US2878402A - Electric circuit-breakers - Google Patents

Description

March 17, 1959 s. KOHN 2,878,402

ELECTRIC CIRCUIT-BREAKERS Filed June 19, 1957 2 Sheets-Sheet 1 March 17, 1959 s. KOHN ELECTRIC CIRCUIT-BREAKERS 2 Sheets-Sheet 2 Filed June 19, 1957 United States Patent ELECTRIC CIRCUIT-BREAKERS Stphane Kohn, Paris, France, assignor to Forges et Atellers de Constructions Electriques de Jeumont, Paris, France, a corporation of France Application June 19, 1957, Serial No. 666,624

Claims priority, application France June 28, 1956 10 Claims. (Cl. 307-133) This invention relates to electric circuit-breakers for alternating current.

Numerous suggestions have already been made for facilitating the operation of circuit-breakers by the separation of their break contacts at the moment of the passage of the alternating current through zero value. Up to the present, these attempts have not given practical results, principally by reason of the difficulty of obtaining a sufiiciently precise timing of the separation of the contacts, this difiiculty being increased by the fact that the precise instants of the passages through zero of the current to be interrupted shifts in time according to the conditions of the current-interruption.

The present invention has for its main object to overcome these difficulties by synchronizing the movements of the circuit-breaker with the alternations of the current, by an appropriate arrangement of the contacts and by a suitable co-ordination of their time-constants of opening with the exact timing of their respective control operations.

According to the invention, a circuit-breaker having main contacts and auxiliary break contacts is controlled by a transmitter of periodic pulses of very short duration, synchronised with the alternations of the main current to be interrupted, a first pulse passing through an operating circuit to close the break contacts and then to open the main contacts a short time before the passage through zero of the current to be interrupted, and a second pulse passing through another operating circuit to open the break contacts after the main contacts, but before the said passage through zero.

The invention is hereinafter described with reference to the accompanying drawing, in which:

Fig. 1 is a circuit diagram and Fig. 2 an explanatory diagram representing one half-period of the current to be interrupted.

Fig. 3 is a schematic diagram of the transmitter covered herein. Fig. 4 is a schematic diagram of the apparatus for operating the circuit breaker by remote control.

Fig. 1 shows a high-tension source 1 passing through a disconnecting switch 2 with its operating mechanism 2A, a fixed main contact 3 of the circuit-breaker, a cooperating movable main contact 4 with its operating mechanism 4A, a fixed auxiliary break contact 5, a movable break contact 6 and its operating mechanism 6A. In accordance with the usual arrangement, the break contacts 5 and 6 are connected in parallel with the main contacts 3 and 4 which are connected in series with the disconnecting switch 2.

A current transformer 7, which can be replaced by a shunt resistance, transmits a control current proportional to the main current I in the phase line 1 to a pulse transmitter 8 which can be fed by any appropriate source of energy, such as a battery 9. The whole is supported and insulated from earth either by an insulator 10 or by an appropriate insulating suspension.

In the first place, it will be assumed that the transmitter 8 is an electronic apparatus arranged to generate 2,878,402 Patented Mar. 17, 1959 ice a succession of very short control current pulses i and i directed selectively through control circuits 11 and 12. These pulses, which are preferably unidirectional and generated or controlled by the alternating voltage supplied by the transformer 7, are synchronous with the main current in the phase line 1, but suitably shifted or dephased in relation to that current.

The pulse i initiates the operation of the mechanisms 4A and 6A to etfect first the closure of the auxiliary break contacts 5 and 6, which are normally open, and then the opening of the main contacts 3 and 4, which are normally closed. This order of the operations can be ensured for example by the appropriate choice of the corresponding mechanical and electrical time-constants of the masses in movement and of the electrical circuits.

The pulse i transmitted after the first pulse i initiates the operation of the mechanisms 6A and 2A for the opening first of the auxiliary contacts 5 and 6 and then the disconnecting switch 2; the durations of these opening movements are likewise determined by the corresponding time-constants. Appropriate interlocking contacts 14 and 15 may be provided in the circuits 11 and 12 to give all desired security and to prevent operation of the circuit-breaker if certain conditions are not fulfilled. Thus, the apparatus may be arranged to produce the control pulses i and i; only under the following conditions: at the start of the half-period, when t=0 (see Fig. 2), the value of the first derivative dl/dt must have a predetermined sense and this value must be greater than a certain minimum, but less than a certain maximum.

If these conditions are fulfilled, and assuming a frequency of 50 cycles a pulse 1', is transmitted at a moment such that at the end of a definite time t for axample 9 milliseconds :5%, the auxiliary break contacts 5 and 6 are closed and the main contacts 3 and 4 are opened. The second pulse i is then produced at a moment such that at the end of a time t for example 9.5 to 9.7 milliseconds, but less than 10 milliseconds, the auxiliary contacts 5 and 6 shall be opened.

