US3293496A

US3293496A - Switching device for interruption of alternating current

Info

Publication number: US3293496A
Application number: US256702A
Authority: US
Inventors: Induni Giovanni
Original assignee: Bbc Brown Boveri & Cie
Current assignee: BBC Brown Boveri AG Germany
Priority date: 1962-02-14
Filing date: 1963-02-06
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20
Also published as: CH390347A; DE1160923B; JPS4718498B1

Description

G. lNDUNl Dec 20, 1966 SWITCHING DEVICE FOR INTERRUPTION OF ALTERNATING CURRENT 2 Sheets-Sheet 1 Filed Feb. 6, 1965 21 2 k ItJ INVENTOR GLovcmnL Indurm BY 191W JW 29 [mm MIA/{5Y5 Dec. 20, 1966 Filed Feb. 6 1963 G. INDUNI SWITCHING DEVICE FOR INTERRUPTION OF ALTERNATING CURRENT 2 Sheets-Sheet 2 v my i yo

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INVENTOR GLovannL IncLunL United States Patent 3,293,496 SWITCHING DEVICE FOR INTERRUITIUN 0F ALTERNATING CURRENT Giovanni Induni, Baden, Switzerland, assignor to Alttiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Filed Feb. 6, 1963, Ser. No. 256,702 Claims priority, application Switzerland, Feb. 14, 1962, 1,774/ 62 Claims. (Cl. 31711) This invention relates to electric switches for use in interrupting currents of the alternating type. More particularly, the invention is concerned with an alternating current switching device of the type which utilizes a main switch which is actuated in an arbitrary manner at the desired time, this main switch serving to carry most all of the load current when the switch contacts are closed, and two subsidiary branch switching circuits connected in parallel with the contacts of the main switch. Each such branch switching circuit contains an electric valve and a branch interrupter connected in series, and the two electric valves are arranged antiparallel so as to have oppositely directed current-passing directions.

Switch devices of the above type have become known wherein the contacts of the main switch are opened simultaneously, or with a certain time lead in relation to the contacts of the two branch switches, so that as a result of the antiparallel connected electric valves lying in the branches, each time there always appears on one of the two branch interrupters a switch-off arc, which is not extinguished until during the next half wave. These devices have the disadvantage that the interrupters lying in the two branches must be constructed as heavy-duty switches or at least as a load switch.

It is an object of the present invention to provide a switch device with which, not only on the main switch but also on the branch interrupters, no load current interruption appears and thus practically no arc formation.

According to the invention it is proposed that at least one device is provided responsive to the branch currents, and at least two additional devices responsive to the recovery voltage appearing on the main switch; they are connected with the branch interrupters in such a way that opening of the switch contacts in each branch circuit takes place each time only within that current half wave for which the branch circuit in each case is blocked by its electric valve.

The foregoing as well as other objects and advantages inherent in the invention will become more apparent from the following detailed description of several representative embodiments thereof and from the accompanying drawings.

In these drawings:

FIG. 1 is a somewhat schematic view of one embodiment of the invention;

FIG. 2 is a curve plot of the current flowing through the switching device of FIG. 1 and which serves to explain its operation;

FIG. 3 is a schematic view similar to FIG. 1 but showing a modified embodiment wherein the devices responsive to the recovery voltage are connected individually in parallel;

FIG. 4 is also a schematic view of a further embodiment of the invention wherein the device responsive to current in the branch circuit lies in a common current path; and

FIG. 5 is a curve plot of the current flowing through the switching device of FIG. 4.

With reference now to FIG. 1, the main switch for interruting the load current is shown schematically at 1.

