US2680164A - Contact speed control in springdriven step type switches - Google Patents

Description

June 1, 1954 T. c. LENNOX 2,680,164

CONTACT SPEED CONTROL IN SPRING-DRIVEN STEP TYPE SWITCHES Filed March 19, 1952 it 42 4a Inventor: Thom as O. Lenncx,

y u A HIS flute? figy June 1, 1954 T. c. LENNOX 2,680,164 CONTACT SPEED CONTROL IN SPRING-DRIVEN STEP TYPE SWITCHES Filed March 19, 1952 2 Sheets-Sheet 2 Inventor; Thomas OL'ennox,

Hus fittorney.

Patented June 1, 1954 CONTACT SPEED CONTROL IN SPRING- DRIVEN STEP TYPE SWITCHES Thomas C. Lennox, Pittsfield, Mass, assignor to General Electric Company, a corporation of Application March 19, 1952,

6 Claims.

This invention relates to spring-driven electrical switching mechanisms and more particularly to contact speed control nisms of the step type.

Step type switching mechanisms are widely used in connection with step voltage regulators in which a voltage is adjusted by stepping a contact member from one voltage tap to another.

classes. The first of these classes is the type in which the step contacts are moved by a spring drive, with the spring itself being energized by a motor drive. The second broad class is that in which the step contacts are actuated by a direct motor drive.

The speed with which the movable contacts of a step type switching mechanism are moved with respect to the stationary contacts of the mechanism is an important factor with respect to the the contact speed obtainable using direct highspeed direct motor drives for step type contacts requires a starting, stopping, and positioning "system for the motor which is expensive and frequently a source of trouble.

Accordingly, it is an object of my invention to increasing the life expectancy of step type electrical contacts of the spring-driven type.

It is a further object of my invention to provide a new and improved device for obtaining optimum contact speed with spring-driven step type electrical contacts.

In accordance with these objectives, my invention provides in combination with spring driven step-type contacts means for modifying the motion of the movable contacts with respect to the stationary contacts in such manner as to .obtain optimum relative speed of the stationary Serial No. 277,351

2 and movable contacts from the standpoint of life expectancy of the contacts.

The features of this invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and use, together with further objects and advantages thereof, may best be understood by referenc to the following description taken in connection with the accompanying drawing in which Fig. l is a perspective view of a step type voltage regulator apparatus incorporating one embodiment of the contact speed control arrangement of my invention in accordance with which a paddlewheel speed control device is used; Fig. 2 is a view of a modified type of speed control device which is connected view of a modified embodiment of my invention in which the speed control is obtained by use of a piston acting in a dashpot member.

Referring now to the drawing, there is shown therein a pair of power lines I and 2 which may be connected either to the source or load side of an electrical system. Power line i is connected to one end of a shunt winding 3 of a step type voltage regulator in a well known manner. Power line 2 is connected to the mid-tap of a switching reactor 1, through which it is connected to the series winding 4 of the voltage regulator, as will be explained more fully herein- The line I is connected to line I at the point where line I is connected to shunt winding If lines l and 2 are connected to the electrical source, then lines circles described by conducting rings 8 and 9, and by the conducting segments 6.

In order to maintain electrical contact beto the view shown in the drawing, with a pair of contact brushes H and ii which are conductively connected together. Contact H maintains contact with radially inner conducting ring 8 while contact 12 maintains contact with the conducting segments 3 which are connected to the taps 5 of the series winding l. Thus, the upper end of the switching reactor 1 is connected through radially inner conducting ring 8, and contacts ll and I2 to the conducting segments 8 and thence to the taps of series winding 4.

In order to provide electrical contact between the lower end of the switching reactor E, with respect to the view shown in the drawing, and the contact segments 6, the left-hand edge of the contact arm H) is provided with a pair or con tact members l3 and id which are conductively connected together and respectively maintain contact with radially outer conducting ring 3 and the contact segments 6. Thus, the lower end of the switching reactor 1, is connected through conducting ring 9 and contacts l3 and i i to conducting segments 6 which are in turn connected to the respective taps oi the series winding i. The contacts H and i2 carried by contact arm it are insulated from contacts i3 and Hi.

When the position of the contact arm it is such that contact arm If) and contacts Ii, i2, i3 and M are in contact with only a single one of the conducting segments 6 then the respective contacts ll, l2, l3 and M are all at the same electrical potential since they are short circuited by the particular conducting segment s with which the contact arm i0 is in alignment. In this case, the current divides between the two halves of the switching reactor I, the two halves on the winding being in parallel electrical relation with each other. However, if the position on the contact arm i0 is such that it bridges a pair of adjacent conducting segments 6, as shown in the view in the drawing, then each end of the switching reactor 1 is connected across a different tap of the series winding 4. When this occurs, the switching reactor acts as an autotransformer and the voltage derived is half way between the voltages of the adjacent taps to which the respective opposite ends of switching reactor 1 are connected.