The main contacts 3 and 4 thus separate at a moment when the current is equal. to I the recurring voltage at this moment is very low, since the contacts 5 and 6 are closed in parallel, and this opening is therefore effected without arcing at the contacts 3 and 4.

The auxiliary break contacts 5 and 6 now separate, cutting off the low current 1 The recurring voltage is high, but the duration and the energy of the arc are much less than in the course of a conventional interruption, so that the final interruption is effected Without difiiculty at the passage of the current through zero value. The contacts 3 and 4 close again after the opening of the disconnecting switch 2, which is effected by the mechanism 2A controlled as shown by the pulse i Thus it is seen that the transmitter 8 acts both as synchronous control element, and also as discriminatory element, since it only opens the circuit breaker under predetermined conditions, depending on the sense and value of the derivative dI/dt.

Apart from its automatic operation as described above, the transmitter 8 can be remotely controlled by the personnel of the installation or by suitable protective means. For this purpose there may be provided a control device 16 in the form of a suitable generator of hydraulic control pulses, connected to the transmitter 8 by an insulating pipe 17, filled with oil for example, for carrying these hydraulic pulses at acoustic speed.

When the circuit-breaker is closed, it can be opened by pressing a button 18 which controls the hydraulic pulse generator 16 for producing a control pulse capable of actuating the electric transmitter 8.

If the current I in the circuit-breaker is lower than the value causing its automatic opening, this hydraulic pulse will cause the successive production of the electrical pulses i and i which produce the opening of the circuit-breaker, as described above. If the current I is greater than the breaking power of the circuit-breaker, the pulses i and i .are not emitted. If the main current I is practically zero, the transmitter 8 may supply pulses i and i which are not synchronised with the current, for opening the circuit-breaker and interrupting this low current at any moment.

A circuit-closing button 19 actuates the hydraulic generator 16 for transmitting through the conduit 17 different pulse or a plurality of pulses, for example two, resulting in the transmission by the apparatus 8 of a control pulse i passing selectively through a circuit 13 which is suitably connected to the mechanism 2A for causing the closing of the disconnecting switch 2, on condition that one or more interlocking contacts are closed.

In the example of embodiment illustrated, it has been assumed that the main contacts consist of two fixed spheres 3 and 21, mounted in an insulating enclosure 22, which may be filled with a suitable gas at relatively high pressure, and that the movable contact 4 takes the form of a cylindrical plunger of very low weight, actuated by mechanism 4A of hydraulic type for example, mounted close to the part 4.

It has also been assumed that the auxiliary break contacts S and 6 are arranged in the conventional manner, like those of circuit-breakers operating under high vacuum, one of them being sealed by means of an elastic bellows 23; it is known that apparatus of this type is capable of interrupting currents of more than 200 amps. under very high tensions.

Naturally the form of embodiment as described can be modified in various ways, without departing from the scope of the present invention as defined by the appended claims.

Fig. 3 is a schematic diagram of the transmitter 8. This apparatus can be constructed in different embodiments, but one preferred embodiment is shown in Fig. 3. It could, for example, comprise a pair of peaked transformers p1 and p2, the secondary voltage outputs of which are adjustable and applied to control circuits 11 and 12 through thyratrons, or similar valve means, 21 and 22 and suitable amplifiers 11A and 12A. The primary windings of transformers p1 and p2 are energized from the current transformer 7 through a resistance 20. The valve means 21 and 22 are grid biased with a positive voltage from sources of continuous voltage b1 and "b2. These voltage sources are connected in series with the secondaries of a grid transformer 23 having its primary adjustably energized by the voltage variably controlled across resistance 20. The secondary voltage outputs are in the direction shown by the arrows.

At the beginning of each half-cycle of the main current I having a specific polarity, as for example, a positive direction, the transformer 7 saturates the magnetic cores of the peaked transformers p1 and p2 which produce in known manner current pulses of short duration. A reactance coil 26 connected in series with the primary of transformer p2 introduces a suitable time delay between the pulses so that the output pulse of p2 is time delayed and follows the pulse output of pi. If the current I is lower than a certain value, the pulses applied to valve means 21 and 22 are insuflicient in value to fire these thyratrons and they remain effectively blocked so that there is no output from control circuits 11 and 12. If the half-cycle of current I is not positive the pulses cannot pass through valves 21 and 22 which act as rectifiers. If on the other hand the value of the current I is too great, namely if the dZ/dt value is too high, due to a transistory dissymetry of the half cycles, the grid transformer 23, which provides polarization voltages opposed to those of 61 and 62, renders the grids of valves 21 and 22 negative so that they do not fire.