3,293,496 Patented Dec. 20, 1966 Connected in parallel with the contacts of switch 1 are two branch circuits A and B. Branch circuit A contains a circuit interrupter in the form of a branch switch 4 connected in series with an electric valve 2. Similarly, branch circuit B contains a branch switch 5 connected in series with an electric valve 3. It will be noted that the electric valves 2 and 3 are connected antiparallel, i.e. they are arranged so as to conduct current in opposite directions relative to each other in their respective branch circuits. The electrically responsive device for actuating the contacts of switch 4 is indicated schematically at 40, and a similar device for actuating the contacts of switch 5 is indicated schematically at 5a. In accordance with the invention, a current responsive tripping device 6 responsive to the current flow in branch circuit A is connected in series with electric valve 2 and branch switch 4, and this current responsive device 6 is cross-connected so as to exercise a control over the operation of the contact actuating device 5a in branch circuit B. Similarly, a current responsive tripping device 7 responsive to current flow in branch circuit B is connected in series with electric valve 3 and branch switch 5 and this current responsive device 7 is cross-connected so as to exercise a control over the operation of the contact actuating device in in branch circuit A. Two voltage responsive tripping devices 8 and 9 are conneced in series with each other and in parallel to the contacts of the main switch 1. Device 8 is connected to exercise a control over operation of the contact actuating device 5a and device 9 is similarly connected to exercise a control over operation of the contact actuating device 4a. The devices 8 and 9 are so connected as to respond to the recovery voltage appearing across the contacts of the main switch 1. The complete

branch switching device

4, 4a, 7 and 9 is shown only schematically as is also the switching device 5, 5a, 6 and 8. These structures are conventional and details can be found in German Patents 827,- 821 and 959,663, for example.

The operation of the switch device above described is as follows: Let it be assumed that in the operating state the main switch 1 and the branch switches 4, 5 are in switched-in position. That is to say their contacts are closed. If the contacts of main switch 1 are opened at any desired time, for example at the time t according in FIG. 2, at which the positive half wave of the alternating current i flows, then the load current flows on across the secondary branch A, since the electric valve 2 is conductive for this direction of current flow. The device 6 responding to its branch current now effects the opening of the contacts of branch switch 5, eg at the point t in FIG. 2. The time difference between 1 and t is conditioned by the switch-off lag of the device 6 in combination with the branch switch 5. The opening of the contacts of branch switch 5 here takes place practically without power and thus without arc formation as long as t takes place before the load current Zero passage time point t since during the positive current half wave the electric valve 3 blocks. Since the current half wave from time point t on changes its polarity, the secondary branch B however, is then opened as described and there is built up across the main switch 1 the recovery voltage, since the electric valve 2 blocks during the negative half wave. Thus the devices 8, 9 also receive voltage, e.g. at time point t, according to FIG. 2, so that the device 9 opens the contacts of branch switch 4, e.g., at time point t without power output. The time difference between t and t, is here likewise conditioned by the switch-ofi lag of the devices 9 and 4. The response of the device 8 here has no effect insofar as the branch switch 5, as already mentioned, had opened previously.

Insofar as the arbitrary opening point t according to FIG. 2 of the main switch comes to lie shortly before the current zero passage t as a result of the switch-off lag which can not be kept as small as desired, difiicnlties result insofar as the moment of opening t of the branch switch is displaced into the negative half wave, whereby the branch switch 5 would no longer open without power. In order to take care of this, it is proposed according to the invention, as a further improvement, that the

devices

6 and 7 responding to the branch currents are so constructed that they respond, in a manner familiar in itself, only to an increase of their branch current. Their work range is thereby limited only to the first quarter wave each time, in FIG. 2 for example to the range from the diagram zero point up to the peak, lying between t and 2 of the first current half wave, so that in this case at least one switch-oil lag of a quarter period i available. In this it has been assumed that the branch switch 5 is to open already before the point t In order, however, not to place any special requirements with relation to the fast working of the devices 6, '7 and of the branch switches 4 5 it is proposed as a further improvement to design the

devices

6, 7 and the branch switches 4, 5 so that their switch-off lag amounts to at least one period and at most to five quarter periods, with the possibiliy being utilized that, e.g., the device 6, a described above, responds indeed in the first quarter period, but the branch switch 5 opens only during the second positive half wave, namely during the one following the zero passage time point t of the load current as shown in FIG. 2. It can be seen that one can just as well select for the opening, e.g., of the branch switch 5 the range of the third, fourth, etc., positive current half wave, so that it is possible to increase at will the lower and upper limits for the admissible switch-off lag each time by one, two, etc., periods. Thus there is no need for any particularly

fastworking devices

6, 7 responding to the branch current or any rapidly operating branch switches 4, 5.

