US2759125A - Magnetic separation of positive and negative ignitor firing pulses - Google Patents

Description

14, 1955 A. H. MITTAG EI'AL 2,759,125

MAGNETIC SEPARATION OF POSITIVE AND NEGATIVE IGNITOR FIRING PULSES Filed April 25, 1955 ZERO J i g Invent, or's: Albert H. Mittag Burnice D. Bedfor'd,

Their Attorneyhired MAGNETIC SEPARATIGN 9F POSITIVE AND NEGATIVE IGNITQR FRING PULSES Albert E. Editing, Schenectady, and Bur-nice D. Redford, Scotia, N. Y., assignors to General Electric Company, a corporation of New York Application April 25,1955, Serial No. 503,696

Ciaims. Cl. 315-252 tional current conducting devices are not employed to block inverse voltages.

In order to obtain the desired precision of operation of the electric discharge devices of the type contemplated herein, a supply circuit is usually provided which impresses voltages of predetermined wave form, such as voltages of peaked Wave form, on the ignitors or starting electrodes thereof. Only a small inverse voltage is permissible on the ignitors or starting electrodes of such discharge devices or they will either be destroyed or the life thereof will be materially reduced. As a consequence, it is common practice to couple the ignitors of the discharge devices to the supply circuit by means of a transformer, connecting each ignitor in series with a unidirectional current conducting device and connecting the series combination across the transformer output circuit. The unidirectional, current conducting devices are poled to pass current in a direction to initiate discharge of the device and block or eliminate reverse current halfcycles of the alternating current supply. The unidirectional current conducting devices are generally rectifiers or" the selenium type which are subject to failure. Failure of the rectifiers allows the application of inverse voltage on the ignitors and consequently results in the destruction or a substantial reduction in the life thereof.

Accordingly, it is an object of this invention to provide an improved energizing circuit for starting electrodes of pool cathode type values wherein the application of reverse voltages on the starting electrodes is substantially eliminated without the use of blocking rectifiers.

Briefly stated, in accordance with the invention, the usual blocking rectifiers are eliminated by placing a saturable impedance device having a biasing winding in series circuit relationship with each ignitor electrode and supplying a biasing voltage to the biasing windings which saturates the reactor and opposes the magnetizing effect of a reverse current in the circuit. That is to say, each saturable reactor is saturated by the direct current ampere turns of the biasing windings thereon in the same sense as the positive ignitor current tends to saturate them and, in a sense, opposite to that in which a reverse ignitor current tends to saturate them. In this way, each saturable reactor, being already saturated with ampere turns of a sense to aid the magnetizing effect of positive ignitor current, presents a very high impedance to negative ignitor current since its flow is opposed by the saturated impedance device. Thus, the inverse voltage on the ignitors is maintained at a permissible value without the use of blocking rectifiers.

The novel features which are believed to be charatceristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together Patent 0 2,759,125 Fatented Aug. 14, 1956 with further objects and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a schematic representation of a pair of mercury pool cathode discharge devices and their energizing circuits in which the invention is embodied; and

Fig. 2 is a diagram illustrating an operating characteristic of the circuit of Fig. 1.

Referring now to Fig. l, the invention is illustrated in a system for supplying a direct current load circuit having a positive conductor 10 and a negative conductor 11 from an alternating current supply 12. The translating or rectifying apparatus of the illustrated circuit utilizes an anode supply transformer 13 having its primary winding 14 connected across the alternating current supply 12 and its center tapped secondary winding 15 connected to supply the plate potential for the two vapor electric discharge devices or valves 16 and 17.

Each of the two vapor electric discharge devices is of the immersion-ignitor or cathode pool type and each has an anode 18, a pool type cathode 19, and an ignitor or starting electrode 20 immresed in the cathode pool. As previously indicated, the secondary 15 of the anode supply transformer 13 is connected between the anodes 18 of the two valves 16 and 17. The center point or center tap of the transformer secondary Winding 15 is connected to the negative conductor 11 or" the load circuit and the two cathodes 19 of the valves 16 and 17 are connected to the positive conductor 10. The excitation circuits for supplying potential to the ignitors 20 and cathodes 19 as hereinafter described are designed to provide the proper control to these elements so that the valves act as rectifiers. It will be understood, however, that the valves could be arranged to act as an inverter and that the invention is applicable to the type valves contemplated herein when operated as either a rectifier or an inverter. Also, the invention is applicable to the use of a single valve such as 16 or 17.

