BE397813A - - Google Patents

Description

       

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  Electric arc devices.



   The present invention relates to electric arc devices and particularly relates to such devices which operate with a new fixed, weakly conductive ignition device, and to improvements, some of which are of novelty. of a more general nature, which were introduced with the aim of overcoming the difficulties encountered in electrical steam arc devices using the new ignition.



   The present invention is based on a new type of initiation device comprising a means of forming a,, / cathode spot on one of the main electrodes of a.

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 interval or arc device, such as an arc and steam rectifier or inverter or an arc, free air or vacuum switch device, of general utility for closing or opening a circuit, or special utility as in a lightning arrester.



   More particularly, the invention relates to a new flat type of arc and steam rectifier or inverter for which the term "ignitron" has been coined by which one wishes to state the idea that it relates to the transport of current by positive ions or negative ions or electrons.



  This can be explained briefly as follows.



   Research into mercury arc rectifiers and the causes of back-ignitions in them has drawn attention to the fact that the more the return current is reduced, the less return ignitions there will be in them. a given space of time, during periods of non-arcing. This has led to the idea of a new type of rectifier or ignitron in which the average return current approaches almost absolutely zero, preferably being less than one to ten micro-amps per square inch (64.5 mm2) of the effective area of the main anode for a device estimated at 600 volts dc, with lower and higher tolerances for higher and lower voltages respectively.

   This should be compared to the ordinary multi-anode, mercury arc rectifier in which the return current is maintained at a value of 10 to 100 micro-amps per square inch (64.5 mm2) of anode area, only by the use of complicated anode screens, of. baffles and grilles and in which if these screens and grilles are removed, the current in

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 return amounts to 10,000 micro-amps per square inch (64.5 mm2) or even more.



   In conventional types of mercury arc rectifiers used heretofore, there was an arc in the device during the non-arcing period, either as a result of arcs terminating on other main anodes, either as a result of ares ending on a starting anode, or as a result of both at the same time. As a result, the arcing space between the main anodes which are assumed not to conduct current during their non-arcing periods is filled with ions and electrons.

   The result is that an arc space or separation between electrodes which, according to tests, in the absence of free electrons and ions, is able to withstand several voltages. times higher than the voltages applied thereto during operation of the rectifier, frequently pierces with formation of a cathode spot and it is believed that the probability of the formation of such a cathode spot is strongly favored by the existence back currents.



   However, the most important feature of the new rectifier or ignitron is the elimination of all the main anodes except one and the elimination of the ordinary re-ignited arc which burns during periods of no arc formation or, more generally, the elimination of anything that supplies significant amounts of ions or electrons to the arcing space during periods of reverse ignition. This involved the invention and use of the priming device mentioned above.



   In general, the invention consists of an arc discharge device comprising two main electrodes, terminal connections for them and a

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 starting device in the vicinity of the main arc-forming path for causing an arc to occur between these two main electrodes, said starting device comprising a rod of a weakly conductive material having one end in permanent contact with a main electrodes to form a cathode spot thereon, and a separate terminal connection for the other end of this rod.



   The object of the invention is to prevent the onset of back-ignition causes in steam arc rectifiers or reversers rather than simply trying to prevent the back-ignition causes. to become complete return ignitions. The existence of reverse current appears to be essential for a reverse ignition cause to arise, and when the reverse current is reduced, the reverse ignition causes become less frequent and probably do not occur at all. all if the return current is reduced to zero.



   Having eliminated the causes of reverse ignition by substantially eliminating the return current of a few milliamperes during reverse ignition periods, the need for many features which have heretofore been required in rectifiers is avoided. ordinary mercury arc. Thus, in many cases any shielding arrangement in the arcing space can be omitted which makes the rectifier smaller and very significantly reduces arcing or losses in the device. The distance between the main anode and the cathode can be reduced, further reducing the size and the losses.



    @ As there is no return current, no

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 cause of backfiring will not exist if the mercury particles are thrown over the anode from the surface of the cathode or if the mercury particles condense on the anode, so the anode can be placed very close cathode and be exposed directly to it, and that the anode can operate at a fairly cool temperature compared to ordinary practice of mercury arc rectifiers because it is no longer necessary to guard against the cathode. possibility of mercury condensation on the anode, which has always seemed to cause a high frequency of back-ignition causes in previous designs.

   The operation of the anode at a temperature, cold compared to the previous practice of rectifiers, preferably of the order of 80 or 1000 to 2500 or 300 C perhaps, or even more for arc rectifiers at Mercury of the new design, is frequently desirable, also, owing to the proximity of the anode to the cathode, the low temperature of the anode being generally required in order to keep the vapor pressure low to the desired extent, despite the drops of mercury hitting the anode. This reduced vapor pressure further increases the negative voltage that the arc space will withstand without being pierced during periods of non-arcing.



   In operation of the so-called "flat" rectifier as described above, that is to say of a rectifier consisting of a flat anode having dimensions commensurate with the cathode and placed near the cathode, with a spacing of the order of one-half inch to four inches (12.6 mm to 10 cm) or more, the active surface of the cathode comprising a vaporizable reconstruction material, such as mercury or mixtures containing mercury, or gallium or

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 mixtures containing gallium, it is important or desirable to cool the cathode very completely by actually operating it at as cold a temperature as can be conveniently obtained and it is highly desirable to use some sort of cathode spot fixation medium and preferably

   a suitably cooled cathode spot fixing means, as tests have shown that the probability of backfire is very greatly reduced with such an arrangement, probably as a result of the vapor blowing from the cathode being much less intense when the cathode spot is fixed and perhaps because the interaction of this steam blast and the anode somehow causes the back-ignition causes.



   Although the object of the present invention is to reduce the frequency of kickback generation by reducing the magnitude of the kickback current, there are transient times in some cases where the special construction does not produce this result. When a rectifier is traversed by a current, this current increases to a maximum value and then, at the end of the period of arcing, and particularly in the case where the direct current circuit contains a considerable amount of inductances, the rectifier current decreases rapidly to zero and the applied voltage increases rapidly to a high value in the negative direction.

   Immediately after this zero current, the arcing space between the anode and cathode is left in a strongly ionized state and the return current is also very high, therefore with a high probability of reverse ignition. . In a few microseconds, the arcing space regains its dielectric state of

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 low probability of back-ignition and the ions disappear as a result of their diffusion towards the walls of the vessel.



  If a negative voltage is applied to the anode immediately after the current has passed, particularly within a few microseconds after it has passed, there is a danger of piercing or back ignition due to the back current which exists. te for a short period of time during this so-called transition period from an ionized state to a non-ionized state.



   If the direct current circuit fed by the rectifier contains a significant amount of inductors, it is usually necessary to introduce delay circuits to delay the rate at which negative voltages build up on the anode at the end of the arcing periods of the device.

   Similar phenomena were not generally observed in earlier types of mercury arc rectifier devices because in these devices one or more ares reigned somewhere in vacuum space during all periods of non-formation. arcing of any anode, so that there is generally no greater tendency to reverse ignition during the above-mentioned transition period immediately after the arcing period , than at any other time during the non-arcing period, because there was actually no transition from an ionized state to a non-ionized state, the arc space always being ionized with the use of grids and screens around the anode which reduced the magnitude of the return current coming from the ionized space.



   In the practical use of the device, in particular in its application to the transfer of electrical energy in one direction or the other between a three-phase system or a

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 Another polyphase system and a direct current system, it is desirable because each straightening arc is placed in a separate container to cause the arc to prevail for a period of arcing as long as. possible so as to obtain the greatest capacity of a given rectifier or ignitron device, and for this purpose a two-phase transformer triple connection has been applied and improved, comprising a suitable polyphase transformer between phases, as will be described below- after, for use with this device.



   In one embodiment of the invention, a container is used in which a vacuum has been made, which is made substantially entirely of metal, all the parts of this metal being in electrical contact with each other, the cathode being disposed in a quartz cathode receptacle or other insulating receptacle disposed in the bottom of this container, and the main anode being formed on the top wall of the container.



   The flat or ignitron rectifier must be particularly well protected from mercury compounds, which appear to be oxides or nitrides of mercury, or possibly organic compounds which are unstable and which can form. decompose at irregular intervals, with the release of localized pockets of gas which reduce the insulating qualities of the arcing space during periods of non-arcing, causing back ignitions. It is for this reason that the anodes should preferably not be cooled below about 80 or 100 C, because these unstable mercury compounds do not seem to be formed if the temperature is kept above the limits which have just been indicated.

