US2307217A - Voltage regulation compensator - Google Patents

Description

Jan. 5, 1943. c. w. HANSELL 72,307,217

VOLTAGE REGULATION COMP ENSATQR I Filed June 25, 1941 75 m1. a M I the VQZZZZ E/ K d E (11016 2'1 1 L J Am;

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.fizcZEmaZZo Zine Vegas Eggulair 75- mvEN'roR 0201M Wilma ell ATTORNEY Patented Jan. 5, 1943 VOLTAGE REGULATION COMPENSATOR Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application June 25, 1941, Serial No. 399,613

5 Claims.

This invention relates to electrical regulation, and more particularly to a voltage compensator for providing a substantially constant voltage supply to a load. Its purpose is to compensate voltage variations in one load circuit due to fluctuating current input to another load circuit deriving power from the same source.

The present invention finds a particularly useful application in wireless telegraph transmitting systems employing keying of the transmitted si nals and wherein there is need for a system to compensate for voltage drop accompanying the transmitter. keying in the power supply to the transmitter vacuum tube filaments, and also a need for improving and stabilizing the operation of slow acting automatic voltage regulators associated with the transmitters.

In wireless transmitting systems, it has been found that the keying of the transmitter causes an accompanying variation in voltage drop in the power supply to the vacuum tube filaments with an accompanying deleterious effect on the life and efficiency of the vacuum tubes. This is because, in the case of pure tungsten filaments, the life of an incandescent filament, such as is used in a lamp or vacuum tube, depends critically upon the value and constancy of the voltage applied to it. In vacuum tubes the minimum value of filament voltage must be high enough to maintain a required electron emission but if voltage fluctuations are large, the averageand maximum voltages must be higher and even when burnout does not occur quickly on voltage maxima, the rate of evaporation of metal from the filament is increased and the tube life correspondingly shortened.

In vacuum tubes with thoriated tungsten filaments, the filament voltage must be held at a.

correct value to maintain the layer of thorium on the surface. If the voltage is too low, bombardment of the filament surface by gas ions will destroy the thorium layer faster than it is replaced by difiusion of thorium from inside the tungsten. If the voltage is too high, the high filament temperature will evaporate away the thorium faster than it is replaced by diffusion. Thus, either high or low voltages will destroy the usefulness of a thoriated filament tube by destroying the layer of thorium on which the emission depends.

Heretofore, it has been customary to control the average filament voltages by means of manually adjusted rheostats or by relatively slow acting automatically operated regulators of the induction or variably tapped auto-transformer types. In a few cases, automatically adjusted rheostats have been used. The difficulty with these known methods of regulation, however, lies in the fact that they are not capable of functioning quickly enough to prevent rapid fluctuations in voltage due to the keying of the transmitter when there is relatively large impedance in the power supply circuits. Consequently, where the voltage variations due to keying are not extreme. it has been customary to adjust the filament voltage to a value where suflicient emission is obtained when the key is down; i. e., when signals are being transmitted. Then when the key is up; i. e., when signals are not being transmitted, the voltage is higher than necessary and the filament life is thereby reduced. In a few extreme cases of power voltage regulation in outlying radio stations, it has been necessary to employ relays, closed and opened synchronously with the keying, to compensate voltage variations in the filament circuits. These relays were a serious maintenance problem and, in addition, limited the maximum keying speeds to relatively low values.

The present invention provides a system which overcomes the foregoing difficulties and which enables the application of constant voltage to the filament within desired limits, irrespective of the voltage drop in the main line due to the load fluctuations caused by the keying.

A more detailed description of the invention follows in conjunction with a drawing in which Fig. 1 is a schematic diagram of one form of the invention, and Fig. 2 is a modification.

In the figures of the drawing, the same elements are represented by the same reference numerals.

Referring to Fig. 1, there is shown a main alternating current circuit l which supplies a nominal feeder voltage of, let us say, 220 volts by way of an automatic line voltage regulator to a keyed load 2 which may be a wireless transmitter circuit employing suitable vacuum tubes. The filament load for these vacuum tubes is diagrammatically represented by the box 3 which is supplied by voltage over feeder line 4, in turn suitably connected to the main alternating current circuit.

The voltage compensator system comprises an iron core transformer 9 whose prim y Winding 5 has a desired number of turns relative to the secondary winding 6. The secondary winding 6 is ordinarily designed to have more turns than the primary winding-the turns ratio being preferably the same as the ratio of key down load currents in 2 and 3. In shunt to the secondary winding 6, there is provided a rheostat I. The transformer 9 is made to have a rather high exciting reactance so that the exciting current in its high turn winding 6 is small compared to the current in the rheostat I. The two windings 5 and 6 are so wound and connected that their magnetomotive forces are opposed in the laminated iron core on which both are wound.

