US2858500A - Arrangement for control of electromagnetic switches - Google Patents

Description

F. KESSELRING Filed March 17, 1954 IN VEN TOR. Fe/ 7': Kane: E/N

I CI-rlii Oct. 28, 1958 ARRANGEMENT FOR CONTROL OF ELECTROMAGNETIC SWITCHES BY W 9 7 m ATM//Vfi United States Pater fiice Patented Oct. 28, 1958 ARRANGEMENT FQR CONTROL OF ELECTRO- MAGNETIC SWITCHES Fritz Kesselring, Zollikon Zurich, Switzerland, assignor to FKG Fritz Kesselring Geratebau A. 6., Bachtohel- Weinfelden, Thurgau, Switzerland, a corporation of Switzerland Application March 17, 1954, Serial No. 416,843 Claims priority, application Switzerland April 2, 1953 3 Claims. (Cl. 32148) My invention relates to synchronous switching and more particularly to a novel electromagnetic rectifier in which separate electromagnetic means are provided for operating the armature thereof to its closed and opened position.

In the operation of electromagnetic rectifiers, the contacts of the electromagnet must, in a sixty cycle alternating current system, engage and disengage the contacts one hundred twenty times a second making engagement at the beginning of a half cycle and opening the contacts at the end of the same half cycle.

The interval of both engagement and disengagement should preferably be in the instant when the current is passing through which is measurable in fractions of a millisecond. To achieve this requires considerable acceleration and deceleration of the armature and has therefore created serious problems of contact bounce both on engagement of the contacts and on engagement of its back stop after disengagement.

Heretofore attempts have been made to achieve this high speed operation of the contacts by effecting engagement through electromagnetic means and disengagement by spring operation. In order to reduce bounce as much as possible, it has been proposed to bring the armature close to the engaging contacts just prior to energization of the electromagnet for effecting engagement, but this has not proved practical because of difficulties in preventing the armature from over-swinging.

I have discovered that by providing two independently operable electromagnetic systems, one for effecting closing of the contacts and hereinafter called the closing magnetic system, and the second magnetic system for effecting the opening of the contact and hereinafter called the opening system, and by normally spring biasing the contacts to a neutral position intermediate both the engaged and full circuit open position, I can substantially reduce the effect of bounce.

Accordingly, an object of my invention is to provide a novel synchronous switching means in which both opening and closing magnetic forces are provided for operating the armature.

A further object of my invention is to provide a novel electromagnetic rectifier in which the armature is normally biased to a position intermediate its full closed and opened position.

Still a further object of my invention is to provide a novel electromagnetic rectifier having a closing electromagnetic circuit and an opening electromagnetic circuit, the circuits for which are controlled from a saturable core reactor.

Figure 1 is a circuit diagram of one form of my invention.

Figure 2 is a circuit diagram of a second form of my invention.

Figure 3 is a top view of the mechanical construction of the electromagnetic rectifier.

Figure 4 is a side view of Figure 3.

Referring to Figure 2 which is a preferred embodiment, a source of alternating current comprising the primary winding 2 of transformer 1 is connected to an electromagnetic rectifier in which the output in the form of direct currents are supplied to a load 22.

The secondary windings 3, 3', 3" of transformer 1 are respectively connected to the reactor windings 6 of the reactors 4, 4' and 4". Inasmuch as the circuit arrangements for each phase in windings 3, 3 and 3 are identical, only one of these phases is shown with the essential circuit diagram. The winding 6 of reactor 4 is shown connected to the main closing winding 14 of the electromagnetic switch 7. The output of the transformer winding 3 is also connected to the closing winding 15 which in turn is connected to the electron device, in this case a rectifier 17 and thence to the load 22.

The electromagnetic witch 7 further comprises an armature 8 spring biased by the springs 9 to its intermediate neutral position, the ends of the springs 9 being connected to an insulating support schematically shown at 10 and 11.

An opening winding is shown at 16 for providing an opening electromagnetic system when the winding 16 is energized. The winding is connected through the rectifier 19 provided with a by-pass resistor 21 and over conductor 2% to the secondary winding 3 at P At the opposite terminal, the opening winding 16 is connected to the terminal P and thence to the load 22.

