US2157925A - Electric discharge apparatus - Google Patents

Description

y 9, 1939- R. N. STODDARD 2,157,925

ELECTRIC DI SCHARGE APPARATUS Filed March 13, 1937 WITNESSES: I 7 INVENTOR ,Wui, Edi 0h A4 Szaddar'd.

. ATTORN Y Patented May 9, 1939 PATENT OFFICE 2,157,925 ELECTRIC DISCHARGE APPARATUS Ralph N. Stoddard, Pittsburgh, Pa... assi'gnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 1a, 1931, Serial No. 130,755

10 Claims. (01. 115- 294) My invention relates to electric discharge apparatus and has particular relation to apparatus for interrupting an are such as is produced by the opening of switch contacts.

I 5 It is an object of my invention to provide an arc interrupting system of simple andinexpenrive structure. 7

Another object of my invention is to provide an arc interrupting system entirely devoid of 1 mechanical contacts.

, An ancillary object of my invention is to provide a highly certain and eflicient means for initiating the discharge in a discharge device of v the type comprising a mercurypool cathode and 15 a starting electrode composed of boron carbide or silicon carbide to cooperate with the cathode. More specifically stated, it is an object of my invention to provide a system for interrupting I 30' trol potential, thedrop in potential across an open air arc, such as is produced by opening a power switch, is suihcient to initiate a discharge between the principal electrodes. The difference in potential between the principal electrodes when 35 a discharge is thus initiated is substantially smaller than the drop in potential across the arc. Therefore, when a discharge is produced between the principal electrodes, the arc is extinguished.

In the preferred practice of my invention, the

' discharge device utilized is of the Ignitron tube type. The latter comprises an anode, a mercurylike cathode and a starting electrode of the silicon carbide type, which dips into the cathode. By the expression fmercury-llke cathode," I

45 mean a cathode composed of mercury or an element similar to it. The most common example of such an electrode is a pool of mercury. However, other metals such as cadmium and lead, for example, may be utilized and are contemplated 50 as lying within the scope of my invention. By

the expression "a starting electrode of the silicon carbide type, I mean a starting rod which is dipped into the mercury-like electrode and through which a current is transmitted to initiate st a'discharge between the anode and the A silicon carbide rod is the most common example of such an element. However, I have found that numerous other compounds may be utilized. Among these the most common are boron and boron carbide. I contemplate within the scope of my invention, discharge devices' incorporating starting rods of any suitable type.

While the discharge devices of the Ignitron tube type are preferable in the practice of my invention, occasions may arise for the use of discharge devices of other types. For example, under certain circumstances, it may be possible to utilize a hot cathode gaseous discharge device of the arc-like type, such as a Thyratron tube or a grid glow tube. While the Ignitron tube has certain peculiar advantages, the use of discharge devices of other types in accordance with my invention are contemplated as lying within the scope of my invention.

In the practice of my invention, the anode and the cathode of the discharge device utilized are connected directly across the region in which the arc to be extinguished is produced. The starting electrode and the cathode of the discharge device are also connected across the same region through a tuned network. When the arc is produced, high frequency current passes through the tuned network and for the proper polarity of anode cathode potential, the discharge device isenerglzed and extinguishes the arc.

In accordance with an ancillary feature of my invention, the discharge in the discharge device is initiated by a contrivance which I have found to be simple and emcient. The network in the starting c'ircuit'is tuned to a frequency such that the starting electrode"has the maximum skin effect. Accordingly, the starting current flows near the surface of the starting electrode and is highly effective in initiating the main discharge.

The novel features that I consider character- \istic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional obiects and'advantages thereof, will best be under- 4 stood from the following description of specific embodiments when read in. connection with the accompanying drawing, in which Figure 1 is a diagrammatic view showing .an embodiment of my invention; 5 Fig. 2 is a graph illustrating the operation of my invention, and I Fig. 3 is a diagrammatic view showing a modification of my invention.

The apparatus shown in Fig. l comprlses a 5 -sisting of a capacitor 23 and an inductor 25.

inductor and capacitbr are so selected that the conductor 5 through which it may be assumed that alternating current is transmitted. The conductor 5 may be opened under certain circumstances by the disengagement of the movable contactor I of a circuit breaker 9, which may be regarded as symbolical of a circuit interrupter of any general type, from corresponding fixed contacts II;. The circuit-breaker operating mechanism may be of any well known type and since it'does not concern the present invention will not be discussed in detail here.

When the contacts I and II of the circuit breaker 9 are opened, an arc is produced and to break the are an electrode discharge device I3 is provided. The discharge device has an anode i5 composed of an element such as nickel or carbon, a cathode ll of mercury and a starting electrode is consisting of a rod of boron, boron carbide, silicon carbide or the like, which dips into the mercury. The anode it of the discharge device I! is connected directly to one of the fixed contacts II and the cathode I1 is connected directly to the other. The starting rod I8 is connected to a fixed contact ll of the circuit breaker 0 on one side through the mercury cathode l1 and on the other side through a network 2| con- The network 2l is tun to a predetermined frequency.