   In this rectifier or

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 ignitron, it is therefore necessary to take special care to treat the device properly before use and to provide it with a container which does not leak so that nitrogen and oxygen do not enter on the way. air. If these precautions are observed, the container will not require pumping during operation.



   The all-metal construction, with a quartz cathode receptacle or equivalent receptacle, therefore, is particularly suitable for this device and the latter is particularly intended for use in a construction which is permanently sealed without the use of vacuum pumps during operation.



   Since ignitron consists of a single asymmetrically conductive path or arc in each vessel, one can deviate from the usual mercury arc rectifier circuits which employ several rectifier ares, by bringing together the anodes of all the arcs instead. to have the cathodes in common, as was necessarily necessary in devices using a single common cathode. This has particular advantages in the permanently sealed all-metal vessel construction, in which the vessel has the same potential as the anode.

   By bringing the anodes together, the problem of mounting any number of single arc vessels in a rack or other construction is greatly simplified and if ignitrons are used to supply power to a circuit. with direct current in which the negative conductor is earthed, as in railway systems, the tanks will all be at earth potential, which is a very considerable advantage.



  It will be noted that the application of the new principle

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 firing at steam arc rectifiers and inverters has caused many profound changes in the construction and operation of these devices, which have been indicated briefly in part in the preceding paragraphs and which will be explained more fully in correlation with the best mode of application of this principle, which implies many characteristics which, while being particularly established and developed and possibly necessary in correlation with ignitron are, for many of them , capable of general application in usual types of rectifiers.



   In its broadest aspects, the initiating device is not limited in its application to vapor arc devices in which a vacuum has been evacuated and asymmetrically conductive, but it is also applicable to the fields of. switches and lightning arresters, as indicated above.



   In order that the invention may be better understood, several constructive forms that the invention may take will now be described by way of examples and with the aid of the appended drawings.



   Fig. 1 is a circuit and apparatus diagram showing one of the preferred forms of an all-metal, permanently sealed ignitron with a three-phase, two-phase transformer circuit for passing the power through. a three-phase line to a direct current line, with a delay circuit device and with a means of varying the point in the cycle where the starting operates so as to change the direct current voltage or, if this last is fixed; the energy of, direct current which is

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 provided.



   Fig. 2 is a circuit and apparatus diagram showing another of the forms of ignitron which are preferred in large sizes of apparatus with a special inverter connection to supply three phase power at variable frequency from a direct current line.



   Fig. 3 is a diagram given by way of example showing the application of the invention to an arc device other than a rectifier or an inverter, the device being represented here as being a lightning arrester.



   Fig. 4 is a plan view of a modified ignitron construction somewhat similar to that shown in FIG. 2 but with certain changes which are shown in FIG. 5, part of FIG. 4 being in section by the line IV-IV of Fig.5.



   Fig. 5 is a vertical section, with a circuit diagram added, showing one of the first types of ignitron, in which a continuous firing is used, the latter being very completely enclosed so as to reduce as much as possible the return current during periods of non-arcing,
Fig. 6 is a schematic view of circuitry and apparatus showing a modified form of gnitron construction and a modified form of device for adjusting the point in the cycle where the various starting devices operate.



   Fig. 7 is a schematic view of circuits and apparatus in which the primers are supplied by means of a rotary switch device actuated by a synchronous motor receiving energy from the AC system.

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   Fig. 8 is a schematic view of circuits and apparatus showing a dual cathode construction in which either cathode can be put into service by supplying either of two primers to force the ignitron to function as a rectifier or as an inverter, the ignitron having a glass envelope.



   Fig. 9 is a schematic view of circuitry and apparatus showing another glass-cased construction utilizing a main graphite anode, a sheltered initiating anode conductor, and a screen interposed in the formation space. arc between the main graphite anode and the cathode.



   Fig. 10 is a schematic view showing the application of the keep-alive device to a conventional mercury arc rectifier construction having multiple anodes and a single cathode in a vacuum vessel. .



   Figs. There to 18 are explanatory diagrams which will be discussed in the following.



   Fig. 1 shows a rectifying system using six rectifying devices or ignitrons, all of similar construction, but for simplicity only one of the ignitrons is shown in detail, the other five being shown schematically, since it is understood that their construction is identical to that of the ignitron mentioned first.



  The ignitron construction shown here is that which is preferred for small devices for a capacity range of 100 to 500 amps, although the construction is not limited to any particular capacity. To give an idea of the enormous compactness produced by this construction, we can

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 note that the section in FIG. 1 is a full-size view of an ignitron designed for a capacity of 100 amps at 600 volts DC, achieving this remarkable output with a construction in which the diameter of the arcing space is approximately three inches (76 mm).



   This is only a preliminary build which can be perfected by other modifications as experience may dictate, so that ultimately a capacity of 150 or
200 amperes can be obtained from the same construction dimension,
As shown in Fig, 1, this particular embodiment of ignitron consists of a permanently sealed container 1 in which a vacuum has been evacuated and composed substantially entirely of metal such as iron, all the parts of this metal being in electrical contact with each other, A cathode 2 made of mercury or another vaporizable material which reconstructs itself is placed in a cup or receptacle 3 made of quartz or another insulating material, placed at the bottom of the tank 1.

   The quartz or other insulation between the mercury cathode and the cell should be of a type which is not easily covered as a bridge by impurities or particles of mercury and for this purpose it is preferably surmounted by 'a steel guard ring 4 which keeps the mercury away from part of its surface.



   For ease of construction, the metal vessel 1 will ordinarily be made in several pieces which can be manufactured separately and then assembled and welded to each other. As shown in the drawing, this vessel comprises a cup-shaped base part 5 which contains the cathode receptacle 3 and the guard ring 4.

   At the top of this base part 5 is welded a main anode in

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 iron 6 having a flat bottom surface spaced a distance of the order of 1 inch (25 mm) from the surface of the mercury cathode, the spacing being as small as is compatible with the limitations of the construction and not being in any way so small that there is a risk of forming a conductive bridge between the main anode and the cathode by the stirring of liquid mercury during operation of the device.



   A water jacket 7 is provided above the main anode 6 and is surmounted by an air-cooled water condenser 8, which receives the vapor from the water jacket, condenses it and launches it. returns to the water jacket, which maintains the anode at a temperature a little higher than 100 C, depending on the vapor pressure which is allowed to occur in the condenser, this pressure being limited, by a safety valve 9 , at a value corresponding to a temperature of 200 C for example or another maximum temperature determined in advance.



   The main anode 6 which constitutes the top of the vessel is provided with a central opening in which is sealed an insulator of any suitable type, the latter being shown in FIG. 1 in the form of a glass member 10 which is sealed by means of a glass seal 11 to a copper ring 12 covered with nickel, the lower end of which is brazed to the main anode 6.

   The glass or other isolator 10 carries a sealed tungsten cathode conductor 13 which extends downwardly centrally through the device, into contact with the mercury cathode 2, and a tungsten cathode conductor 13. starter anode conductor 14 which supports a conductive tube 15 terminating at its lower end in a nickel tubular support 16

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 for a tubular starter rod 17 of a weakly conductive material such as carborundum molded with a clay binder or other binder which does not emit gas under operating conditions, or other weakly material. conductive that is not destroyed under operating conditions, such as carborundum crystal, globar rod, Nernst filament material, ferro-silicon,

   galena and probably other similar materials. This initiating member 17 is fixedly supported so that its lower end is immersed in the cathode 2 of liquid mercury and remains immersed in all operating conditions. Its support tube 15 is insulated from the centrally disposed cathode conductor 13 by means of a quartz tube or other insulating tube 18 and preferably 11 is externally protected also by means of a larger tube. quartz or other insulating tube surrounding tube 15 as shown in FIG. 1.



   The starting rod 17, which is submerged in the meroure, should have a resistance such that an increase of about 100 volts per inch (25 mm), or more, along the rod does not impractically flow current. tall,
If the rod is to be of ordinary dimensions and not in the form of a very thin film, this requires that it be of a material having a resistivity greater than 1P-2 ohms per cubic centimeter. At the same time, its resistivity should not be too high because, as will be explained, when the starting rod is in operation, an arc forms with the cathode on the mercury and with the anode. momentarily to the side of the primer rod.

