US2958808A - Electrical arc suppressor - Google Patents

Description

Nov. 1, 1960 MILLER 2,958,808

ELECTRICAL ARC SUPPRESSOR Filed April 12, 1957 FIG. I FIG. 2

+ WI LOAD I||||I- LOAD 70 /4 /0 /4 2e 26 FIG. 3

a. LOAD FIG. 4 32 0.0. T0 A.C. RECTIFIER 30/ CONVERTER j FILTER \34 I l 72 I LOAD FIG. 5

RECTIFIER A TORNIEY United States Patent ELECTRICAL ARC SUPPRESSOR William Miller, Greenwich, Conn., assignor to American glachine & Foundry Company, a corporation of New ersey Filed Apr. 12, 1957, Ser. No. 652,543

12 Claims. (Cl. 317-11) This invention relates to are suppression circuits.

When contacts of switch gear are opened, an arc will often appear across the contacts being separated if certain current and voltage conditions are present and particularly when the load upon the circuit is inductive in nature. A similar arc will also result if the contacts bounce as the switch gear is being closed. To suppress such an arc, the ideal solution is to provide a zero impedance path shunting the contacts at the instant of opening and when the distance between the contacts is increased to a point where it will no longer sustain an arc at any practical voltage, the value of the impedance should rapidly change from zero to an infinite value. The zero impedance is designed to short-circuit the voltage appearing across the contacts at the instant of opening and during the period when the contacts are separat ing, while the infinite resistance should provide an open circuit when the contacts are disengaged.

One form of arc suppression is to parallel the contacts with a resistor of appropriate size. Appropriate resistor size may be chosen for practically any set of circuit breaking conditions but for circuits having any appreciable current magnitude, the resistor which must be shunted across the contacts is of such low value that there is an undesirably large current flow after the contacts are open. On the other hand, if the resistor connected across the contacts is of too high a value, little or no suppression results. The ideal circuit for are suppression, then, would be the shunting of the contacts with a low or zero impedance before and immediately after contacts have begun to open and then switching, without use of any further contacts, the resistance from one of a low value to one of an infinitely high value, after the main contacts have opened.

In accordance with one broad feature of this invention, a practical embodiment of the ideal arc suppression circuit is provided by connecting in parallel with the contacts whose arc is to be suppressed a circuit comprising, in series, an asymmetric impedance device of the type which exhibits minority carrier storage, and a source of electrical potential for biasing the asymmetrical impedance in a forward current direction. When the contacts are closed, the asymmetric impedance and bias source are short-circuited so that the asymmetric impedance is biased in a forward direction. For a finite period of time immediately after the contacts are opened, the impedance of the series circuit is very low due to the time period required for the asymmetric impedance device to reach an equilibrium state of reverse bias. The transition from the forward to equilibrium reverse biasing condition is not instantaneous because of the phenomenon of minority carrier storage. After the recovery time is past, the asymmetric impedance device is biased highly in a reverse or high impedance direction by the normal load voltage source which is applied directly across the series circuit because of the open contacts.

Conductivity in certain types of asymmetric impedance devices, particularly germanium and silicon semi-conductors, is associated with two types of electrical carriers, poles and electrons. In such material both types of carriers are present but one is in excess of the other. Those in excess are known as majority carriers while those in the minority are known as minority carriers. In that type of material designated as N, the majority carriers are electrons and the minority carriers are holes; in that type of material generally designated as P, majority carriers are holes and minority carriers are electrons. In such asymmetric impedance devices it has been found that the flow of majority carriers has associated therewith a flow of minority carriers in the opposite direction. Minority carriers tend to recombine with the majority carriers and the probability of recombination per unit time is related to the minority carrier lifetime. During forward current flow, an equilibrium is reached between the number of minority carriers pumped into a given region per unit time and the number of recombinations which take place per unit time.

