US2947838A

US2947838A - Snap action reversing switch for load tap changing transformer

Info

Publication number: US2947838A
Application number: US610539A
Authority: US
Inventors: Benon F Ureda
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1956-09-18
Filing date: 1956-09-18
Publication date: 1960-08-02
Anticipated expiration: 1977-08-02

Description

B. F. UREDA REVERSING Aug, 2, 1960 SNAP ACTION SWITCH FOR LOAD TAP CHANGING TRANSFGRMER 3 Sheets-Sheet l Filed Sept. 18, 1956 a m .wal fd /A nm M f m w B. F. UREDA REVERS Aug. 2, 1960 SNAP ACTION ING SWITCH FOR LOAD TAP CHANGING TRANSFORMER 3 Sheets-Sheet 2 Filed Sept. 18, 1956 B. F. UREDA REVERS Aug. 2, 1960 SNAP ACTION ING SWITCH FOR LOAD TAP CHANGING TRANSFORMER 3 Sheets-Sheet 3 Filed Sept. 18, 1956 gig 8 United States Patent O SNAP ACTION REVERSING SWITCH FOR LOAD TAP CHANGING TRANSFORMER Benon F. Ureda, Calabasas, Calif., assiguor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Sept. 18, 1956, Ser. No. 610,539

2 Claims. (Cl. 200-92) This invention relates in general to step type voltage regulating apparatus and in particular to an improved reversing switch Iassembly for such apparatus.

Step type voltage regulating apparatus are used extensively in electrical distribution systems where it is desired to maintain the voltage of a circuit between predetermined limits. Most apparatus of this type comprise an exciting winding connected across the circuit to be regulated, and atapped series winding connected in series with the circuit through a load tap changing mechanism. The load tap changing mechanism includes a tap changing switch having a plurality of stationary contacts connected respectively to the taps on the series winding, and movable contacts which cooperate with the stationary contacts to insert diiierent portions of the series windings in the circuit to be regulated.

In order to employ the same series winding and tap changing mechanism to eiiect a change in voltage both above and below normal, the load tap changing mechanism usually includes a reversing switch assembly which is operable to reverse the connections of the tapped winding of the regulator with respect to the circuit to be regulated. Most reversing switches include a pair of contacts connected, respectively, to opposite ends of the series winding and a third contact member connected to a supply terminal of the regulator. In a first position of the reversing switch one end of the series winding is connected to the supply terminal, and in a second position of the switch the other end of the series winding is connected to the terminal. The reversing switch thus resembles a single pole double throw switch.

In order to operate the reversing switch from one position to the other when it is not carrying current, a camrning arrangement is employed between the loadftap changing mechanism and the reversing switch assembly which causes the reversing switch to move when the movable contacts of the tap changing switch are at the zero tap position of the regulator.

The switching action of the reversing switch usually starts prior to the switching of the movable contacts of the tap changer from the zero tap position to insure that the reversing switch is suitably positioned prior to completion of the tap changing operation to either side of the zero tap.

In known prior art apparatus of the above type no provision is made to positively position the reversing switch in the event that a tap changing operation from the zero tap to an adjacent tap is started but not completed. For example, it often happens that in regulating the voltage of a load circuit the tap changer is on the zero tap position when the control circuit for the regulator calls for a tap change. The motor which operates lthe tap changing mechanism is then energized and a tap changing operation is started which, through a camming arrangement, starts to move the reversing switch. If at some time prior to the time that the movable contacts of motor is deenergized by the control circuit because con- ICC ditions in the load circuit have corrected themselves, the movable member of the reversing switch is leftv floating somewhere between the two stationary contacts of the reversing switch. It is thus possible for arcing to occur between the movable member and the stationary contacts of the reversing switch due to the fact that a charge is built up on the series winding under these conditions. This arcing results in radio and television interference in addition to shortening the life of the reversing switch cont-acts.

In accordance with the present invention the above mentioned disadvantages of prior art regulators are eliminated .by providing a reversing switch assembly in which the movable member of the switch is caused to return to its initial position in the event the tap changing operation from the zero tap is not completed or caused to be positioned midway between stationary contacts.

Itl is therefore an object of the present invention to provide lan improved reversing switch assembly for a step type voltage regulator.

A further object :of the present invention is to provide in a step type voltage regulator, a reversing switch assembly which returns the switch to its initial position in the event the switching operation is started but not completed or to a position where arcing between the movable members and the stationary member is avoided.

Objects and advantages other than those mentioned above will be apparent from the following description when read in connection with the drawings in which:

Fig. l is a diagrammatic illustration of a step type voltage regulating apparatus;

Fig. 2 is a front View in elevation of the tap changing mechanism for the step type regulator shown in Fig. 1;

Fig. 3 is a side view in elevation of the tap changing mechanism shown in Fig. l;

Fig. 4 is an isometric view of the improved reversing switch assembly shown in Figs. 2 and 3; and

Figs. 5-9 illustrate the oper-ation of the reversing switch lassembly shown in Fig. 4.