   If this momentary current must flow in the side of the rod without excess voltage, 1 if ±, the resistivity must not be too high, A

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   resistivity of less than 10 + 5 ohms per cubic centimeter will generally be low enough for this application. A change in resistivity usually involves a change in the current at which the starting device operates and the voltage required to be applied to it to produce that current.



  Several theories have been considered in attempting to explain the operation of the carborundum rod or other priming device and currently the following theory is preferred; which is presented on a trial basis without any desire to limit the invention to any particular theory of operation. If a positive potential is applied between the top of the rod and the mercury, a current flows through the rod to the mercury. In the case of a solid starter rod or a rod whose cross-sectional area is not very small, it is necessary to use a material whose resistivity is greater than 10-2 ohms per cubic centimeter, which is perhaps at least about 100 times greater than the resistivity of mercury.

   From the point of view of theory, the resistance of mercury will therefore first be neglected.



  The actual current flow will follow the lines marked 20 in the diagram of FIG. 11. Equipotential lines 21 are also shown in FIG. 11. Under these conditions, the current density along the surface of the rod below the mercury level increases from the bottom of the rod to the point of exit of the mercury rod, the point designated by number 22, and at this point the current density becomes infinite, according to the mathematical theory, if the rod and the mercury are supposed to be perfectly continuous, that is to say if we do not consider the atonic structure

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 real. Likewise, the voltage gradient along the surface of the rod becomes infinite as one approaches the junction with the mercury from above.

   Mathematically, the gradient along the surface of the rod near the mercury junction is given approximately by
V d / 2 X00 / VY, formula in which d is the diameter or thickness of the rod, X00 is the gradient along the rod at a large distance from mercury and y is the distance from the junction mercury at the point on the surface of the rod where the gradient is obtained. As one would expect the above formula to be applicable down to atomic distances, i.e. up to a value y = 10-8 cm, it can be seen that with Xoo of the order of 100 volts per centimeter, the gradient at an atomic distance from the mercury junction will be of the order of 106 volts per centimeter.



   Several researchers have demonstrated that a voltage gradient of 106 volts per centimeter is sufficient to force electrons out of matter. It is therefore reasonable to suppose that electrons will be extracted from the surface of the mercury near its junction with the rod and that the cathode of an arc can be started there, the current of this arc flowing first. to the side of the rod and then flowing to higher and higher points on the surface of the rod as the gas space becomes more and more ionized, to eventually bridge the rod and reach the metal support of the rod.

   An arc will therefore be initiated by the rod if a voltage is applied to it giving an average gradient along the rod of the order of 102 volts per centimeter, and this arc will form a bridge on the rod if the voltage is sufficient for allow a current

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 considerable amount of flowing from the side of the rod in the initial arch. If the applied voltage is insufficient for this last purpose, the arc does not form a bridge on the rod but appears as a very small spark at the junction of the mercury and the rod.



   According to the theory proposed, the resistivity of the rod must then be such as to allow the application of a gradient of the order of 100 volts per centimeter along it without an excessive current flowing. If the current absorbed by the rod must be limited to the order of ten amperes, the resistance of the rod per centimeter of length must be of the order of ten ohms. By employing special methods of excitation, for example, by discharging capacitors, it may sometimes be practical to use larger currents to initiate the arc at the rod. In these methods momentary excitation currents of 1000 amps or even 10,000 amps may be practical. For such currents, the resistance of the rod per unit length can be as low as on the order of 10-2 ohms.



   According to the theory proposed, it is also necessary that a sufficient current flow in the arc starting at the junction of the mercury so that it advances rapidly along the rod and forms a bridge over it. If the resistance per unit length of the rod is too large, excessive voltage is required for this purpose and for this reason an upper limit of 105 ohms per centimeter of rod length is imposed.



   Although, the theory given above applies to a single rod, it is evident that modifications can be made in the shape or that combinations of completely insulating materials with conductive materials could be employed to fill the gap. stem function.

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  The invention should then be interpreted generally as providing a means of initiating an arc at a conductor surface by producing a very high local gradient for its onset and by passing a sufficient current through that initiating arc to. ensure its rapid growth.



   With a solid starter rod of molded carborundum, consisting of about 70% carborundum and 30% clay binder and some carbon black, having a resistivity of about 2 ohms per cubic centimeter, the rod having a diameter of about one-quarter inch (6.3 mm) and having a length of about X one-fifth of an inch (5 mm) between its support and the mercury surface when the device is not In operation, it has been found that a cathode spot is formed at the junction of the surface of the rod with the surface of the mercury for a current of 7 amps in the rod, requiring 35 volts.



   The voltage required to operate the starter rod is preferably taken from the AC circuit to which the ignitron is connected and is preferably also taken directly from the main anode of the ignitron in which the ignitron is connected. priming is placed. As soon as a cathode spot is formed at the junction of the primer rod surface and the mercury surface, an arc arcs from the main anode to the mercury pool. The ignition arc is in series with a voltage consuming device large enough to force this arc to disappear immediately, because it cannot operate in parallel with the main arc which has a much lower voltage. than the general voltage of the starting circuit.

   The priming arc therefore operates quite momentarily to produce a cathodic spot.

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 dic on the main cathode at the start of the ignitron arcing period and it does not arcing at any other time, so there is no source supplying ions or electrons. to the arc-forming space of the ignitron during the non-arcing period thereof. As indicated above, this is an essential feature of the invention, namely the substantial elimination of the return currents which are normally produced in other steam arc rectifiers by ions and electrons present in the arcing space during periods of non-arcing thereof.



   Although the theory of this initiating device has been given with particular reference to a mercury cathode, it is evidently not necessary that the material of the cathode be mercury or even be a liquid. The essential characteristic appears to be the presence of a sufficiently high potential gradient at the junction point between the surface of the starting rod and the surface of the cathode. In fact, the ignition according to the present invention works very well when immersed in a bronze cathode, which can be achieved by dipping the rod in molten bronze and solidifying the bronze around one end of the bronze. this one.

   The starter rod will also work when it is simply in contact with the surface of the bronze or other electrode, in which case, however, it must be held securely lowered in place so that its end does not separate. not from the cathode, which will quickly burn the end of the rod.



   When the upper end of the rod is held in a support of bronze or other solid metal,. jthe voltage required to send sufficient current through

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 the rod to form a cathode spot on the support, when the support is negative with respect to the mercury cathode, can be much greater than the voltage needed to form a cathode spot on the mercury when the mercury is negative compared to to the support, this being probably due to the differences in the nature of the contact and the boiling and electron emission characteristics of the support.

   This voltage difference can be made still greater by the fact that we make the end of the rod which is in the section support much larger than that which immerses in the mercury, as will be indicated in connection with Fig. , 2, One can count on this difference in the operating voltages of the starting to oblige the starting to pierce only when the support is positive compared to the mercury and this asymmetry can be favored by appropriate means as will be described below in connection with Figs, 2 and 8, but it is preferred to employ some kind of auxiliary rectifier device to supply the ignition with potential only during the positive half cycles of the alternating voltage applied to the apparatus.

   The voltage drop in the auxiliary rectifier also helps to eliminate the starting arc as soon as the main arc arises.



   In Fig. 1, each firing rod 17 receives its energy by means of a hot cathode rectifier 23 from its own main anode 6. In the particular system shown in this figure, the main anodes and the tanks of the six rectifiers are connected. together on a common bar 24 which is connected to the grounded negative conductor of a DC load circuit 25, The point in the cycle where the starting rods receive enough current to start the arcs can be controlled through

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 any suitable means, shown schematically in FIG. 1 in the form of a rheostat 26 which is connected between the main anode bar 24 and a firing anode bar 27.

   This rheostat 26 can also serve as a switch to open circuit all the starting circuits, which forces all the rectifiers to cease functioning.



   The links of the alternating currents shown in FIG. 1 comprise a three-phase supply line 28 to which is connected the primary delta winding 29 of a transformer or of a series of transformers having a triple secondary winding 31 with two phases. In this way, the primary winding 29 has three windings, and each of these windings is coupled to two secondary windings or to a single secondary winding having a connection point 32 in its middle, the terminals of the secondary windings being connected to the terminals. Cathode conductors 13 of two of the ignitrons or rectifiers.

   The three midpoints 32 of the secondary windings are connected to the terminals of a three-phase phase-to-phase transformer 33 having a neutral connection 34 which is connected to the positive conductor of the direct current load circuit 25.