Accordingly, if an asymmetric impedance device of the type described has been biased or is conducting in a forward direction, that is, in a direction of majority carrier flow, and is suddenly biased negative, the influx of minority carriers is cut oif. However, immediately after reverse bias is applied, there is a large number of excess minority carriers present which permit a large reverse current to flow through the impedance device and its forward biasing source and last for a period of time of the order of the lifetime of the minority carriers. The number of minority carriers drops back to its equilibrium value which is many orders of magnitude smaller than the number present during forward current flow. When the number of minority carriers has reached its equilibrium value, the current which flows in the reverse direction is of the order of microamperes or less, depending upon the type of material which com rises the asymmetric impedance. The reverse impedance of the asymmetric impedance device then varies from an order of magnitude in ohms to megohms within a few microseconds. Accordingly, it will be seen that the reverse transient conditions in an asymmetric impedance device of the type herein described can be used to provide a low resistance across the contacts as they are opened which rapidly changes to a high resistance as the minority carriers recombine. Thus, heavy load current switching is substantially performed by the asymmetric impedance device in shunt across the contacts rather than by the contacts themselves.

It is, accordingly, an object of the invention to provide an improved arc suppression circuit.

It is another object of the invention to provide an arc suppression circuit having means for shunting switch gear contacts with a low impedance for a selected period of time after contacts have been opened and then shifting the impedance to a high value without the use of impedance switching contacts.

These and other objects and features of the invention will be more fully understood in the following detailed description and the drawing in which:

Fig. 1 is a schematic diagram of a circuit embodying the principles of the invention.

Fig. 2 is a modification of the embodiment of the invention shown in Fig. 1.

Fig. 3 is another embodiment of the invention particularly adapted for use in alternating current circuits.

Fig. 4 is a schematic diagram, partially in block form, showing a further modification of the embodiment of the invention shown in Fig. 1.

Fig. 5 is a schematic diagram of a modification of the embodiment of the invention shown in Fig. 3.

Referring now to the drawings, there is shown in Fig. 1 a source of electrical potential 10 which may be a battery or any other suitable source of voltage connected in series with a pair of switch contacts 12 and a load 14. Load 14 may beany type of electrical load and may be either resistive, capacitive or inductive in nature. Contacts 12 may be contacts associated with a manually operated switch or an electrically energized relay or any other type of circuit-breaking device, Well-known in the art.

Across contacts 12 is'connected a series circuit comprising asymmetric impedance device 16 and associated source of biasing potential18 which, for purpose of illustration, is shown as a battery. The value of potential for battery 18 is selected to provide a flow of current of such a magnitude in the forward direction through asymmetric impedance device 16 that the resistance of device 16 is very low in comparison with the load impedance. However, potential source 18 generally has only a fractional value of that of potential source 11 When switch contacts 12 are opened to interrupt the electrical load circuit and flow of current through load 14, the series circuit comprising asymmetric impedance device 16 and bias battery 18 presents a low impedance across contacts 12 until the minority carriers have reached an equilibrium state with the majority carriers in the impedance device 16. Thereupon, the impedance of the series circuit then rises to an extremely high value so that a substantially open circuit appears across contact 12. Asymmetric impedance device 16 may be any suitable type of asymmetric impedance which is capable of exhibiting minority carrier storage. The choice of a suitable asymmetric device will depend upon the potential of the voltage source 111, the nature of load 14, and the rapidity with which shifting of asymmetric impedance device 16 from a forward to an equilibrium reverse state is desired. Typical asymmetric impedance devices which may be used are point contact semi-conductor diodes or P-N junction diodes of the type which usually include silicon or germanium as the major semi-conductor material.

In circuits where the load current conducted by device 16 is in excess of a selected devices normal current carrying capacity, it will be understood that a number of such devices may be connected in parallel. Furthermore, if the open circuit voltage appearing across contacts 12 eX- ceeds the reverse or back voltage rating of the asymmetric impedance device 16, it will be further understood that a number of such devices may be connected in series to satisfy the back voltage requirements.

Applicant found that the recovery time of device 16 and, thus, the substantially zero impedance period existmg after contacts 12 have opened may be varied selectively by changing the value of bias source 18. In most applications, the forward current through asymmetric impedance device 16 is very small so that the drain on bias source 18 is negligible. However, in heavy duty applicat1ons, particularly when one or more devices 16 are connected in parallel, the forward current may rise to a value sufiicient to cause moderately heavy drain on bias source 18. Therefore, in accordance with the modificat on shown in Fig. 2, an additionalpair of contacts 20 for disconnecting the bias source may be connected in series with asymmetric impedance device 16 and bias source 18, and operatively ganged with contacts of switch 12. It is preferable that the contacts of switch 20 close just before the contacts of switch 12 open in order to allow the forward bias from source 13 to be applied to the device 16 for a short interval prior to the opening of contacts 12. If desired, switch 20 may be of the type which remains closed while switch 12 is opening but open with the final opening movements of switch 12 after the need for the arc suppression is completed. In this manner not even a reverse current of a few microamperes would flow in the circuit. f V