The switching arm i0 is driven by a shaft 15 which is actuated by a spring-driven Geneva gear mechanism which will now be described.

A motor it drives a pinion l? which engages a gear l8. Gear H3 is fixed to a shaft H3 at the opposite end of which is positioned a pinion ill. Pinion 26 engages a gear 2! which is loosely mounted on and rotates freely about shaft 22. A pin 23 is integrally attached to gear 2| and rotates therewith. A lug member 24 is integrally attached to shaft 22 and is in the path of rotation of pin 23. A crank 25 is rigidly attached to one end of shaft 22. The radially outer portion of crank 25 is pivotally attached to a pair of spiral spring members 26 and 21 which are each respectively fastened at their opposite ends to fixed pivot points.

When gear 2| is caused to rotate, pin 23 engages lug 24 and causes the rotation of shaft 212. Rotation of shaft 22 causes an elongation of spring members 26 and 2'5. When crank mem ber 25 moves slightly past the dead center position, which is about 180 displaced from the posi tion of crank 25 as shown in the drawing, the action of springs 26 and 21 causes the crank 25 and shaft 22 to move rapidly back to the position shown in the drawing thereby discharging the energy stored in the springs during the period in which they were being elongated. At the other end of shaft 22 segment 28 having projecting ears i9 is rigidly mounted on and turns with shaft 22. A Geneva gear driver 36 is loosely mounted on shaft 22 and is in engagement with Geneva gear 32 mounted on shai't it. During the portion of the cycle of rotation of shaft 22 when shaft 22 and crank 25 are being moved back from overcenter position by the springs 26 and .21, the segment 28 engages the Geneva gear driver 3B in driving relation and causes pin member iii of the Geneva gear driver 30 to drop into the slot between a pair of adjacent teeth of Geneva gear 32 to thereby advance the Geneva gear 32 by one tooth pitch with a rapid motion. Motion of Geneva gear 32 actuates shaft it] so as to move contact arm it from one conducting segment 6 to another.

As mentioned hereinbefore, it has been found that the speed with which the contact arm I0 is moved by the action of the spring drive mechanism just described is such that the life of contacts carried by contact arm it, such as contacts H, l2, l3 and i l, and also the life of the stationary conducting segments 6, is sometimes reduced considerably below the life expectancy which could be obtained if the contact speed were not so high as that produced by the rapid action of the overcenter springs ".25 and 2'? which drive the Geneva gearing mechanism.

One theory which explains the reduced contact life with the contact speeds normally produced by spring driven mechanisms is described hereinafter. It will be understood, of course, that while this theory provides a theoretical explanation of the improved performance obtained in accordance with my invention, that there may also be other explanations of the changes in contact liie characteristics observed due to the operation of my invention.

The erosion of the moving and stationary contacts is known to be related to the value of the current, to the voltage which appears across the open contacts, to the duration of the arc and to the resistance of the are. There may also be some increase in the erosion due to bouncing of the contacts when closing.

The first two items just mentioned are determined by the design of the regulator windings and circuit, but the other three, namely, duration of the arc, resistance of the arc, and bouncing oi the contacts, may be varied by varying the contact speed in opening or closing. When contacts carrying alternating current are opened under oil or other insulating liquid, the current usually stops at a current nerd-that is, at a point when the alternating current wave is passing through zero. lhe result is that if the actual interruption occurs at the first current zero following the physical opening of the contacts, little more can be done to shorten the duration of the arc. On the other hand, the resistance of the arc is afiected by the length of the are so that if the contact speed is made very high so as to draw the are out to considerable length during the period before the first current zero the resistance may be unnecessarily increased. As an increase in resistance will result in increase of energy dissipated in the arc and possibly an increased burning of the contacts, such increased arc resistance should be avoided.

Considering these factors, I have determined that there can be an optimum condition where serted between the paddle wheel and the speed of the opening of the contacts is sufficient to cause a current interruption at the first current zero but yet not high enough to unduly lengthen the are physically during the interval between the mechanical opening of the contacts and the point at which the first current zero is reached. In other words, too low a contact opensistance before the first current zero is reached. The optimum s eed consequently is between these two extremes.

In accordance with my invention, I provide a means for controlling the speed of the moving contacts, and particularly the speed with which the contacts are opened, by use of an energy absorbing device which will now be described.