The operation of this circuit will now be apparent. Assuming that the positive half Wave is to be rectified as determined by the connection of the rectifier unit 17, the transformer winding 3 then has a positive voltage at the bottom of the winding 3 and its upper terminal negative. During this cycle, current flows from the output of transformer 3 through the closing winding 15 and rectifier 17 to the load 22. Energization of the electromagnetic system controlled by the winding 15 will operate the armature 8 against the bias of spring 9 to effect closing of the contacts 12 and 13. This condition obtains at the beginning or make interval of the cycle when the current rate of change in the reactor 6 is so small that substantially all of the voltage appears across the winding 6 and accordingly substantially no current flows in the winding 14 at the beginning of the cycle.

At this time, the positive voltage appears at the top of the reactor and negative at the bottom of reactor coil 6. However, at the end of the make step, as the current in this cycle rises in value and the core 4 becomes saturated, the voltage across the winding 6 is reduced to substantially 0 and now the main current flows through the winding 14 and over the contacts 12, 13 and armature S to the load 22. This operation which is not novel here is described in greater detail in co-pending application Serial No. 257,398, filed November 20, 1951, now Patent No. 2,756,380.

It will be noted that the winding 14 is of few turns compared to the winding 15 and of much larger diameter so as to permit the flow of a substantial part of the load current through the winding 14, thus achieving a contact pressure of the armature 8 against the contacts 12 and 13 which increases in pressure as the amplitude of the current increases during the cycle and is therefore proportional to the amplitude of the current at any instant.

The rectified phase thus carries current from the alternating current source to the load 22. As this cycle now reaches its end, the current of this phase decreases towards 0. When the current has reached a predetermined low value in this cycle, the core 5 of the commutating reactor again unsaturates. Again substantially all of the voltage of the phase appears across the Winding 6 but in the opposite direction of the previously described make step, that is the bottom of the winding 6 is positive and the top is negative.

This corresponds to a transformer voltage which is also in the opposite direction, that is, winding 3 is positive at the top and negative at the bottom.

This voltage on winding 6 also appears in the winding connected in series with the rectifier 17 and in the winding 16 in series with the rectifier 19. However, because of the reversal in the voltage, rectifier 17 wiil block the flow of current while at the same time the rectifier 19 which had blocked the previous flow of current now becomes a good conductor and therefore current flows to the winding 16.

In other words, the reversal in voltage which appears between P and P permits current flow through the coil 16 and rectifier 1'9 and blocks the flow of current through the winding 15 due to the rectifier 17.

Blocking of any current through the winding 15 now permits the spring 9 to effect disengagement of the armature 8. The current flowing through the winding 16 now energizes its opening magnetic circuit to achieve opening of the armature 8 at a greater acceleration than could be achieved by the spring 9 within the break step.

After the contact has opened, the full reverse voltage of the rectifier still appears between the point P and P This increased reverse voltage through the coil 16 increases and holds the contacts open so long as this reverse voltage exists.

The separation of the armature 8 from the fixed contacts 12 and 13 increases with the rate of change of voltage during the second half cycle so that the space between the armature 8 and the contacts 12 and 13 is a direct function of the voltage and prevents a voltage break down in the gap.

As will be described hereinafter, the armature 8 is provided with aback stop but it may be preferable to so construct this that the armature will not be moved fully to its back stop position to thus further insure against rebounce.

As the second half of the cycle now passes its peak value and approaches the end of the full cycle to 0 and the system is approaching the next make part of the second cycle, the magnetization of the winding 16 decreases until it loses all of its magnetization and the cycle described above is repeated.

As a result of this operation, there are alternate actions between the closing winding 15 and the opening winding 16, the winding 15 operating during the rectified half of the cycle to close the contacts whenever the voltage across it is positive and the winding 16 to hold the contacts open whenever the voltage across it is negative.

In Figure 1 I have shown an alternate system in which the connections of winding 15 are the same as that described in connection with Figure 2. However, the circuit for winding 16 is not provided with the circuit including the rectifier 19 and conductor 20. In this case, the winding 16 is connected directly across the fixed contacts 12 and 13.

