US3246100A

US3246100A - Load transfer switch mechanism

Info

Publication number: US3246100A
Application number: US242444A
Authority: US
Inventors: Raymond G Russell
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-12-05
Filing date: 1962-12-05
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12

Description

April 1966 R. G. RUSSELL 3,246,100

LOAD TRANSFER SWITCH MECHANISM Filed Dec. 5, 1962 2 Sheets-Sheet l I 2 INVENTOR.

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ATTOR N EYS April 6 R. G. RUSSELL 3,246,100

LOAD TRANSFER SWITCH MECHANISM Filed Dec. 5, 1962 2 Sheets-Sheet 2 BY 25/ MVENTOR. FIG.4 7f% ATTO RN EYS United States Patent Oflice 3,246,100 Patented Apr. 12, 1966 3,246,100 LOAD TRANSFER SWITCH MECHANESM Raymond G. Russell, Scituate, Mass. (211 Northern Ave., Boston, Mass.) Filed Dec. 5, 1962, Ser. No. 242,444 11 Claims. (Cl. 20092) The present invention relates to a transfer switch mechanism and more particularly to a mechanism for automatically transferring an electrical load from a preferred power source to an emergency power source when the preferred power source fails. 1

An object of the present invention is to provide an improved transfer switch for A.C. or DC. systems which functions to transfer an electrical load from a preferred power source to an emergency source when normal voltage fails or is significantly reduced below accepted limits and then to restore the load to its original preferred source automatically when the preferred power source is restored to a desired level.

Another object of the present invention is to provide a transfer switch mechanism of the type described which is rugged in design and is reliable in operation.

It is also an object of the present invention to provide a design which is capable of embodying transfer mechanisms having high in-rush and thermal capacities and in which arcing may be minimized. A further object of the present invention is to provide a mechanism which is adapted to either motor or manual operation.

Switching time in transfer switches of the type described is critical in many applications where continuity of power is essential. The transfer of power from a preferred to an emergency source must be substantially instantaneous, not only to minimize power interruption but also to minimize damage to the contacts in that the mechanism due to arcing which occurs in slow transfer mechanisms. It is therefore also an object of this invention to provide high speed transfer mechanism wherein switching may be elfected between a high power preferred source and an emergency high power source in less than 3 cycles in a 60 cycle system.

A further object of this invention is to provide a transfer mechanism wherein closed contacts are positively locked closed to prevent inadvertent opening due to strong stray magnetic fields which occasionally have a tendency to open such contacts.

A further object of the invention is to provide a transfer mechanism wherein the preferred and emergency power source terminals are arranged in tandem in such a manner as to prevent inadvertent short circuiting from one power source to the other, and wherein the contact mechanism cannot lock inadvertently into a neutral position.

A further object of the present invent-ion is to provide a transfer mechanism wherein substantial kinetic actuating energy is created in the form of spring loading just prior to the actuation of the switching mechanism whereby the actual switch-ing action takes place at a speed more rapid than heretofore possible.

The present invention attains these and other objects by providing an improved switching mechanism of the type described wherein the switching mechanisms for transferring an electrical load from a preferred power supply to an emergency power supply or vice versa is arranged in tandem pairs, with each tandem mechanically interlocked to prevent the switching mechanisms in the tandem pair from assuming the same closed or open positions. Also provided is a structure wherein mechanically interlocked tandem pairs of switching mechanisms are actuated by a power source symmetrical with the tandem pairs. Such arrangement includes a gear motor functioning through a crank and interlocked link arrangement to actuate the switching mechanisms of the tandem pairs in phase opposition. The crank and link arrangement is designed in conjunction with the switchinng mechanism to preload the switching mechanism through a spring link means whereby spring elements within each of the switch mechanism functions when actuated, to cooperatively move the contact arms with a positive force. This cooperative movement is in part attained through the mechanical interlock of the contact arms in the tandem pairs.

These objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of a preferred embodiment of the present invention illustrating a 3-pole switch,

FIGS. 2 and 3 represent schematic elevations of the switch shown in FIG. 1 respectively in two different positions of operation; and

FIG. 4 is a schematic view of the circuitry associated with the mechanism.

While the present invention will be described in conjunction with a 3-p0le switch, it should be understood thta the principles herein disclosed are applicable to single or other multiple pole switches. The construction is also susceptible to various modifications, adaptations and other uses. Moreover, it may be actuated manually or automatically as described. In its preferred form the present invention is useful for transferring a load from a normal or preferred powered source to an emergency source automatically, on the occasion of a partial or complete failure of the preferred power source and an automatic return to the preferred power source to its desired level.