The operation the apparatus is illustrated in Fig, 2. In this graph, the sine curve 21 corresponds to the potential which would be impressed across the fixed contacts ii if they were not bridged by the movable contactor I. The same potential would be impressed between the anode l5 and the cathode ll of the discharge device It. The polarity of the ordinates of the curve 21 correspond to the polarity of the potential impressed between the principal electrodes of the discharge device. Accordingly, if the circuit breaker contacts I and II were open, the left hand half wave would impress a negative anodecathode potential while the right'hand half wave would impress a positive potential.

The actual potential across the contacts II is represented by the heavy line 29. At the beginning of the half cycle illustrated in Fig. 2, the contacts 1 and H are closed and the potential across the contacts is zero as represented by the line 0i along the abscissa.

Let us assume now that the circuit breaker 9 is opened atgan instant late in the negative half cycle. At this instant an arc is ignited between the contacts and the potential drop rises from zero to the negative value corresponding to the potential drop across the open air arc; This is represented by the'line 33 below the abscissa.

The are produced cooperates with the tuned network 2| tosinitiate a high frequency disturbance inthe circuit incorporating the tuned network, the starting electrode is and the cathode ii. The disturbance is illustrated in the lower portion of Fig. 2 by a high frequency wave 38.

I attains a predetermined value.

While current is now being transmtited through the starting electrode l9 and the cathode n, the

discharge device is not energized because the anode-cathode potential is of improper polarity. The open air arcthus continues to burn until the anode cathode potential passes through zero and becomes positive, and its potential may be repreand the potential drop across the fixed contacts ll decreases to a comparatively small value as represented by the heavy line-31 above the :abscissa. The magnitude of this new potential drop between the anode l5 and the cathode i1 and therefore across the contacts I I is such that the are between the contacts 'I and H is extinguished. The discharge devices then continue to pass current until the end of the positive half cycle during which it was energized and then it is exting'uished. Since the are between the contacts I and H is now also extinguished, and has been extinguished for the larger part of a half cycle, it is not reignited during the succeeding half cycle. The discharge device is not reignited duringthe subsequent positive half cycle since in the absence of the are no high frequency currents flow through the tuned circuit and thus the system is reverted to a deenergized condition with circuit breaker 9 open.

As I have indicated hereinabove, the network in series with the starting rod i9 is tuned to a;

predetermined frequency. I have found that it should be so tuned that the maximum skin eil'ect is manifested in the conductivity of the rod. When the frequency is such that the conductivity .of the rod manifests the maximum skin eifect,

the current passing through the rod is most eiiicient in initiating the main discharge. If the frequency is higher, the current passes over the surface of the rod and is not efl'ective' in energizing the discharge device. If it is lower, the current passes in a region well within the rod and while the main discharge will be ignited, the current required is generally considerably greater than that required where the frequency corre-,

sponds to the maximum skin eflect. Therods commonly utilized in discharge devices of the Ignitron tube type are% inch in diameter and one inch long, and -I have found that for these the network should be tuned to a frequency of the order of 150,000 cycles.

As is apparent from Fig, 2, there is some dela in the extinction of the are produced at the contacts 1 and II of the circuit breaker 9'when only a single discharge device it is connected across the fixed contacts. If this delay is undesirable, a pair of discharge paths may be utilized to replace the single one of the embodiment of Fig. l.

'A system for instantaneously extinguishing the arc is illustrated in Fig. 3. Here, a pair of discharge devices 39 and 4| are provided. The discharge devices are connected in anti-parallel so that the anode-cathode polarity of one of them always corresponds to the anode-cathode polarity which would exist across the fixed contacts ll were they open. The tuned network 2! is now connected between the starting electrodes I! of the discharge devices and through the corresponding cathodes H to the flxed' contacts ll of the circuit breaker. When the circuit breaker is opened and an arc is ignited, high frequency impulses pass back and forth in the circuitincluding the cathodes H, the starting rods I9 and the tuned network 2|. The discharge device for which the anode-cathode potential is of the proper polarity is then immediately energized and the arc is extinguished in the same half cycle.

While in thefembodiment shown in Fig; 3, two distinct discharge devices 39 and I are shown as utilized, they'may be replaced by a single discharge device having a pair of mercury-like cathodes intoeach of which starting rods dip. When one of the cathodes is positive and the other is negative, the former functions as an anode and the latter as a cathode so that a discharge may be ignited between the two by the starting rod immersed in the latter. When the polarities are reversed, the former cathode becomes an anode and the former anode becomes a cathode.

While my invention has herein been illustrated as applied. to the extinction of an arc produced by switching or circuit breaker operations, it should be recognized that it has certain broader aspects. For example, it may be applied in apparatus in which a discharge device of the Ignitron tube type is to supply power. Under such circumstances, an arc may be produced in a spark gap or other device and utilizedto ignite the discharge device. My invention may also be applied in resistance welding. In this field of application, the contacts I and H may be replaced by a drum contact or may be associated with a suitable timer so that the conductor 5 is periodically open circuited and closed circuited. The welding electrodes are connected to conductor 5 and the arcing stress on the interrupting contacts 'I and ii is relieved by the discharge devices 39 and 4! (H8. 3).

