US3504233A - Electric circuit interrupting device with solid state shunting means - Google Patents

Description

March 31, 1970 R. HURTLE ELECTRIC CIRCUIT INTERRUPTING DEVICE WITH SOLID STATE snumme MEANS Filed June 20, 1967 LOAD EAC

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RALPH L. Hum-LE BYWM A T TOR/V5 Y US. Cl. 317-11 6 Claims ABSTRACT OF THE DISCLOSURE An electric circuit breaker of the type including a pair 'of stationary contacts and a movable bridging contact member has a pair of parallel-connected oppositely conducting controlled rectifiers connected in parallel therewith; manual or automatic opening of the bridging contact member causes a triggering voltage to appear on both the controlled rectifiers, one of which fires (depending on the instantaneous polarity) by-passing current around the contacts momentarily. Since the bridging contact member is connected to the trigger electrodes, and is disconnected from the stationary contacts 'when the breaker opens, no conduction occurs on the reverse half-cycle, since there is no triggering voltage. In a modified form, a current limiting device is included in series relation with the controlled rectifiers.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to contact-operating electric circuit interrupting devices, and more particularly to arc-suppression or eliminating means therefor.

Description of the prior art It has been proposed in accordance with the prior art to utilize controlled conductivity solid state devices to relieve the arcing duty on contact operating devices. Such circuits in the past have required special means for assuring that the supplementing solid state devices will be turned off and maintained in the 011 condition following opening of the contacts of the contact operating device. This requirement has necessitated various undesirable complications.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric circuit interrupter including separable contacts and controlled conductivity solid state device by-passing current around the contacts only during opening operation of the device.

It is a further object of the invention to provide a circuit interrupter of the type described in which no special circuitry is required to maintain the by-passing solid state device in non-conducting condition following opening of the circuit interrupter.

It is a further general object of the invention to provide a circuit interrupter Which is simple in construction and inexpensive to manufacture.

In accordance with the invention in one form, an electric circuit interrupter is provided including a pair of spaced stationary contacts and a movable bridging contact member. A pair of uni-directional controlled conductivity devices such as silicon controlled rectifiers (SCRs) are connected electrically in parallel with the contacts of the circuit interrupter. The control or gate electrodes of the SCRs are connected through a resistor to the movable or bridging contact member of the circuit breaker. Upon opening movement of the bridging contact member whether manually or by automatic means, a pair of arcs are drawn, developing a voltage drop there-across. Since United States Patent 3,504,233 Patented Mar. 31, 1970 ice the control electrodes of the SCRs are connected to the bridging contact member, the arc voltages appear as triggering or turn-on voltages on each of the SCRs. The current thereupon shifts from the circuit breaker path to the by-passing path. through one of the SCR devices (depending on polarity). Thereafter, the arcs are extinguished in the circuit interrupter. When this occurs, the bridging contact member becomes disconnected from the circuit, or at a floating potential, and with it the control electrodes of the SCR devices, thereby removing all triggering voltages and preventing any flow of current when the polarity of the source voltage reverses.

The invention will be more fully understood from the following detailed description, and its scope will be pointed out in the appended claims.

DESCRIPTION OF THE DRAWING In the drawing:

FIGURE 1 is a schematic representation of the invention in one form, and

FIGURE 2 is a schematic representation of another embodiment of the invention, and FIGURE 3 is a schematic representation of a third embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGURE 1, the invention is shown as incorporated in an electric circuit including an electric circuit breaker indicated generally at 10 and including a pair of spaced stationary contacts 11 and 12, and a movable bridging contact member 13. The circuit breaker 10 also includes operating means indicated schematically at 14 for operating the movable contact member 13. The operating means 14 may be of any suitable kind and may be manually or electrically operable, or both. In the pictured embodiment, a form of circuit breaker has been represented including manual operating means including an operating handle 15 and automatic operating means (not shown) for causing opening of the contacts upon the occurrence of predetermined abnormal current conditions. One type of automatic operating means is shown for example in Patent No. 3,315,189, issued Apr. 18, 1967 to E, B. Heft et al., and assigned to the same assignee as the present invention.

The circuit breaker 10 is connected electrically in series with a load 17 and a suitable source of alternating current, connected between input terminals 18A, 18B.

The main current path, therefore, under normal conditions, with the circuit breaker 10 in closed condition, is from the source terminal 18A, through the load 17, to the circuit breaker terminal 10A, to the stationary contact 11, to the movable contact 13, to the stationary contact 12, through the circuit breaker trip device 16, to the circuit breaker output terminal 10B, to the opposite side of the source terminal 18B.

