US3376474A

US3376474A - Arc suppression circuit and compound impedance element for use therein

Info

Publication number: US3376474A
Application number: US492351A
Authority: US
Inventors: Norman I Glover; Louis I Knudson; Harry G Shoemaker
Original assignee: GEN LAB ASSOCIATES Inc
Current assignee: GEN LAB ASSOCIATES Inc; GENERAL LABORATORY ASSOCIATES Inc
Priority date: 1965-09-03
Filing date: 1965-09-03
Publication date: 1968-04-02
Anticipated expiration: 1985-04-02

Description

April 2, 1968 N. I. GLOVER ETAL 3,3 76,474 ARC SUPPRESSION CIRCUIT AND COMPOUND IMPEDA ELEMENT FOR USE THEREIN Filed Sept. 3, 1965 NOE //7 ve/lfors T T Norman G/ol er J Lou/'5 J. Knuason Harry G. Shoemaker Al/omey Unit This invention relates to an arc suppression circuit and to a compound impedance element including parallel first and second impedances and having characteristics suitable for use in an arc suppression circuit.

Ignition circuits are common examples of electrical circuits in which a set of breaker contacts is periodically opened and closed while a relatively high potential of electrical energy is applied to the breaker contacts. An ignition circuit typically includes an inductor connected in series with the breaker contacts between positive and negative power supply terminals. Upon opening of the breaker contacts the current flow through the series circuit is interrupted, and a voltage of typically a very high potential is induced in the inductor.

In the absence of an arc suppression circuit, the high potential will cause arcing between the breaker contacts, upon opening. As the contacts start to open, the actual area in which the surfaces of the contacts are touching decreases rapidly and becomes smaller and smaller. As a result, the current density through the area in which the contacts are touching increases tremendously. Just before final separation of the contacts, the current density is so high that the contact material melts; part of the molten contact material is drawn into a fine thread between the separating contacts. Due to the high current density, this fine thread tends to ignite and vaporize, providing a highly conductive path through which an arc passes between the contacts. The are is maintained between the contacts as they separate, causing additional intense heating and melting of the contact surfaces. As the contacts open wider, the potential drop in the arc across the gap between the contacts exceeds the potential applied to the contacts, and the arcing terminates. The arcing causes erosion or pitting of the breaker contacts, resulting in shortening their useful life and requiring frequent replacement of the contacts.

rates atent A common are suppression circuit comprises the connection of a capacitor of substantial electrical capacitance across the breaker contact terminals, and thus in parallel with the breaker contacts. While the contacts are closed, a minimal potential exists between the terminals of the breaker contacts and the capacitor is not charged. Upon opening of the contacts, the potential at the breaker contact terminals is applied both to the capacitor and to the gap between the breaker contacts. With a capacitor of suitable electrical capacitance, the potential at the breaker contact terminals produces a current flow through the capacitor, charging the capacitor and thereby substantially decreasing or eliminating arcing between the breaker contacts. The shifting of the current flow from the breaker contacts to the parallel-connected capacitor is a type of commutation.

The use of a single capacitor is not completely satisfactory, however. The capacitor must have substantial capacitance to limit the potential induced in the inductor and to receive the resultant current flow which occur upon opening of the breaker contacts; as a consequence of its large capacitance, the capacitor has a slow charging rate. Although the impedance of the air gap between the breaker contacts increases rapidly as the contacts open wider, the impedance upon the initial opening of the contacts is of rather small magnitude. As a result, arcing between the breaker contact upon their initial opening, since commutation of the current to the capacitor is not completed until the impedance of the air gap through which the arc travels exceeds the impedance of the capacitor including the elfective given inductance associated therewith. In addition, as the breaker contacts subsequently are brought together to close, but prior to their complete closing, the charge stored in the capacitor tends to discharge by establishing an are between the breaker contacts. Since the capacitor is of large capacitance, the stored charge is substantial, and the current flow in the arc is also substantial. Thus, deleterious arcing between the breaker contacts is not completely avoided, and erosion and pitting and even welding of the breaker contacts occurs.

Numerous arc suppression circuits have been proposed in the prior art which are of more complex nature than the common circuit employing a single capacitor, described above. Many of these prior art circuits are very effective in suppressing arcing, but are undesirably complex and expensive. Others of the prior art circuits employ a number of components of undesirably large size, again limiting their usefulness.

These and other objections of prior art arc suppression circuits are overcome by the arc suppression circuit of the invention, which eliminates arcing between a pair of breaker contacts, both upon opening and closing of the contacts. The circuit is very low in cost, and preferably is provided by a novel compound impedance element. The novel compound impedance element is of compact size and resembles a standard two terminal capacitor in its external appearance. The compound impedance element is connectable directly across the terminals of breaker contacts and thus is adaptable for replacing the single capacitor of the common are suppression circuit described above.

It is therefore an object of this invention to provide an improved arc suppression circuit.