In the embodiment of my invention shown in Fig. 1, I provide an impeller 33 of the paddle wheel type which is driven by shaft l through the engagement of gear 34 which is rigidly attached to the outer end of shaft l5 and pinion 35 which is mounted on the same shaft with impeller 33. The relative diameters of gear 34 on shaft l5 and pinion 35 are such that the angular velocity of pinion 35 is substantially greater than that of a shaft [5. The impeller 33, as well as all of the other operating elements shown in Fig. l, is immersed in oil or some other insulating liquid. Hence, a considerable amount of energy is required to cause the rotation of the paddle wheel in the liquid. Thus, a large part of the energy of the springs 26 and 27 is absorbed by the impeller 33 and, as a result, the speed of rotation of the shaft is reduced below what the speed would be if an energy absorbing device were not used.

When the springs 26 and 2! discharge, moving the shaft i5 through the required angle, the speed of the shaft 1 5 instead of rising to a maximum which is limited only by the inertia of the parts and incidental friction, as would be the case without the use of the energy absorbing device of my invention, will instead rise only to such speed absorbing substantially the whole torque imparted to the system by the springs.

The best or optimum speed of opening of the contacts may be determined by tests on specific cases, and then a mechanism designed to move the contacts at the required speed. In applying an impeller or paddle wheel to a spring-driven switch for the purpose of obtaining the required speed, a favorable factor is that the torque resulting from the movement of such an impeller in the insulating liquid varies approximately as the square of the speed, thus making it much easier to obtain a desired speed than would be the case if the torque-speed relation were purely linear. Having determined the relation of the torque to speed for a given size of the impeller or paddle wheel, appropriate gearing may be inthe spring drive such that substantially the full torque imparted by the springs will be balanced by the reverse torque of the paddle wheel at the required speed. If, then, due allowance is made for the friction and inertia of the switch contacts, the design is fixed.

- The reduction in speed obtained using the impeller device in accordance with my invention has the further advantage that it reduces the tendency of the contacts to bounce when closing.

This tendency to bounce decreases rapidly as the speed of the contacts is decreased and, consequently, a decrease in speed to obtain the optimum speed condition at opening reduces the tendency of the moving contact to bounce when closing. The burning of the contacts due to bouncing is primarily due to the drawing of short arcs while the contacts are open during the bouncing. Each such are burns or erodes the contacts to some degree. In experiments which I have made I have found that in contact systems suitable for step-voltage regulators bouncing of the contacts on closing is substantially completely eliminated when the speed of the contacts is such as to provide the optimum opening speed as hereinbefore described.

A further feature of my invention as shown in the embodiment of Fig. 2 is the provision of an impeller or paddle wheel device havin a iiy wheel or inertia characteristic to aid in the closing of the contacts. It is known that satisfactory action of a spring driven switch for a step-voltage regulator usually involves inertia forces. That is, the closing of the contacts occurs without any tendency to stop at the position where the contacts first engage because of the inertia of the rapidly moving parts. When, however, the speed of the contacts is substantially reduced in order to obtain optimum arcing conditions, this inertia effect is substantially reduced, and may be less than required for satisfactory closing of the contacts. The energy stored in the moving contact system varies as the square of the speed of the contact motion. Thus, if the speed is reduced to one-third, for example, the stored energy is reduced to one-ninth. In order to avoid diiiiculty of this nature, the inertia forces may be restored by addingweight to the rim of the impeller or paddle wheel which is geared so as to operate at higher speeds than the contacts themselves.

There is shown in Fig. 2 my preferred arrangement for providing optimum speed for opening spring-driven electrical contacts and, at the same time, providing sufficient inertia to the contact closing system to insure that the contact as will result in the impeller 33 properly closes without sticking. In the embodiment of Fig. 2 I have provided a flywheel effect for the impeller or paddle wheel by adding ciroumferentially distributed weight to the radially outer portion of the impeller. In the particular structure shown in Fig. 2, I have provided the impeller 48 with a disk member 49 having most of its weight concentrated in its radially outer or rim portion. However, it will be understood that the flywheel effect may be obtained in other ways such as, for example, concentrating weight in the radially outer portions of the paddle members 36 of the impeller 33 of Fig. l. The amount of weight that must be added to the impeller rim to restore the necessary inertia forces which pre- Thus, if the rim of disk 69 moves five times as fast as the contacts themselves, only as much weight need be added to the impeller rim as to the contacts to store the same energy.