   The phase-to-phase transformer 33 has windings arranged to balance the direct current flow while maintaining the currents in the three phase terminal connections substantially equal to each other. As shown in Fig, 1, this is achieved by winding the phase-to-phase transformer on a three-branch magnetizable core 35, each branch carrying a winding.

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   Figs. 12 and 13 show typical voltage and current waveforms of one of the rectifiers or ignitons connected to one of the transformer windings of FIG. 1. The heavy line 36 of FIG. 12 shows the voltage from the anode to the cathode of a rectifier. The dashed line 37 of the same figure shows the voltage across the transformer winding. Fig. 13 shows the current entering the anode of the rectifier. When the current reaches zero, at point 39, the voltage across the arc space inside the rectifier changes very rapidly from a very small positive value, indicated by point 40 in fig. 12, to a negative value 41, which very quickly applies a negative voltage to the main anode.



   As shown in fig. 14, the reverse current or return current which flows through the arcing space immediately after the completion of the arcing period is relatively high; therefore according to the present theories, the causes of back-ignition are made very frequent. Within a small number of microseconds, with low vapor pressure, or within a hundred to a thousand microseconds, with higher vapor pressure, the arcing space develops the ability to resist. at considerable voltage with a low probability of reverse ignition, due to the noticeable reduction in reverse current, as shown in fig. 14.



   In order to prevent puncture during the transition period immediately following the completion of the arcing period, it is desirable to cause the negative voltage to build up slowly, in accordance with curve 42 in accordance with curve 42. chafnette lines in fig. 12 or a similar curve, so that high voltages are not

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 not applied to the arcing space until it has had time to lose most of its ionization.



   As shown in fig. 1, the establishment of a negative voltage on the main anode, with respect to the main cathode, -or what amounts to the same, the establishment of the positive voltage on the main cathode with respect to the ano- of main, - can be delayed to any desired extent by the fact that each rectifier is bypassed by means of an external circuit comprising a capacitor 44 of sufficient size. When this combination is employed the capacitance must be charged before a reverse voltage can be applied between the main anode and the cathode, and the time required for this charging operation will be determined by the inductance normally present in the cells. external connections of the rectifier arc circuit or path, and the resistance of the capacitor circuit.

   Usually a separate small resistor 45 is connected in series with the capacitor 44, which is desirable in any case for the purpose of damping the circuit to prevent oscillations. In the event that the reactance in series with the rectifying arc is not sufficient, a small external reactance 46 can be used, the latter having the property of being saturated for a very low current so as to offer a very low reactance. low at normal load currents during the arcing period.



   In the small ignition shown in fig. l, no special cooling means is provided for the cathode since the losses in this device are extremely low, so that the evaporation of the mercury can be relied upon for

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 maintain the cathode of the device sufficiently cold to prevent the onset of a discharge between the main cathode and the main anode during periods of non-arcing, which discharge, as it is a current in re- turn, would greatly increase the likelihood of reverse ignition.



   This will be understood more easily with the help of. Fig 15 which shows the voltage at which a discharge begins in a non-ionized space filled with mercury vapor, this voltage being plotted as a function of the product pd in which p is the vapor pressure in millimeters of mercury and d is the distance between the electrodes in centimeters. The minimum starting voltage, about 470 volts, occurs when the product pd is equal to approximately 6. The normal operating range of the rectifier is obtained when the product pd is around unity or less, of so that the starting voltage is several thousand volts. The vapor pressure of mercury obviously depends on the temperature.

   It is. It is therefore necessary to maintain, with the spacings used, temperature conditions such as to prevent the product pd from appreciably exceeding a safety value, such as unity for example.



   In large ignitrons, such as that shown in fig. 2, it is usually necessary or desirable to employ positive means of cooling the cathode. At the same time, it is very desirable to employ a means of securing the cathode spot, which has the advantage of considerably reducing cathode blowing, thus decreasing the turbulence of the cathode and limiting the. amount of vapor evaporated.

   This new feature,

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 although being of considerable advantage in older types of multi-anode rectifiers, is particularly desirable in rectifiers in which the anode covers substantially the entire cathode and is spaced therefrom a sufficiently large distance. for mechanical play to avoid splashing forming liquid bridges across the space between the main anode and the cathode, it is furthermore extremely desirable that these means of securing the cathode spot be very completely cooled, especially in ignitrons.



   In accordance with the principles which have just been explained, the ignitron represented in FIG. 2 has been provided with a very efficient means of cooling the cathode and a means of fixing a water-cooled cathode spot. A water jacket 47 is provided below a metallic cathode receptacle 48 in which there is disposed a quantity of liquid mercury 49 or other vaporizable cathode material which reconsolidates itself.

   A coolant such as water, which is as cold as possible, enters through an inlet pipe 51 into a middle compartment 51 of the water jacket, from where it is discharged through horizontal pipes. cooling 52 for the attachment of the stain, which extend radially from the middle of a mercury basin so that the tops of the pipes are approximately flush with the upper surface of the mercury when the device. tif is not running. Water is drained from the outer ends of these spot fixing pipes 52 into an annular compartment 53 of the water jacket, where it is drained through an outlet pipe 54.



   At least the upper halves of the spot fixing pipes 52 are coated with galvano-

 <Desc / Clms Page number 27>

 plasticized or covered with a sheet of stain fixing material 55 which, if in the form of a sheet, is welded to the pipe so as to be in good thermal contact therewith, this stain fixing material being molybdenum-. ne or tungsten or other non-splashing material, which is wetted with mercury and prevents the pipe from burning from the arc.



   The cooling pipes 52 for the fixation of the spot are placed close enough to each other that the calculated temperature of any point on the mercury surface except the cathode spot cannot rise to the point. -above about 60 C or possibly 80 C, and preferably it is much less, possibly going down to 50 C or less.

   Since the cathode spot fixation pipes 52 extend radially, they are spaced further apart at their outer ends than at their inner ends. dull, and between their outer ends additional cooling means may be used in the form of solid metal tabs 56 which are welded to the top of the metal cathode receptacle 48 as shown in vertical section in FIG. 2 and in plan in FIG. 4.



   The ignitron shown in FIG. 2 comprises a container in which a vacuum has been made, comprising a bottom, a top, and side walls, the bottom being closed by the cathode receptacle 48 which has just been described. The top is formed by a main anode plate 57 and the side walls are formed by an insulator ring or a porcelain cathode nozzle 58, which is clamped and hermetically sealed between the cathode receptacle 48 and the plate.

 <Desc / Clms Page number 28>

 anode 57, using any suitable sealant as indicated at 59.

   To better enable the insulating ring 58 to act without being shortened by liquid mercury or impurity particles, its inner wall is corrugated as shown and it is also protected by an annular guard piece. or a cylindrical baffle 61 for the vapors, having a hole 62 in its lower part to allow liquid mercury to return to the cathode basin.



   The active surface of the anode consists of the flat bottom plate 63 of a protrusion 64 which extends downward from the anode plate 57 and provides a cooling jacket for the anode, the air or other suitable coolant being introduced through an inlet pipe 65 and discharged through an outlet pipe 66. This downwardly projecting protrusion, or anode cooling jacket, substantially fills the space at the bottom. interior of baffle cylinder 61 such that the lower plate or effective area 63 of the main anode has substantially the same diameter as the upper surface of basin 49 of the mercury cathode. The spacing between the main node and the main cathode in the particular model shown in fig. 2 is an inch and a quarter (31 mm).



   As the cathode is strongly cooled in the model shown in fig. 2, the vapor pressure is lowered by the cathode cooling means, so that there is no need to rely on the anode cooling means for this purpose. Consequently, the main node of ig. 2 can operate at a higher temperature, for example up to 300 C, and it is de- @ ..'..-

 <Desc / Clms Page number 29>

 It is desirable to do so, possibly due to its effect in preventing the formation of nitrides or other deleterious substances on the surface of the cathode.



   In the ignitron shown in fig. 2, the priming anode is a short solid rod 67 of carborundum or other aforementioned starting material, this rod being carried by a support 68 at the lower end of a supporting rod. steel 69 which is suspended from a priming anode plate 70. The priming support rod 69 is centrally disposed and passes through a central opening 71 in the main anode plate 57. That priming anode 70 is separated from the main anode plate 57 by a tubular porcelain spacer 72 which is suitably sealed to the two plates as indicated at 73.

   As in all the priming models according to the present invention, the priming rod
67 extends deep enough into the mercury basin 49 to give the certainty that it is still in contact with the mercury since otherwise its action would be faulty and it would be quickly burned.