A further object of this invention is to provide an improved arc suppression circuit which is low in cost and which substantially eliminates arcing between a pair of breaker contacts, both upon opening and closing of the contacts.

Another object of this invention is to provide a compound impedance element having characteristics ideally suitable for use in arc suppression circuits.

It is another object of this invention to provide a compound impedance element which is low in cost.

Still a further object of this invention is to provide a compound impedance element for connection in parallel with a set of breaker contacts to provide arc suppression both upon opening and closing of the breaker contacts.

Yet another object of this invention is to provide a compound impedance element having first and second parallel impedances comprising an arc suppression circuit having only two external terminals, facilitating its connection to the terminals of a set of breaker contacts.

In accordance with a preferred embodiment of the invention, the arc suppression circuit comprises first and second impedances connected in parallel between a pair of terminals. The first impedance includes a first capacitor of relatively small capacitance and a minimum efiective series inductance, and thus has a short natural period of oscillation or, conversely, a rapid charging rate. The second impedance includes a second capacitor of relatively large capacitance and a substantial effective series inductance, and thus has a longer natural period of oscillation, or, conversely, a slower charging rate. The first and second impedances are connected at the pair of terminals in parallel with a set of breaker contacts in an energizing circuit. The energizing circuit produces a current flow through the breaker contacts when the latter occurs for a short period are closed. As discussed above as the breaker contacts open, a fine thread of molten metal tends to form between the contacts. The impedance of the first capacitor is lower than that of the fine thread, and as a result a substantial portion of the current flow from the energizing circuit communicates rapidly to the first impedance, and rapidly charges the first capacitor. As the contacts continue to separate, the current gradually commutates to the larger capacitor which accepts the major portion of the current flow. The second capacitor has a capacitance which is sufliciently high that the sum of its impedance and that of its effective series inductance is lower than the sum of the impedance of the gap between the contacts and the impedance of the connection between the contacts and the terminals. Further, the capacitance of the second capacitor is sufficiently high that the rate of increase of the voltage across the second impedance, as the second capacitor charges, is smaller than the rate of increase of the breakdown voltage across the gap between the separating contact-s. As a result, the current continues to flow through the second impedance, and arcing between the separating contacts is prevented. Upon subsequent closing of the breaker contacts, the charge on the first capacitor discharges rapidly, but, due to its small magnitude, is dis sipated without damaging effects to the breaker contacts. The charge on the second capacitor, although of large magnitude, is prevented from rapidly discharging by virtue of the substantial series inductance included in its circuit. As a result, the parallel first and second impedance of the invention enable the breaker contacts to be both opened and closed while under high potential without any substantial degree of arcing and thus without deleterious erosion or pitting of the breaker contacts. The first and second irnpedances are provided preferably by a novel compound impedance element comprising first and second pairs of electrode sheets or plates the electrode sheets of each pair being insulated from each other to define the first and second capacitors. A first pair of tabs is joined to the first pair of electrode sheets at opposed positions thereon and a second pair of tabs is joined to the second pair of electrode sheets at displaced positions thereon. The first and second pairs of electrode sheets preferably are wound through multiple installed convolutions into a cylindrical configuration one upon the other, and corresponding ones of the first and second pairs of tabs are electrically joined to provide two external terminals between which the first and second capacitors are connected in parallel. The first pair of tabs cooperate with the first pair of electrode sheets to produce oppositely directed charging current flows in the first pair of electrode sheets. The oppositely directed charging current flows have opposed fields, whereby the first pair of electrode sheets, and thus the first impedance, has a minimum effective series inductance. The second pair of tabs cooperate with the second pair of electrode sheets to produce charging current flows in the same or common direction in the second pair of electrode sheets. The charging current flows, since of the same direction, have additive or reinforcing fields whereby the second impedance has substantial effective series inductance.

For a better understanding of the invention, reference may be had to the following description and drawings, in which:

FIG. 1 shows a completely assembled compound impedance element formed in accordance with the invention;

FIG. 2 is a perspective view of the compound impedance element of the invention in partially wound condition, prior to final assembly;

FIG. 3 is a diagram representing the structure and electrical connections of a compound impedance element having two pair-s of electrode sheets comprising first and second parallel-connected impedances, in accordance with a first embodiment of the invention;

FIG. 4 is a diagram representing the structure and electrical connections of a compound impedance element having two pairs of electrode sheets comprising first and second parallel-connected impedances, in accordance with a second embodiment of the invention;

FIG. 5 is a schematic of an ignition circuit including a set of breaker contacts and an arc suppression circuit of the invention connected in parallel with the breaker contacts; and

FIG. 6 is a graph showing a current waveform representing current flow in the energizing circuit portion of the circuit shown in FIG. 5, upon opening of the breaker contacts.

In FIG. 1, the compound impedance element 1 of the invention is shown as a completed assembly having a sealed body 2 of substantially cylindrical form, and a pair of external terminals 3 and 4 projecting axially from its opposite ends. Insulating sleeves 3a and 4a commonly are fitted over the terminal leads 3 and 4 (both shown in broken views).

