US2721292A - Device for adjusting the electrode gap in polyphase-current arc lamps - Google Patents

Description

Oct. 18, 1955 c; LOBBE DEVICE FOR ADJUSTING THE ELECTRODE GAP IN POLYPHASE-CURRENT ARC LAMPS I Filed March 9, 1955 INVENTORY M4 GEQKGES LOBBE United States Patent DEVICE FOR ADJUSTING THE ELECTRODE GAP IN POLYPHASE-CURRENT ARC LAMPS Georges Lobb, Brussels, Belgium Application March 9, 1953, Serial No. 341,104 Claims priority, application France March 19, 1952 12 Claims. (Cl. 314-418) This invention relates in general to are lamps and has particular reference to are lamps of the type supplied with polyphase current for use as a source of constant light.

In arc lamps of this type this constant-light feature is secured only by keeping the electrodes-at their are forming point of convergenceto a strictly accurate gap value. Indeed, as long as the electrodes are kept burning they should remain centered geometrically with respect to the desired spot or axis while having the desired electrical gap therebetween, especially in those applications Where the light emitted is reflected by an optical collecting device.

Thus, if a three-electrode system is to be maintained under the conditions broadly set forth hereinabove so that they are gradually fed as they burn, the rate of feed being based on the consumed length per time unit, it will be seen that their respective gaps cannot be maintained to a constant value as the latter is influenced by variables such as the internal resistance of the electrodes, leaks in the step-down transformer through which the electrodes are supplied with current, resistances due to contact surfaces, the electric power applied to each electrode, etc., so that the degree of wear will vary for each electrode taken separately.

In order to overcome these drawbacks a known method' consists in making each electrode mechanically independent of the other and to feed it by means of a small electromotor controlled by an element responsive to voltage or current variations taken at the electrode itself.

Devices of this type are based on the feed control of the various electrodes according to the variations in voltage taken at the terminals thereof and have a good efficiency in that they make it possible to operate several electrodes provided that the source of trior polyphase current displays a constant potential in each phase, according to the number of electrodes employed for forming the are.

Unfortunately this imperative condition is never met because potential variations in the phases may be origihated either at the current source or by the voltage drop resulting in the supply circuit on account of a singlephase overload, for instance. in this case the device remains operative but the point of convergence of the electrodes is displaced by an amount proportional to the voltage drops of the faulty phase or phases so that the geometrical center of the arc crater is displaced.

If the light emitted from this crater is transmitted for example through an optical collecting device with a view to projecting a picture through a mechanical gate centered on the optical axis of a mirror, each variation in the potential or" one of the supply phases will displace the arc crater across the optical axis so that each variation will require a manual optical re-centering to realign the light beam.

This phenomenon may be explained as follows. Assuming a three-electrode apparatus wherein the electrode points are arranged at the edges of a trihedron wherein they crater-forming point of convergence represents the 2,721,292 Patented Oct. 18, 1955 vertex of the aforesaid trihedron, if these electrodes are electrically connected to a source of three phase current across a leak transformer, the arc will be stricken and its maintenance is conditioned by the regular feeding of the electrodes as they are consumed by the are. If an individual-feed electrode control system is used, wherein the rate of feed is conditioned by the voltage increases resulting from the widening electrode gaps, and wherein the difference is potential corresponding to each electrode is utilized for actuating a relay responsive to this difference, it is obvious that each time a voltage difference due to a worn electrode occurs the relay controlling the feed of the electrode concerned will be energized to reset the electrode gap at the proper time.

This will take place as long as the potential difference is controlled by electrode wear, but if this potential variation (which is extremely small) is caused by a voltage drop in one of the supply phases it will reproduce automatically this difference in the secondary circuit through which the electrode proper is supplied with current, so that this electrode will be fed to an additional extent whilst the other two will move back, thereby displacing the geometrical center of the triangle constituted by the electrode points; this center will move around the optical axis and the value of this displacement will be proportional to the difference in voltage between the phases. From a low phase drop percentage up, the system is no more controllable and its operation is disturbed completcly.

It is the scope of this invention to maintain the geometrical or optical centering of the are crater in spite of potential variations in any one of the current supply phases.

