US2039043A - Electric regulating system - Google Patents

Description

April 28. 1936.

w. F. WESTE NDORP ELECTRIC REGULATING. SYSTEM Filed July 1, I933 Fig. l.

CURRENT Inventor I stu- .mrum r m/s Willem .F We stendo'rp,

Patented Apr. 28, 1 936 ELECTRIC REGULATING SYSTEM Willem F. Westendorp, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 1, 1933, Serial No. 678,640

9 Claims.

.My invention relates to electric regulating systems and more particularly to such systems in which the current transmitted to a load circuit from a supply circuit is maintained substantially constant by means including one or more electric valves. While my invention is of general application, it is particularly useful in maintaining constant the current drawn by a plurality of series connected gaseous discharge lamps or by other 10 load circuits having negative or flat volt ampere characteristics.

Gaseous discharge lamps, that is, exhausted envelopes containing an ionizable vapor or gas, such as mercury vapor, sodium vapor, neon,

argon, etc., or combinations thereof and provided with a spaced anode and cathode, either incandescent or otherwise, have found increasing favor for general purpose or specialty lighta ing. These devices have certain characteristics in common; under starting conditions their terminal voltage drops rapidly from a deionized or unillumined state to operation at normal full loadcurrent; further, they have a negative or flat volt ampere characteristic. By the term negative volt ampere characteristic is meant that the voltage across the device decreases with increasing current, and by the term flat volt ampere characteristic is meant that voltage across the device is independent of current. Devices having such volt ampere characteristics involve special problems in regulation. For the sake of convenience devices having such negative or flat volt ampere characteristics will be referred to as devices having the volt ampere characteristics of an arc discharge, as that type of device is, perhaps, the best known example.

In the past it has been customary to regulate the voltage applied to such gaseous discharge devices utilized in alternating current circuits by means of stabilizing reactances or impedances connected in series with the lamps, or by means of constant current transformers, orboth, while in direct current circuits series resistances have been used. Such regulating systems have, in general, been accompanied by poor power factor on the alternating current circuit supplying the discharge lamps, or by relatively high power losses in the series resistances, in the case of direct current operation, and by relatively poor regulation characteristics in both cases. My improved regulating system is particularly useful in connection with the regulation of the current supplied to such gaseous electric discharge lamps,

although it is also of general application in load It is another object of my invention to provide an improved regulating system for maintaining substantially constant the current supplied to a load circuit having the volt ampere characteristics of an arc discharge.

It is a further object of my invention to provide an improved regulating system for maintaining constant the current supplied to a plurality of series connected gaseous discharge lamps which will substantially improve the power factor on the alterating current supply circuit.

In accordance with one embodiment of my invention, a plurality of series connected, gaseous discharge lamps are connected to be energized from an alternating current source through a pair of electric valves connected in a conventional manner to secure full wave rectification. A smoothing reactance is preferably connected in the load circuit of the apparatus and the electric valves are preferably of the discontinuous control type, such, for example, as gaseous or vapor electric discharge valves. A control circuit is provided for each of the valves, including a source of positive bias potential and a source of alternating potential comprising a series of repeated transients dependent in amplitude and wave form upon the load current of the apparatus. This alternating control potential may be derived from a resistance connected to carry current proportional to the load current of the system so that the potential thereacross has a wave form similar to that of the load current of the system. The alternating component of control potential opposes the source of positive bias during the nonconductive periods of the valve, with the result that the point in each cycle at which a particular valve is rendered conductive is that point at which the instantaneous value of the" system for energizing a plurality of serially connected gaseous discharge lamps from a source of single phase alternating current; Fig. 2 shows certain operating characteristics of the circuit of Fig. l to aid in the understanding of the invention; Fig. 3 illustrates a modified form of the control for the regulating system, while Fig. 4 shows an operating characteristic of one of the circuit elements of the arrangement of Fig. 3.

Referring now more particularly to Fig. 1 of the drawing, there is shown a system for energizing a plurality of serially connected gaseous discharge lamps Ill-i3, inc., from a single phase alternating current supply circuit l4. Each of the discharge lamps Ill-l3 may be any of the several types well known in the art and, as illustrated, comprises an elongated, exhausted envelope containing an ionizable gas or vapor, and having sealed therein an anode l5 and a cathode li, indirectly heated by a heater element II. There is provided a supply transformer 18, having a primary winding connected to the supply circuit l4 and a secondary winding provided with an electrical midpoint connected to one side of the load circuit l9 through a smoothing reactor 20, the load circuit l9 comprising the terminals of the series connected lamps ill-i3. The end terminals of the secondary winding of the supply transformer i8 are connected to the other side of the load circuit i9 through a pair of electric valves 2| and 22. A resistance device 23 is also included in the system and provided with an electrical midpoint connected to the lower side of the load circuit is and with end terminals connected to the cathodes of the electric valves 2| and 22, as illustrated. Electric valves 2! and 22 are each provided with an anode, a cathode and a control grid or electrode, and may be of any of the several types well known in the art, although I prefer to use valves of the discontinuous control type, such, for example, as vapor or gaseous electric discharge valves. By the term discontinuous contro I refer to that type of valve in which the starting of current in the valve is determined by the potential of its control electrode, but in which the current in the valve can be interrupted only by reducing its anode potential below the critical value.

