US2730661A - Initiating the arc in mercury pool tubes - Google Patents

Description

\/ PRODUCING Jan. 10, 1956 H. KELLOGG 2,730,661

INITIATING THE ARC IN MERCURY POOL TUBES Filed Jan. 15, 1952 Figj.

Inventor:

Harry L..Kello22,

His Attorney.

Lam

. 7 21,730,661 INITIATING THE ARC IN MERCURY POOL TUBES 1 Harry LhKellogg, Scotia, N. Y., assignor to General Elec- This invention relates to vapor electric discharge devices of the type employing a'pool-type cathode and particularly to devices of this character having improved dis-.

charge initiating means. t

In one form of pool cathodeelectric discharge device,

a starter electrode is employed in which the starter is continuously immersed in the pool cathode and through which a predetermined minimum current is passed to form a cathode spot and initiate'th'e discharge. The starting electrode, while oftelatively high resistance compared with a metallic conductor, is'ofrelatively low resistance as compared withadielectric.

It is common practice to energize starting electrodes of thetype referred to above from a transformer output winding through a unidirectional conducting device the purpose of which is to eliminate reverse current half-cycles 'off the alternating current supply thereby to increase the life of the starting electrode. Such unidirectional convducting. devices or rectifiers may failunless constructed with an adequate margin of safety. Upon failure of such rectifiers, 'each half cycle of alternating current is suppliedto the starting electrode. Since proper operation of States Patent 2,730,661 Patented Jan. 10, 1956 2 2 and 3 are diagrams to aid in understanding the prin ciples of operation of the arrangement shown in Fig. 1.

In Fig. l, a polyphase alternating current circuit is indicated by the lines 1, 2 and 3. This alternating current circuit energizes the primary 4 of a power transformer having a secondary winding 5. The winding 5a of secondary winding 5 is connected to the electric valves 6 and a mercury pool type valve is accomplished with its starting electrode energized during positive half-cycles only, failure of a rectifier in the supply circuit for the starting electrode results in substantially reducing the life of the starting electrode since the electrode is required to conduct current during negative half-cycles as well as during posi tive half cycles. 1

One object of this invention is to provide an improved energizing circuit for the starting electrodes of mercury cathode valves. t

Another object of this invention is the provision of an arrangement wherein unidirectional conducting devices commonly used at present in starting electrode circuits are eliminated.

' According to the invention, a transformer for energizing 1 the starting electrode of a mercury pool tube is provided with a biasing winding arranged to saturate the transformer core and to oppose the magnetizing effect of the half-cycle of alternating current during which the starting change in the transformer flux is effected, resulting in a substantial output voltage from the transformer to the starting electrode. During alternate half-cycles of the alternating current supply, the magnetizing effect thereof is in the same effective direction as that of the biasing winding. Since the transformer is already saturated, the change influx and the resulting voltage output from the transformer are sufiiciently smallas not to cause damage to the starting electrode.

The invention both as to its organization and method I electrode is to be energized, In this way, a substantial I 7. Each of the valves 6 and 7 is provided with an anode 8, a control electrode 9, a holding anode 10, and a starting electrode 11 immersed in a mercury pool cathode 12. Since the circuits for controlling the control grids 9 and the holding anodes 10 form no part of the present invention, these have been omitted from the drawing. Suitable circuits for this purpose are well known and could be of the type disclosed in patent 2,517,129, Mulhern, granted a August 1, 1950, and assigned to the assignee of this invention. As shown in Fig. l, the cathodes 12 of the valves 6 and 7 are both connected to a positive conductor 13, while the center point of the secondary winding 5 of the power transformer is connected to a negative direct current conductor 14. Thus, if the polyphase circuit comprising conductors 1, 2 and 3 is energized from a source of electric energy, and if a direct current load is connected across the conductors 13 and 14, the arrangement comprising tubes 6 and 7 will operate as a rectifier provided I proper control is supplied to the control elements of these valves.

It will be understood that the valves 6 and 7 could be arranged to operate as an inverter and thatthe invention is applicable to mercury pool type valves when operated as either rectifiers or as inverters. Furthermore, the principles of the invention are applicable to a single valve, such as 6 or 7.