Referring to FIG. 1 there is illustrated a transfer switch mechanism which may be mounted on a suitable switchboard 12, having associated circuitry, described later in connection with FIG. 4, for operating the transfer switch mechanism of the present invention. In the embodiment illustrated three circuit breakers or

switching mechanisms

13, 14 and 15, each having terminals 13A, 14A and 15A for connection to normal or preferred powered sources are secured to the switch-board 12. Circuit breakers or

switch mechanism

16, 17 and 18 each having terminals 16A, 17A and 13A for connections to an emergency power source are also secured to the switchboard 12. The individual circuit breakers in the first group of switch mechanisms are arranged in parallel or tandem with individual circuit breakers in the second group of switch mechanisms. Thus

circuit breakers

13 and 16; 14 and 17; and 15 and 18; are arranged in parallel or tandem pairs.

These circuit breakers are preferably constructed with an over-center spring actuated toggle action best illustrated schematically in FIGS. 2 and 3. The construction of these circuit breakers, which will be described specifically in connection with the circuit breaker 14 which applies to each of the circuit breaker mechanisms, is one which is presently commercially available. These circuit breakers each are provided with contact terminals 14A adapted to receive a power supply load. This terminal 14A is electrically connected to a fixed contact 24. A contact arm 20 is pivotally supported at one end 21 to allow the moveable contact 22 to pivot into and out of engagement with the fixed contact 24. The contact arm 20 is actuated through a toggle mechanism 28. This toggle mechanism comprises

links

26 and 27 pivotally interengaged at adjacent ends 29. One end of the toggle mechanism 28 is pivotally interengaged with the contact arm 20 intermediate its ends at 30, and the other end of the toggle mechanism is pivotally secured to a fixed member 31. In actual commercial embodiments the member 31 may comprise a frame pivotally secured for limited movement to a base support such as base support 35. The toggle mechanism is actuated by a lever 34 pivotally supported on a fixed support 35 at one end 36, with its other end interengaged with the interconnected ends 29 of the

links

26 and 27 by the spring link 39. In actual commercial embodiments a pair of springs are used one on either side of the toggle and are each connected to lever 34 by a connecting pin.

These circuit breakers have a bi-stable condition with the two positions illustrated at the right ends respectively of FIGS. 2 and 3. The condition illustrated at the right end of FIG. 2 is a normal condition while that illustrated in FIG. 3 is an alternate or emergency condition. When the lever 34 moves in a clockwise direction from the position illustrated in FIG. 2, to that illustrated in FIG. 3, the contact arm 20 will remain in a normally open position until the lever 34 reaches an over center position. This over center position is a position wherein the lever 34 has passed pivot point 31. Until approximately that point of movement of the lever arm 34, spring link 39 expands and preloads the toggle mechanism. When the lever 34 reaches its over center position the spring link causes the toggle to actuate at a rapid rate throwing the contact arm from a position illustrated in FIG. 2 to that illustrated in FIG. 3.

While the circuit breaker mechanism 14 has been described in schematic terms, it should be understood that elaborations of these constructions are contemplated and in fact are available in commercially manufactured structures at this time.

A more detailed arrangement of an actual commercially avialable circuit mechanism is illustrated in FIG. 1. As illustrated, such additional features as a De-ion arc quencher 44 may be used. This De-ion arc quencher consists of parallel steel plates partially surrounding the contacts and enclosed by a fibre wrapper or ceramic support. This quencher is used to draw the are from the contacts into the plates as the contacts .are open or closed. These plates function to disperse the arcs and reduce heat, thereby rapidly removing ions from the arc and improving the build-up-time of the dielectric between the contacts. In addition, constructions are available in which double toggles and spring links are used for more rapid actuation. However, in each of the preferred embodiments it is important to use a circuit breaker embodying the over center spring actuated mechanism of the type herein described.

The preferred power supply is normally connected to the output or

load terminals

50, 51 and 52. Output or load terminal 50 is connected by

bus bars

53 and 54 respectively to

circuit breakers

13 and 16. Load terminal 51 is connected respecively by

bus bars

55 and 57 to

circuit breakers

14 and 17, while load terminal 52 is connected by

bus bars

58 and 59 respectively to

circuit breakers

15 and 18.