Let us assume that the normal voltage in the main atlernating current circuit I is 220 volts and that the keying of the transmitter 2 takes 100 amperes of current and that the filament load takes 10 amperes of current. .Let us also assume that the keying of the transmitter causes a 10% fluctuation in the power supply voltage on line lin other words, causes a 22 volt variation between 220 volts and 198 volts. Because the transformer turns ratio is the same as the ratio of load currents, it will be apparent that the active turns in the primary winding 5 will be 11 while the turns in the secondary winding 8 will be 101:. Since it is desired that the voltage applied to the filament load 3 over feeder 4 be constant, the rheostat 1 is then set by means of its tap 8 to produce a 22 volt drop therein due to the filament load current. In other words, the rheostat will be set at about 2.2 ohms to satisfy the condition of 10 amperes filament load as sumed above. Thus the voltage drop produced in the rheostat is made equal to the drop in line voltage when the keyed portion of the load is applied.

When the key is up in the transmitter circuit 2 so that there is no load current taken by the transmitter, there will be substantially no current flowing through the primary winding 5 and the high transformer exciting reactance will force most of the filament supply current through the rheostat I and thus reduce the filament supply voltage to 198 volts. When, however, the key in the transmitter circuit 2 is pressed down in order to transmit signals, the main load will be thrown on the circuit l to draw 100 amperes of current, in which case the current in the low turn winding 5 will have equal and opposite magnetomotive force to that of the current in the high turn winding 6 which is now passed around the rheostat through the transformer. The balancing of the ampere turns in the two transformer windings 5 and 5 prevents any appreciable voltage drop in either transformer winding. Therefore, the filament supply voltage thus remains at 198 volts and the drop in power supply voltage to the main load has not been increased. Another way to explain the operation of the voltage compensator is that normally the filament load is designed to take its rated current with the minimum voltage on the main alternating current circuit I, and when this voltage is higher then the extra voltage is automatically absorbed in the rheostat. When, however, the voltage on the circuit I has been reduced, due to application of the keyed load, to the minimum value, then the current through the primary winding 5 is such that there occurs an effective short circuit across the secondary winding 6. This short circuit will cause the full voltage supply across the line I to be effective ior the filament load, and since this full voltage supply with the key pressed down is identical with the voltage supply on feeder 4 when the key is up, due to the IR drop in the resistor I, it will be evident that the filament voltage restat i0 is provided by means of which the exact value of filament supply voltage may be adjusted, after compensation, to a desired value.

Experimental tests have indicated that by means of the present invention, by suitably adjusting the rheostats 'Iand I0 and by choosing a suitable value of filament supply voltage at 4, the filament voltage can be sufliciently compensated to produce nearly constant filament voltage supply even when the load ratio varies from a value of five times the transformer turns ratio to one-quarter of the turns ratio. Optimum conditions are, of course, experienced when the ratio of the keyed load to the filament load is equal to the turns ratio in the transformer, because, in this case, there is no loss of power in the rheostat l for the key down condition.

Any convenient type of transformer of suitable turns ratio could be used for element 9, the rating of which is suflicient to handle therequired operating potentials and to carry the required load currents. However, it is preferable, to prevent transformer failures in case of accidental short circuits in the loads, that the transformer windings be insulated for the line voltage. It is preferred that the transformer be provided with a number of taps, as indicated in the drawing, in order to adjust its turns ratio to suit any particular set of conditions. By means of these transformer taps, the rheostat adjustment and the customary rheostat in the filament circuit, it is possible to set the filaments to a correct voltage which will not fluctuate due to the keying of the transmitter.

It has been found in practice that automatic line voltage regulators of standard types customarily used in power distribution systems do notfunction properly in the power input to keyed radio transmitters. Starting and stopping of keying and variations in percentage key down time cause a continual undesired closing and opening or the regulation control relays and an undue amount of wear in the relays and mechanism besides causirg continual variations in the efi'ective base voltage. To prevent this excessive operation, I arrange to apply the compensated voltage to the control coil l2 of the automatic line voltage regulator l3. Thus, the regulator will function in response to variations in eifective base voltage of the power supply system but will not respond in an undesired manner to variations in the keying conditions in the transmitter. This compensation for load fluctuations in the control of automatic line voltage regulators may be utilized in a wide variety of applications in power supply and distribution systems.