The starting electrodes 11 of valves 6 and 7 are respectively energized by the secondary windings 15 and 16 of transformers generally designated by the numerals 17 and 18. Transformer 17 is provided with a primary winding 19, while transformer 18 is provided with a primary winding20. As indicated in Fig. 1, these primary windings 19 and 20 are connected in series and are energized from a common source 21 designated as a Narrow pulse producing circuit. This narrow pulse producing circuit could be of any known type, and since the specific components thereof form no part of the present invention, the details thereof have been omitted from Fig. 1. A suitable circuit for energizing the primaries 19 and 20 could be of the type disclosed in Patent 2,523,027, Kellogg et al., granted September 19, 1950, and assigned to the assignee of this invention. As is indicated in Fig. l, the pulse producing circuit 21 is energized from a suitable source of alternating current represented by the con-' ductors 22 and 23. The circuits including the transformer secondary windings 1S and 16 and the starting electrodes 11 of valves 6 and 7 respectively do not include a unidirectional conducting device.

Inaccordance with this invention, conventional rectifier means is eliminated from the circuit used to energize starting electrodes such as are designated by the numeral 11, due primarily to the fact that the transformers 17 and 18 are respectively provided with a biasing winding 24 and 25. As indicated in Fig. 1, these biasing windings are connected in series and are energized from a source of direct current indicated by the battery 26 through an adjustable resistance 27. Also, as is indicated in Fig. 1, the winding 24 is wound in a reverse direction from the winding 25. Thus, with enough direct current bias applied to the transformers 17 and 18, the iron thereof is saturated so that each transformer supplies a different half-cycle of voltage to the ,ignitors 11 of the valves 6 and 7. For example, a positive halfcycle of energy supplied from the circuit 21 to the windings 19 and 20 could be arranged to oppose the magnetizing action of the winding 24 and to be 3 in the same direction as the magnetizing action of the winding 25. Under such conditions, the flux in transformer 17 would be changed substantially due to the positive half-cycle of current from the circuit 21 while the flux in transformer 18 would not change appreciably since this transformer is already magnetized in the same direc tion due to the biasing winding 25. Under such circumstances, the ignitor 11 of valve 6 would be energized and a very low voltage would be applied to the ignitor 11 of valve 7, so that valve 6 would be operably energized whereas'valve 7 would not be energized.

During a negative half-cycle supplied from the circuit 21, the ignitor 11 of valve 7 would be'op'erably energized so as to render that valve conductive while the valve 6 would remain inoperative.

In Fig. 2, the curve 25 represents the secondary voltage output of the secondary winding 15 of transformer 17, or the output voltage in the secondary winding 16 of transformer 18. Since the curves of Figs. 2v and 3 are applicable to either transformer 17 and its associated ignitor, or to transformer 18 and its associated ignitor, reference to Figs. 2 and 3 will be made in conjunction with the transformer 17 only. Thus, in Fig. 2, the curve i1 represents the current flowing in the primary winding 19, while the curve iz represents the current flowing in the secondary winding 15. Thus, it will be observed that between the time designated by the letter A and that designated by the letter B, the voltage (ls supplied to the ignitor 11 of valve 6 is of peaked wave form, while the current in both the primary and secondary windings of transformer 17 is substantially sinusoidal. Since the circuit including the secondary winding 15 of transformer 17 is not provided with any rectifying means, there is no D. C. component of current which flows in this circuit. Therefore, the current iz during the positive half-cycle must be balanced by a secondary current i2 in the negative direction. Such a current as is indicated in Fig.2 flows from the time designated by the letter B to the time designated by the letter C. Likewise, the secondary voltage of transformer 17 is designated by the curve 65 during the time between that designated B and that designated C It will'be understood that the positive portion of the voltage es, being of peaked wave shape and of substantial magnitude, is adequate to energize the ignitor 11 of valve 6, while such voltage in the negative direction is not of sufiicient magnitude to energize the ignitor. During the negative half-cycle of energy supplied by circuit 21,- the primary current in primary winding 19 is represented by the curve ii between the time designated by the letter D" and bythe time designated by the letter B. The secondary current and voltage in winding 15 between the time D" and timeE are represented in Fig. 2 and are of a very low order of magnitude and wouldnot be sufficient to energize the ignitor 11. Thus, by the arrangement of Fig. l, the ignitor I 1 is energized only during apositive half-cycle of the energy supplied by circuit 21.