The essential feature of the invention is that the feed of each electrode is produced by a separate electromotor the current supply of which is controlled by a biased relay the energizing circuit of which comprises two rectifying systems connected in opposition and the control voltages of which are taken from the primary phase and the secondary phase, respectively, of the supply circuit for the electrode concerned.

Under the practical operative conditions of the system claimed, a primary voltage drop in any one of the current phases which develops a secondary voltage drop at the electrodes will not actuate the relay so that the electrode will not be forced away from its position as the supply of current to the relay will not energize the latter in this case.

On the other hand, if a voltage variation is created in the secondary of any one electrode due to the combustion thereof which tends to increase the electrode gap and therefore to create this variation, the latter will produce the want of balance required for energizing the relay so as to close the circuit of the electromotor controlling this electrode. As soon as the electrode is reset in proper position the relay is de-energized. Practical tests carried out with a system according to this invention proved that a centering point along the optical axis could be maintained with plus or minus 25% variations in the phase potential.

The accompanying drawing forming part of this invention illustrates diagrammatically by way of example two forms of embodiment of the invention. In the drawing:

Figure l is a diagrammatical illustration of a threephase are projected onto a plane at right angles to the optical axis of a projector;

Figure 2 is a diagrammatical axial view of the arrangement of Figure 1 but taken across the plane of two electrodes for the sake of clarity;

Figure 3 is a view similar toFigure 1 showing the consequence of an excessive feeding of one electrode;

Figure 4 is a corresponding view similar to Figure 2;

Figure is a wiring diagram showing one form of embodiment of the invention; and

Figure 6 is a diagrammatical illustration of a modified mechanism for feeding the electrodes.

In Figures 1 and 2 the reference numerals 1, 2, 3 designate the three electrodes of a three-phase arc which may be arranged to form the edges of a trihedron converging toward a center 4 positioned along the optical axis 5 of a mirror 6 designed to reflect the light emitted from the arc crater consisting of the triangle 7 inscribed in the electrode points.

As already set forth hereinabove, any voltage increase applied to one electrode, for instance electrode 1, may result not only from an excessive spacing of this electrode with respect to the other electrodes but also from a voltage variation in a primary phase connected to this electrode. In this case if the feed of electrode 1 were controlled simply by the voltage measured at this electrode, the aforesaid voltage variation would bring the electrode concerned to position 1' shown in Figures 3 and 4 and the other electrodes would remain in their back positions 2 and 3' with their points held back so that the center of convergence would be displaced to 4, i. e. in a position ofl-set with respect to the optical axis.

With the device according to the invention this inconvenience is avoided completely.

In the practical form of embodiment illustrated in Figure 5 illustrating the application of the invention to a three-electrode are fed with three-phase current, the electrodes are indicated at 11, 12, 13 and the electrode holders at 14, 15, 16. The convergent feed of these electrodes is controlled by three separate electromotors 17, 18, 19. The electrodes are supplied with current from the star-connected secondary phases 20, 21, 22 of a supply transformer the delta-connected primary phases of which are indicated at 23, 24, 25.

According to this invention, each motor 17, 18, 19 is energized through a biased relay the energized current of which is in turn dependent on two opposed voltages from rectifier system the voltages of which are taken from the primary and secondary phases connected to the corresponding electrode. Each motor may be equipped with a separate relay associated to a pair of corresponding rectifiers, in which case the arrangement would require three relays and six rectifiers. However, the arrangement may also comprise a single relay with two rectifiers constituting a unit common to three electrodes; besides, a single source of current may be used for the three motors provided that this common unit is successively connected through a system comprising three sets of switches closed by a single rotary member to the separate circuits corresponding to the various electrodes. An arrangement of this type is exemplified in Figure 5. To simplify the illustration, only one complete electrode-controlling circuit is shown in this figure, but it will be readily understood by anybody conversant with the art that the circuits controlling the other electrodes may be easily traced from the reference numerals indicated in this figure.