The

devices

6, 7 can, according to the invention, also be so designed that they respond, in a manner familiar in itself, only to a decrease of their branch current. Their working range is thereby limited only to the second quarter wave each time, in FIG. 2, for example to the range from the peak lying between t and 1 of the current half wave up to the current zero passage t For the currentless opening of the contacts of branch switch 5 within the next half wave following on the point from the same considerations as above, there results for the admissible switch-oft lag a lower limit of a threequarter period and as the upper limit, one period. It can be seen that for the opening, e.g., of the branch switch 5 it is also possible here to choose the area of the third, fourth, etc., positive current half wave, so that it is possible to increase at will the lower and upper limits for the admissible switch-ofl lag each time by one, two, etc. periods.

The devices 8 and 9 responding to the recovery voltage, with their coordinated branch switches 5 and 4, according to the invention are so tuned with respect to the switch-cit lag that the switch-off lag amounts at most to a. quarter period. Thereby it is assured that in the selected example according to FIG. 1, the contacts of branch switch 4 open after the response of the device 9 at the latest by the load current zero passage time point t according to FIG. 2. It is further provided according to the invention to undertake the opening of the branch switch 4 during the following negative current half wave. Thus there is available a switch-off lag of at least 1 period and at most 5 quarter periods. It can easily be seen that in an analogous manner, as described above for the interplay between the device responding to the branch currents with their branch switches it is likewise possible here to select the next but one etc. negative current half wave, so that it is possible to increase at will the lower and 4 upper limits for the admissible switch-off lag each time by one, two, etc. periods.

In the cases where one is interested in a rapid interruption of the alternating currents, vacuum switches according to the invention are utilized as interrnpters in the branch circuits A and B.

In FIG. 3 is represented a further typical design of the new switch device. The same reference numbers for the individual parts are used as in FIG. 1, with the auxiliary switches 11, it), connected with the branch switches 4, 5 being added as an extension to FIG. 1. The devices 8, 9 responding to the recovery voltage across the contacts of the main switch I lie, in this case, in individnal circuits parallel to the main switch 1, and with the auxiliary switches 10, 11 being connected in series therewith for the respective control of the voltage responsive devices 8 and 9.

The operation of the switch device according to FIG. 3 is the same as the one described for FIG. 1; but there takes place, in addition, a separation of the devices 8, 9 by the auxiliary switches In, 11, so that they are no longer continuously under tension in the switch-off position of the switch device l, and thus a complete galvanic separation of the interrupted main parts is achieved.

FIG. 4 represent a further typical design of the switch device according to the invention. Again the same designations are used as in FIG. 3. In extension FIG. 3, however, the

devices

6, 7 which respond to the current in the branch circuits are connected with a polarized change-over device 12 which for its part is connected with a device 13. This latter contains as component parts a release impulse sender 13a, a current reproducer 13b, and a transformer 13c, across which the device 13 is connected with the common current path of the secondary branches.

