US2099716A - Constant current system - Google Patents

Description

Nov. 23, 1937. E YOUNG 2,099,716

' CONSTANT CURRENT SYSTEM Original Filed May 12, 1936 20d Q/v I 205 2/9 7 204' 2/ Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE ONSTANT SYSTEM 0riginal application May 12, 1936, Serial No. 79,329. Divided and this application April 5,

1937, Serial No. 134,970

1 Claim.

My invention relates generally to electrical control systems, and it has particular relation to systems of the constant current type.

In the operation of electric lamps, such as incandescent lamps for street lighting and the like, it is desirable that the current be held constant, or substantially so, in order to provide the desired illumination and to prolong the life of the lamps as much as possible. The lamp life is materially decreased by eyen slight increase in current above the rated value and it is, therefore, desirable to operate the lamps under such conditions that the rated current value will not be exceeded, even tothe slightest degree. i

For street lighting applications where a large number of lamps is operated at the same time, it is customary, in many cases, to connect the lamps in series circuit relation for-'the purpose of reducing installation and operating costs to a minimum. Some regulating device is provided for maintaining the current in the series circuit constant regardless of the number of lamps connected or the voltage of the supply circuit. Various types of regulating devices may be used. In my copending application, Serial No. 33,706, flied July 29, 1935, I have disclosed a monocyclic type of regulator in combination with grid controlled arc rectifying tubes which are arranged to control the voltage applied to the regulator or the current flowing in the load circuit as a function of the supply voltage or of the load current. While the various systems there disclosed are satisfactory for certain operating conditions, I have discovered that they require dependence to a considerable degree on the reliability of the grid controlled arc rectifying tubes for their continued operation and that, if the tubes fail, the entire system may be put out of service until they are replaced.

It is therefore an object of my invention to provide a constant current system which shall be simple, efficient, and reliable in operation, and which may be readily and economically manufactured and installed. v

The principal object of my invention is to provide for preventing the current flow in a circuit requiring constant current from exceeding the constant value of the current at which the circuit is designed to operate most efllciently.

, An important object of my invention is to provide for variably shunting a load circuit connected to a constant current device to maintain the current in ttlhe load circuit constant regardless of variations 1 line voltage applied to the device. A further object of my invention is to provide for shunting the excess current from a circuit requiring constant current in such manner that the system can still function even though the ap paratus used should be disabled.

A still further object of my invention is to 5 provide regulating means for shunting the excess current from a circuit requiring constant current which will be operative only when the load current tends to exceed the constant value of the current and which will permit functioning of the 10 system even thoughv the regulating means may be disabled.

Still another object of my invention is to pro vide for controlling the conductivity of an electric valve connected across the load terminals of 15 a constant current device in accordance with the load current to prevent the load current from exceeding its constant value.

A more specific object of my invention is to provide for controlling the conductivity of a pair of inversely connected electric valves connected across the load circuit of a monocyclic square to shunt therethrough all current from the load circuit in excess of the normal constant current that would otherwise flow through the load circult.

Other objects of my invention will, in part, be obvious and, in part, appear hereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shown in the accompanying drawing, and it comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the appended claim.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following detailed description taken in connection with the accompanying drawing.

The single figure of the drawing is a diagram- Mi; matic view of a system embodying my invention.

This application is a division of my copending application for Constant current system, Serial No. 79,329, filed May 12, 1936. 5

The commercial power systems of the present day are so arranged and constructed that the line voltage and frequency are maintained at fairly constant values. In order to provide constant current for operating a group of series con- 50 nected incandescent street lamps, a static regulator of the monocyclic-type may be provided. As long as the supply voltage and frequency remain constant, the current which is supplied by the monocyclic square will remain constant re- 1 quency, however slight, will cause corresponding changes in the current flowing in they load circuit. If the supply voltage is increased over its normal rated value, there will be a corresponding increase in the current flowing in the load circuit, and, as a result, the life of the lamps connected therein will be materially shortened. These slight changes in the supply voltage may be caused by faulty operation of regulating devices or by system disturbances which are ordinarily encountered in the operation of such systems.

In practicing my invention, I take advantage the normally constant voltage characteristics of a power transmission system of the present day. and provide a static regulator of the monocyclic type for supplying the required constant current for operating a group of series connected incandescent lamps. In addition to this apparatus, I provide a variable shunt across the load terminals of the monocyclic square which is called into operation only when the current in the load circuit tends to exceed the normal constant value thereof. At all other times the shunt circuit is ineffective and therefore, if for some reason it should fail, such failure would not aflect the energization of the lamps, although they would be subject to the flow of excess current on increase in the supply voltage applied to the monocyclic square.

According to the illustrated embodiment of my invention, I have provided a monocyclic square which may be energized from a three phase source of alternating current. The load terminals are connected to a circuit including the series connected incandescent lamps which may be used for street lighting purposes. A pair of inversely connected grid controlled arc rectifying devices is connected across the load circuit, and the conductivity thereof is controlled by means of a phase shifting circuit, the operation of whichi in the load circuit tends to exceed a predetermined value, the arc rectifying devices are rendered conducting to shunt therethrough the excess current. By changing the'time in each half cycle at which each of the arc rectifying devices is rendered conducting in accordance with the excess current which tends to flow in the load circuit, greater or-less amounts of the current may be shunted with the result that the excess current is prevented from flowing through the lamp .circuit.

In some applications it is desirable to transform from a three-phase alternating current source into a constant current single-phase load circuit comprising the series connected incandescent lamps. This transformation can be effected and a balanced load applied on each of the phases of the three-phase system by use of the connections shown in the drawing.