The potential on the ignitors 20 and cathodes H of the valves 16 and 17 is supplied from the center tapped secondary or output winding 25 of an ignitor supplying transformer 23 which has its primary or input winding 24 connected to be energized from the main alternating current source 12 through a phase shifting circuit 21 and a voltage peaking circuit 22. The center tap of the ignitor supplying transformer secondary winding 25 is connected to the cathode 19 of each of the tubes, and thus it is also connected to the positive conductor 19 of the direct current load circuit. The individual ignitors 24) of the valves 16 and 17 are connected in series with main windings 26 and 27 respectively, of saturable core impedance devices 28 and 29, and each such series circuit is connected across one-half the secondary winding 25 of the anode supplying transformer. As illustrated, the ignitors 20 are connected to be energized from opposite end terminals of the secondary Winding, and thus they are supplied with a positive firing potential on alternate half cycles of the alternating current supply.

The saturable core impedance devices 23 and 29 are employed in series with the ignitors 24 to reduce inverse voltages on the ignitors, i. e., to suppress negative ignitor current. in order to accomplish this result, the saturable core impedance devices 28 and 29 are provided with direct current biasing windings 3i and 31 respectively. The biasing windings as illustrated are connected in series with each other and across a direct current source 32 which preferably is of sutficient magnitude to provide enough ampere turns to saturate each reactor. The biasing windings are connected in their direct current circuit in such a manner that their magnetizing action on their respective reactors is to aid the magnetizing efiect of a positive firing half cycle flowing in the main winding and oppose the magnetizing effect of a negative ignitor current. Reactors 28 and 29 then offer very little impedance to a positive firing current in their respective circuits since they are already saturated in an aiding direction but present a very high impedance to negative ignitor currents which tends to build up ampere turns in opposition to the established direct current ampere turns. The actual ignitor voltage wave form is illustrated in Fig. 2 of the drawing and will be explained in more detail hereinafter.

The wave peaking circuit 22 is employed to provide an alternating current of peaked wave form to be applied to the ignitors 20. As illustrated, the peaking circuit is of the type disclosed and claimed in U. S. Patent 2,431,- 903, granted December 2, 1947, on an application of E. F. W. Alexanderson and A. H. Mittag. The wave peaking circuit 22 comprises a saturable firing reactor 33 and a firing capacitance 34, which together constitute a resonant circuit of the non-linear type. That is, the circuit is non-linearly resonant with respect to the magnitude of the voltage of source 12, the inductive reactance of firing reactor 33 having a value which is substantially greater than the capacitive reactance of the phase shift circuit 21 (described in detail hereinafter) within the lower region of the source voltage, and smaller than the capacitive reactance thereof within the upper region so that an impulse of voltage is produced when the firing reactor 33 saturates. These impulses occur twice during each cycle of voltage at times relative to the supplied voltage wave which are determined by the saturation of the non-linear firing reactor 33. A linear reactor 35 is connected between the phase shift circuit 21 and peaking circuit 22 to prevent discharge of the capacitor 34 back to the phase shift circuit and to limit the magnitude of the current derived from the supply.

in order to shift the. phase of the firing voltage impressed on the ignitors 2t) and thereby control the magnitude of the unidirectional load voltage, the previously referred to phase shifting circuit 21 is interposed between the alternating current source 12 and the peaking circuit 22. The phase shifting circuit illustrated is of the type disclosed and claimed in U. S. Patent 2,3 62,294, granted November 7, 1944, to Albert H. Mittag. The phase shift circuit utilized comprises the series combination of an inductive reactance 36 and a capacitor 37, and a saturable core impedance device 38 having its main winding 39 connected in one supply line. The output of the phase shift circuit is taken across the series combination of the inductive reactance 3.6 and capacitor 37.