In Figure 3 there is shown another embodiment of the novel arc suppressor circuit which provides for the dis- 7 will be noted that the bridge circuit is so arranged that when switch 12 is closed, alternating current is free to flow in both directions through the circuit, but when switch 12 is opened, the flow of current is shut ofi by the opposed polarity of the rectifiers for each A.C. half-cycle. Since switch 12 interrupts a current always flowing in the same direction, the arc resulting from the interruption of this current is suppressed effectively in the same manner as described above. Asymmetric impedance device 16 is biased in a forward direction by bias source 18 in the manner as described heretofore. Diode rectifier units 26 may be any diode unit of the type well-known in the art and having suitable characteristics for the particular application to which the circuit is put, and having appropriate load ratings.

Figure 4 is a modification of the invention in which only passive elements are used in the arc suppression portion of the circuit. Such an arrangement is particularly suitable where long, unattended operation of the invention is desired withou t ha ving to replace the source of forward biasing voltage 18, as is eventually necessary when a conventional, electrolytic type battery is used for source 18.

A resistor 28 is connected in the main load circuit and has an ohmic value suitable for providing a source of DC. voltage thereacross for energizing DC. to A.C. converter 30. The converter maybe any of the known DC. to A.C. translating devices such as an electronic valve oscillator, a transistor oscillator or a mechanical type vibrator.

The AC. output of the oscillator or vibrator comprising converter 30 is transmitted through a coupling transformer 32 to a conventional rectifier-filter 34 which rectifies and filters the AC. output of transformer 32 in the usual manner and provides a DC. output of a value selected to suitably bias asymmetric impedance 1 6 in the forward direction. Transformer 32 isolates asymmetric impedance device 16 from resistor 23 and the main load circuit when switch 12 is opened to prevent a by-pass circuit around asymmetric impedance device 16 from forming and re-energizing the load 14. As only passive elements are used to provide the forward biasing source, the entire arc suppressor circuit is deenergized when switch 12 is opened. i

If one of the well-known transistor oscillator circuits is chosen for converter 30, then only a few volts need be supplied by the drop across resistor 23. its ohmic value can be held to a minimum with little insertion effect on the main load circuit. Furthermore, by utilizing a simple transistor oscillator and sub-miniature components for transformer 32 and rectifier-filter 34, the packaging of the bias elements is reduced to a minimum.

The modification of the invention shown in Fig. 4 may be further modified as shown in Fig. 5 when the passive element, forward biasing feature is utilized in conjunction with an AC. load voltage source 22. Converter 31) is omitted and transformer 32 is connected in series with the load circuit. Rectifier-filter 34 connected to transformer 32 provides the forward bias voltage for asymmetric impedance 16. The remainder of the circuit is the same as that shown in Fig. 3 and described hereinabove.

While the, present invention has been disclosed by means of specific. illustrative embodiments thereof, it would be obvious to those skilled in the art that various changes and modifications in the means of operation described or in the apparatus, may be made without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. An arc suppressor comprising a source of electrical potential, a load connected to said source of potential, a pair of movable contacts serially connected between said source and said load, an auxiliary circuit including an asymmetric impedance device exhibiting minority carrier storage connected in parallel across said contacts, said auxiliary circuit including means for causing current to flow through said asymmetric impedance device in a forward direction for at least a portion of the period when said contacts are closed, said source of potential being sufficient to bias said asymmetric impedance device in a reverse direction when said contacts are open.

2. In combination, a pair of movable electrical terminals, a source of electrical potential connected to said terminals, an asymmetric impedance device exhibiting minority carrier storage connected to one of said terminals, a source of bias potential serially connected to said asymmetric impedance device and said other terminal and adapted to bias said asymmetric impedance device in a forward direction when said terminals are in engagement with each other, said source of electrical potential being sufficient to bias said asymmetric impedance device in a reverse direction when said terminals are disengaged.