It is to be noted, moreover, that the network II is a series tuned network. In the structure specifically dlsclosedherein a network of this type is desirable because the discharge devices It, 39 and U require ansmission 'of current through the rods, I! for arting, i. e., the rods operate most eificiently for high current and low potential. Discharge devices of other types, such, for example, as grid controlled gaseous devices, which are contemplated as included within the scope of my invention may require high potential and low current for starting. when the latter discharge devices are utilized in the practice of my invention, the series tuned network 2! should be replaced by a parallel tuned network or a combination of series and parallel tuned networks.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not, to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Apparatus for interrupting the flow of current through a conductor comprising means to be actuated for producing an open gap in said conductor, a pair of separate sets of electrodes delining electric discharge paths connected in antiparailel. across the position in said conductor where said gap is to be opened, the potential drop across the electrodes of each or said discharge paths when it is energized being substantially smaller than the potential drop across an arc 'producedacross said gap when said means is actuated, and means common to both said discharge paths for initiating an arc in the one corresponding to the direction of flow of current in said conductor at the instant that said gap is opened.

2. Apparatus for interrupting the flow oi current through a conductor comprising means to be actuated for producing an open gap in said conductor, a pair of separate sets of electrodes defining electric discharge paths connected in antiparallel-across the .position in said conductor where said gap is to be opened, the potential drop across the electrodes of each of said discharge paths when it is energized being substanti ly smaller than the potential drop across an produced across said gap when said means, is

actuated, and means common to both said discharge paths and including a network cooperative with an arc across said gap to produce high frequency current flow for initiating an arc in the one corresponding to the direction of flow of current in said conductor at'the instant that said gap is opened upon the opening of said gap.

3. Apparatus for interrupting the flow of current through a conductor comprising means to be actuated for producing an open gap in said conductor, an electric discharge path, defined'by an anode, a mercury like cathode and including an electrode comprising a rod of the silicon carbide type dipping into the cathode between which and the cathode a current is conducted to initiate a discharge between said anode and cathode, said anode and cathode being connected across the position in said conductor where said gap is opened, the potential drop between said anode and cathode when .a discharge is initiated therebetween being substantially smaller than the potential drop across an arc produced across said gap when said means is actuated, and means consisting of a network extending from one terminal of the gap, through impedances tuned to the frequency at which the current flowing through said electrode would have the maximum skin eiIect, said electrode, said cathode to the other terminal of said gap, for initiatinga discharge between said anode and cathode upon the opening of said gap.

4. In combination, electric discharge path means comprising a cathode of the mercury type. a collecting electrode to cooperate with said cath- -ode, and a rod electrode of the silicon carbide type dipping into said cathode between which and' the cathode a current is to flow to initiate a discharge in said path means and means for transmitting between said i'od electrode and said cathode a current of a frequency at which the electrode manifests the maximum skin effect to initiate said discharge. I

5. In combination, electric discharge path means comprising a cathode of the mercury type, a collecting electrode to cooperate with said cathode, and a rod electrode of the silicon carbide type dipping into said cathode between which and the cathode a current is to flow to initiate a discharge in said path means and means including an arc and a tuned network connected across said arc for transmitting between said rod electrode and said cathode a current of a frequency at which the electrode manifests the maximum skin eflect. to initiate said discharge.

7. In combination, in effect, a pair ofeiectric discharge path means connected in anti-parallel, each path means comprising in effect a cathode of the mercury type, a collecting electrode to cooperate with said cathode, and a rod electrode of the silicon carbide type dipping into said cathode between which and the cathode a current is to flow to initiate a discharge in saidpath means and means consisting of an arc and a network extending from one terminal of the are, through a cathode of one discharge path means, the corresponding rod electrode, a pair of impedances consisting of an inductor and a capacitor, the rod electrode of the other path means, the corresponding cathode to the other terminal of the arc, for initiating a discharge in either of said path means.

8. Apparatus according to claim 7, characterized by the fact that the inductor and capacitor are of such magnitude that current flows through the network at a frequency corresponding to the maximum skin effect of the rod electrodes.

9. Apparatus according to claim 7, characterized by the fact that the rod electrode has a dimeter or the order of and the inductor and capacitor are of such magnitude that current flows through the network at a frequency. of the order of 150,000 cycles.

10. Apparatus for interrupting ,the flow of ourrent through a conductor comprising means to be actuated for producing an open gap in said conductor, a pair 01 separate sets of electrodes defining electric discharge paths connected in antiparallel across the position in said conductor where said gap is to he opened, the potential drop across the electrodes of each of said discharge paths when it is energized being substantially smaller than the potential drop across an are produced across said gap when said means is actuated, each said sets of electrodes including an ignition electrode in contact with one of the other electrodes of its set, and a single network interconnecting-the ignition electrodes of each said set and responsive to the opening of said gap for initiating an arc in the one corresponding to,

the direction oi flow of current in said conductor at the instant that said gap is opened.

RALPH N. STODDARD,

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