Each of the circuit breakers in each of the respective groups are tied to the other circuit breakers in their group by suitable means for synchronous operation. Such means may comprise a cross tie bar 66), 61, which may be suitably mounted by brackets to the contact arms 20. Thus each contact arm 20 in the first group of circuit breakers .13, 14 and 15 are actuated simultaneously by cross tie bar 60, and

circuit breakers

16, 17 and 18 in the second group are simultaneously actuated by bar 61.

The first group of

circuit breakers

13, 14 and 15 are mechanically interlocked to the second

group circuit breakers

16, 17 and 18 so that they work in opposition. That is, when the first group of

circuit breakers

13, 14 and 15 are opened thereby disconnecting the load from the preferred power source, the second group of

circuit breakers

16, 17 and 18 are closing, and thereby connecting the load to the secondary or emergency power supply. These two groups of circuit breakers are mechanically interlocked by at least one tie rod 70. The tie rod 7'0 is pivotally interengaged at its

ends

71 and 72 with

rigid projections

74 and 75 fixed respectively to the arms 20 of a circuit breaker in each group. In a preferred embodiment of a three-pole transfer mechanism, mechanical interlocks or tie rods 70 are provided on each of the outer pair of circuit breakers in the group of three. It has been found that this symmetrical arrangement of the interlocking tie rods provides an improved and more balanced arrangement.

The first and second groups of circuit breakers are automatically operated by means of a motor mechanism generally illustrated at 80. This mechanism has a shaft 31 rotatable in one direction which shaft carries a crank 82. The end of crank 82 has the connecting

rods

83 and 84 pivotably secured to it. The other endof the connecting rod 83 is pivotably connected to lever 3.4 of the circuit breaker 14, While the other end of the connecting rod 84 is pivotably connected at 87 to the lever 34 of the circuit breaker 17. As illustrated in this preferred embodiment the connecting rods in a double throw three pole system are symmetrical with respect to the rods 70. They also function in part as a mechanical interlock.

The motor preferably comprises a unidirectional high torque motor having a single speed reduction, means which may comprise a worm and

gear arrangement

86, 87, with the worm coupled directly to the crank shaft of the motor and the gear to the crank arm. The motor also has a pair of

limit switches

90, 91 incorporated into its housing to permit incremental successive rotations of 1-80" with the motor power controlled by these switches.

Referring now to the mechanical arrangement of FIGS. 2 and 3, the motor mechanism 80 is actuated incrementally to cause the crankarm 82 to move 180 on each actuation. Thus, the crank arm 82 moves from a position wherein its end 82a (FIG. 2) will move from one stable position shown in FIG. 2 to a position'180" out of the phase with that position shown in FIG. 2. When actuated the motor will cause the

links

83 and 84 to pivot the levers 34 on the opposite circuit breakers. Because the circuit breakers of each group are tied together, all levers 34 in each group will move simultaneously. ,Because of the spring links 39, the crank 82 will move over an angle of 90 during which time the toggle mechanism 28 will remain stationary. However, during this time, the spring links 39 preload the toggle mechanism so that when the crank is rotated to just beyond 90, the levers 34 assume an over center position and the kinetic energy in the spring links 39 cause a rapid change over of the contact arms 20 from one stable position such as shown in FIG. 2 to the other stable position shown in FIG. 3. By proper selection of the spring links 39 and other parameters, the switch-oversgenerated by the kinetic energy of the springs will cause the contact arms to close more rapidly than possible under the influence of the motor 80. In the switched position the toggle mechanismpositively locks the closed contact such as illustrated in FIG. 3 at the right with a knee locking action.

One limit switch 91 controls the normal position and the other switch 90 controls the emergencyposition. The switches are operatively mounted on and controlled by the motor shaft. To transfer from a normal load condition as illustrated in FIG. 4 to an emergency position the motor 80 is actuated to rotate its shaft 180. This occurs when there is a failure or partial failure of power from the normal source. When this occurs power in the

normal power lines

93, 94, drops. Thisdeenergizes coil 95 of the normal power control relay A causing contacts 96 to open and 97 to close. Emergency power control relay G is also closed if the emergency power source is high enough above a selected minimum level, as for example 90%, to maintain coil 98 energized. Under these conditions energy will pass through lines 99, contacts 98, .line 100, contact 97 and line 101 to terminals 3 of the motor. Since limit switch 91 is normally closed the motor will actuate through when the motor itself opens switch 91 and closes switch 90.