The common source of current for energizing the motors consists of a winding 26 associated to the primary of the transformer and in series with a movable contact member 27 inserted in a circuit comprising a common portion 28 and three parallel-connected portions 29, 30, 31 corresponding to the three motors. The movable contact member 27 is actuated by a biased relay 32 energized through a circuit 33 supplied from two rectifier units 34, 35. The inputs of the rectifiers of unit 34 are connected to a supply circuit the common portion 36 of which is splitted into three sections 37, 38, 39 each comprising one portion of a relevant potentiometer 4t), 41, 42; each of these otentiometers is connected across the corresponding electrode and the neutral 43 of the secondary, so that the voltage taken by the rectifiers 34 from any potentiometer is proportional to the voltage measured at the relevant electrode. The rectifiers 35 are fed from a circuit the common portion 44 of which is connected to three parallel portions 45, 46, 47 each comprising one of the windings 48, 49, 50 mounted on the primary phases corresponding to the electrodes 11, 12, 13.

The separate circuits of each electrode for energizing the feed motor and both rectifier units are controlled by a set of three switches closing simultaneously; the sets of switches controlling the three electrode circuits are indicated at 51, 52, 53 and actuated in succession by a rotary cam member 54 driven by a small motor indicated diagrammatically at 55. In the figure each pair of movable contacts is designated by the reference numeral of the separate circuit closed by this pair of contacts; the figure also shows the connection between one contact of the pair concerned with the common portion 28, 36, 44 of the corresponding circuit; the other contacts are connected to the wires having the same reference numerals, that is, 29, 37, 45 for electrode 11, and 30, 38, 46 for electrode 12.

For each electrode the relay energizing system is so adjusted that no current will flow through the circuit 33 (during the closing of the corresponding set of switches) when the electrode is properly positioned and that any increase in the electrode voltage which is not caused by an increase in the primary voltage will create a state of unbalance in this circuit 33, thereby causing the rectifiers 34 to supply this circuit with energizing current for the electromagnet so that the latter will actuate the movable contact 27 to close the supply circuit of the motor controlling the electrode concerned when the set of switches of this electrode are actuated by the rotary cam 54.

Thus, if a primary-voltage drop brings about a corresponding secondary-voltage drop, for instance in the phase connected to the electrode 13, the voltages supplied from rectifiers 34 and 35 (when the set of switches 53 are closed) will both vary in the same ratio while remaining in opposition and the relay will remain de-energized. On the contrary, if the voltage increase at the electrode 13 is due to its wear and to the resulting greater gap between its point and the desired arc center, the voltage supplied from rectifiers 34 will no more be compensated by that of rectifiers 35 and as a consequence relay 32 will be energized to supply current to the motor 19 and move the relevant electrode 13 to its proper setting.

Of course, the frequency and duration of the closing time of the successive sets of switches will be selected to suit the velocity of consumption and the rate of setting of the electrodes.

The motors 17, 18, 19 may consist of any desired and electrically-controlled driving mechanism. Therefore, any small electromotors of the conventional rotary type may be used, but it is also possible to use simple electromagnets actuating the electrodes in the manner shown diagrammatically in Figure 6.

In this figure 56 is an electrode slidably mounted in an electrode socket 57 provided at one end of a tubular electrode holder 58 having associated thereto a casing 59. These three members may constitute an integral unit. In the casing 59 there is rotatably mounted a friction wheel 60 in frictional driving engagement with the electrode 56. This friction wheel 60 is fast with a ratchet wheel 61 adapted to be actuated by a control rod 62 mounted for axial sliding movement in the tubular holder 58 as shown, the front or operative end of this rod extending through an oval-shaped bearing 63. A return tension spring 64 urges this rod 62 backwards by causing the operative end of the rod to slide on the ratchet teeth and this backward movement is restricted by the engagement of a stop member 65 fixed on the rod with a check member 66. The rear end 67 of the rod 62 is adapted to be acted upon by a pivoted armature member 68 normally urged to an inoperative position by a tension spring and appertaining to an electromagnet unit 69 the winding 70 of which is supplied with direct or alternating current, for example as the motors of Figure 5. When the electromagnet is energized, the rod 62 is driven forwards and causes the ratchet wheel 61 and therefore the friction wheel 60 to rotate, thereby feeding the electrode by a corresponding amount toward the optical axis; when the rod is retracted by its return spring 64 and the electromagnet is de-energized, the operative end of the rod engages the next tooth of the ratchet wheel in a position ready for another feeding step of the electrode when another current pulse is supplied to the electromagnet.