It can therefore be seen that the valves or 'thyratrons are fired or triggered only if the half-cycle of the main current I has a specific direction or polarity, if the dissymmetry of the main current half-cycles is not too great and if the value of dl/dt is located between a predetermined maximum and minimum level. When these conditions are realized the control circuit 11 selectively transmits to the contact operating mechanisms a pulse i and at the end of a specific time delay the circuit 12 transmits another pulse The electrical and mechanical time constants of the circuitry and mechanisms, which intervene in the operation, are suitably selected so that the successive openings of the main and auxiliary contacts are efiected in accordance with Fig. 2 a short period of time just before current I passes through zero.

In order to provide for remote control of the circuit breaker the apparatus 8 may comprise a source of continuous voltage comprising a battery 9 connected to a twodirection switch 24 for connecting the source 9 to a conductor 25 for energizing the primaries of transformers p1 and 172 or to connect the source 9 to control circuit 13 in order to close the switch 2.

It will be understood, however, that the circuitry of Fig. 3 is illustrative only and that other circuitry can be employed in order to produce pulses having a duration of less than 1 microsecond.

The apparatus shown in Fig. 4, which is a schematic diagram of the device shown at 16 for operating the circuit breaker by remote control, can be constructed as, for example, according to the French Patent 976,710 filed October 13, 1948. The apparatus comprises a metallic deformable bellows device 27 filled with an insulating liquid. The bellows 27 is connected through line 17 to a second bellows device 27A intermediate of which is connected an expansion chamber 17A. The bellows device 27A is connected to switch 24 to operate it so as to connect source 9 to conductor 25 or to control circuit 13 in the manner indicated heretofore with respect to the apparatus shown in Fig. 3. Bellows 27 is operatively connected to two solenoids 28 and 29. When they are in a de-energized condition they allow the switch 24 to remain in an intermediate position in a manner shown in Fig. 4. The plungers of solenoids 28 and 29 are so constructed that when switch 18 is closed, power is provided from a source 30 energizing the operating coil of solenoid 29, moving the plunger toward the right thereby to elongate bellows 27, and bellows 27a moving the contact arm of switch 24 toward the right so as to connect the source 9 across the primaries of the transformers p1 and p2. The source 9 successively saturates the transformers p1 and p2 so that they produce and transmit the successive pulses i and i which control the opening of the circuit breaker. When switch 19 is depressed the operating coil of solenoid 28 is energized from the source 30 moving the plunger thereof in a direction toward the left so that the bellows 27 is compressed and thereby bellows 27A operatively moves the contact arm of switch 24 to the left whereby source 9 is connected to control circuit 13 so that the current i will operate mechanism 2A to close the disconnect switch2. It will be understood, of course, that the switches 18 and 19 can be operated manually or automatically, as preferred.

What I claim is:

1. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arrangedin. parallel to said main contacts, said auxiliary contacts being normally open, mechanism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse generating and discriminating means for producing under control of main-current half-cycles of a predetermined sense and value a plurality of successive short control current pulses in synchronism with said half-cycles and in accordance with the first derivative of the main current, selective control circuit means for applying one of said current pulses to said'mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through zero, and other selective circuit means for subsequently applying another of said current pulses to said mechanisms for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero, the suitable timing of said contact movements being determined by the respective electrical and mechanical timeconstants of said generating means, circuit means and moving members of said main and auxiliary contacts.

2. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, a disconnecting switch normally closed to carry the current, separate mechanisms for operating said main contacts, said auxiliary contacts and said disconnecting switch, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, selective circuit means for applying one of said current pulses to the first and second of said mechanisms in sequence thereby to close after a suitable time delay, said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through zero, other selective circuit means for subsequently applying another of said current pulses to the second and third of said mechanisms for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero and then to open said disconnecting switch, a third circuit means for operating the third of said mechanisms to close said disconnecting switch, and remote control means for energizing said third circuit means.

3. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, mechanism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, a current transformer energized by the main current and connected for controlling said generating means, circuit means for applying one of said current pulses to said mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through zero, and circuit means for subsequently applying another of said current pulses to said mechanism for operating said auxiliary contacts to open said auxiliary contacts just before said main current value passes through zero, said openings of main and auxiliary contacts being suitably timed with respect to said pulses by coordination of suitable mechanical and electrical time-constants of said contacts, mechanisms, circuit means and generating means.

4. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, mechanism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse gencrating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, selective circuit means for applying one of said current pulses to said mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through zero, and means for subsequently applying another of said current pulses to said mechanism for operating said auxiliary contacts to open said auxiliary contacts just before said main current value passes through zero, said openings of main and auxiliary contacts being suitably timed with respect to said pulses by coordination of respective mechanical and electrical time constants of said contacts, mechanisms, circuit means and generating means.

5. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, mechnism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, selective circuit means for applying one of said current pulses to said mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passages through zero, and means for subseqeuntly applying another of said current pulses to said mechanism for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero, the suitable timing of said openings of main and auxiliary contacts being determined by the respective electrical and mechanical time-constants of said selective circuit-means, of said generating means and of moving members of said main and auxiliary contacts and mechanisms.

6. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, said main contacts including fixed electrodes mounted in an insulating enclosure filled with a gas under pressure, one of said electrodes comprising a cylindrical plunger of low inertia forming a movable contact in relation to the other of said electrodes, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, mechanism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, means for applying one of said current pulses to said mechanisms in sequence thereby to close said auxiliary contact and then to open said main contacts a short time before the instantaneous main current value passes through zero, and means for subsequently applying another of said current pulses to said mechanism for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero.

7. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts including electrodes mounted in an insulating enclosure under high vacuum and being normally open, mechanism for operating said main contacts, mechanism for operating said auxiliary contacts, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production if the first derivative of the main current is outside of definite maximum and minimum limits, means for applying one of said current pulses to said mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through Zero, and means for subsequently applying another of said current pulses to said mechanism for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero.

8. An electric circuit-breaker for alternating current, comprising main contacts normally closed to carry the main current, auxiliary contacts arranged in parallel to said main contacts, said auxiliary contacts being normally open, a disconnecting switch normally closed to carry the current, separate mechanisms for operating said main contacts, said auxiliary contacts and said disconnecting switch, impulse generating means for producing in dependence upon main current half-cycles having a definite sense, at least two successive and suitably timed synchronous control current pulses of short duration, discriminating means for withholding said pulse production it the first derivative of the main current is outside of definite maximum and minimum limits, means for producing hydraulic pulses adapted to effect remote control operation of said generating means for applying one of said current pulses to the first two of said mechanisms in sequence thereby to close said auxiliary contacts and then to open said main contacts a short time before the instantaneous main current value passes through zero, for subsequently applying another of said current pulses to the second and third of said mechanisms for operating said auxiliary contacts to open said auxiliary contacts just before said current value passes through zero and to open subsequently said disconnecting switch, and means for producing difierent hydraulic pulses for remote control of said generating means so as to produce a control current selectively transmitted to the third of said mechanisms for reclosing said disconnecting switch.

9. In a circuit-protective system the combination con1- prising a circuit breaker having, relatively separable main contacts connected in series in an alternating current primary circuit to be interrupted, normally open auxiliary contacts connected in parallel with the main contacts, a disconnect switch in said primary circuit, an electro-rcsponsive synchronizing apparatus for generating a first and a-second unidirectional impulse signal in timed relation with alternations of a given polarity of the alternating current in said primary circuit, the pulses having a duration less than an interval of time corresponding to one half cycle of the alternating current and the syn chronizing apparatus having means to transmit the impulses only when the alternating current exceeds a selected minimum value, means coupling said synchronization apparatus to said primary circuit, a first control circuit comprising first means rendered operative .by the first impulse for closing the auxiliary contacts and second-means for subsequently separating the main contacts at thebeginning of a selected time interval prior in time to the passing ofthe alternating current through zero and in dependence upon the instantaneous value of the alternating current at the beginning of said selected time interval, a second control circuit receptive of the second impulse to actuate said auxiliary contact closing means and to open said auxiliary contacts subsequent to the separation of the main contacts and prior in time to the passing of the main current through zero and including means rendered operative by said second impulse for opening said switch subsequently to the opening of the auxiliary contacts and substantially at the moment said current passes through zero.

10. In an automatic control system for a circuit breaker having relatively separable main contacts connected in series in an alternating current primary circuit to be interrupted, the combination comprising normally open auxiliary contacts connected in parallel with the main contacts, a disconnect switch in said primary circuit, an electro-responsive synchronizing apparatus for generating a first and a second unidirectional impulse signal in timed relation with alternations of a given polarity of the alternating current in said primary circuit, the pulses having a duration less than an interval of time corresponding to one-half cycle of the alternating current and the synchronizing apparatus having means to transmit the impulses only when the alternating current exceeds a selected minimum value, means coupling said synchronization apparatus to said circuit thereby to detect the current conditions in the primary circuit, a first control circuit comprising first means rendered operative by the first impulse for closing the auxiliary contacts and second means for sequentially separating the main contacts at the beginning of a selected time interval prior in time to the passing of the alternating current through zero and after the current passes through its peak value and dependent upon a selected instantaneous value of the alternating current at the beginning of said selected time interval, a second control circuit receptive of the second impulse to actuate said auxiliary contact closing means therebyto open said auxiliary contacts subsequent to theseparation of the main contacts and prior in time to the passing of the current through zero and including means rendered operative by said second impulse for opening said switch subsequently to the opening of the auxiliary contacts and substantially at the moment said current passes through zero.

No references cited.

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