3. The invention defined in claim 1 wherein said asymmetric impedance device is a semi-conductor.

4. The invention defined in claim 3 wherein said semiconductor is a P-N junction semi-conductor.

5. The invention defined in claim 3 wherein said semiconductor is a point contact semi-conductor.

6. In combination, a pair of movable electrical terminals, a source of electrical potential connected to said terminals, an asymmetric impedance device exhibiting minority carrier storage connected to one of said terminals, a source of bias potential serially connected to said asymmetric impedance device and said other terminal and adapted to bias said asymmetric impedance device in a forward direction when said terminals are in engagement with each other, said source of electrical potential being sufiicient to bias said asymmetric impedance device in a reverse direction when said terminals are disengaged, and a normally closed switch connected in series with said source of bias potential and said asymmetric impedance device and operative in response to the closing of said terminals to disconnect said bias source from said asymmetric impedance device.

7. An arc suppressor circuit comprising a source of A.C. electrical potential, a load connected to said source of A.C. potential, a pair of movable contacts serially connected between said source and said load operative to form a closed circuit, means connected in said closed circuit operative to permit only a D.C. potential to appear across said contacts when said contacts are opened, an auxiliary circuit including an asymmetric impedance device exhibiting minority carrier storage connected in parallel across said contacts, said auxiliary circuit including means for causing current to flow through said asymmetric impedance device in a forward direction for at least a portion of the period when said contacts are closed, the potential appearing across said contacts when open being sufficient to bias said asymmetric impedance device in a reverse direction.

8. The invention defined in claim 7 wherein said means for allowing only a D.C. potential to appear across said contacts includes a bridge rectifier circuit having two pairs of arm junction terminals, one of said pairs being 6 connected between said A.C. source and said load, and said contacts are connected between the remaining pair of said arm junction terminals.

9. The invention defined in claim 7 wherein said means for causing current to flow through said asymmetric impedance device in a forward direction includes a transformer having an output winding and an input winding serially connected between said source and said load, means connected to said output winding for translating A.C. voltage into D.C. voltage, and connections between said. asymmetric impedance device and said voltage translating means for applying a forward biasing voltage to said asymmetric impedance device.

10. In combination, a pair of movable electrical terminals, a source of D.C. electrical potential connected to said terminals, an asymmetric impedance device exhibiting minority carrier storage connected to one of said terminals, a source of bias potential serially connected to said asymmetric impedance device and said other terminal and adapted to bias said asymmetric impedance device in a forward direction when said terminals are in engagement with each other, said source of forward bias potential including a D.C. to A.C. converter, means connected between said source of electrical potential and said terminals for energizing said converter with a selected D.C. voltage, means for detecting and filtering the output of said converter to provide a forward D.C. bias for said asymmetric impedance device, said source of D.C. electrical potential being sufiicient to bias said asymmetric impedance device in a reverse direction when said terminals are disengaged.

11. The invention defined in claim 10 wherein said converter comprises a generator of electrical oscillations.

12. An arc suppressor comprising a source of electrical potential, a load connected to said source of potential, a pair of movable contacts serially connected between said source and said load, an auxiliary circuit including an asymmetric impedance device exhibiting minority carrier storage connected in parallel across said contacts, said auxiliary circuit including means for causing current to flow through said asymmetric impedance device in a forward direction for at least a portion of the period when said contacts are closed, said auxiliary circuit means including means responsive to current flowing in said load for generating a first voltage, means connected to said first voltage generating means for generating a second selected voltage representative of said first voltage, means for isolating said second voltage from said first voltage, means connected to said auxiliary circuit for applying said second voltage to said asymmetric impedance device to bias said impedance device in a forward direction, said source of potential being sufficient to bias said asymmetric impedance device in a reverse direction when said contacts are open.

References Cited in the file of this patent UNITED STATES PATENTS 2,011,395 Cain Aug. 13, 1935 2,782,345 Kesselring Feb. 19, 1957 2,791,739 Light May 7, 1957 2,859,400 Kesselring Nov. 4, 1958 2,873,419 Brandt Feb. 10, 1959 FOREIGN PATENTS 613,832 Germany July 19, 1930 517,083 Germany Jan. 15, 1931 611,317 Germany May 28, 1932 638,981 Germany Nov. 5, 1936 874,152 France July 30, 1942

Images