Referring to the drawing and particularly to Fig. l the step regulator illustrated therein comprises generally an exciting winding 11, a series winding 12 which is provided with a plurality of taps 13, a load tap changing mechanism 14 for connecting various portions of winding 12 in the circuit 15, 4and a reversing switch assembly 16 which operates to connect either end 17 or end 18 of winding 12 to supply terminal 19 of the regulator.

As shown in Fig. 1 exciting winding 11 is adapted to be connected across a circuit to be regulated and series winding 12 is adapted to be connected in series with the circuit to be regulated, the windings being inductively related by means of a magnetic core 20. As is well known, the voltage of the circuit 15 is varied in steps by operation of the load tap changing mechanism 14, the reversing switch 'assembly 16 of mechanism 14, being employed to eifect variations in voltage either below or above the voltage supplied to exciting winding 11. While the illustrated embodiment shows the series winding 12 provided with taps, it should be understood that other suitable arrangements of the windings and taps known in the art may be employed with the improved reversing switch assembly 16, Fig. 1 being merely illustrative of one type of regulating apparatus in which the present invention may be advantageously employed.

As shown in Figs. 2 and 3 the load tap changing mechanism 14 comprises generally a dial type tap changing switch 22 and a quick break mechanism 23. Tap changing switch 22 comprises a plurality of circumferentially spaced stationary contacts 24 and a pair of movable contacts 25a and 25b. The stationary contacts 24 are mounted on an insulating panel 26 and connected respec-- tively to taps 13 of series winding 12, except for the zero tapV contact`24 which isconnected to terminal 19 of the regulator.

The movable contacts 25 of the tap changing switch 22 are Xed to a shaft 2S and are circumferentially spaced apart.V so that by rotation of shaft 28 both contacts 25a and 2517 maybe. disposed on one stationary contact 24,. or in a bridging relationship with respect to. adjacentl stationary contacts 24. Movable contacts '25. are connectedV to the circuit through a midtap reactor 27.

Y Shaft 28 and movable contacts 25 are moved in steps with' a snap action by means of quick break mechanism 23. QuickA break mechanism 23 comprises generally a stationary indexV plate 29, a drive sprocket 30, an actuating disk 31, a detent means 32, and a latch device 33. which isiixedly attached to the actuating disk 31 and engageable with a notch 34 in the stationary index plate 29; A crank like member 35 links the actuating disk 31 to the shaft 28 of tap changing switch 22.

Detent means 32 as shown comprises a pair of spring assemblies 36a and 36b which are disposed between the drive sprocket 3d and the actuating disk 31. Each spring assembly 36 is connected between the drive sprocket 30 and the actuating `diskl by means of pin members 37. Quick break mechanism 23 is driven by motor 38 through a chain 39, motor 3S being energized by means of a suitable condition responsive control circuit (not shown) associated with the circuit 15 connected to the load terminals of the regulator. l The reversing switch assembly 16 comprises generally the reversing switch 40 and a rocker assembly 41 to actuate switch 40 in accordance with the movement of the tap changing switch 22. Reversing switch 4% as shown comprises three arcuately spaced

fixed contacts

42, 43 and 44 and a pair of movable contacts 45.

Contacts

42 and 44 are connected respectively to opposite ends of series winding 12 while Contact 43 is connected to source termina-l 19 of the regulator. Movable contacts 45 of switch 40 operate in one position to connect end 17 of winding 12 to the supply terminal 19 of. the regulator, and in the other position to connect. end 18 to the supply terminal 19.

MovableV contacts 45 are xedly attached to a shaft 46 which is suitably positioned in insulating panel 26 on which

stationary contacts

42, 43 and 44 are suitably mounted. Contacts 45 of the reversing switch 40 are pivoted from one position to the other by means of rocker assembly 41. Assembly 41 shown in detail in Fig. 4 includes a rst drive member 50 which is pivotally mounted on the vertical mounting panel 51 of the quick break mechanismY 23, and a second member 52 which is attached to member 50 by cross arms 53. Drive member 50 is provided with a recessed portion 54 for receiving a drive pin 55 attached to the drive sprocket 30.. Member 52 is; provided with. a slot `56 for receiving a connecting pin 57 extending from, the movable portionV of the reversing switch 40. Pin l55 is disposed on the sprocket 31 so thatY

members

50 and 52 are forced toA pivot abouta shaft v58 at the start of the tap changing operation which isto move theY movable contacts 25 of the tap changer `22 from the. zero tap position 24.