In the arrangement of Fig. 2, which is the preferred embodiment of my invention, the impeller is connected into the gearing system in a somewhat different manner than is shown in Fig. 1. In the arrangement of Fig. 2, shaft 29 is driven by a motor in the same manner as shown in Fig. 1 and pinion 20 is attached to shaft 59 and drives gear M which is loosely mounted on shaft 22. Pin 23 is attached to gear 2! and rotates therewith. When pin 23 engages lug 24 which is rigidly attached to shaft 22, shaft 22 is caused to rotate and tensions spring 26 due to the rotation of crank 25 at the end of shaft 22. The arrangement thus far described is the same as that of Fig. 1. In accordance with the modified arrangement, the impeller 48 is directly driven by the shaft 22 through the gears 51 and 52 rather than being driven by the shaft Hi to which the Geneva gear 32 is attached, as in the arrangement of Fig. 1. Gear 5! is rigidly attached to shaft 22 and rotates therewith. Gear 5| drives pinion 52, which is rigidly mounted on the same shaft as impeller 48 causing the rotation of impeller l8. With this arrangement, the power imparted by the spring 28 to the shaft 22 divides and the major portion is transmitted directly through gears 5i and 52 to the impeller 48 and only that part of the power which is needed to operate switch arm I is transmitted through the Geneva gearing mechanism. Thus, the wear on the Geneva gear is reduced as com pared to the arrangement of Fig. 1. Moreover, as the impeller 48 is always connected through gears and 52 to shaft 22 no undue acceleration of shaft 22 occurs and hence there is no danger that Geneva driving pin 3! will enter the slot of Geneva gear 32 at excessive speed.

With the arrangement shown in Fig. 2 it will be observed that the impeller 48 is put into motion during the winding or extending of the spring by the motor. However, this occurs at relatively low speed and hence does not place any appreciable additional load on the motor.

There is shown in Fig. 3 a modified embodi-- ment of my invention in accordance with which a piston and dash-pot arrangement is substituted in place of the paddle wheel impeller 33 of Fig. 1 and serves the same function as the paddle wheel.

As seen in Fig. 3, a piston rod 31 is pivotally attached at one end to crank member which is in turn 'igidly attached to shaft 22. The piston rod 31 is attached at its other end to a piston 38 which moves in a cylinder 39 in such manner as to expel oil or some other liquid from a suitable orifice 10 in the cylinder 39. The cylinder 39 is immersed in an insulating liquid and the liquid is drawn into the cylinder through orifice t9 on the upstroke of the piston, and expelled through orifice so on the downstroke of the piston. Thus, the motion of the piston in the cylinder provides a dashpot action whic absorbs some of the energy transmitted from the springs 26 and 21 to the shaft i5 in a manner similar to that previously described in connection with impeller 28.

A further feature of the construction shown in Fig. l and which may also be used with the embodiment of Fig. 2 is an arrangement for re versing the polarity connections of the series winding 3 when the switch arm l0 passes through its neutral position. A reversing switch 4% is provided in series with line 2. Reversing switch i! is movable into engagement with either contact 12 or 43, these respective contacts being connected to opposite ends of the series winding i. A pin member A l is attached to Geneva gear 32 at a position such that as Geneva gear 32 passes through the neutral position corresponding to the position at which switch 41 should be moved from contact :32 to contact 43 or vice versa, the pin 44 engages the slot in Geneva segment 8 l5 and causes a rapid'rnotion of reversing shaft 46 which is connected to Geneva segment 45 through link 41. Shaft :26 is connected to switch ll in such manner that motion of shaft 46 causes switch member ti to move from contact 62 to contact at or vice versa.

From the foregoing, it can be seen that I have provided in accordance with invention a new and improved arrangement for controlling the speed of step type contacts of the spring-driven type by providing an arrangement for absorbing a part of the energy supplied to the spring-driven contacts. In providing such an energy absorbing device for speed control of the contacts, I have substantially increased the life expectancy of such contacts, and studies which I have made indicate that the life expectancy of contacts whose speed is controlled in accordance with my invention is increased as much as 500% over the life expectancy of the prior art springdriven step type contacts.

While there have been shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such chan es modifications as {all within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent or the United States is:

1. In an electrical switching mechanism of the step type in which a movable electrical contact is moved with a rapid motion out of engagement with a first fixed electrical contact and into engagement with a second electrical contact, a spring driven operating means for moving said movable electrical contact, said operating means comprising an overcenter spring, and an energy absorbing device operatively connected to said operating means to retard the speed with which said movable contact moves out of engagement with said first fixed contact, said energy absorbing device comprising a paddle wheel rotatable in a liquid, said paddle wheel having a substantial portion of its mass circumferentially distributed about its radially outer periphery to provide a iiywheel effect to prevent sticking between said movable contact and said second fixed contact upon initial engagement of said movable contact and said second fixed contact.