The operation of the switch device according to FIG. 4 is as follows: in the closed state the main switch 1 carries the load current practically alone. In this operating condition, branch switches 4 and 5 are likewise closed, and also closed are their correlated auxiliary switches 10 and 11 which always take the same position as the switches 4 and 5. The polarized change-over switching device 12, which can take the form of a conventional polarized relay, takes a. center position as indicated on FIG. 4 so long as the main switch 1 is closed since the latter virtually alone carries the load current in the line. When the main switch 1 is opened at any instant for the purpose of switching off the current flowing in the load circuit, the load current will continue to to flow in the side branch (through 4 or 5) dependent upon whether the one-way valve 2 or 3 is than conductive. Do to their anti-parallel connection, one valve is in a conductive state while the other one is in a blocking state. On one half-wave of the alternating current flowing in the load circuit, valve 2 will block while valve 3 Will conduct. In the next half wave, valve 2 will conduct while valve 3 will block. If, for example, the contacts of switch 1 open at an arbitrary time point, e.g., 1, according to FIG. 5, during a positive half-wave, the load current continues to flow, through the primary of current transformer 13c, valve 2 and branch switch 4, the current reproducer 13b produces in a manner familiar in itself a phase-true, amplitude-limited control current i which according to FIG. 5, e.g., at the point t during the positive current half wave, brings the switchover device 12 in a preparatory way into the position designated with Now, when during the interval At which lies between time points t and t the load current reverses its direction, a current pulse is generated in release impulse sender 13a and this current pulse is applied to the current responsive tripping device 7 with the result that the branch switch 4 is opened without arcing e.g., at the moment t since with the current reversal of the negative half-wave, valve 2 then becomes blocked.

During this negative half-wave, the changeover device 12 returns to its center position without delay and reaches it at about time instant i In the following, positive half wave valve 3 now blocks so that the returning voltage can then build up over the open switch 1. Since auxiliary switch is still closed, the voltage tripping relay 8 is energized and gives a tripping command to the branch switch 5 so that it likewise breaks in an areless manner during the positive half-wave in which valve 3 is blocked. In the event that the main switch 1 is actuated during a negative half-wave of the load current, the change-over device 12 will shift from its center position to the position indicated by and a similar sequence of switching-out events takes place except that the time sequence is reversed with respect to the opening of branch switches 4 and 5, i.e., switch 5 opens first, followed by opening of switch 4. Since, along with the branch switches 4 and 5, the auxiliary switches 10 and 11 have also opened, the switching device is now interrupted in all branches and hence, there is now a complete galvanic separation. As a switch-off lag there is thus nearly a half period available, namely the time interval between L; and t In analogous manner to that described under FIG. 1, heretoo the use of less rapidly responding tripping

devices

6, 7 and branch switches 4, 5 is possible insofar as, e.g., the opening point for the branch switch 4 is placed in one of the following negative half waves.

In the case of a variation of the arrangement described according to FIG. 4 the two voltage paths 8, 10 or 9, 11 are switched directly parallel to the main switch 1, namely connected between it and the device 13. For the switching-on, the switch device can in familiar manner be activated by :a separate drive, and here it is expedient for the main switch and the branch switches to be actuated at about the same time.

The new switch device is not limited to the use of mechanical switching devices as branch switches. According to the invention the branch switches can be designed as interrupters without mechanical switch contacts, e.g., as mercury vapor switches or as magnetically or electrically influenced semiconductor switch elements, which possess a magnetically or electrically controlled blocking layer whose resistance changes in familiar manner under influence of a magnetic field or electrical field in considerable measure, e.g., by several orders of magnitude. In the case of a variation of the described arrangement according to FIG. 1, for this case elements 4 and 5 represent such semiconductor switch elements with the current

responsive devices

6, 7 and the voltage responsive devices 8, 9 being so designed that they exercise a current-blocking efiect on their coordinated switch elements 5 and 4 by means of a suitable magnetic field or electrical field. The operation is then the following: if at any point the main switch 1, which, e.g., can itself be designed as a semiconductor switch element, interrupts, then the secondary branch A in question (624) whose electrical valve 2 is conductive for the momentaneous current half wave, takes over the current. This current flows first up to the next current Zero passage, while the other secondary branch B (5-37) is currentless by means of the valve 3, with its switch element 5 receiving a continuous blocking order across the device 6. Now if the current reverses its direction, then it finds the secondary branch (537) blocked, although the electrical valve 3 would now conduct. The branch circuit 624 is now blocked through valve 2. Now across the main switch 1 the recovery voltage builds up, whereby across the devices 8 and 9 the blocking orders are maintained on the branch switches 5.

In the typical designs shown, the new switch device is represented each time for single phase current circuits. It is clear that they can likewise be used on polyphase circuits comprising two, three or more phases.