Fig. 3 represents a hysteresis loop for transformer 17 or transformer 18. In Fig. 3, it will be seen that the transformer is saturated at the time designated by the letter A so that a positive current ii flowing in the winding 19 will desaturate the transformer 17 by decreasing its flux to some value indicated by the letter B. Such a substantial reduction in flux in the transformer 17 obviously is responsible for the peaked voltage of substantial magnitude which appears as s in Fig. 2 between the times A and B. After the. flow of primary current ii ceases, the magnetization of the transformer 17 due to secondary current 1: moves from the point B through zero and up to the point C, as the secondary current i2 decreases to zero, the direct-current bias of winding 24 being indicated. The negative half-cycle of current from circuit 21 drives the flux to some point designated by the-letter D without effecting any appreciablechange in the flux of transformer 17. Thus, if no appreciable change in the flux is effected, there is no appreciable voltage generated in the secondary winding 15 of the transformer 17. This fact is demonstrated in Fig. 2' by the curve 65 between time D and the time B.

From what has been said above in connection with transformer 17, it will be understood that the operation of transformer 18 is identical to that of transformer 17 and could be explained by curves identical to those indicated in Figs. 2 and 3 except such curves would be representative of the negative half-cycle of current supplied by the circuit 21 rather than of the positive half-cycle.

While I have described a particular embodiment of the invention, I do not wish to be limited thereto and intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. 7

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

l. A circuit for energizing the starting electrode of a mercury pool type tube comprising a transformer having a primary input winding energized with alternating current, a secondary output winding interconnected with the start ing electrode, and a biasing winding energized with direct current, the magnetizing elfect of said biasing winding being in opposition to the magnetizing effect of alternate half-cycles of said alternating current during which said tween said electrode and the cathode of said valve, a

primary winding energized with alternating current, and a biasing winding energized with direct current, the magnetizing effect of said biasing winding being sufficient to saturate said transformer, the magnetizing effect of said primary winding being effective to aid the magnetizing action of said biasing winding during alternate halfcycles of the alternating current so that said starting electrode is not operably energized during such half-cycles.

3. in combination, a pair of electric valves of the mercury pool cathode type each having a starting electrode, said valves being connected to conduct alternate halfcycles of alternating current, a pair of transformers each having a secondary winding connected to energize the starting electrode of one of said valves, the primary windings of said transformers being connected to a source of alternating current energy, a biasing winding on each of said transformers, said biasing windings being connected across a source of direct current energy and each of said biasing windings being arranged so that the magnetizing effect thereof aids the magnetizing eifect of the current in the associated primary winding during alternate half-cycles thereby to prevent the associated starting electrode. from being operably energized during such half-cycles.

4. A circuit for energizing the starting electrode of a mercury pool type tube comprising a voltage peak.- ing circuit for producing an alternating voltage which is symmetrical with respect to positive and negative half cycles and which is of a peaked waveform, a transformer having a primary input winding connected to said peaking circuit for energization thereby, a secondary output winding interconnected with the starting electrode, and a biasing winding energized with direct current, the magnetizing effect of said biasing winding being in op position to the magnetizing effect of alternate half cycles of said alternating voltage during which said starting electrode is operably energized.

5. In combination, a voltage peaking circuit for pro ducing an alternating voltage which is symmetrical with respect to positive and negative half cycles and which is of peaked waveform, an electric valve of the mercury pool cathode type having a starting electrode, a transformer having a primary input winding connected to said peaking circuit for energization thereby, a secondary winding connected between said electrode and the cathode of said valve, and a biasing winding energized with direct current, the magnetizing effect of said biasing winding being sufiicient to saturate said transformrent so that said starting electrode is not operably energized during such half cycles.

6. In combination, a peaking circuit for producing an alternating voltage which is symmetrical with respect to positive and negative half cycles and which is of a peaked waveform, a pair of electric valves of the mercury pool cathode type each having a starting electrode, a pair of transformers each having a secondary Winding connected to energize the starting electrode of one of said valves and a primary. winding connected to said voltage peaking circuit for energization thereby, a biasing Winding on each of said transformers, said biasing windings being connected across a source of direct current in such a manner that their magnetizing effect aids the magnetizing eifect of the current in the associated primary winding during alternate half cycles to prevent the associated starting electrodes from being operably energized during such half cycles.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,561 Grifiith et al. Nov. 16, 1937 2,120,565 Lord June 14, 1938 2,157,834 Schmidt May 9, 1939 2,175,920 Schnarz Oct. 10, 1939 2,193,649 Schmidt Mar. 12, 1940 2,273,586 Moyer Feb. 17, 1942 2,361,846 Garman Oct. 31, 1944 2,466,028 Klemperer Apr. 5, 1949

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