   In fig. 2, the upper end of the carborundum starter rod 67 is enlarged as indicated at 74, in order to increase the negative voltage required to form a cathode spot on the support 68 without affecting the formation. of a cathode spot on the mercury when the starting anode is positive, this effect being obtained at the support as a result of the increase in cross section, and consequently, of the decrease in resistance of the starting rod to its upper end.



   The central opening 71 in the anode plate

 <Desc / Clms Page number 30>

 main 57 is made of ample dimensions to facilitate the evacuation of gases from the interior of the container therethrough.



  This evacuation is effected by means of a pump connection 72 which is attached to an upper flange 76 separated from the priming anode plate 70 by another tubular porcelain spacer 77 which is also sealed from the starter. appropriately to the two plates at its top and at its base, as indicated at 78.



   Although this is probably not entirely necessary in the model shown in fig. 2, a guard piece or tubular screen 78 is provided, suspended from the starter anode plate 70 and extending downward into the opening 71 of the main anode plate 57, this piece of starter anode plate 57. tubular guard having a diameter much larger than the starting rod 69. At the top of this tubular guard piece, a water jacket 79 is provided to ensure that all the mercury vapor is condensed before it reaches. the pumping connection. A suitable coolant is supplied to the jacket 79 through inlet and outlet pipes 80 and 81.



   In order to protect the seals 59 at the top and at the base of the insulating ring 58 between the main anode plate 57 and the steel cathode receptacle 48, water passages 82 in the main anode plate and in the cathode receptacle are preferably provided, as close as possible to the seals, with a view to preventing excessive heating of the seals since these are located at the hottest part of the container.



   Fig. 2, shows an inverter system using six ignitrons such as the one previously described to pass the energy of a DC power supply circuit.

 <Desc / Clms Page number 31>

   a new application. In the longer winding 88, therefore, equal direct currents flow in opposite directions in the two halves. In the short winding 87, the direct current in the 1/3 branch is exactly twice the direct current in the 2/3 branch and is opposite in direction which produces a neutralization of the DC magneto-motor forces.



  The neutral point connection 89 of the phase-to-phase transformer is connected to the positive conductor of the direct current circuit 83 in order to receive energy from the direct current circuit, instead of being connected to the negative conductor so as to pass the power through. energy to the direct current circuit as in the rectifier connection of fig. 1.



  In fig. 2, the six cathodes 48 are permanently connected together to a cathode bar 90 which is in turn connected to the grounded negative conductor of the direct current circuit 83, so that all of the cathode receptacles 48, which constitute the bottoms of the ignitron tanks are at earth potential, which considerably facilitates the assembly problem.



  In fig. 2, the six firing anodes 67 receive energy from their respective main anode conductors, by means of six mechanically actuated switch rings 91 which can be actuated from a variable speed and reversible motor 91a, powered by the direct current line. Each of the switch rings 91 has a conductive segment 91b, the successive segments being moved 60 from each other. Two brushes 92 are supported on each switch ring ,. one brush of each pair being connected to one of the starting anodes 67 and the other brush of the same

 <Desc / Clms Page number 32>

 pair being connected to the corresponding main anode conductor.

   A six-pole switch 93 is provided in the starting anode connections so that the main arcing circuits of the ignitrons can be interrupted without requiring the use of heavy-duty switches. negative voltage pulse necessary to bring about the completion of the arcing period of the different main anodes 57, any capacitor system is provided, for example three capacitors 94 connected across the three pairs of diametrically opposed terminals of the six phase transformer winding.



   The inverter system shown in fig. 2 can be used advantageously to supply variable frequency power to an induction motor 95 which derives its power from the three phase AC cost circuit 84 which is supplied by the inverter. The frequency and direction of phase rotation can be controlled by means of the DC motor 91a. Usually also some sort of means of varying the voltage of the three phase motor 95, particularly at start-up, will be desirable and this means is generally indicated by means of a variable resistor in the positive conductor d. feed to the inverter.



   In fig. 1 and 2, the invention has been shown in the case of tanks where there is a vacuum, containing asymmetrically conductive steam arcs, respectively for use as a rectifier or as an inverter.



   In fig. 3, the invention is shown applied to an open-air arc device 97 which can be used generally as a switch or, as has been shown, in 16, a particular case of switching which is involved. '' evacuation of a lightning strike from a power line

 <Desc / Clms Page number 33>

 alternative and the resulting powerful de-1-lare extinction.



   The arc device 97 'of FIG. 3 consists of two bronze electrodes 98 mounted in the ends of a long fiber tube 99. The fiber tube and preferably also at least one of the electrodes 98 are drilled with numerous holes 100 for the purpose of evacuating. the gas pressure when an arc occurs. A priming device is provided for each of the electrodes 98, this device preferably comprising two short rods 101 made of a starting material such as that which has been described previously. In fig. 3, the starter rods 101 are shown as comprising crystals of carborundum.

   Each rod or firing crystal is embedded at one end in one of the bronze electrodes 98 which is molded around the crystal, the other end of the rod being held or embedded in a small bronze holder 102 having a terminal connection 103 which passes through an insulating sleeve 104 in the side of the fiber tube 99. The terminal connections 103 of the two start rods are joined through an external resistor 105.

   One end of the arc device 97 is grounded as indicated at 108, and the other end is connected by a '. suitable device 107 with spark bursting gaps, for an alternating current line conductor 108 which must be protected from excessive voltages, this conductor being shown by way of example as an 11,000 volt, 60 cycle line . The spark bursting interval device 107 is shown as a multiple interval in series with shunt resistors 108 '.



     @ When an excessive voltage affects line 108,

 <Desc / Clms Page number 34>

 spark gap 107 produces a spark and applies excess line voltage to arc device 97. Resistor 105 is of such value as to allow the passage of current necessary to cause the formation of a cathode spot at the exit point of the carborundum crystal of bronze plate 98 which happens to be negative at this time. If the starting device begins to operate at a current of two amps and the normal line voltage is 11 kilovolts, it can be assumed that spark gap 107 arcs for twice the line voltage and that resistor 105 should have a value of about 11,000 ohms.



   As soon as the firing crystal acts to form a cathode spot, an arc is produced in the fiber tube 99 and extends from one end electrode 98 to the other. These electrodes are spaced a sufficient distance apart so that the arc which spurts out between them will surely extinguish and not spring back on its own at the end of the half cycle in which the arc has arisen, at line voltage. normal for which the device is established, in this case 11,000 volts.



  Under the heat of the arc, a decomposition of the fiber of tube 99 occurs which causes such intense gas blowing through the arc that the arc is extinguished with electrode distances much less than those. which would be necessary in the open air. When it is said that the distance between the electrodes is large enough to prevent splash back, this is understood to mean that it is sufficiently large, under any deionizing influences which may be present, to prevent back splash. Until now, it has not been possible to cause an arc to shoot out in the midst of strongly deionizing influences.

   It was necessary to cause the arc to shoot out at a point which is largely

 <Desc / Clms Page number 35>

 apart from the deionizing influences and then to try to make the arc pass to a point which is in sufficiently strong deionizing influences to ensure the more or less rapid extinction of the arc.



   Figs. 4 and 5 show a variant of the ignitron construction used in FIG. 2. The main feature of this modified construction, which is one of the earliest ignitron constructions, is the fact that an ignition arc is used which operates all the time in the vessel but which is so completely sheltered that the current back to the main anode, during the non-arcing period, is low enough to reduce the firing frequency back to a value which is tolerable for some applications of an ignitron as a rectifier , inverter, switch or switch.

   As only one main anode is used in each tank and since the ignition arc is very completely sheltered, there is no really open arc acting in the device during periods of non-formation. arc.



   In the rectifier shown in fig. 5, the ano- of maintenance 109 is a small tungsten rod which. dipped bare into the top of the surface of the mercury cathode 49 and which is supported by the lower part of a support rod 110, similar to rod 69 of FIG. 2, except that in the present case measures must be taken for the vertical adjustment of the position of the support rod because the tungsten maintenance anode 109 is very sensitive as to the small amount which it can dip into. in mercury.

   This vertical adjustment of the position is ensured by means of an angled lever 111, one arm of which supports

 <Desc / Clms Page number 36>

 the support rod 110 and the other arm of which can be horizontally adjustable by means of a rod 112 extending through a metal bellows 113 which is forced inward or outward by means of adjusting nuts 114. The metal bellows prevents loss of vacuum while allowing a slight range of motion.