The new switch arrangement has the advantage over the known designs that it makes it possible to use simple and space-saving devices as the main switch and branch switches, since no requirements need to be placed on it with respect to switching ability. As a result of the freedom with regard to the switch-off lag, even sluggishly operating current response and voltage responsive tripping devices and branch switches, can be used, with so-called synchronous controls not being needed. As areas of application with higher currents and voltages there present themselves particularly step switch devices for transformers, welding devices, and the like, while with use of semiconductor switch elements, the new switch device represents an advance particularly in regulating technology.

I claim:

1. In a switching apparatus for interruption of alternating current loads, the combination comprising a main switch inserted in the circuit carrying the alternating current to be interrupted, two branch switching circuits connected in parallel with said main switch, each said branch circuit including a branch interrupter and a one-way electric valve connected in series, said one-way electric valves being connected antiparallel so as to have oppositely directed current passing directions, said branch interrupters being closed when said main switch is closed and said main switch then carrying substantially all of the load current, at least one tripping device responsive to current fiow in said branch circuits and at least two other tripping devices responsive to the recovery voltage appearing across the contacts of said main switch when opened, and circuit means connecting said tripping devices with said branch circuit interrupters such that opening of the interrupter in each said branch circuit takes place only during that half wave of the alternating current for which the appertaining one-way electric valve is blocked.

2. Switching apparatus as defined in claim 1 wherein said branch circuit interrupters are constituted by vacuum type switches.

3. Switching apparatus as defined in claim 1 wherein said branch circuit interrupters are constituted by interrupters of the type without switch contacts.

4. Switching apparatus as defined in claim 1 wherein said tripping device responsive to current flow in said branch circuits is connected in a current path common to the two branch circuits.

5. Switching apparatus for interruption of alternating current loads comprising a main switch inserted in the circuit carrying the alternating current to be interrupted, two branch switching circuits connected in parallel with said main switch, each said branch circuit including a branch interrupter and a one-way electric valve connected in series, said one-way electric valves being connected anti-parallel so as to have oppositely directed current passing directions for the positive and negative half-waves, respectively of said alternating current, said branch interrupters being closed when said main switch is closed and said main switch then carrying substantially all of the load current, a tripping device responsive to current flow in said branch circuits and connected in a current path common to both of said branch circuits, said tripping device comprising a current reproducer, a change-over device, and a release impulse sender, said current reproducer serving to produce a phase-true amplitude limited control current for the activation of said change-over device to establish a conductive path between said release impulse sender and a means actuated thereby which effects opening of the branch interrupter in that branch circuit which is then currentless, said release impulse being produced in the vicinity of the passage of the alternating current through zero, and a pair of voltage responsive tripping devices energized by the recovery voltage appearing across the contacts of said main switch when opened, said voltage responsive tripping devices being correlated respectively to said branch circuits and which serve to operate the branch interrupter in that particular branch circuit from a closed to an open position at a time following operation of the branch interrupter in the other branch circuit to its open position.

6. Switching apparatus as defined in claim 5 wherein the energizing circuit of each of said voltage responsive tripping devices includes an auxiliary interrupter which is open when the interrupter in that branch circuit is open and is closed when the interrupter in that branch circuit is closed.

7. Switching apparatus for interruption of alternating current loads comprising a main switch inserted in the circuit carrying the alternating current to be interrupted, two branch switching circuits connected in parallel with said main switch, each said branch circuit including a branch interrupter and a one-way electric valve connected in series, said one-way valves being connected anti-parallel so as to have oppositely directed current passing directions for the positive and negative half-waves, respectively of said alternating current, said branch interrupters being closed when said main switch is closed and said main switch then carrying substantially all of the load current, a current responsive tripping device individual to and for actuating each of said branch interrupters, the tripping device correlated to the branch interrupter in one of said branch circuits being actuated in response to current flow through the other branch circuit, and a pair of voltage responsive tripping devices energized by the recovery voltage appearing across the contacts of said main switch when opened, said voltage responsive tripping devices being correlated respectively to said branch circuits for actuating the branch interrupter therein to open position.