It is obvious that the system according to the invention, of which the scope is to maintain an arc crater of a plurality of electrodes fed with polyphase current in a position defined geometrically in the space, may be applied to any polyphase current are lamp system, with or without reflector; when the system is used with reflecting mirror of any desired shape such as spherical, elliptical, parabolic or else, the center of the arc crater is positioned centrally of the optical focus of the mirror.

It will be readily understood that the forms of embodiment described hereinabove and illustrated in the attached drawing are merely illustrative of the invention and that many alterations or additions may be devised without departing from the spirit and scope of the invention. Thus, the rectifier input circuit may include adequate filter means and the electrical circuits may be provided with any desired or suitable protecting members such as capacitors or shunt resistors, etc.

I claim:

1. A device for adjusting the electrode gap in polyphase current are lamps comprising a polyphase transformer for supplying current to the electrodes, a separate electromotor for moving axially each electrode, a biased relay for controlling the energization of said motor, two rectifier units mounted in opposition for energizing said relay and means for supplying control voltages to said rectifier units from the primary phase and the secondary phase respectively of the supply circuit for said electrode.

2. A device for adjusting the rate of feed of each electrode gap in triphase current arc lamps with three electrodes, comprising a triphase transformer for supplying current to the electrodes, a separate electro-motor for moving axially each electrode, a biased relay for controlling the energization of said motor, two rectifier units mounted in opposition for energizing said relay, means for supplying a control voltage to one of said rectifier units from the primary phase for said electrode and means for supplying a control voltage to the second rectifier unit from the corresponding secondary phase through a part of a potentiometer connected between said electrode and the neutral of the three secondary phases in star connection.

3. A device as claimed in claim 2, in which the means for supplying a control voltage to one of the rectifier units from the primary phase comprise a winding associated with the winding of said primary phase on the same magnetic core.

4. A device as claimed in claim 2, comprising two rectifier units, common for energizing the motors of the three electrodes, a first group of three electrical circuits for supplying one rectifier unit from the three primary phases of said transformer, a second group of three electrical circuits for supplying the second rectifier unit from the three secondary phases of said transformer and a third group of three circuits for supplying the motors from the relay energized by said rectifier units, a set of three switches with several contacts, each for closing the circuit of each group corresponding to one of the electrodes, a cam for operating successively said switches and power means for operating said cam, the said different circuits of each group 6 having a common portion and separate portions in parallel corresponding to the various electrodes.

5. In an arc lamp for multiphase alternating current, in combination, a plurality of arc-forming electrodes equal in number to the number of phases of said alternating current, said electrodes being arranged to form therebetween an arc when suitably energized; multiphase alternating current transformer means having primary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; electrode position adjusting means operatively associated with each of said electrodes; and control means for said electrode position adjusting means in circuit with said primary and secondary windings for individually actuating said electrode position adjusting means solely in response to changes in voltage across said secondary windings which are not the result of corresponding changes in current through their corresponding primary windings.

6. In an arc lamp for multiphase alternating current, in combination, a plurality of arc-forming electrodes equal in number to the number of phases of said alternating current, said electrodes being arranged to form therebetween an are when suitably energized, multiphase alternating current transformer means having primary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; electrode position adjusting means operatively associated with each of said electrodes; and control means for said electrode position adjusting means in circuit with said primary and secondary windings responsive to changes in voltage across said secondary windings which are not due to changes in current through their corresponding primary windings, and non-responsive to changes in voltage across said secondary windings which result from changes in current through their corresponding primary windings for individually actuating said electrode position adjusting means.