For the purpose of relieving the arcing duty on the circuit breaker contacts in a manner to be described, a by-pass circuit is provided comprising a pair of controlled-conductivity solid state devices, such, for example as silicon controlled rectifiers 20 and 21, connected electrically in parallel with the circuit breaker 10. The directions of conductivity of the controlled rectifier devices 20 and 21 are arranged to be opposite each other as shown. The gate electrodes 20A and 21A of the controlled rectifiers 20 and 21 are connected electrically in common and are connected through the limiting resistor 22 to the movable contact member 13 of the circuit breaker 10 by means of a flexible conductor 23.

3 OPERATION In operation, it will be observed that in the condition illustrated in FIGURE 1, the contacts of the circuit breaker are in open condition and therefore there is no current path through the circuit breaker. It will also be observed that since the gates A, 21A, of the controlled rectifiers 20 and 21 are connected to the movable contact member 13 which in this condition of the circuit is electrically isolated, there is therefore no turn-on bias on the control rectifiers at this time, and therefore they do not conduct.

When the circuit breaker 10 is in closed condition, the current path is complete through the load 17 by way of the circuit breaker 10, the current flowing between the stationary contacts 11 and 12 by way of the movable member 13. In this condition, there is no significant bias voltage on the gate electrodes 20A, 21A, since the closed circuit breaker places them at substantially the same potential as the corresponding cathode electrodes.

When the movable contact member 13 is moved from closed toward open circuit position, however, a tact member 13 and the stationary contact members 11 and 12 respectively. The voltage drops across these arcs, each of which is in the neighborhood of 1015 volts, appears as turn-on bias on the SCR devices 20, 21 respectively. Since the total voltage drop appearing across these arcs is substantially higher than the voltage drop through one of the controlled rectifiers 20, 21, the current from the load 17 will change its path and flow through whichever one of the controlled rectifiers 20, 21, is conducting in the proper direction for that half cycle. Upon the shifting of the curent to the controlled rectifier path, the arcs between the stationary contacts 11 and 12 and the movable contact member 13 are rapidly extinguished.

At the end of that particular half cycle, the line voltage will of course reverse. No further conduction will occur, however, through the controlled rectifiers 20, 21 since the movable contact member 13 is now in open circuit position placing the gate electrodes of the controlled rectifiers at a floating potential.

FIGURE 2 FORM In the form of the invention shown in FIGURE 2, the construction and operation of the invention is similar to that shown and described in connection with FIGURE 1, except in addition to the parts shown in FIGURE 1, a current limiting device 125 is also included which as shown is connected electrically in series with the controlled rectifiers 120, 121 in the parallel or by-pass circuit shunting the circuit breaker 10. The current limiter 125 is preferably of the type shown in my prior Patent No. 3,117,203, issued Jan. 17, 1964 and assigned to the same assignee as the present invention, or in my application Ser. No. 660,982, filed Aug. 16, 1967, and assigned to the same assignee as the present invention. As described in the aforesaid patent, the current limiter 125 comprises a ceramic spacer, not shown, sandwiched between a pair of metallic electrodes, not shown, and having one or more small apertures or holes therethrough interconnecting the electrodes and filled with mercury. Under normal conditions, the mercury is in the liquid metallic state, but upon the occurrence of unusually high current conditions such as short circuit conditions, the mercury is transformed to a mercury vapor state under super-pressure and acts as a resistor, greatly limiting the flow of current. The short circuit current is reduced and maintained or regulated at a low value without being completely interrupted by the device, which function is performed by a suitably selected automatic interrupting device which may be of conventional form, associated with the current limiter, as described in the aforesaid patent.

While a regulating current limiter may be used as descr bed above, further beneficial results are achieved by utilizing the form of current limiter described in my aboveme'ntioned co-pending patent application and referred to as a quenching current limiter. In this form, the current limiter acts to reduce the current to zero and to maintain it at zero for a short time interval.

The operation of the invention as shown in FIGURE 2 is similar to that described in conection with FIGURE 1 with the following exception. It will be observed that when current transfer occurs following opening of the movable contact 13, the current is shifted to the shunting path including one of the controlled rectifiers 20, 21, and this rectifier continues to conduct until the completion of that particular half cycle, as described above. The necessity of possibly conducting current for a major part of a half-cycle imposes certain size or capacity requirements on the rectifiers 20, 21. In order to reduce this required capacity, in the form of the invention shown in FIGURE 2, the current limiting device 125 is included. Thus when the current is shifted from the circuit breaker A through the by-pass path, the current limiting device is initially in a high conductivity condition, but shortly thereafter the mercury is transformed to a vapor condition and the device assumes its high resistance condition, thereby limiting the fiow of current for the remainder of that half-cycle. At the end of the half-cycle the line voltage reverses. There is, however, no turn-on bias on either SCR device however at this time since the bridging contact 113 is out of contact with any other circuit element.