   In fig. 5, the maintenance anode plate 115, which supports the top of the support rod 110 through the vertical adjuster just described, is separated from the plate 116 which supports the. tubular screen 117 surrounding the maintenance device, the two plates 115 and 116 being separated by a tubular porcelain insulator 118 suitably sealed to these plates. As the maintenance arc acts constantly, it is necessary that the tubular screen 117 of FIG. 5 extends down very close to the mercury surface, to an eighth of an inch (3 mm) thereof in the pattern shown. It is also provided with a bottom member 119 in the form of a disc comprising an opening 120 through which the tungsten rod 109 extends.

   The plate 116 which supports this maintenance screen 117 is shown provided with a terminal connection 121 which is sometimes used in the processing operation to produce an arc between the bottom of the screen 117 and the mercury 49.



   The maintenance anode plate 115 is provided with a maintenance anode terminal 122 and current is supplied from this plate to the maintenance support rod 110 by means of a free conductor or jumper 123.



   As indicated in the electrical connections shown at. fig. 5, current is supplied to the maintenance anode terminal 122 from the posi-

 <Desc / Clms Page number 37>

 from a direct current source such as a battery 124, via a suitable ballast resistor 125, the negative end of the battery being connected to the cathode receptacle 48. The main anode 57 receives power from an AC circuit 126 and cathode 48 supplies current to the positive conductor of a DC load circuit 127, the negative conductor of which is connected to the midpoint of a transformer 128 on the AC circuit.



   The tungsten maintenance rod 109, in fig. 5, is maintained so as to establish a slight contact with the mercury so that when the arc is extinguished, the catho- de of the sustaining arc is always immediately near the tungsten rod and by therefore under the screen.



   Fig. 6 shows an embodiment of ignitron which appears to have many manufacturing advantages and which shows some variation in construction. In this model, the main cooling of the interior space of the ignitron is carried out by means of a water-cooled baffle which separates the main anode from the main cathode and serves to a great extent to render unnecessary the Adoption of special delay circuits to avoid reverse ignitions during the transition period. This model also uses closer to normal constructions for the main anode and the main cathode.



   If we refer to fig. 6 in detail, it can be seen that the ignitron shown consists of an evacuated vessel, comprising a water-cooled tubular side wall 130, to which are securely attached.

 <Desc / Clms Page number 38>

 stainable an upper main anode plate 131 and a lower cathode assembly 132, with use, as assembly means, of rubber gaskets 133 or other easily detachable hermetic sealing means. As these seals work in relatively cool parts of the vessel, no difficulty is encountered in making them easily removable.



   The main anode plate 131 at the top of the vessel supports a steel main anode head 134 which extends downwardly inside the vessel and is supported in isolation by the main anode plate, by means of a porcelain insulator mount 135 of the kind which has been brought to a high degree of perfection with respect to conventional forms of metal tank and mercury arc rectifiers.



   The anode head 134 is supported by an anode conductor rod 136, the apex of which may carry fins 137 forming a radiator for cooling the anode head, as in the usual constructions of rectifiers. The anode porcelain 135 is hermetically sealed to the anode plate 131 by means of a permanent weld seal 138, of a pattern which has become normal in prior construction vessels of multiple anode rectifiers.



   The cathode assembly 132 of FIG. 6 comprises an upper flange 140 which is detachably connected but not insulated to the portion 130 of the tubular wall of the vessel, by means of the two previously mentioned rubber-lined seals 133. A steel cathode receptacle 141 is provided for the cathode assembly, this receptacle being separated from the upper flange 140 by means of a porcelain.

 <Desc / Clms Page number 39>

 cathode tubular 148 which *, is permanently sealed to top flange 140 and cathode receptacle 141 by non-releasable welded seals 143.

   The upper flange 140 and the cathode receptacle have overlapping, but not touching, ring-shaped protrusions 144 and 145, respectively, which serve to shield the cathode porcelain 142 from most of the direct heat of the vessel. the arch. A basin of mercury or other cathode material 146 is disposed at the bottom of the cathode receptacle. A cathode screen, in the form of a quartz cylinder 147, is also provided and is clamped in position around the edge of the mercury basin by means of a spring clip 148 disposed in the bottom of the basin and pressing the handle. Quartz cylinder up against a steel clamp ring or guard ring 149 carried by upper flange 140. The cathode assembly is completed by a water jacket 150 under the cathode basin.



   The starting anode in fig. 6 includes a carborundum rod 151 held in a terminal holder or iron clamp 152.



   The priming support 152 is supported by the end of a rigid retaining rod 153 which may be of steel, this supporting rod passing through a long sleeve of quartz or other tubular insulator 154 which in turn , passes through a hole in the side wall 130 of the tank, this hole being surrounded by an iron tube 155 welded in place so as to constitute a part of the tank. The iron tube 155 terminates in a flange 156 which is hermetically and insulated with a similar flange 157 which is connected to the end of the support rod 153, the connection between the two flanges comprising an insulating ring. porcelain

 <Desc / Clms Page number 40>

 158 and rubber lined seals 159 or their equivalent at the ends of the porcelain ring.



   The ignitron shown in FIG. 6 is also provided with a water-cooled baffle 160 which is suspended from the anode plate 131 by means of the two pipes 161 and 162 through which water is brought into the baffle and discharged therefrom, the baffle being hollow. Thanks to this construction, a large amount of the energy loss in the rectifier, which appears as heat, is removed through the baffle so that the need to cool the main anode and cathode is less severe. .



  In addition, because of the interposition of the water-cooled baffle between the main anode and the cathode, the cathode is protected from the heat radiated from the anode in the event that the latter becomes too hot during cooling. 'overload, and the main anode is protected from direct exposure to cathode spots on the cathode and the blast of mercury vapor from it, making the device less prone to backfires during difficult period of transition mentioned above.



   The circuit connections shown in Fig. 6 show a different kind of phase-to-phase transformer and a slightly different form of the drive means for the firing anodes 151. In this circuit the six cathodes 141 are all joined to a cathode bar. 163 which is connected to the positive conductor of the direct current load circuit 164. The six anode heads 134 are connected to the six phase terminals of the transformer 165.



   The three neutral points of the main transformer 165, in fig. 6, are connected to a transformer

 <Desc / Clms Page number 41>

 phase-to-phase three-phase 165 'consisting of three separate, single-phase transformer cores each having two windings connected in a well-known interconnected star connection. In the diagram, the phase-to-phase transformer windings which are wound on the same core are shown in each case as being parallel to each other. The neutral point of the phase-to-phase, interconnected star transformer 165 'is connected to the negative conductor of the DC load circuit 164.



   The starting anodes 151 of FIG. 6 are connected to their respective anode conductors 136 by means of small three element rectifier tubes 166 which are provided with grids 167, the tubes being of the kind known as positively controlled tubes requiring a positive preponderance. of about 30 volts for the arc to shoot between the plate or anode 168 and the filament cathode 169.



   The preponderance voltage applied to the gates 167 of the small rectifier tubes in the starting circuits is applied by means of a variable direct current source such as a battery 170 which is connected, between the main cathode bar 163 is a gate control bar 171, the voltage varying, for example from about 30 positive volts to about 30 negative volts, applied to the gate control bar 171 relative to the main cathode bar 163 of the ignitrons.



   The control grid 167 of the small firing circuit rectifier of each ignitron receives its energy from the secondary winding 172 of a small transformer 173 whose primary winding 174 receives its energy from the neighboring directing phase of the six-phase windings of

 <Desc / Clms Page number 42>

 transformer 165, each of the secondary windings 172 being connected between its gate 167 and the gate control bar 171. Since the gate control currents are on the order of milli-amps, the six transformers 173 are actually of very small dimensions, having a lower capacity than that of a bell actuator transformer.



   The operation of the gate control circuits is shown with the aid of figs. 16, 17 and 18, on which the horizontal line 175 represents the preponderance voltage (with respect to the cathode) which must be applied to the auxiliary rectifier tubes 166 before they begin to straighten and supply voltage. current to their respective starting anodes 151. The parts of alternating voltages applied to the main anodes 134 (fig. 6), where these voltages are positive with respect to the cathode bar, are represented by the lines in lines. solid 166 in fig. 16 to 18.

   The voltage developed in the secondary winding 172 of the small gate transformer 173 is represented by the sinusoidal curve 177 in broken lines, having as a base line the voltage of the preponderance battery 170, as shown. by the horizontal dashed line 178.