7. In an arc lamp for multiphase alternating current, in combination, a plurality of arc-forming electrodes equal in number to the number of phases of said alternating current, said electrodes being arranged to form therebetween an are when suitably energized; multiphase alternating current transformer means having primary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; an electric motor electrode position adjusting means operatively associated with each of said electrodes, respectively; and control means for said electrode position adjusting means in circuit with said primary and secondary windings for individually actuating said electrode position adjusting means solely in response to changes in voltage across said secondary windings which are not the result of corresponding changes in current through their corresponding primary windings.

8. In an arc lamp for multiphase alternating current, in combination, a plurality of arc-forming electrodes equal in number to the number of phases of said alternating current, said electrodes being arranged to form therebetween an are when suitably energized; multiphase alternating current transformer means having primary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; an electromagnetic electrode position adjusting means operatively associated with each of said electrodes, respectively; and control means for said electrode position adjusting means in circuit with said primary and secondary windings for individually actuating said electrode position adjusting means solely in response to changes in voltage across said secondary windings which are not the result of corresponding changes in current through their corresponding primary windings.

9. In an arc lamp for multiphase alternating current, in combination, a plurality of arc-forming electrodes equal in number to the number of phases of said alternating current, said electrodes being arranged to form therebetween an arc when suitably energized; multiphase alternating current transformer means having primary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; electrode position adjusting means operatively associated with each of said electrodes; and control means for said electrode position adjusting means in circuit with said primary and secondary windings comprising a pair of rectifier means, each having input and output terminals, the input terminals of one of said rectifier means being connected to said primary windings and the input terminals of the other of said rectifier means being connected to said secondary windings, a comparison circuit connected to said output terminals for deriving from said rectifier means a control voltage in response to changes in the voltage across said secondary windings which are not the result of changes in current through their corresponding primary windings and for deriving no control voltage output in response to changes in voltage across said secondary windings resulting from corresponding changes in current through the corresponding primary windings, current supply circuit means for said electrode position adjusting means, and means coupled to said last-named means and said comparison circuit for selectively connecting said current supply circuit means to said electrode position adjusting means in response to said control voltage.

10. In an arc lamp for three phase alternating current, in combination, three arc-forming electrodes arranged to form therebetween an are when suitably energized; three 9 phase alternating current transformer means having pri mary windings and secondary windings, each of said secondary windings being connected to a different one of said electrodes for supplying energizing voltages of different phase thereto; electrode position adjusting means operatively associated with each of said electrodes; and control means for said electrode position adjusting means in circuit with said primary and secondary windings comprising a pair of rectifier means, each having input and output terminals, the input terminals of one of said rectifier means being connected to said primary windings and the input terminals of the other of said rectifier means being connected to said secondary windings, a comparison circuit connected to said output terminals for deriving from said rectifier means a control voltage in response to changes in the voltage across said secondary windings which are not the result of changes in current through their corresponding primary windings and for deriving no control voltage output in response to changes in voltage across said secondary windings resulting from corresponding changes in current through the corresponding primary windings, current supply circuit means for said electrode position adjusting means, and means coupled to said last-named means and said comparison circuit for selectively connecting said current supply circuit means to said electrode position adjusting means in response to said control voltage.

11. In an arc lamp as set forth in claim 10, said means for selectively connecting said current supply circuit means to said electrode position adjusting means including cam-driven switch means.

12. In an arrangement of the character described, in combination, transformer means including at least one primary winding and one secondary winding; a pair of rectifier means, each having input terminals and output terminals, said input terminals of said one of said rectifier means being connected to said primary winding, and said input terminal of said other rectifier means being connected to said secondary winding; comparison transformer means connected to the output terminals of said rectifier means in such phase that changes in voltage across said secondary winding due to changes in current through said primary winding cause no voltage drop across said comparison transformer means and changes in voltage across said secondary winding not due to changes in current through said primary Winding cause a control voltage to be produced across said comparison transformer means; an arc-forming electrode connected to said secondary winding and deriving its arcing potential therefrom; electrode position adjusting means operatively associated with said arcing electrode; and control means connected to said electrode position adjusting means and responsive to said control voltage for actuating said electrode position adjusting means.

References Cited in the file of this patent UNITED STATES PATENTS 2,136,309 Muller Nov. 8, 1938 FOREIGN PATENTS 454,822 Canada Mar. 1, 1949

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