The compound impedance element 1 of the invention comprises first and second impedances connected in parallel internally of the body 2 and between the external terminals 3 and 4. Each impedance comprises a pair of electrode sheets insulated from one another, at least one of the electrode sheets of the first impedance also being insulated from a corresponding one of the electrode sheets of the second impedance. The pairs of elec trode sheets are wound through multiple, insulated convolutions into a cylindrical configuration, preferably with one pair of electrode sheets wound coaxially about the cylinder formed from winding of the other pair of electrode sheets.

In FIG. 2, the cylindrical configuration of the wound pairs of electrode sheets is indicated in a perspective view; the first impedance 40 is shown in partially unwound form to illustrate its component elements. The first impedance 40 includes a pair of electrode sheets 10a and 11a separated by a first dielectric sheet 12. A second dielectric sheet 13 overlies the interior surface of the electrode sheet 11a and insulates it from the electrode sheet 10a of preceding convolutions.

The first impedance 40 is shown wound about a second impedance 41; the order of winding may be reversed, however. The second impedance 41 comprises a pair of electrode sheets 10b and 11b (not identified in FIG. 2) which are interleaved with the

dielectric sheets

12 and 13 in a similar manner to the electrode sheets 10a and 11a, respectively. At least one of the electrode sheets 10a and 11a is positioned on the

dielectric sheets

12 and 13 so as to have its end separated from the adjacent end of one of the electrode sheets 10b and 11b, respectively, such that at least one of the electrode sheets 10a and 11a of the first impedance 40 is insulated from the corresponding one of the electrode sheets 10b and 11b, respectively, of the second impedance 41.

The electrode sheets 10a, 10b, 11a, and 111) are of rectangular shape and each has a width approximately equal to the axial length of the body 2. The length of the electrode sheets is determined by the electrical characteristics desired in each impedance. The

dielectric sheets

12 and 13 conveniently are of slightly greater width than the electrode sheets so as to prevent contact between the longitudinal edges of the electrode sheets 10a, 10b and 11a, 11b and of a length greater than the combined lengths of either the electrode sheets 10a and 10b, or 11a and 11b, whereby the electrode sheets and dielectric sheets are wound continuously into the cylindrical configuration in the described insulated relationship.

Prior to being wound, a first pair of

connector tabs

14 and 15 is attached to opposite longitudinal edges of the electrode sheets 10a and 11a to provide electrical connections to the first impedance 40; a second pair of

connector tabs

16 and 17 is attached to opposite longitudinal edges of the electrode sheets 10b and 11b (not shown in FIG. 2), respectively, to provide electrical connections to the second impedance 41. The

tabs

14 and 16 and the

tabs

15 and 17 extend from opposite axial ends of the cylindrical structure and are electrically joined to two external terminals 3 and 4 in the completely assembled compound impedance element 1, as shown in FIG. 1. The electrode sheets and 11a and the electrode sheets 10b and 11b of the first and

second impedances

40 and 41 are in spaced, insulated relationship, and therefore define first and second capacitors, respectively. In addition, the tabs 14 to 17 cooperate with their respective associated electrode sheets to determine the inductive characteristics of the

impedances

40 and 41; the positions and effects of the tab positions are shown and described with reference to FIGS. 3 and 4, which show two embodiments of the invention.

In FIG. 3, an edge view representing the lengths of the electrode sheets 10a, 11a and 10b, 11b is shown. The dielectric sheets have been omitted for clarity in illustration. The first impedance 40 of the compound impedance element 1 comprises the first pair of spaced, parallel electrode sheets 10a and 11a which are understood to have substantial surface area dimensions in a plane passing through the lines illustrated and perpendicularly to the plane of the paper. The second impedance 41 comprises a second pair of spaced parallel electrode sheets 10b and 11b which likewise are understood to have substantial surface area. The electrode sheets 10a and 10b are in opposed relationship to, and are insulated from the foils 11a and 11!), respectively; in addition, the sheets 10:: and 11a are spaced from and hence insulated from the sheets 10]) and 111), respectively.

Using primed numerals in FIG. 3 to represent connector tabs corresponding to those shown with unprirned numerals in FIG. 2, a first pair of tabs 14' and is attached to the electrode sheets 10a and 11a, respectively, at opposed positions. The term, opposed positions, means that the tabs are attached to the sheets at corresponding, or opposite, positions along the lengths of the sheets, regardless of the relative locations of the positions across the width of the sheets. A second pair of tabs 16 and 17' are attached to the electrode sheets 1% and 11b respectively, adjacent opposite ends thereof, and thus in relatively displaced positions. The term, displaced positions, means that the tabs are attached to the sheets at positions displaced relatively along the lengths of the sheets, regardless of the relative locations of the positions across the width of the sheets. The lengths of the sheets are usually considerably greater than the widths and hence lengthwise displacement of the tab connectors is more significant with respect to the electrical characteristics than crosswise displacement. The tabs 14' and 16' are attached to corresponding longitudinal edges of the sheets 10a and 1% to extend from one end of the cylindrical body, as represented by the

connector tabs

14 and 16 in FIG. 2, and the tabs 15' and 17' are connected to the opposite, corresponding longitudinal edges of electrode sheets 10b and 11b to extend from the opposite end of the cylindrical body, as represented by the

connector tabs

15 and 17, respectively in FIG. 2. The tabs 14 and 16' are electrically joined to a first terminal 3' and the tabs 15 and 17' are electrically joined to a second terminal 4. The terminals 3' and 4 correspond to the external terminals 3 and 4 of the compound impedance element 1 of FIG. 1.