In Fig. 2 I have shown a modification of Fig. 1 in which there is employed a continuously variable auto-transformer 9', of a type readily available in the United States. type of such auto-transformer is manufactured and sold by the General Radio Company, of Cambridge, Massachusetts, under the trade name of Variac. A similar type of transformer is manufactured by the American Transformer Company, of Newark, New Jersey, and sold un-- der the trade name of Transtat.

By means of a suitably designed transformer of this type, a wide variety of conditions may be dealt with which may be met in practice. The functioning of the arrangement of Fig. 2 is similar to that of Fig. 1.

It should be understood that the rheostat I of mains substantially constant. Additional rheo- F 1 nd 2 m y be connected across the other For example, one

winding, or portion of winding, if the resistance value is s"itably decreased and provided the runtual coupling between the windings is high enough in proportion to their leakage reactances and that resistances proportioned between the two windings may be used. A resistance across one winding can be the equivalent of another value of resistance across the other winding, the amount depending upon the transformer turns ratio, as is well known in transformer practice.

I also have found that, by adjusting the rheostats I of Figs. 1 and 2, or their equivalent in resistances across either or both windings, to higher values than those described, the voltage applied to the filament circuits may be made to rise by any desired amount, over a range, due to increasing current in the variable or keyed load. A slight rise in filament voltage in response to application of the keyed load is sometimes desirable in radio transmitters to compensate for the cooling effect upon the filaments of drawing out the emission and to give a slight lowering of filament potential to conserve tube life when part cular transmitters are operated a large part of the time in a standby condition. with filaments on but anode current off.

It should also be noted that the rheostats i of Figs. 1 and 2. or their equivalent as described, may be replaced by suitable values of reactance, or by complex impedances comprised of both resistance and reactance.

What is claimed is:

1. In combination, an alternating current circuit. a variable load adapted to take a certain maximum current, a second load adapted to take a second current, a transformer having a number of turns associated with said first load and a num ber of turns associated with said second load, the ratio of said turns being substantially the same as the ratio of said maximum current to said second current. a resistor in shunt to the turns associated with the second load, a circuit coupling said variable load to said alternating current circuit through a connection including the turns associated therewith, and a circuit coupling said second load to said alternating current circuit through a connection including the turns associated with said second load, whereby the voltage supplied to said second load is maintained substantially constant irrespective of variations in the voltage of said alternating current circuit caused by changes in said first load, and a voltage regulator for said alternating current circuit under control of the voltage on said second load.

2. In combination, an alternating current circuit, a variable load, a second load adapted to take a different current from said first load, a transformer having a number of turns associated with said first load and a greater number of turns associated with said second load, the ratio of said turns being substantially the same as the ratio of the maximum currents taken by said loads, a re sister in shunt to said larger number of turns,

separate connections coupling said, loads to said alternating current ci cuit comprising connections from said first and second loads to the smaller and larger turns respectively, whereby the voltage supplied to said second load is maintained substantially constant irrespective of variations in the voltage of said alternating current circuit caused by changes in said first load, and a voltage regulator for said alternating current circuit under control of the voltage on said second load.

3. In combination, an alternating current power supply line, a variable load adapted to take a certain maximum current, a second load adapted to take a different and smaller current, a metal core transformer having a primary and a secondary winding, a rheostat in shunt to said secondary winding, a connection from said variable load to one side of said line, another connection from said variable load to a point on said primary winding, a connection from the other side of said line to another point on said primary winding, 3. connection from said second load to one side of sai line, another connection from said second load to a terminal on said secondary winding, a connection from the other side of said line to another terminal on said secondary winding, the ratio of the number of turns between said points on. said primary winding and said terminals on said secondary winding being substantially the same as the ratio of said maximum current to said different current, whereby the voltage supplied to said second load is maintained substantially constant despite variation in the voltage of said alternating current circuit caused by changes in said first load, and a voltage regulator for said power supply line under control of the voltage on said second load.

4. In combination, means to reduce voltage variations in one load circuit due to current variations in another load circuit deriving power from the same source comprising an inductive coupling element connected between the two load circuits, said element including windings positioned upon a common core and having a ratio of turns inversely proportional to the ratio of load currents, said windings being so wound as to produce opposing magneto-motive forces due to currents ir. the two load circuits, a voltage regulator for said source, and means responsive to voltage on said, first load for controlling said voltage regulator.

5. In combination, a power supply system of variable voltage, a voltage regulator to compensate for the system voltage variations at a load point on the system, a constant load and a rapidly fluctuating load connected to the system at the load point, means to prevent the fluctuating load from causing variations in voltage applied to the constant load, and means responsive to voltage on the constant load to control the voltage regulator.

CLARENCE W. HANSELL.

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