The saturable core impedance device 38 is provided with a suitable control means such as a control winding 48'. The control winding 49 is connected to be supplied from a direct current source 41 and may be controlled manually by means of a current controlling variable resistance 42 or in response to a predetermined controlling influence such as the voltage of an associated circuit. The variable inductive impedance 38 cooperates with the impedance of the circuit into which it works, i. e., its load circuit, to constitute a phase shifting network. The phase of the output voltage of the network may be shifted over a wide range. by varying the impedance of the reactance 38. In this manner, the time of firing of valves 16 and 17 is determined and, consequently, the. magnitude of the direct current potential to the load circuit is determined within limits. The series circuit comprising the inductance. 36. and capactor 37 in the phase, shift circuit is provided to maintain the voltage supplied by the circuit to its load at a substantially constant value throughout .an appreciable range. of phase shift of the output voltage.

Utilizing the circuits illustrated, the voltage impressed upon the primary winding 24 of. the ignitor supplying transformer 23' is of a peaked wave form having symmetrical positive and negative half cycles occurring every electrical degrees. The duration of the peaks are approximately eighteen electrical degrees. Since the reactors 28 and 29 in the ignitor circuits are arranged to suppress inverse voltage peaks in their respective circuits, the voltage wave form on the ignitor 20 in either circuit comprises positive peaks of approximately eighteen electrical degrees duration and spaced by 342 electrical degrees, i. e., occurring once every 360 electrical degrees.

This wave form is illustrated in Fig. 2.

Also, as may be seen from Fig. 2, a small inverse voltage, represented by the magnitude 0, flows for the remaining 342 electrical degrees of each cycle. This small inverse voltage is not enough to damage the ignitors 20. For the best results, the applied voltage peak should be of as short duration as possible since the areas of the positive and negative portions of the wave tend to become equal to each other. Therefore, the shorter the positive pulse, the smaller the inverse voltage 0 applied to the ignitor 20'.

In practice, it would be possible to peak the voltage from the secondary of the supply transformer 25 rather than peaking the voltage supplied thereto. This arrangement would, however, require careful selection of circuit elements and would require elements of corresponding high ratings.

Connecting the main windings 26 and 27 of the saturable reactors in the output circuit of the ignitor supplying transformer secondary 25, as illustrated, has definite advantages over connecting such windings in the primary circuit. It would appear that the magnetizing ampere turns required of reactor biasing windings and reactor winding insulation, problems would be minimized if the saturable reactor were placed in the primary circuit of the circuit of the ignitor supplying transformer. However, the main winding of a reactor, which is connected in series with the primary winding of a transformer, must necessarily carry the transformer no load current (i. e., the magnetizing current and the current required to supply hysteresis a'nd eddy current losses). Thus, the biasing winding must furnish enough ampere turns to overcome the efiect of the transformer no load current in the main winding if it is to maintain the reactor in its saturated condition. When the saturable reactor is connected in the secondary circuit, the biasing windings are not required to supply ampere turns to overcome such a current.

Additional factors are the tendency of the, areas of the positive and negative portions of the applied voltage wave to become equal to each other in the transformer primary and secondary circuits and the fact that the impedance of the ignitors is non-linear. That is to say that the impedance of the ignitors is higher with respect to negative currents than with respect to positive currents flowing therein and, consequently, are instrumental in reducing reverse current flow. Since the ignitors themselves tend to limit the flow of current in a reverse direction in their circuits, the ampere turns which must be suppliedby a biasing winding of a saturable reactor in such a circuit to maintain the saturable impedance device in its saturated condition can be reduced accordingly. Therefore, since the biasing windings of a saturable core impedance device in the output circuit of the ignitorsupplying transformer does not have to overcome the transformer no load current, and since the reverse' current in the secondary circuit is normally reduced due; to the non-linearity of the ignitor impedance, a much lower bias suffices for areactor in the secondary circuit" than is required for a reactor placed in the primary circuit to suppress inverse voltages in the ignitors.