8. Switching apparatus as defined in claim 7 wherein said current responsive tripping device in each said branch circuit is constructed so as to be actuated only upon an increase in its branch current.

9. Switching apparatus as defined in claim 8 wherein said current responsive tripping device in each branch circuit and the interrupter in the other branch circuit correlated thereto have a switch-off lag of at most a quarter of one period of said alternating current.

10. Switching apparatus as defined in claim 8 wherein said current responsive tripping device in each branch circuit and the interrupter in the other branch correlated thereto have a switch-off lag of at least one period and at most five quarter periods of said alternating current.

11. Switching apparatus as defined in claim 7 wherein said current responsive tripping device in each said branch circuit is constructed so as to be actuated only upon a decrease in its branch current.

12. Switching apparatus as defined in claim 11 wherein said current responsive tripping device in each branch circuit and the interrupter in the other branch circuit correlated thereto have a switch-ofi lag of at least a threequarter and at most one complete period of said alternating current.

13. Switching apparatus as defined in claim 1 wherein said tripping devices responsive to the recovery voltage appearing across the contacts of said main switch when opened are connected individually in circuits parallel to the contacts of said main switch and each said circuit also includes an auxiliary switch in series with the recovery voltage responsive tripping device, each said auxiliary switch being actuated by the actuating mechanism of a branch circuit interrupter coordinated therewith.

14. Switching apparatus as defined in claim 13 wherein said tripping devices responsive to the recovery volt-age together with their respective interrupters have a switchoif lag of at most a quarter period of said alternating current.

15. Switching apparatus as defined in claim 13 wherein said tripping devices responsive to the recovery voltage together with their respective interrupters have a switchol'f lag of at least one period and at most five quarter periods of said alternating current.

References Cited by the Examiner UNITED STATES PATENTS 3,018,414 1/1962 Albright 31711 FOREIGN PATENTS 638,981 11/1936 Germany. 688,720 3/1953 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

I. D. TRAMMELL, Assistant Examiner.

Claims

1. IN A SWITCHING APPARATUS FOR INTERRUPTION OF ALTERNATING CURRENT LOADS, THE COMBINATION COMPRISING A MAIN SWITCH INSERTED IN THE CIRCUIT CARRYING THE ALTERNATING CURRENT TO BE INTERRUPTED, TWO BRANCH SWITCHING CIRCUITS CONNECTED IN PARALLEL WITH SAID MAIN SWITCH, EACH SAID BRANCH CIRCUIT INCLUDING A BRANCH INTERRUPTER AND A ONE-WAY ELECTRIC VALVE CONNECTED IN SERIES, SAID ONE-WAY ELECTRIC VALVES BEING CONNECTED ANTIPARALLEL SO AS TO HAVE OPPOSITELY DIRECTED CURRENT PASSING DIRECTIONS, SAID BRANCH INTERRUPTERS BEING CLOSED WHEN SAID MAIN SWITCH IS CLOSED AND SAID MAIN SWITCH THEN CARRYING SUBSTANTIALLY ALL OF THE LOAD CURRENT, AT LEAST ONE TRIPPING DEVICE RESPONSIVE TO CURRENT FLOW IN SAID BRANCH CIRCUITS AND AT LEAST TWO OTHER TRIPPING DEVICES RESPONSIVE TO THE RECOVERY VOLTAGE APPEARING ACROSS THE CONTACTS OF SAID MAIN SWITCH WHEN OPENED, AND CIRCUIT MEANS CONNECTING SAID TRIPPING DEVICES WITH SAID BRANCH CIRCUIT INTERRUPTERS SUCH THAT OPENING OF THE INTERRUPTER IN EACH SAID BRANCH CIRCUIT TAKES PLACE ONLY DURING THAT HALF WAVE OF THE ALTERNATING CURRENT FOR WHICH THE APPERTAINING ONE-WAY ELECTRIC VALVE IS BLOCKED.