As shown in the drawing, transformer means at is provided, comprising two transformers, one having a primary winding 9i and the other a primary winding 92, for connection to the three phase source 5! of alternating current. The primary windings 9| and 92 are connected to the source M by the well known Scott connection. The terminals of the primary winding 9| are connected to two of the phases of the'source 5|, while one terminal" of the winding '92 is connected to the remaining phase. The other terminal of the primary winding M is connected to a mid-tap 93 on the primary winding 9 l The transformer means 90 is provided with secondary windings 9d and 95, one for each transformer, in which voltages in quadrature with each other will be induced. The secondary winding 94 is connected directly across the supply terminals of a regulator or monocyclic square in, while the secondary winding 95 is connected in series circuit relation with the load circuit comprising conductors i2 and i3 and the series connected incandescent lamps i l, and the combined circuit is connected across the load terminals of the monocyclic square lll as illustrated. Since the voltage appearing across the load terminals of the monocyclic square Iii is in quadrature with the voltage impressed thereon from the secondary winding 94, the voltage induced in the secondary winding 95 may be readily combined therewith to cause the flow of constant current through the conductors i2 and it while maintaining a balanced load on each of the phases of the source M as is readily understood by those skilled in the 'art.

As long as the voltage applied by the generator 5i to the regulator I9 remains constant, the current which flows through the load circuit to the lamps It will likewise remain constant. However, if the voltage of the generator St, for some reason, tends to rise, there will be a corresponding tendency to increase in the current flowing through the load circuit. This excess current is shunted by means of a pair of inversely connected arc rectifying devices 29 and N which are connected, as illustrated, between the conductors l2 and i3 and across the load terminals of the regulator iii. The are rectifying devices or valves 20 and 2! are provided, respectively, with anodes 20a 9 and 2 I a, with cathodes 20c and 2lc, which may be of the hot type, and control electrodes 20g and 2 ,Since the current in the load circuit is maintained 'at a substantially constant value, a series transformer, shown generally at 96, may be provided having a primary winding 91 connected in the load circuit, and a secondary winding 98. A

grid transformer, shown generally at 22, is provided with secondary windings and 25 connected to the grid or control electrodes 20g and Iiig, respectively. Secondary winding 24 is connected to conductor l3 and secondary winding 25 is connected to conductor l2. The primary winding 26 of the grid transformer 22 is connected for energization between a mid-tap 99 on the secondary winding 98 and a common connection 29 between a potentiometer 3|, having. a movable connection 32, and a variable inductor 33. A phase shifting circuit 34, comprising the potentiometer 3| and the inductor 33, is connected to the ends of the secondary winding 98.

In order to control the inductance of the inductor 33, a regulator 40 is provided having an armature 4i forming a movable core within the turns of the inductor 33. The armature 4| is mounted at one end of a lever arm 42 which is pivoted at 33 and has provided at its other end an armature M, the position of which is controlled by means of a winding 45 connected in series circult relation with the conductor l3 as shown. A biasing spring 46 is provided to cooperate with the armature 44 for controlling the position of the armature 4|.

In operation, as long as the current flowing through the lamps I4 and the winding 45 does not exceed a predetermined value which is the value at which the lamps I4 operate most efiiciently, the valves 20 and 2| remain in the non-conducting state. This is accomplished by adjusting the phase shifting circuit 34 so that the control potentials applied to the control electrodes 20g and 2Ig under these conditions will have such phase relationship with respect to the corresponding cathodes 20c and 2 I that there is no tendency for current to flow therethrough. However, as soon as the current flowing through the lamps I4 and the winding 45 tends to exceed a predetermined value, the armature 44 is moved upwardly against the biasing force of the spring 46 to effect a corresponding downward movement of the armature 4|. The inductance of the inductor 33 is then decreased to shift the phase of the voltage which is applied for energizing the primary winding 26 of the grid transformer 22. This shift in phase is reflected in the control potential which is applied to the control electrodes 20g and 2|g, so that the valves 20 and 2| are rendered conducting during the half cycles of the alternating current which they are adapted to conduct at times corresponding to the degree of phase shift. The degree of phase shift will be controlled by the amount of excess current which tends to flow through the lamps |4. Thus more or less current will be shunted by the valves 20 and 2|, depending upon the time in each half cycle at which they are rendered conducting.

It will be observed that the valves 20 and 2| are employed only for conducting the excess current which would otherwise flow to the lamps l4. Since this excess current will usually be comparatively slight, the size or conducting capacity of the valves 20 and 2| need not be very great. It is necessary only that they be of such size as to be capable of conducting the excess current which would otherwise flow to the lamps M.

It will also be observed that the lamps. M will function even though one or both of the valves 20 or 2| should become inoperative. In such case, the excess current, to a greater or lesser extent, would flow through the lamps l4, depending upon whether one or both of the valves 20 or 2| became inoperative. Although the life of the lamps I4 would be correspondingly shortened, they would still be available for illumination purposes, and thus complete reliance for illumination is not placed on the continuity of functioning of the valves 20 and 2|.

I claim:

A constant current system comprising, in combination, transformer means having primary windings Scott connected to a three phase source of alternating current and two secondary windings, a monocyclic square connected for energization across one of said secondary windings, circuit means for connecting a load circuit requiring substantially constant current across said monocyclic square through the other secondary wind- 1 ing, variable conducting means directly connected across said load circuit, and regulating means disposed to be responsive to the current flow in said load circuit for controlling the conductivity of said variable conducting means to maintain the load current substantially constant on variation of the voltage or frequency of said alternating current source.

HUGH E. YOUNG.

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