Each of the electrode sheets 10a, 10b 11a and 11b has an inherent inductance, and, when wound into a cylindrical configuration, each has an inductance determined by the number of turns or convolutions through which it has been wound. By proper positioning of the tabs 16' and 17 on their respectively associated electrode sheets, there may be selected a desired value of inductance which is eifectively in series with the capacitance of the impedance 41.

'In the first impedance 40, a direct electrical potential applied between the terminals 3' and 4' is applied to the electrode sheets 10b and 11b,

tabs 14 and 15', and thus to a central portion of each electrode sheet 10a and I la. Although each of the electrode sheets 10a and 11a is conductive, each has a finite resistance, and the locations of the tabs 14' and 15 determine charging current flow paths in the electrode sheets 10a and 11a, respectively. The application of a positive potential at the tab 14' produces a charging current fiow in the electrode sheet 10a in a direction away from the tab 14, and thus toward the opposite ends of the electrode sheet 10a, as indicated by the arrows. Conversely, the lower potential applied at tab 15 creates charging current flow in the electrode sheet 11a in a direction toward the tab 15' and thus from the opposite ends of the sheet 11a, as indicated by the arrows. Since the charging current flows are in opposite directions in the electrode sheets 10a and 11a along the lengths thereof from the tabs 14' and 15', the fields generated by the charging current flows are in opposition. As a result, the first impedance 40 has substantially no effective series inductance, or at most only a minimal value of effective series inductance.

It should be noted that this elfect is achieved so long as the tabs 14' and 15' are in opposed relationship, regardless of their positions along the lengths of the electrode sheets 10a and 11a, respectively.

"In thesecond impedance 41, the potential between the electrode sheets 1% and 11b in any opposed positions along their lengths is substantially constant. Although each of the electrode sheets 10b and 11b is conductive, each has a finite resistance, and the locations of the tabs 16' and 17 determine charging current flow paths in the electrode sheets 10b and 11b, respectively. Upon the application of a positive potential to the tab 16', and a lower potential to the tab 17', there is established a charging current How in the direction indicated by the arrow adjacent the electrode sheet 1%. The electrode sheet 11b is parallel to the electrode sheet 10b and a constant potential difference is established between any opposed positions of the sheets 10b and 11b. As a result, the tab 17' cooperates with the electrode sheet 111) to produce charging current flows therein in the same direction as in the electrode sheet 10b, as indicated by the arrow adjacent the electrode sheet 11b. Since the chargmg current flows are in the same direction in the and due to the close spacing of the electrode sheets 10b and 1%, the fields generated by the fiows of charging current are closely coupled and reinforce one another. Thus, the second impedance 41 has a substantial, effective series inductance.

The value of the inductance is determined in part by the number of turns of the pair of electrode sheets 10b and 11b for the common portions thereof between the tabs 16' and 17'.

It will be appreciated that by varying the position of either the tab 16' or the tab 17 along the length of the respectively associated electrode sheets 1% and 11b, thereby to decrease the displacement or separation between, the

tabs

16 and 17, the inductively effective length of the electrode sheets is reduced, correspondingly reducing the value of inductance; however, since the total area of the opposed electrode sheets 10b and 11b remains constant, the value of capacitance remains unchanged. Therefore, the eifective inductance may be varied without changing the capacitance. For example, in the configuration shown in FIG. 3, the impedance 41 has maximum inductance and, by moving the tabs -16' and 17 toward one another, the inductance may be decreased.

FIG. 4 represents a second embodiment of the invention including a first impedance 40' and a second impedance 41'. The first impedance 40' includes a first separate electrode sheet 20b. A single or common electrode sheet 21 extends between and forms a second electrode in each of the impedances 40' and 41. The portion 21a of the common electrode sheet 21 which corresponds to, or is in opposed relationship to the electrode sheet 200 provides the second electrode for the first impedance 40, similarly, the portion b of the common electrode sheet 21 which corresponds to, or is in opposed relationship to the separate electrode sheet 2012 forms the second electrode of the second impedance 491'. The electrode sheets 20a and 20b and their respectively associated portions 21a and 21b of the common electrode sheet 21 are in spaced, insulated relationship, and therefore define first and second capacitors in the first and second impedances, respectively.