From the foregoing analysis and description, it will be apparent that, by the use of the saturable impedance devices 2 8 and 29in the ignitor circuits, the need for blocking rectifiers therein is eliminated. Itwill also be apparent that by the combined treatment of the saturable' impedance device and the peaking circuit 22, the possibility of a harmful inverse voltage occurring on the ignitors 20 is further reduced.

While the invention has been shown and described as being applied to a particular system of connections and embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention. Consequently, the aim is to cover such changes and modifications as fall within the true spirit and scope of our invention as defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric discharge device of the cathode pool type having a starting electrode, a transformer having a primary input Winding to be energized with alternating current and a secondary output winding, and a saturable reactance device having a main winding and a biasing Winding, the main winding of said saturable reactance device and said starting electrode and the cathode of said discharge device being connected in series with each other across at least a part of the output Winding of said transformer, the biasing winding of said saturable reactance device being energized with direct current, the magntizing eflect of said biasing winding being to saturate said saturable reactance device, the magnetizing eflect of said main winding being to aid and oppose the magnetizing action of said biasing winding on alternate half-cycles of said alternating current so that said saturable impedance device tends to pass and suppress current flow on alternate half cycles.

2. A circuit for energizing the starting electrode of a cathode pool type electric discharge device comprising a transformer having a primary input Winding to be energized with alternating current and a secondary output winding, and a saturable impedance device having a main Winding and a biasing winding, said main winding of said saturable impedance device and at least a part of said secondary output winding of said transformer being connected in series with each other and interconnected with the starting electrode, said biasing winding of said saturable impedance device being energized with direct current, the magnetizing efiect of said biasing winding being in opposition to the magnetizing efiect of alternate half cycles of said alternating current.

3. In combination, a pair of electric discharge devices of the cathode pool type having a starting electrode, said discharge device being connected to conduct alternate half cycles of alternating current, a transformer having a primary winding connected to be energized from a source of alternating current energy and a secondary output winding, and a pair of saturable reactance devices, each of said saturable reactance devices having a main winding and a biasing winding, the main win-ding of each saturable reactance device being connected in series with one of said starting electrodes and its associated cathode, each of said series circuits being connected across at least a portion of said secondary output winding, said biasing winding on each of said saturable impedance devices being connected across a source of direct current energy, said biasing windings being arranged in such a manner that their magnetizing action aids and opposes the magnetizing action of the current in the associated main winding on alternate half cycles so that each saturable impedance device tends to pass and suppress current How on alternate half cycles.

4. In combination, a voltage peaking circuit for producing an alternating voltage which is symmetrical with respect to positive and negative half cycles and which is of peaked wave form, an electric discharge device of the cathode pool type having a starting electrode, a transformer having a primary input winding connected to said peaking circuit for energization thereby and a secondary output winding, and a saturable reactance device having a main Winding and a biasing winding, the main winding of said saturable reactance device and said starting electrode and the cathode of said discharge device being connected in series with each other across at least a part of the output winding of said transformer, the biasing winding of said saturable reactance device being energized with direct current, the magnetizing ellect of said biasing winding being sufiicient to saturate said saturable reactance device, the magnetizing efliect of said main winding being to aid and oppose the magnetizing effect of said biasing winding on alternate half cycles of said alternating current so that said saturable impedance device tends to pass and suppress current flow on alternate half cycles.

5. In combination, a voltage peaking circuit for producing an alternating voltage which is symmetrical with respect to positive and negative half cycles and which is of a peaked wave form, a pair of electric discharge devices of the cathode pool type having a starting electrode, said discharge devices being connected to conduct alternate half cycles of alternating current, a transformer having a primary input winding connected to said peaking circuit for energization thereby and a secondary output winding, and a pair of saturable reactance devices, each of said saturable reactance devices having a main Winding and a biasing winding, the main winding of each saturable reactance device being connected in series with one of said starting electrodes and its asscciated cathode, each of said series circuits being connected across at least a portion of said secondary output winding, said biasing winding on each of said saturable impedance devices being connected across a source of direct current energy, said biasing windings being arranged in such a manner that the magnetizing efiect aids and opposes the magnetizing effect of the current in the associated main winding on alternate half cycles so that each saturable impedance device tends to pass and suppress current flow on alternate half cycles.

No references cited.

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