Accordingly, when the contacts are opened and the break step is over, the full reverse voltage appears across these contacts. This reverse voltage causes a current flow through the winding 16. Winding 16 is accordingly energized and operates the armature 8 away from the fixed contacts 12 and 13 in proportion in the voltage appearing across the winding 16 during the second half cycle.

Figures 3 and 4 show embodiments of such switches in top and side views. In these figures, the stationary contacts and 31 are bridged by the armature 32 including the current bridge 33 (see Figure 3), upon energization of the short circuit winding 34. A leaf spring 35 screwed to the insulating pieces 36 and 37 is attached to the armature 32 for biasing it to its neutral position. 33 and 39 are yokes of a magnet separated by an insulation 40. They end above in the pole shoes 41, 41a and 42, 42a, which are fastened to the stationary contacts 30 and 31 by means of the rivets 43 and 44. 45 is the main current winding, 46, the closing winding, 47 and 43 the connections. The opening magnetic system is disposed above the armature 32 and consists of the U-shaped yoke 49 with the pole shoes 50 and 51, the opening Winding 52 and the auxiliary winding 53. 54 is a rectifier, a permanent magnet with which a constart: pre-excitation of the closing magnetic systems 38, 39 could be produced. It will be seen that with the excitement of the windings 45 and 46, the armature 32 is moved downward, whereby the stationary contacts 30 and 31 are connected by way of the current bridge 33.

When the opening winding 52 is unexcited, the distance between the current bridge 33 and the stationary contacts 31) and 31 should preferably be at most 0.1 mm., so that at a slow mean opening speed of, for instance, only thirty cm./sec., one may nevertheless open in times which are considerably smaller than one millisecond. If now the coil 52 is connected to the blocking voltage, as described in connection with Figures 1 and 2, the armature 32 is pulled upward against the action of the spring 35, whereby the distance between the current bridge 33 and the stationary contacts 30, 31 is increased in proportion to the rise of the blocking voltage. In general, it will be desirable not to let the armature 32 hit the pole shoes 51), 51 even at the highest blocking voltage, so that a bouncing back and additional wear are safely avoided.

Rather, the armature glides hack and forth in the rhythm of the blocking voltage; by suitable selection of the spring characteristic and, if required, an eddy current damping in the short circuit winding 34, an overswing in the opening direction will be avoided. That is, the cur rent induced in short-circuit Winding 34 will be in a direction to maintain the flux in the armature in the same direction to which it has been previously flowing. This will affect the magnetic fluxes created by the opening and closing magnetic structures in such a .way that armature travel from one magnetic structure to the other will be slightly inhibited; hence, overswing of the armature will be avoided since the armature velocity is decreased. if desired, the ends of the auxi iary winding 53 may be connected to a rectifier 54 in such a manner that the damping of this winding is effective only during the opening process. With this type connection, only opening coil 52 would be effective to energize motion of armature 32 since the auxiliary winding 53 will not pass energizing current in the blocking direction of rectifier 54. If the damping of the short circuit winding 34 is sutficient, the auxiliary winding 53 may also serve to bias the opening system, in particular when the spring 35 is so set that the current bridge 33 rests upon the stationary contacts 3%}, 31 under the sole effect of the spring.

If the opening time is in the region of higher voltages, as in the case in rectifiers with voltage regulation by means of delaying the closing point of the contact, this may be taken into account in either of two ways. Either the contact distance in the rest condition is chosen somewhat larger, or the rectifier 19 (see Figure 1) is bridged by a suitably chosen resistance 21 in such a way that prior to the opening such a strong excitation of the coil 16 is produced that the current bridge always adjusts itself to a sufficiently large distance.

it will now be obvious to those skilled in the art that it may be desirable to have the opening force begin at a predetermined interval prior to the O passage of current.

The energization of the electromagnet 16 in the manner described above achieves this result.

To avoid an overswinging of the armature in the closing and opening direction as much as possible, it may be found suitable to employ damping means, for example, by producing eddy currents in the armature or in a Winding of the armature, or that a damping winding be disposed in the closing magnetic system. By means of a rectifier, care may be taken that the damping is efiective, for instance, only in the opening direction, i. e., when the magnetic flux decreases.

