are double make/break contacts. That is, eachcontact18 has a movingcontact28 and a pair ofstationary contacts30. In the preferred embodiment, each movingcontact28 comprises acopper bar32 with silver cadmium oxide contact points34 on each end. The silver cadmium oxide contact points34 carry the amp switching load. Each movingcontact28 is held in afollower36 which is keyed into thehousing38 of theswitch10. Thefollower36 is acted upon by the shaft-mountedcam20.

Preferably, twostationary contacts30 are located on either side of eachmoveable contact28 and are be made of the same materials as themoveable contacts28. Thestationary contacts30 are keyed into the housing orbody38 of theswitch10, and are connected toelectrical terminals31 for fastening external body wires to theswitch10. Some of theelectrical terminals31 are connected by electricallyconductive bridges33 to other terminals in thesame section16 of anadjacent section16.

Eachcam20 has a profile cut into thecam20 that determines the switching pattern. The profile may includelow sections21 and/orhigh sections23. Eachfollower36 is connected to aspring40 that biases the moveable andstationary contacts28,30 in a closed (together) position when thecam20 is rotated such that alow section21 of the cam profile faces thefollower36. The moveable andstationary contacts28,30 are mechanically opened when thecam20 is rotated to ahigh section23 of the cam profile. Opening thecontacts18 does not require use of thespring40.

Theshaft22 connects all thecams20 together, and is itself connected to an operating handle42. The operating handle42 can be turned by the operator. The operating handle42 is part of the handle assembly24.

By varying the shape of thecams20 and the orientation of thecams20 into theshaft22, various switching patterns can be achieved. Four different switching patterns or positions shall now be described.

In the DRIVE or normal position, shown schematically inFIG. 6, electrical power is routed through theswitch10 to the inverter drive11, from the inverter drive11 back to theswitch10, 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 inFIG. 7, electrical power is routed from the incoming power source through the inverterbypass safety switch10 directly to the motor. Thus power is eliminated from both the input and output side of the inverter drive11. In the LINE mode, the inverter drive11 can be physically removed from service while the motor is left operating at full speed-full voltage.

In the OFF position, shown schematically inFIG. 8, electrical power is disconnected from both the inverter drive and the motor.

The TEST position, shown schematically inFIG. 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 handle42 to the desired setting. Turning the handle causes thecams20 to rotate, which acts upon themoveable contacts28, either opening or closing the electrical connections between the moveable and stationary contacts.

As shown inFIGS. 10A,10B and10C, the handle assembly24 has at least three embodiments. In the embodiment referred to herein as the “Selector Style” (FIG.10A), thehandle assembly24a comprises abackplate44a, anoperating handle42a mounted to thebackplate44a, and a gasket (not shown) mounted to the side of thebackplate44a opposite thehandle42a. If an electrical disturbance occurs, the operator can turn thehandle42a from, say, the DRIVE position to the OFF or LINE position and interrupt the flow of electricity through theinverter10.

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 thehandle42b in the LINE, OFF, DRIVE, or TEST positions. In this way, theswitch10 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 anextension shaft46c and an extension shaft coupling48c. Theextension shaft46c and extension shaft coupling48c allow theswitch10 to be mounted on the rear panel of theenclosure26, as shown inFIG. 5, while thehandle assembly24c is mounted on the front of theenclosure26.

The unique features of the inverterbypass safety switch10 include the following. First, unlike conventional switches, the present invention has positive removal of the electrical power from the inverter drive. In other words, theswitch10 can be used to disconnect power from both the incoming lines into the inverter drive11 and outgoing lines from the inverter drive11, as shown in FIG.7.

Second, the present invention features entirely mechanical operation. That is, theswitch10 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 acontact18 “weld”, the operating handle42 cannot be turned, thus assuring the operator that when the operating handle42 has been turned thecontacts18 have been transferred. If the operating handle42 is able to be turned, thecontacts18 transfer.

It is anticipated that theswitch10 may be enclosed in a UL listed nonmetallic enclosure such as the one shown inFIG. 5 or other enclosure as desired, allowing for easy installation of the switch on a wall. It is also anticipated that theswitch10 may be connected to a fuseblock to protect the motor against short circuits. It is further anticipated that theswitch10 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 theswitch10 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.