Tabs

22 and 23 are attached to the separate electrode sheet 20a adjacent opposite ends thereof and on a common edge; tabs 24 and are attached to the corresponding portion 21a of the common electrode sheet 21 in opposed relationship to the

tabs

22 and 23, respectively. A tab 26 is attached adjacent one end of the separate electrode sheet 20b of the first impedance 40 and a tab 27 is attached adjacent the opposite end of the corresponding portion 21b of the common electrode sheet 21. The

tabs

22, 23 and 26 are electrically joined to a first terminal 28 and

tabs

24, 25 and 27 are electrically joined to a second terminal 29. The first and

second terminals

28 and 29 correspond to the external terminals 3 and 4, respectively of the assembled impedance element 1 in FIG. 1.

The tabs 22, 2'3 and 24, 25 establish charging current flow paths in the electrode sheet 20a and in the electrode sheet portion 21a respectively. The application of a positive potential to the terminal 28 and thus to the tabs 22 and 2-3 and a lower potential at the terminal 29 and thus at

tabs

24 and 25 produces charging current flows in an inward direction from the

tabs

22 and 23 in the electrode sheet 20a and charging current flows in an outward direction toward the

tabs

24 and 25 in the electrode sheet portion 21a as indicated by the arrows. Since the charging currents flow in opposite directions in corresponding or opposed portions of the electrode sheet 20a and the electrode sheet portion 21a, the fields created by the charging current flows are in opposition. As a result, the first impedance 40' has a minimal efiective series inductance.

The

tabs

26 and 27 establish charging current flow paths in the electrode sheet 20b and the electrode sheet portion 21b, respectively. The application of a positive potential at terminal 28 and thus at tab 26, and a lower potential at terminal 29, and thus at tab 27, produces charging current flows in the electrode sheet 20b from the tab 26 toward the opposite end of the electrode sheet 26b and in the electrode sheet portion 21b from its free end and toward the tab 27. Since the charging current flows are in a common direction, and due to the close spacing of the electrode sheets, the fields generated by the charging current flows are closely coupled and reinforce one another. As a result, the second impedance 41' has a substantial effective series inductance.

When the electrode sheets of

impedances

40 and 41 are wound into cylindrical configuration, the value of inductance of the second impedance 41 is determined principally by the number of turns of the electrode sheet 20b and the electrode sheet portion 21b for the common lengths thereof between the

tabs

26 and 27 as above discussed. Decreasing the displacement between the

tabs

26 and 27 will correspondingly decrease the inductance, without altering the value of capacitance.

FIG. 5 shows an ignition circuit incorporating the arc suppression circuit of the invention. The ignition circuit includes an induction coil 30 having a primary winding 31 connected at one end to a positive power supply terminal 32 and at the other end to a junction 33. A switch 34, representing a set of breaker contacts (which may be operated either by coil 30, or by a motor-driven or enginedriven cam) is connected between the junction 33 and a second junction 35, which comprises a negative power supply terminal or ground.

The induction coil 30 further includes a secondary winding 36, usually having a greater number of turns than primary winding 31. The secondary winding 36 is connected in series with a diode rectifier 37 and a storage capacitor 38. Output terminals 39 are connected across the capacitor 38.

A unidirectional source of potential is applied to the

power supply terminals

33 and 35. The rapid changes in current flow through winding 31 due to the opening of the breaker contacts 34 cause a voltage to be induced in the primary winding 31 which is stepped up by the inductor 30 to produce a much higher voltage in the secondary winding 36. This higher voltage is rectified by the diode 37 and stored by capacitor 38. A spark gap is connected to output terminals 39 and a spark is produced at that gap when the potential on capacitor 38 exceeds the breakdown potential of the gap.

In the absence of an arc suppression circuit, each time that the breaker contacts start to separate, the field developed in primary coil 31 tends to maintain the flow of current with the result that arcing between the breaker contacts of switch 34 occurs. As discussed in detail above, the current density increases tremendously as the area in which the contacts are touching decreases, with the result that the contact material melts andis drawn into a fine thread as the contacts separate. The current tends to ignite and vaporize this thread, producing a conductive path through which the arc passes between the contacts. The arcing continues until the contacts have separated sufficiently that the breakdown voltage through the gap between the contacts exceeds the potential applied across the contacts. The arcing causes erosion or rapid deterioration of the breaker contacts, and wastes energy which should be delivered to storage capacitor 38, and therefore must be suppressed.

The are suppression circuit of the invention preferably is provided by the compound impedance of the invention, and will be described in relation to the novel compound impedance element. The compound impedance element (as described in relation to either FIG. 3 or FIG. 4) is represented in its schematic equivalent circuit as connected between the

junctions

33 and 35 and thus in parallel with the breaker contacts 34. The compound impedance includes a first impedance 40" comprising a capacitor C and a series inductance L having electrical values as in the capacitance and effective series inductance of the first impedance 40 or 40', as hereinbefore described. The compound impedance also includes a second impedance 41" comprising a capacitor C and an inductor L having electrical values as in the capacitance and effective series inductance of the second impedance 41 or 41', as hereinbefore described. It is to be understood that the arc suppression circuit of the invention may comprise physically separate capacitors C and C associated with eifective series inductances L and L respectively, and therefore is not limited to the use of the compound impedance element.