2. A sprlng-actuated electrical switching device comprising, in combination, a motor, afirst shait, a crank member, said crank member being rigidly mounted on said first shaft, a spring, one end of said spring being pivotally connected to the radially outer end of said crank, said spring being tensioned by rotation of said crank, said spring moving said first shaft with a rapid motion when said spring is moved to an overcenter position by rotation of said crank, a second shaft, gear means connecting said first shaft in driving relation to said second shaft, an electrical contact carried by said second shaft, a fixed electrical contact engageable with said contact carried by said second shaft, engagement of said contacts normally completing an electrical circuit, second shaft being driven by said first shaft to disengage said contacts when said first shaft is moved by said spring, and an energy absorbing means mounted for rotation in a liquid and directly driven by said first shaft to decrease the speed of rotation of said first shaft when said first shaft is driven by said spring.

3. In an electrical switching mechanism of the p type in which a movable electrical contact is moved with a rapid motion out of engagement with a fixed electrical contact, a spring driven operating means for moving said movable elec" trical contact, said operating means comprising an overcenter spring, and an energy absorbing device operatively connected to said operating means to decrease the speed with which said movable contact moves out of engagement with said fixed contact, said energy absorbing device comprising a piston movable in a liquid-containing dashpot.

4. An electrical switching device of the step type comprising a plurality of spaced apart fixed electrical contact members lying on the circum-- ference of a circle, an arm mounted for rotation about an axis which passes through the center of said circle upon which said contact members lie, said arm carrying a contact member engageable with at least one of said fixed contact members in substantially all positions of said arm, said arm being rotatable in both a clockwise and a counterclockwise direction, means for rotating said arm comprising a motor, a shaft driven by said motor, a crank member attached to said shaft, a spring member pivotally connected to a radially outer portion of said crank member, said spring member being tensionedby rotation of said crank, said shaft being operatively connected to said contact-carrying arm, rotation of said spring member past overcenter position causing said spring member to discharge and move said shaft with a rapid motion, the contact carried by said arm being moved out of engagement with a first fixed contact and into engagement with a second fixed contact during said rapid motion of said shaft, and an energy absorbing device driven by said shaft to reduce the speed with which said contact carried by said rotatable arm moves out of engagement with said first fixed contact.

5. An electrical switching device of the step type comprising a plurality of spaced apart fixed electrical contact members lying on the circumference of a circle, an arm mounted for rotation about an axis Which passes through the center of said circle upon which said contact members lie, said arm carrying a contact member engageable with at least one of said fixed contact members in substantially all positions of said arm, said arm being rotatable in both a clockwise and a counterclockwise direction, means for rotating said arm comprising a motor, a shaft driven by said motor, a crank member attached to said shaft, a spring member pivotally connected to a radially outer portion of said crank member, said spring member being tensioned by rotation of said crank, said shaft being operatively connected to said contact-carrying arm, rotation of said spring member past overcenter position causing said spring member to discharge and move said shaft with a rapid motion, the contact carried by said arm being moved out of engagement with a first fixed contact and into engagement with a second fixed contact during said rapid motion of said shaft, and a liquid-immersed energy absorbing device rotatably driven by said shaft to reduce the speed with which said contact carried by said rotatable arm moves out of engagement with said fixed contact.

6. An electrical switching device of the step type comprising a plurality of spaced apart fixed electrical contact members lying on the circumference of a circle, an arm mounted for rotation about an axis which passes through the center of said circle upon which said contact members lie, said arm carrying a contact member engageable with at least one of said fixed contact members in substantially all positions of said arm, said arm being rotatable in both a clockwise and a counterclockwise direction, means for rotating said arm comprising a motor, a shaft driven by said motor, a crank member attached to said shaft, a spring member pivotally connected to a radially outer portion of said crank member, said spring member being tensioned by rotation of said crank, said shaft being operatively connected to said contact-carrying arm, rotation of said spring member past overcenter position causing said spring member to discharge and move said shaft with a rapid motion, the contact carried by said arm being moved out of engagement with a first fixed contact and into engagement with a second fixed contact during said rapid motion of said shaft, and a liquid-immersed energy absorbing device rotatably driven by said shaft to reduce the speed with which said contact carried by said rotatable arm moves out of engagement with said first fixed contact, said energy absorbing device comprising a paddle wheel, said paddle wheel having a substantial portion of its mass circumferentially distributed about its radially outer periphery to provide a flywheel effect to prevent sticking between said movable contact and said second fixed contact upon initial engagement of said movable contact and said second fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS

Images