   If we change the value of the vol- tage 178 of the preponderance battery, by a maximum positive potential shown in FIG. 16, towards zero as shown in FIG. 17, and finally towards a negative maximum potential, as shown in FIG. 18, the point at which the gate voltage, represented by the displaced sine curve 177, crosses the horizontal line 175 representing 1%, the voltage necessary to be applied to the grill 167 before its auxiliary rectifier tube 166 operates.

 <Desc / Clms Page number 43>

 ne, is delayed more and more as indicated by points 181, 182 and 183 in figs. 16, 17 and 18 respectively, so that the arc between the main anode 134 (fig;

  6) and the cathode 141 of the different ignitrons springs up later and later in the half cycle in which the main anode is positive, which reduces the energy transferred to the load circuit 164 (fig. 6) at direct current. , as indicated by the hatched surfaces in fig. 16, 17 and 18.



  In this way, the voltage of the DC load circuit 164 can be changed or, if this is set by the load itself, only the energy supplied to the load by the rectifier assembly can be changed.



   Fig. 7 shows a circuit arrangement for using single anode ignitrons, whereby energy can be transferred in either direction between an AC circuit 184 and a DC circuit 185 In this system two ignitons 186 and 187 are used having their main anodes 188 and 189 permanently connected to the two conductors of the single phase circuit 184 and having their cathodes 190 and 191 connected to a common cathode bar 192.

   The starting anodes 193 and 194 of the two ignitrons are connected to their respective main anodes by means of rotary switches 195 and 196 comprising brushes 197 mounted in a brush holder 198 adjustable by rotation, these brushes resting on a drum rotary switch operated by a synchronous motor 199 having its primary winding 200 supplied by the AC line 184. The primary winding 200 may be provided with a midpoint connection point which is connected to a bar 202.



    @

 <Desc / Clms Page number 44>

 
The cathode bar 192 and the bar 202 of the midpoint connection point are connected respectively to the positive and negative conductors of the direct current circuit 185 for operation as a rectifier, the connections being reversed for operation as an inverter, the reversal being effected. by means of a switch or inverter 203. At the same time as the inverter is reversed, the adjustable brush holder 196 should be moved about 180 so that the primers receive energy. to operate the main arc for a half cycle in which the average applied voltage is negative rather than positive. The adjustable brush holder 198 also provides a means of varying the point in the cycle at which the primers receive their energy.

   To make operation as an inverter possible, it is usually necessary to use a capacitor 204 mounted between the two main anode conductors in order to provide the negative impetus necessary to complete the successive periods of training. of the arc.



   Fig. 8 shows another ignitron circuit in which energy can be transferred in either direction between an AC circuit 184 and a DC circuit 185, but in which it is not. no need to use any switch in the main power circuits. For this purpose, two double-ended ignitrons 205 and 206 are used, each of which consists of an inverted U-shaped tube having two mercury basins 207 and 208, each basin being provided with a starter anode 209.

   By supplying energy to one or the other of the two firing anodes of each ignitron, it is possible to make a cathode of either of the

 <Desc / Clms Page number 45>

 two basins of mercury 207 and 208, the other basin functions as an anode without cathodic spot on it.



   The two mercury basins marked 208 with the two ignitrons of fig. 8 receive their energy between the terminals of the alternating current circuit 184, these basins being connected directly to this one or supplied by means of the secondary winding 210 of a transformer 211. The two mercury basins marked 207 in the two ignitrons are linked together and are connected either with the positive conductor or with the negative conductor of the direct current circuit 185, the other conductor of the direct current circuit being connected to a connection point median 212 of the secondary winding of transformer 210. As shown in FIG. 8, the two mercury basins 207 are connected to the negative conductor of the direct current circuit and the circuits to feed the four starting anodes.



  209 will be explained taking this connection into account.



   The change from operation as a rectifier to operation as an inverter is effected by means of a small double-stroke switch 213 which must be traversed only by the small control currents of the starting anodes 209. When the double-stroke switch is in its upper position, the two ignitions function as a rectifier, the middle connection 212 of the secondary transformer winding 210 being connected to the priming anodes immersed in the two basins of mercury 208, in series with current limiting resistors 214,

     which gives the certainty that the starting anodes receive sufficient current to form a cathode spot on the surface of each of the mercury pools designated by the figure 208 when the pool is negative with respect to a-

 <Desc / Clms Page number 46>

 starter node, without forming a cathode spot on the starter anode support 215 when the latter is negative with respect to the corresponding cathode 208. This is possible, as explained previously, because of the difference in current at which a cathode spot forms on the solid metal support compared to the mercury of the cathode, and this difference in current can be further increased by the use of insulating screens 216 near the junction of the ignition anode rod 209 and its support 215.



   When the double-stroke switch 213 is moved to its lower position, the two firing anodes 209 which are associated with the two mercury basins 207 are connected via two pairs of switch brushes 217 and 218. , respectively, across the alternating current, or across the secondary winding 210, or any equivalent power supply means for receiving current from the alternating current circuit 184. The switching device consists of this case in a single switching drum 219 having a single conductive segment 220, the two brushes of each pair 217 or 218 being mounted in axial alignment with each other or moved only a small distance circumferentially, as in have represented it in the drawing for clarity.

   The switch is actuated by a synchronous motor 221 supplied by the AC line. In accordance with this connection, the mercury pools 207 are forced to be cathodes by the formation of cathodic spots on them at the points of emergence of the priming anodes dipping into the mercury, while the mercury pools 208 are not activated in this way and therefore function only as anodes, allowing

 <Desc / Clms Page number 47>

 so current to flow only in the direction in which power is supplied from the DC line 184 to the AC line 185.



   In fig. 9, ignitron is shown as having ¯ a glass vessel 222 having a mercury cathode 223 and a cathode conductor 224 at its bottom, a graphite main anode 225, and a main anode conductor 226 at its top. , a small carbonundum starter rod 227 immersed in mercury and held by a support 228 at the end of a rigid starter conductor rod 229 which is housed by a quartz tube 230 and which s' extends through a seal 231 in the side of the glass container. The ignitron is also provided with an iron baffle disc 232 which is supported by a rod 233 held in a seal 234 on the other side of the tube.



  The baffle disk 232 is disposed between the main anode 225 and the cathode 223 and performs the same function as the baffle 160 previously described with reference to FIG. 6 except that the water-cooled operation is deleted in FIG. 9.



   The ignition circuit control system shown in fig. 9 is a little different from the control systems shown previously. A small auxiliary rectifier 235 is used to supply power to the firing anode 227, but instead of being connected directly into the firing anode circuit, it is mounted in a separate way. - ries with the primary winding 236 of a small auxiliary transformer 237, the secondary winding of which is connected between the starting anode 227 and the negative conductor of the direct current charging circuit 238.

   From this den, the ignition anode receives the necessary impulse to

 <Desc / Clms Page number 48>

 started only during the period when the main anode 225 is to be the terminal of a main current conducting arc between this main anode and the cathode 223.



   Fig. 9 shows that the starting device does not have to be fed directly from the main cathode circuit but can receive its energy via an auxiliary transformer winding which is indicated in 239, the current conditions and voltage best suited for the starting operation can be easily determined.



   The improved starting device is not limited, in its application, to tubes or tanks with a single anode, in the field of rectifiers and inverters. This is a very great improvement if it is used instead of the usual start-up anode means in an ordinary rectifier tank with several anodes, as shown in FIG. 10, where an iron rectifier vessel 240 contains a mercury cathode 241 and six main anodes 242 of a design which was customary prior to the present invention, the representation of FIG. 10 being purely schematic, without attempting to show the constructional details of this old form of vessel.

   To start the operation of such a tank, it has been necessary until now to provide a mobile start-up anode and to provide means, outside the tank, for moving the start-up anode. train inside the vessel, and the start-up anode required a special voltage source and special resistors and other control equipment.



   It has been deleted in FIG. 10 the usual setting anode

 <Desc / Clms Page number 49>

 in process and has been substituted for one of the new starting anodes 243 which is connected via a small external rectifier 244 to any one of the six anode conductors 242. With this arrangement, it is simply necessary, in order to start the rectifier, to close a switch such as switch 245 connecting the rectifier to its load circuit 246. Then, at the beginning of the first conductive period of the main anode to which the firing anode is connected, the firing anode receives energy and turns on the main rectifier.