The current waveform of the graph of FIG. 6 represents the current passing through the primary winding 31 of the energizing circuit of FIG. 5, the abscissa of the graph representing time and the ordinate, the amplitude of the current. Time t represents the opening of the breaker contacts of switch 34 subsequently to the application of a positive potential to the terminal 33. Due to the inductance of inductor 31, the current prior to time t gradually increases. (The current would attain a steady state or constant amplitude, 1 after a sufficiently long closure period of the breaker contacts 35; however, the contacts are typically opened and closed at too rapid a rate to permit such a steady state to develop).

Upon opening of the contacts at time t the current previously conducted through the breaker contacts commutates almost entirely and immediately to the first impedance 40", charging capacitor C The tendency of the current to form a thread of molten material and thereafter to vaporize the thread and establish an are between the contacts is thereby avoided. Capacitor C charges more slowly than the capacitor C as a result of the greater natural period of oscillation of the second impedance 41", due both to the greater capacitance of capacitor C and to the substantial value of inductance of inductor L Capacitor C therefore would not sufiice, by itself, to suppress arcing upon initial opening of the contacts 34; however, the natural period of oscillation of the second impedance 41" permits sufiiciently rapid charging of capacitor C to enable gradual commutation of the current from capacitor C to capacitor C the latter receiving a major portion of the current flow due to its greater capacitance. As discussed above, capacitor C charges at a rate such that the voltage across it increases at a slower rate than the rate of increase of the breakdown voltage across the gap between the separating contacts. As a result, capacitor C operates to prevent the generation of an are between the contacts.

The relative magnitudes of both the currents in, and the oscillation periods of, the first and second impedances 40" and 41" are represented by the small oscillations 40a superposed on the major oscillations 41a, respectively, as shown in FIG. 6. The superposing, of course, represents the addition of the separate currents in the parallel first and second impedances 40" and 41", the total representing the current flowing in the inductor winding 31.

The oscillatory currents in each of the first and second impedances 40" and 41" "are damped by inherent dissipation, and the total current flow gradually decreases to a minimal value. During this time, the breaker contacts move rapidly to a widely spaced condition such that the breakdown voltage through the gap between the contacts far exceeds any potential which may be applied across the contacts. After the breaker contacts 34 have been opened for a su'fiiciently long time, the damped current oscillation of FIG. 6 substantially subsides and a voltage approaching that of the source potential is stored in capacitors C and C In the absence of inductors L and L the capacitors C and C would tend to discharge as the breaker contacts approached closed position, thereby causing arcing between the breaker contacts. The inductance of inductor L although minimal, tends to. oppose this discharging of capacitor C in addition, the small capacitance of C results in its having a very small discharge current which does not have any substantial deleterious effect on the breaker contacts. The large inductance value of L prevents a rapid discharge of capacitor C and thereby avoids deleterious arcing between the breaker contacts as a result of the discharge current from capacitor C The major discharge of capacitor C therefore occurs after the breaker contacts 34 have closed, whereby no arcing occurs.

In summary, the suppression circuit of the invention provides greatly improved operation, substantially eliminating arcing between a pair of breaker contacts, both upon opening and closing of the contacts. It is apparent that the number of parallel imped'ances may be increased and the capacitance and inductance of each impedance adjusted to provide desired arc suppression characteristics in the circuit. It has been shown, in addition, that the compound impedance element of the invention has highly advantageous characteristics for use as an arc suppression circuit. Since only two external terminals are necessary, the compound impedance element may be used as a direct replacement of conventional capacitors commonly employed in simple arc suppression circuits, with greatly improved results. As noted above, however, while the compound impedance element illustrated has substantial advantages over other arc suppression devices,

nevertheless, the principal results of that device, as far as arc suppression is concerned, may be secured in an apparatus in which the capacitors C and C are physically separate, instead of being wound together, as long as they are respectively associated with efiective series inductances proportioned as described herein. The compound impedance element of the invention is very easy to manufacture in accordance with known manufacturing techniques and employs a minimum number of inexpensive components. The compound impedance element is compact in size and has an external configuration similar to that of common capacitors. It may readily be designed to incorporate desired values of capacitance and inductance in either of the first and second impedances; in addition, the compound element may readily be constructed to include three or more such parallel impedances of selected, or desired, capacitance and inductance values.

Numerous modifications and adaptations of the invention will readily occur to those skilled in the art, and therefore it is intended by the appended claims to cover all such modifications and adaptations which fall within the true spirit and scope of the invention.