Generally, it has been advantageous to adjust the distance between stationary and movable contacts in the rest position to values below 0.1 mm. for instance, to 0.05 mm. and to apply a value of the opening force so that the speed of impact upon the stationary contact at most amounts to 30 cm. This Will very largely eliminate bouncing and wear and a minimum of noise will be produced. Under certain conditions, it may be of advantage that the armature, for example by means of a spring, first rest on the stationary contacts and then is brought to its rest position by bias magnetization of the opening magnetic system. In this case it is possible to produce the closing by weakening of the opening bias magnetization.

To increase the life of the arrangement, the opening magnetic system is preferably so designed that its pole shoes are not touched by the armature even at the highest blocking voltage which occurs. This measure also aids considerably in the reduction of noise.

While I have described the preferred forms of my invention, it will be obvious to those skilled in the art that my invention may take many other forms and I therefore wish to be limited only by the claims as herein set forth.

I claim:

1. In an electromagnetic switch, a contact, an opening magnetic circuit, a closing magnetic circuit, an armature operated by said closing magnetic circuit when the latter is energized to engage said contact and operated by said opening magnetic circuit when the latter is energized to disengage said contact, circuit connections including a single saturable core reactor connected in series with said contact for energizing said closing magnetic circuit during one half cycle of an alternating current source and for energizing said opening magnetic circuit during the alternate half cycle of an alternating current source means for normally biasing said armature to a neutral position at a predetermined distance of the order of 0.1 millimeters from said contact, said opening magnetic circuit when energized operating said armature against said spring bias to a distance from said contact which is proportional to the amplitude of the voltage of the alternate half cycle, said single saturable core reactor becoming effective to initiate energization of said opening magnetic circuit at least by the beginning of the alternate half cycle of-the alternating current source.

2. In an electromagnetic switch, a contact, an opening magnetic circuit, a closing magnetic circuit, an armature operated by said closing magnetic circuit when the latter is energized to engage said contact and operated by said opening magnetic circuit when the latter is energized to disengage said contact, circuit connections including a single saturable core reactor connected in series with said contact for energizing said closing magnetic circuit during one half cycle of an alternating current source and for energizing said opening magnetic circuit during the alternate half cycle of an alternating current source, means for normally biasing said armature to a neutral position at a predetermined distance of the order of 0.1 millimeters from said contact, said opening magnetic circuit when energized operating said armature against said spring bias to a distance from said contact which is proportional to the amplitude of the voltage of the alternate half cycle, said single saturable core reactor becoming effective to initiate energization of said opening magnetic circuit during the decay toward zero of said one half closing cycle.

3. In an electromagnetic switch, a contact, an opening magnetic circuit, a closing magnetic circuit, an armature operated by said closing magnetic circuit when the latter is energized to engage said contact and operated by said opening magnetic circuit when the latter is energized to disengage said contact, circuit connections including a single saturable core reactor connected in series with said contact for energizing said closing magnetic circuit during one half cycle of an alternating current source and for energizing said opening magnetic circuit during the alternate half cycle of an alternating current source, means for normally biasing said armature to a neutral position at a predetermined distance from said contact, said opening magnetic circuit when energized operating said armature against said spring bias to a distance from said contact which is proportional to the amplitude of the voltage of the alternate half cycle, said single saturable core reactor becoming effective to initiate energization of said opening magnetic circuit at least by the beginning of the alternate half cycle of the alternating current source.

References Cited in the file of this patent UNITED STATES PATENTS 1,265,354 Mershon May 7, 1918 2,619,628 Kesselring Nov. 25, 1952 2,691,128 Wagener Oct. 5, 1954 2,740,934 Kesselring Apr. 3, 1956 2,756,380 Diebold July 24, 1956 2,770,766 Kesselring Nov. 13, 1956 FOREIGN PATENTS 875,968 France Oct. 9, 1942 113,439 Sweden Mar. 13, 1945 870,447 Germany Mar. 12, 1953

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