. The reversing switch assembly 16 further includes means for causing the movable contacts 45 to` be positively positioned, either on the stationary contacts or midway between stationary contacts 42-44. This means as shown comprises a pair of spring assemblies 60. The spring assemblies 60 are disposed on opposite sidesof the axis of shaft 58 about which the drive members 50 `andSZ pivot. Each assembly 60 comprises a spring guide tube 61 fixed at one end 62 to the drive member 50, and provided with an elongated slot 63 for receiving a pin element 64 secured to the mounting frame 51 of the quick break mechanism 23. A compression spring 65 is disposed in the guide tube 61 and. acts between the drive member. 50 and the pin element 64 to urge the drive member 50 to a positive position when 4 a. the drive pin 55 attached to sprocket member 30 is not in engagement with the side portion ofthe recess 54. The pins 64 are on a line removed from the center of the rocker assembly 41, and the springs 65 cooperate with the drive member 50 to form a toggle mechanism that tends to maintain the rocker assembly in one of the stable positions shown in Figs. 5, 7 and 9.

Assuming that the movable contacts 25 of the tap changing switch 22V are on the zero tap position 24 as shown in Figs. 1, 2 and 3, and that the rocking assembly 41 is in the-position shown in Figs. 2, 3 and 5, the operation of the regulating apparatus from the Zero tap position is substantially as follows.

Motor ,315 is suitably energizedpby the` control circuit (not shown) in response to a'conditi'on of circuit 15. Motor 38 is energized presumably so that sprocket member 30 rotates counter-clockwise as shown in Fig. 2. Rotation of sprocket 30 causes pin member 55 to move assembly 41 from the position shown in Fig. 5- to that shown in Fig. 6. Rotation of sprocket 30 also causes spring assemblies 36a of detent means 32 to become biased.`V Energy from motor 38 is stored in biasing means 32 becausev one endV of assembly 36a is iiXed to actuating disk 31 whichis kept from moving by latch device 33, while the other end of assembly 36a is fixed to the sprocket 30: Latch device 33 is arranged so that it does not release until the assembly 4'1 is substantially on the center position illustrated in Fig. 7.

1f motor 3S remains energized so that the tap change from the zero tap 24 is completed, assembly 41 is moved to the'po'sition shown in Fig. 9. The movable contacts 45J of reversing switch 4i) are operated to the position shown iniFig. 4 by means of pin 57.

However, if motor 38 is deenergized prior to the time assembly 41 reaches an overcenter position which corresponds to the tripping time for `latch device 33, the detent means 32` returns the sprocket 30 towards its initial starting position, allowing the spring assemblies 6G to move assembly 41 back to its original starting position.

y It willf thus be seen that the movable contacts 45 of the reversingswitch 40 are always in one of three positive positions and cannot oat between the stationary contacts 42', 44 in the event a .tap changing operation is started but notcompleted.

While only oneV embodiment of the present invention has been illustrated and described it will be apparent to those skilled in the art that modication may be made therein without departing from the spirit of the inventionor from lthe, scope of the appended claims.

- What is claimed is:

1. A. reversing switch assembly for a load tapl changing transformer comprising a reversing switch mounted on a shaft. and having two xed contactv positions, a rocker assembly pivotally mounted on a frame of a tap changer and engageable at a point removed from its pivot. byY a. relatively slow moving motor driven element of said tap changer to pivot said rocker assembly between three stable positions, two of which correspond to the fixed contact positions of said reversing switch and the third position corresponding to a position intermediate said iixed contact positions, said switch Vshaft engaged with said rocker assembly for transmitting the-pivotal movement of said rocker assembly to said reversing switch, andV toggle means cooperating with opposite sides of saidrocker assembly and supported on said frame at two-points located on opposite sides of said pivotal mount and on a line removed from said pivotal mount to urge said rocker assembly to one of said three positions to positively position said reversing switch independently of said motor. Y Y

2'. A reversngswitch assembly for a quick break load tapchanging; ,transformerl comprising a reversing switch mounted on a shaft and having two positionsV each corresponding` to one of' two operating positions of a tap changer, a rocker assembly pivotally mounted on a frame of said tap changer, said rocker assembly being engageable at a point removed from its pivot by a pin carried by a relatively slow moving motor driven element of said tap changer to pivot said rocker assembly, preparatory to the quick break operation of the tap changing switch from a zero position into one of said operating positions, between three operating positions, two of which correspond to said positions of said reversing switch and the third position corresponding to a position intermediate said operating positions, said switch shaft engaged with said rocker assembly for transmitting the pivotal movement of said rocker assembly to said switch, and a pair of spring means cooperating with opposite sides of said rocker assembly and supported on said frame at two points located on opposite sides of said pivotal mount and on a line removed from said pivotal mount to urge said rocker assembly to one of said three positions to positively position said reversing switch independently of the operation of said motor.

References Cited in the file of this patent UNITED STATES PATENTS