What is claimed is:

1. Arc suppression apparatus adapted for continuous connection between a cooperating pair of openable and closable contacts, comprising:

(a) a pair of terminals respectively connectable to said contacts;

(b) first capacitive impedance means connected permanently between said terminals and having relatively small series capacitance and substantially minimum elfective series inductance; and

(0) second capacitive impedance means connected permanently between said terminals in parallel with said first impedance means and having relatively large series capacitance and a substantial elTecti-ve series inductance.

2. Are suppression apparatus as recited in claim 1 wherein:

(a) said first impedance means comprises a first pair of electrode sheets and a first pair of tabs attached to said first pair of electrode sheets in substantially opposed positions, said first pair of tabs and said first pair of electrode sheets determining the relative location of charging current flow paths in said first pair of electrode sheets and the relative directions of charging current flow along said paths so as to substantially minimize inductance in said first impedance means; and

(b) said second impedance means comprises a second pair of electrode sheets and a second pair of tabs attached to said second pair of electrode sheets in displaced positions, said second pair of tabs and said second pair of electrode sheets determining the relative location of the charging current flow paths in said second pair of electrode sheets and the relative directions of charging current flow along said paths so as to produce a substantial effective series inductance in said second impedance means.

3. Arc suppression apparatus as recited in claim 1 wherein:

(a) said first impedance means comprises a first pair of electrode sheets and a first pair of tabs attached to said first pair of electrode sheets at substantially opposed positions, said first pair of tabs cooperating with said first pair of electrode sheets to produce oppositely directed charging current flows having opposed fields whereby said first impedance means has a substantially minimal effective series inductance; and

(b) said second impedance means comprises a second pair of electrode sheets and a second pair of tabs attached to said second pair of electrode sheets in displaced positions, said second pair of tabs cooperating with said second pair of electrode sheets to prowherein corresponding ones of said first and of electrode sheets comprise portions of a single electrode sheet opposed to corresponding other ones of said first and second pairs of electrode sheets.

6. An arc suppression circuit for connection in with a set of separable contacts between a pair of terminals to which an electrical potential is applied to suppress arcing between said contacts, comprising:

duce charging current flows in a common direction having reinforcing fields whereby said second impedance means has a substantial effective series inductance. 4. Arc suppression apparatus as recited in claim 2 second pairs 5. Arc suppression apparatus as recited in claim 2 wherein:

(a) said first and second pairs of electrode sheets are wound through multiple, insulated convolutions into a general cylindrical configuration; and

(b) corresponding ones of said first and second tabs are attached to opposite edges of said electrode sheets of each of said first and second pairs of electrode sheets, respectively, whereby said corresponding ones of said first and second pairs of tabs extend axially from opposite ends of said generally cylindrical configuration of said electrode sheets.

parallel (a) first impedance means having a first capacitor of relatively small capacitance and a substantially minimum effective series inductance, the electrical potential on said terminals commutating to said first impedance means substantially unimpeded by said substantially minimum effective series inductance and charging said first capacitor upon opening of said contacts;

(b) second impedance means connected in parallel with said first impedance means and including a second capacitor of relatively large capacitance and a substantial effective series inductance, the electrical potential on said terminals commutating to said second impedance means and charging said second capacitor at a slower rate than the commutation to said first impedance means upon opening of said breaker contacts;

(c) both said first and second impedance means undergoing a damped oscillation upon opening of said contacts; and

(d) said substantial effective series inductance of said second impedance means opposing rapid discharge of said second capacitor to prevent arcing between said contacts upon subsequent closing thereof.

7. An arc suppression circuit as recited in claim 7 wherein:

(a) said first impedance means comprises a first pair of electrode sheets providing said first capacitor; (b) said first impedance means further includes a first pair of tabs attached to said first pair of electrode sheets at substantially opposed positions and cooperating with said first pair of electrode sheets to produce oppositely directed charging current flows having opposed fields whereby said substantially first impedance has said minimal effective inductance in series with said first capacitor;

(c) said second impedance means comprises a second pair of electrode sheets providing said second capacitor; and

(d) said second impedance means further includes a second pair of tabs attached to said second pair of electrode sheets at displaced positions to produce charging current flows in said second pair of electrode sheets in a common direction and having reinforcing fields, whereby said second impedance means includes said substantial effective inductance in series with said second capacitor.

8. A compound impedance element comprising:

(a) a first pair of electrode sheets insulated from each other to define a first capacitor and a first pair of tabs 12 attached to the first pair of electrode sheets at substantially opposed positions;

(b) a second pair of electrode sheets insulated from each other to define a second capacitor and a second pair of tabs attached to said second pair of foils at displaced positions;

(c) said first pair of tabs cooperating with said first pair of electrode sheets to produce oppositely directed charging current flows having opposed fields whereby said first impedance means has a substantially minimal effective series inductance; and

((1) said second pair of tabs cooperating with said second pair of electrode sheets to produce charging current flows in a common direction having reinforcing fields whereby said second impedance means has a substantial effective series inductance.