When the power in the normal circuit returns, coil95 is reenergized causing contacts 96 to close and contacts 97 to open. When contacts 97 open the motor cannot be energized through motor contact 3 regardless of the condition of switch 91. However switch 90 which is now closed permits power to pass to the motor through motor contact 1, line 105, contact 96 and 93 on reestablishment of normal power. This causes the motor 80 to rotate a second 180 until switch 90 is opened and switch 91 is closed.

As previously indicated the main switch contacts are connected to the operating mechanism through a spring loaded device that preloads through the first 90 degrees of travel and then allows the main contacts to transfer at high speed ahead of the motor operated mechanism. If by'chance, the motor is jogged to a position just beyond 90 degrees, sufiicient to transfer the circuit breaker but not suificient to operate the limit switch, and if the power from the source to which the circuit breaker has just transferred fails, the mechanism would assume a neutral position electrically and could not be transferred to the other position until the limit switch contacts have transferred. To prevent this an electrical interlock circuit is provided with auxiliary contacts 110, 111 connected to the bars 60, 61 of the circuit breakers with switch 110 normally open and switch 111 normally closed to indicate the position of the circuit breaker main contacts. With the limit switch contacts in such a neutral position after the circuit breakers have transferred, in order to retransfer the first position, the motor mechanism is energized through the control relay (A) and through the electrical interlock contacts 110 and 111 to complete the previous cycle and then allow for transfer in the other direction if power is available from that other source.

What is claimed is:

1. In a transfer mechanism for transferring a load between first and second power supplies,

first and second switch mechanisms respectively operable to connect and disconnect a load to and from said first and second supplies,

said switch mechanisms each having a toggle mecha nism connected to a contact arm and adapted to move said arm between an open position and a closed position,

and also having a lever with a spring link between said lever and toggle mechanism for snapping said arm from one of said positions to the other,

said lever and spring arranged to permit movement of said lever to a dead center position before said toggle mechanism is actuated,

means rigidly interlocking said arms for simultaneous movement thereof, whereby only one of said arms may be closed at one time, and,

means operatively interengaging said levers for simultaneous opposed movement of said contact arms whereby when one switch is opened the other is closed said means operatively interengaging said levers comprising a crank arm with a pair of connecting links pivotably connected thereto with one of said links connected to one switch mechanism and the other link connected to the other switch mechanism, said crank arm constructed and arranged to rotate over an arc of 180 to cause each of said switch mechanism levers to pass through said dead center positions to actuate said toggle mechanisms.

2. A transfer switch mechanism for transferring a load from a first to a second power supply comprising,

first and second switch mechanisms each having bistable conditions with first and second spring means for preloading said mechanisms without changing said conditions and for coacting to change said conditions on continued loading beyond selected positions,

said first switch mechanism having a first contact arm and said second switch mechanism having a second contact arm,

6 a tie rod pivotably interconnected with said first and second contact arms for normally maintaining said arms in asymmetrical bistable conditions, and, means for synchronously actuating said first and second 5 spring means to said selected positions at a first rate of speed which is slower than the rate at which said spring means changes said conditions beyond said selected positions. 3. A transfer switch mechanism for transferring a load 10 from a first to a second power supply comprising,

a rigid tie rod pivotably interconnected with said first and second switch mechanisms for normally maintaining said mechanisms in asymmetrical bistable conditions, means for synchronously actuating said first and second spring means to said selected positions at a first rate of speed which is slower than the rate at which said spring means changes said conditions beyond said selected positions,

said means for synchronously actuating said first and second spring means comprising a unidirectional motor with limit switch means adapted to deenergize said motor on rotation of its shaft over a preselected arc of rotation and after a time interval during which the bistable conditions of said switch mechanisms may be changed.

4. A switch mechanism as set forth in claim 2 wherein three pairs of switch mechanisms are provided and said pairs are symmetrically arranged with respect to said actuating means.

5. A transfer switch mechanism for transferring a load from a first to a second power supply comprising,

first and second switch mechanisms each comprising a toggle means connected to a contact arm, said contact arms each having bistable conditions with first and second spring means for preloading said first and second mechanisms without changing said arm conditions with said spring means coacting to change said conditions on continued loading beyond selected positions,

a tie rod having its ends pivotally engaging respectively said first and second switch mechanism arms whereby said arms are maintained in asymmetrical bistable conditions, unidirectional motor means for synchronously activating said first and second spring means to said selected positions including a crank operated by said motor means and engaging a pair of longitudinally aligned connecting rods at adjacent ends with the other ends of said rods respectively engaging different switch mechanisms at a pivotable lever of each mechanism,

said lever of each mechanism being connected to said toggle means of each mechanism by one of said spring means,

said motor means constructed and arranged to simultaneously move said first and second spring means through said tie rods to an over center position of said first and second switch mechanisms at a first rate of speed with said spring means adapted to move said switch mechanism when in said over center position at a second rate of speed in excess of said first from one bistable to the other condition, said connecting rods and said tie rod providing a knee-locking action to lock said arms in their bistable conditions.