   As soon as the rectifier starts up, the starting arc which is in series with the external auxiliary rectifier 244, the assembly being shunted by the main arc in the rectifier tank, goes out because the circuit d Ignition requires a higher voltage than the main arc.



   Then, throughout the operation of the main rectifier, the starting anode remains inactive, its only function being to start the operation of the rectifier as soon as the main current circuits are closed, no control switch being necessary. .



   Fig. 10 also shows a usual rectifier-transformer connection which is obviously applicable to single anode ignitrons although the two-phase triple connections shown and described previously are preferred. There is shown in FIG. A double star connection enclosing a transformer 247 having a delta-mounted primary winding 248 and a se- winding; six-phase conductor 249 which is mounted in two three-phase Y-connections providing two neutral points 250 and 251 which are connected to the terminals of a single phase-to-phase transformer 252 having a midpoint which is connected,

 <Desc / Clms Page number 50>

 by one pole of the switch 245, to the negative conductor of the direct current load circuit 246.



   In the above specification, when speaking of an AC line or a DC line, this is generally understood to mean the terminals or conductors for carrying AC or DC current, respectively, it does not matter whether these terminals are connected to an energy source, to a motive power consumer or to a distribution line to which both a source and a consumer are connected.



    CLAIMS ---------------------------
1.- In an arc discharge device comprising two main electrodes, terminal connections for them and an ignition device located in the vicinity of the main arc-forming path to cause an arc to arise between these two main electrodes , this initiating device comprising a rod of a weakly conductive material having one end in permanent contact with one of the main electrodes to form a cathode spot thereon, and a separate terminal connection for the other end. of this rod.


    

Claims (1)

2.- A device according to claim 1, wherein the two main electrodes are separated, with respect to the deionizing influences present, to the point that if an arc spurts out between them, it is surely extinguished and does not re-emerge on its own. the end of the half-cycle in which the arc has burst for the expected arcing voltage under which the device is intended to operate. 3. A device according to claim 1 or 2, ' <Desc / Clms Page number 51> characterized by means for energizing the firing rod with the energy supplied to the two main electrodes so that the material of which that rod is composed becomes an auxiliary anode of sufficient positive potential to form a cathode spot at the point of junction between its surface and the surface of the cathode-forming electrode, during the half-cycle in which the arc must burst between the main electrodes, this material being able to withstand a sufficient current density at this point of rush-. tion to produce the necessary voltage gradient, causing the cathode spot, at this point, without destroying the material. 4. - A device according to claims 1 to 3, characterized in that at least part of the ignition anode has a resistivity at least about a hundred times greater than the resistivity of the cathode in which - the ignition anode is permanently submerged. 5. - A device according to claims 1 to 3, characterized in that the starting anode comprises a short rod having a resistivity of the order of about 10-2 to about 10 + 5 ohms per cm3. 6. A device according to claims 1 to 3, characterized in that the rod constituting the starting anode comprises a part having at least one resistivity and dimensions such as the resistance along the path of passage of the current. is on the order of about 10-2 to 10 + 5 ohms per centimeter of length. 7. - A device according to claims 1-3, charac- terized in that the part of the priming device ve-. contacting or immersed in the cathode has electrical and geometric characteristics such that it withstands a gradient of 100 volts per cent. <Desc / Clms Page number 52> be along this part, without a current of prohibitive magnitude. 8. A device according to the preceding claims, for use on an alternating current circuit and in which one of the main electrodes comprises a reconstructable vaporizable cathode, characterized by means for applying intermittent pulses of energy into it. one direction to the starter rod only during positive half cycles of this AC circuit. 9. - A device according to claim 1¯8, charac- terized in that the means for applying intermittent energy pulses in a single direction to the starting rod comprises an auxiliary rectifier connected between this rod and the anode electrode. 10. A device according to claim 9, characterized by a means for controlling the operation of the auxiliary rectifier. 11. A device according to claim 9 or 10, characterized in that the cathode of the auxiliary rectifier is connected to the starting rod. 12. - A device according to either of the preceding claims, characterized in that the priming rod is made of carborundum. 13. A device according to any one of claims 1 to 11, characterized in that the priming rod is made of carborundum, carbon black and a binder which emits substantially no gas. gas or vapors when heated under operating conditions. 14. - A device according to claim 1 or 2, characterized in that the spacing of the main electrodes <Desc / Clms Page number 53> is less than the diameter of either of them. 15. - A device according to any one of the preceding claims, characterized by means for cooling the cathode and by means for cooling the anode to a temperature of the order of 80 C to 300 C. 16. - A device according to any one of the preceding claims, characterized by a cooling means separate from the cathode, disposed in contact with the path of the vapor arc and in which a cooling fluid circulates. 17.- A device according to any one of the preceding claims, characterized in that an external circuit from impedance to capacitance and resistance shunts the arc between the main anode and the main cathode to delay the rise of voltages. negative arcing during transitional periods immediately following completion of arcing periods of the device. 18.- A device according to any one of the preceding claims, characterized in that the side walls of this device are formed by an insulating ring which is hermetically sealed to the cathode and to the main anode and between these. 19. - A device according to one of the preceding claims, characterized in that the main anode has an arc end portion formed by the underside of a projection extending downward. 20. A device according to any one of the preceding claims, characterized in that the main anode has a central hole through which the starting rod extends. <Desc / Clms Page number 54> 21. - A device according to claims 18 and 19, characterized by a baffle between the projection of the main anode and the insulator ring. 22. A device according to any one of the preceding claims characterized by a capacitor connected to the upper main electrode for periodically reversing the voltage thereon at the end of each conduction period. 23. A device according to any one of the preceding claims, characterized in that the initiating rod is enlarged at one end and provided with a separate end support for this enlarged end. 24. A device according to claims 2 and 14, characterized in that the main electrodes are spaced from about one-half inch (12.6 mm) to about 3 inches (76 mm). 25. A device according to claim 15, characterized in that the means for cooling the cathode comprises horizontal pipes immersed in the material of the cathode, the upper parts of these pipes having cathode spot fixing surfaces. . 26. A device according to claim 25, characterized in that the temperature of the cooling fluid circulating in the horizontal pipes immersed in the material of the cathode and the proximity of these pipes are such that the calculated temperature of n Any point on the cathode surface, except the cathode spot, cannot be hotter than about 200 C, and is preferably about 60 or 80 C. 27. A device according to claim 25, characterized in that the horizontal pipes immersed in the material of the cathode have a surface composed of a substance. <Desc / Clms Page number 55> this indestructible metallic, wetted by mercury, suitable for the fixation of the cathode spot. 28. The combination of six arc discharge devices, according to any one of the preceding claims, characterized by a bar terminal common to all the devices and by six phase current terminals in one direction, transformers comprising three windings connected to the three-phase line, a separate winding coupled, in inductive relation with each of the three windings first mentioned, respectively, each coupled winding being connected between two of these phase-to-current terminals in a direction only and having a midpoint, and a three-phase phase-to-phase transformer having three terminal phase connections joined at the three middle connection points, respectively, and having a neutral connection, this phase-to-phase transformer having windings arranged to balance the flow of direct current while keeping the currents substantially equal to each other in the three terminal phase connections, with the direct current line connected between the neutral connection between phases and the bus terminal, common to arc discharge devices. 29. The combination of claim 28, characterized in that the three-phase phase-to-phase transformer comprises two Scott-connection single-phase transformers. 30.- The combination according to claims 28 and 29, characterized in that the three-phase inter-phase transformer consists of two separate single-phase transformers, one of which has a winding having approximately 0.866 times the number of turns of the one. 'other coils- <Desc / Clms Page number 56> ment, the shortest winding being connected, to a terminal, to the approximate midpoint of the longest winding and having a connection point for this neutral connection located approximately one third of the distance from this midpoint terminal. 31.- A device according to any one of claims 1 to 7, 12, 13, for use as a lightning arrester on alternating current circuits, characterized in that the starting device of which one is provided for each of the main electrodes receives energy by a means acting under the effect of an excessive voltage. 32. A device according to claim 31, characterized in that the means acting under the effect of an excessive voltage is composed of a device which is normally substantially non-conductive, to be pierced when Excessive voltage affects the AC circuit and to help extinguish the arc following an excessive voltage discharge. 33.- A device according to claim 31 or 32, characterized in that the main electrodes are kept spaced from one another by means of a perforated tube of insulating material. 34.- A device according to claim 31, 32 or 33 characterized by an external resistance which electrically connects the starting devices of the two main electrodes.