9. A compound impedance element comprising:

(a) a first pair of electrode sheets insulated from each other to define a first capacitor and a first pair of tabs attached to the first pair of electrode sheets at substantially opposed positions;

(b) a second pair of electrode sheets insulated from each other to define a second capacitor and a second pair of tabs attached to said second pair of electrode sheets at displaced positions;

(c) said first pair of tabs and said first pair of electrode sheets determining the relative location of charging current flow paths in said first pair of electrode sheets and the relative directions of charging current fiow along said paths so as to substantially minimize inductance in said first capacitor; and

(d) said second pair of tabs and said second pair of electrode sheets determining the relative location of charging current flow paths in said second pair of electrode sheets and the relative directions of charging current flow along said paths so as to produce a substantial effective series inductance in said second impedance means.

It). A compound impedance element as recited in claim 9 wherein corresponding ones of said first and second pairs of tabs are electrically joined to provide a pair of external terminals on said compound impedance element between which said first and second capacitors are connected in parallel.

45 11. A compound impedance element as recited in claim 9 wherein:

(a) said first pair of tabs is attached to said first pair of electrode sheets at central positions on opposite edges thereof;

(b) said second pair of tabs is attached to said second pair of electrode sheets adjacent opposite ends and on opposite edges thereof; and

(c) corresponding ones of said first and second pairs of tabs are electrically joined to provide a common pair of external terminals on said compound impedance element between which said first and second capacitors are connected in parallel.

12. A compound capacitor as recited in claim 9 where- (a) first ones of said first and second pairs of electrode sheets each comprises a separate electrode sheet; (b) second ones of said first and second pairs of electrode sheets each comprises a corresponding, opposed portion of a common, single electrode sheet; and

(c) said first and second separate electrode sheets and said first and second corresponding, opposed portions of said single electrode sheet comprise said first and second capacitors, respectively. 13. A compound impedance element as recited in claim 12 wherein there is further provided:

(a) a third pair of tabs, first ones of said first and third pairs of tabs being attached to said separate electrode sheet of said first capacitor adjacent opposite 75 ends thereof and second ones of said first and third pairs of tabs being attached to said first correspond- (b) said second ones of said first, second and third ing opposed portion of said common electrodesheet pairs of tabs are electrically joined to a second terin substantially opposed relationship to said first ones rninal; and

of said first and third pairs of tabs, respectively; and (c) said first and second capacitors are thereby con- (b) a first one of said second pair of tabs is attached to 5 nected in parallel between said first and second tersaid separate electrode sheet of said second capacitor minals.

adjacent one end thereof and a second one of said 16. A compound impedance element as recited in claim second pair of tabs is attached to the corresponding, 8 wherein said first and second pairs of electrode sheets opposed portion of said common electrode sheet adare wound through multiple, insulated convolutions into a jacent an end thereof opposite aid one end of aid 10 generally cylindrical configuration, one upon the other. separate electrode sheet.

14. A compound impedance element as recited in claim References Cited 9 wherein said second tab of said second pair of tabs is UNITED STATES PATENTS attached to said common electrode sheet adjacent the 2199909 5/1940 Burton et a1 end thereof 15 2,849,659 8/1958 Kesselrin 317 11 15. A compound impedance element as recited in claim 13 Wheremi MILTON O. HIRSHFIELD, Primary Examiner.

(a) said first ones of said first, second and third pairs of tabs are electrically joined to a first terminal; LUPO Asslsmm Exammer- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,376 ,474 April 2 1968 Norman I. Glover et al.

ears in the above identified It is certified that error app e'by corrected as patent and that said Letters Patent are her shown below:

In the heading to the printed specification, lines 4 and 5, "Louis I. Knudson, Norwich, N. Y., and Harry G. Shoemaker, Norwich,

Conn.," should read Louis I. Knudson, and Harry G. Shoemaker, Norwich, N. Y., Column 3, line 6, "communicates" should read commutates line 43, "installed" should read insulated Column 11, line 50, the claim reference numeral "7" should read H 6 Signed and sealed this 12th day of August 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. ARC SUPPRESSION APPARATUS ADAPTED FOR CONTINUOUS CONNECTION BETWEEN A COOPERATING PAIR OF OPENABLE AND CLOSABLE CONTACTS, COMPRISING: (A) A PAIR OF TERMINALS RESPECTIVELY CONNECTABLE TO SAID CONTACTS; (B) FIRST CAPACITIVE IMPEDANCE MEANS CONNECTED PERMANENTLY BETWEEN SAID TERMINALS AND HAVING RELATIVELY SMALL SERIES CAPACITANCE AND SUBSTANTIALLY MINIMUM EFFECTIVE SERIES INDUCTANCE; AND (C) SECOND CAPACITIVE IMPEDANCE MEANS CONNECTED PERMANENTLY BETWEEN SAID TERMINALS IN PARALLEL WITH SAID FIRST IMPEDANCE MEANS AND HAVING RELATIVELY LARGE SERIES CAPACITANCE AND A SUBSTANTIAL EFFECTIVE SERIES INDUCTANCE.