Claims (5)

1. An inverter bypass safety switch for rerouting electrical power either through or around an inverter drive during electrical disturbances and suitable to directly handle high power motor loads, said switch comprising one or more sections joined together by throughbolts to form a substantially cylindrical contact block having a central axis, a rotatable shaft disposed along the central axis, electrically conductive exterior interconnections for connecting selected stationary contacts, externally mounted electrical contacts for receiving electrical wires, and a handle mounted on one end of the shaft that can be turned by an operator, each section comprising:

a cam mounted on the shaft;

at least one pair of stationary contacts contact connected to the contact block; and

at least one radially sliding moveable contact operably connected to the cam by a spring-loaded follower that biases the moveable contact into engagement with the pair of stationary contacts contact when a low profile section of the cam faces the follower;

wherein manual rotation of the shaft causes the cam to rotate and act upon the moveable contact to cause the moveable contact to move either into or out of engagement with the stationary contacts contact, thus causing electrical power to be directed either through or around the inverter drive.

2. The inverter bypass safety switch ofclaim 1 wherein the shape of the cams, the placement of the cams within the sections and in relation to the other cams, the placement of exterior interconnections of the stationary contacts and the attachment of exterior wires are all selected to provide four discreet switching patterns, namely:

a DRIVE pattern, wherein electrical power is routed through the inverter bypass safety switch to the inverter drive, from the inverter drive back to the inverter bypass safety switch and then to an application;

a LINE pattern, wherein electrical power is routed from an incoming power source through the inverter bypass safety switch and directly to the application;

an OFF pattern, wherein electrical power is disconnected from both the inverter bypass safety switch and the application; and

a TEST pattern, wherein electrical power is routed through the inverter bypass safety switch to the inverter drive, but no power is sent from the inverter drive to the application.

3. An inverter bypass safety switch for rerouting electrical power around an inverter drive during electrical disturbances, said switch comprising:

a base having two sides;

one or more power sections stacked on one side of the base and joined together by throughbolts to form a substantially cylindrical contact block having a central axis, each power section comprising a body portion, a cam mounted on a rotatable shaft extending through the power sections along the contact block central axis, at least one pair of stationary contacts keyed into the body portion of their respective section of the contact block and electrically connected to externally mounted electrical terminals for fastening external wires, and at least one radially sliding moveable contact operably connected to the cam by a spring-loaded follower that biases the moveable contact into contact with the pair of stationary contacts when a low profile section of the cam faces the follower;

one or more auxiliary sections stacked on the base side opposite the power sections for controlling auxiliary devices; and

electrically conductive exterior interconnections for connecting selected externally mounted electrical terminals;

wherein manual rotation of the shaft causes the cams to rotate and act upon the moveable contacts to cause them to move either into or out of contact with the stationary contacts, thus causing electrical power to be disconnected from both the incoming lines into the inverter drive and the outgoing lines from the inverter drive.

4. The inverter bypass safety switch ofclaim 1 wherein the shape of the cams, the placement of the cams within the sections and in relation to the other cams, the placement of exterior interconnections of the stationary contacts and the attachment of exterior wires are all selected to provide three discreet switching patterns, namely:

a DRIVE pattern, wherein electrical power is routed through the inverter bypass safety switch to the inverter drive, from the inverter drive back to the inverter bypass safety switch and then to an application;

a LINE pattern, wherein electrical power is routed from an incoming power source through the inverter bypass safety switch and directly to the application; and

an OFF pattern, wherein electrical power is disconnected from both the inverter bypass safety switch and the application.

5. The inverter bypass safety switch ofclaim 1 wherein the shape of the cams, the placement of the cams within the sections and in relation to the other cams, the placement of exterior interconnections of the stationary contacts and the attachment of exterior wires are all selected to provide two discreet switching patterns, namely:

a DRIVE pattern, wherein electrical power is routed through the inverter bypass safety switch to the inverter drive, from the inverter drive back to the inverter bypass safety switch and then to an application; and

a LINE pattern, wherein electrical power is routed from an incoming power source through the inverter bypass safety switch and directly to the application.

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