6. A mechanism as set forth in claim 5 wherein three aligned pairs of switch mechanisms are provided.

7. A mechanism as set forth in claim 6 wherein said 75 connecting rods are connected to the center pair of said switch mechanisms and said tie rod is connected to one end pair of said switch mechanisms.

8. A mechanism as set -forth in claim 7 wherein a second tie-rod is connected at its end to the other end pair of said switchmechanisms whereby said rods are symmetrically and parallelly arranged in respect to said connecting rods.

9. A transfer switchmechanism in accordance with claim and further comprising an electrical circuit with limit-switch means for deenergizing'said motor means on-rotation of its shaft over a preselected arc of rotation after a time interval during which the bistable conditions of said switchmechanism are changed.

10. A transfer switch mechanism in accordance with claim 9 wherein said electrical circuit comprises means for sensing a partial failure of said first power supply and for simultaneously actuating said motor meansto transfer'from a first bistable condition to a second bistable condition and for sensing reestablishment of said first power supply to actuate said motor means to return said switch mechanisms to said one bistable condition. 11. A transfer switchmechanism in accordance with claim 10 wherein said electrical circuit further-comprises 'means 'for preventing said mechanism from assuming an electrically neutral position.

References Cited by the Examiner UNITED STATES PATENTS 1,250,674 12/1917 Scott ZOO- 50 2,807,684 9/1957 Ayers 0767 2,849,581 8/ 1958 Bingenheimer 200-67 2,904,649 9/1959 Ranson 200 ROBERT K. SCHAEFER, Acting Primary Examiner. BERNARD A. GILHEANY, Examiner.

Claims

1. IN A TRANSFER MECHANISM FOR TRANSFERRING A LOAD BEBWEEN FIRST AND SECOND POWER SUPPLIES, FIRST AND SECOND SWITCH MECHANISMS RESPECTIVELY OPERABLE TO CONNECT AND DISCONNECT A LOAD TO AND FROM SAID FIRST AND SECOND SUPPLIES, SAID SWITCH MECHANISMS EACH HAVING A TOGGLE MECHANISM CONNECTED TO A CONTACT ARM AND ADAPTED TO MOVE SAID ARM BETWEEN AN OPEN POSITION AND A CLOSED POSITION, AND ALSO HAVING A LEVER WITH A SPRING LINK BETWEEN SAID LEVER AND TOGGLE MECHANISM FOR SNAPPING SAID ARM FROM ONE OF SAID POSITIONS TO THE OTHER, SAID LEVER AND SPRING ARRANGED TO PERMIT MOVEMENT OF SAID LEVER TO A DEAD CENTER POSITION BEFORE SAID TOGGLE MECHANISM IS ACTUATED, MEANS RIGIDLY INTERLOCKING SAID ARMS FOR SIMULTANEOUS MOVEMENT THEREOF, WHEREBY ONLY ONE OF SAID ARMS MAY BE CLOSED AT ONE TIME, AND, MEANS OPERATIVELY INTERENGAGING SAID LEVERS FOR SIMULTANEOUS OPPOSED MOVEMENT OF SAID CONTACT ARMS WHEREBY WHEN ONE SWITCH IS OPENED THE OTHER IS CLOSED SAID MEANS OPERATIVELY INTERENGAGING SAID LEVERS COMPRISING A CRANK ARM WITH A PAIR OF CONNECTING LINKS PIVOTABLY CONNECTED THERETO WITH ONE OF SAID LINKS CONNECTED TO ONE SWITCH MECHANISM AND THE OTHER LINK CONNECTED TO THE OTHER SWITCH MECHANISM, SAID CRANK ARM CONSTRUCTED AND ARRANGED TO ROTATE OVER AN ARC OF 180* TO CAUSE EACH OF SAID SWITCH MECHANISM LEVERS TO PASS THROUGH SAID DEAD CENTER POSITIONS TO ACTUATE SAID TOGGLE MECHANISMS.