It will be observed that interruption takes place at the next succeeding current-zero of the A-C wave, and hence the total time of interruption is approximately a halfcycle or less. The regulating action of the current limiter keeps the current and 'hence the energy required to be dissipated, at a relatively low level.

Further advantages, however, are achieved in accordance with the invention, by use of the quenching type limiter described in my aforesaid application. In this form, the current limiter reduces the current to zero and maintains it at zero long enough to turn off the SCR device which had been conducting. Since the turn-on bias will have been removed by this time as previously described, complete extinction of current can take place in substantially less than one-half cycle.

The form of the invention shown in FIGURE 3 is generally similar to that shown in FIGURE 2, and similar reference number-s designate similar components. As shown in this figure, however, a plurality of loads, L and L are controlled by a plurality of corresponding circuit interrupters including movable bridging contact numbers 113 and 113A respectively.

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

1. An electric circuit interrupter for controlling the flow of current between two terminals adapted to be connected to opposite sides of a power source respectively comprising:

(a) at least one pair of stationary contracts;

(b) a movable bridging contact member;

(c) means supporting said bridging contact member for movement between a closed position in which it is in contact with and interconnects said stationary contacts and an open condition in which it is out of engagement with both of said stationary contacts;

(d) means connecting one of said stationary contacts to one of said terminals when said bridging contact is in said open condition;

(e) means connecting the other of said stationary contacts to the other one of said terminals when said bridging contact is in said open condition;

(f) a pair of controlled rectifier devices each having a control or gate electrode, said controlled rectifiers being connected electrically in parallel with said stationary contacts in opposite conducting sense to each other;

(g) means connecting said gate electrodes of said controlled rectifier devices to each other and to said movable contact member of said circuit interrupter at all times, said connecting means including an electrical resistor.

2. An electric circuit interrupter as set forth in claim 1 wherein said interrupter also includes a current limiting device connected electrically in series with the parallel combination of said controlled recitifiers, said current limiting device comprising means having low resistance normally and changing suddenly upon the increase of current therethrough to a high resistance.

3. An electric circuit interrupter as set forth in claim 2 wherein said current limiting device comprises a current limiter of the vaporizing mercury type.

4. An electric circuit interrupter as set forth in claim 1 wherein said circuit breaker also includes manual and automatic means for operating said movable contact between said closed and said open circuit positions.

5. An electric circuit interrupter comprising:

(a) a pair of controlled rectifier devices connected electrically in parallel in opposite conducting sense to form a parallel circuit combination;

(b) a current limiter device connected electrically in series with said parallel combination of said controlled rectifiers across a pair of main power terminals for connection to a source of electric power;

(c) means connecting said gate electrodes of said controlled rectifiers to each other and to a current limiting resistor;

(d) a plurality of circuit interrupting devices each connected electrically in series with a load to be controlled across said main power terminals;

(e) each of said electric circuit interrupting devices including a pair of spaced stationary contacts and a movable bridging contact member movable between a closed position in which it interconnects said stationary contacts and an open circuit position in which it is spaced away therefrom, and

(f) means connecting said current limiting resistance to said movable contact of each of said circuit interrupting devices.

6. An electric circuit interrupter for controlling the flow of current between two terminals adapted to be connected to opposite sides of a power source respectively compris- (a) at least one pair of stationary contacts;

(b) a movable bridging contact member;

( c) means supporting said bridging contact member for movement between a closed position in which it is in contact with an interconnects said stationary contacts and an open condition in which it is out of engagement with both of said stationary contacts;

(d) means connecting one of said stationary contacts to one of said terminals when said bridging contact is in said open condition;

(e) means connecting the other of said stationary contacts to the other one of said terminals when said bridging contact is in said open condition;

(f) electrical control means connected electrically in parallel with said pair of stationary contacts, said control means being normally non-conductive but being capable of being triggered to conductive condition by the action of a control signal impressed thereon said electrical control means remaining in said conductive condition as long as current flows therethrough and reverting to said non-conductive condition upon the cessation of current therethrough in the absence of said control signal, and

(g) means connecting said bridging member of said interrupter to said electric control means whereby no signal appears between said triggerable means of said control means and either of said stationary contacts when said bridging member is in said closed condition and a trigger signal appears between said electrical control means and each of said stationary contacts when said bridging member moves toward said open position and draws a pair of arcs between itself and said stationary contacts.

References Cited UNITED STATES PATENTS 3/1966 Heft 31733 6/1968 Misencik et al 31711

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