In order to control the electric valves 2l22, and thus the energlzation of the load circuit IS, the grids of the valves 2i and 22 are connected to the electrical midpoint of the resistor 23 included in their common cathode circuit, through current limiting resistors 24, opposite halves of the secondary winding of a control transformer 25, the primary winding of which is connected across the resistor 23, and a biasing capacitor 26. If desired, the electrical midpoint of the primary winding of the grid transformer 25 may be connected to the electrical midpoint of the resistance device 28, as illustrated; also a capacitor 21 is preferably connected across one of the windings of the transformer 25 to compensate for the magnetizing-current of the transformer. A positive biasing potential is produced across the capacitor 26 from a tertiary winding 28 of the transformer iii, a potentiometer 28 and a rectifying bridge of any suitable type, such for example, as acontact rectifier bridge 30. If desired, an adjustable control resistor 3| may be connected in parallel to the resistance device 23.

The general, principles of operation of the above-described apparatus will be well understood by those skilled in the art. In brief, the transformer l8, together with electric valves 2I-22 operate as a full wave rectifier supplying unidirectional current to the series connected discharge lamps Ill-l3, inc. The smoothing reactor 2|! serves to minimize the ripple in the current supplied to the lamps which, if omitted, will comprise a series of half sinusoids; in other words, it tends to maintain the instantaneous values of the load current substantially constant during intervals of one cycle or less. Such a system, without more, is quite unstable, since the discharge lamps ill-l3 have the negative of flat volt ampere characteristic of an arc discharge and are very sensitive to changes in temperature and other operating conditions.

The manner in which the above-described control apparatus operates to maintain substantially constant current on the load circuit I8 will be better understood by reference to the curves of Fig. 2. In this figure the curves a1, dz, represent the potentials impressed upon the anodes of the valves 2! and 22, respectively, with respect to the neutral of the secondary winding of the transformer I8. The solid line portions of these curves indicate the periods during which the respective valves are conductive. In this figure also, the curves in, bz represent the currents flowing in corresponding valves, it being assumed that the conditions under consideration correspond to those at which the grid of the valve 2! is excited at the point to. The average voltage impressed upon the load circuit H, as is well understood by those skilled in the art, will be the-average of the positive and negative portions of the curves a1, a2, etc. In the same figure, the line 0 represents the positive bias appearing across the capacitor 26 which has the effect of displacing the axis of the grid potential from O to O. The curves d1, dz, etc., represent the negative half cycles of the alternating components of grid potential derived from the transformer 25, the positive half cycles being omitted for the sake of simplicity, as the grids are positive only when the valves are conductive and the grid potential during these intervals is immaterial.

It will be seen that the grid potentials d1, dz, etc., comprise a series of repeated transients having a wave form similar to the repeated transients represented by the load current curves in, bz, etc. For any particular circuit, the wave form of the anode currents of the valves 21 and 22, b1, 1):, and of the grid potentials d1, dz, is dependent upon the magnitude of the smoothing reactance 20 and the particular phase angle at which the grids are operating. With this arrangement, it is seen that the electric valve 22 is rendered conductive at the time ti, when the transient dz is equal in magnitude to the positive bias c, that is, when d2 intersects the line 0'. If, due to change in operating conditions of the discharge lamps, the load current tends to increase to some value of hi, the alternating component of grid potential impressed upon the grid of the valve 22 will also increase to the curve represented by dz which does not intersect the axis 0' until the instant ii. The point in the cycle at which the valve 22 is rendered conductive is thus delayed, effectively retarding the phase of the conductive periods of the valves 2I22 with respect to their anode potentials and decreasing the average voltage impressed upon the load circuit to maintain the current substantially constant. Obviously, upon a tendency of the load current to decrease, the reverse operation takes place. The above described regulating action takes eflect at the end of each half cycle, and this, together the regulation.

with the instantaneous regulating action of the smoothing reactance 20, is effective to maintain substantially constant the current delivered to the load circuit I9 and the electric discharge lamps l0-l3, inc.

The particular value which is regulated is, of course, the point at which current is transferred from one valve to the other, as at the point ti, which corresponds to the terminal value of each of the transient current waves b1, In, etc. The accuracy of regulation thus depends upon the deviation of the maximum value of the current transients b1, b2, etc., from their terminal values, which in turn, depends upon the magnitude of the reactance device 20. By suitably selecting the proper value of the reactance device 20 the system may be made to regulate to any desired degree of accuracy. The particular value of current which the circuit operates to maintain may be adjusted by the variable resistor 3! or the potentiometer 29 or both.

The power circuit of Fig. 3 is similar to that of Fig. l, but there is shown a modified form of regulating apparatus to provide, in addition to the instantaneous and half cycle regulation described above, a regulation effective over a period of several cycles but more accurate in its efiect. In this system the alternating component of control potential for the valves 2| and 22 is provided by means of a resistor 23a energized in accordance with the load current of the system by means of a current transformer 32. The potentials appearing across the sections of resistor 23a are identical to those supplied by the transformer 25 of Fig. 1 and produce a similar controlling action. As in the arrangement of Fig. 1, the common portion of the grid control circuits of the valves 2! and 22 includes also a positive bias capacitor 26 energized from the circuit I4 through a rectifier bridge 30 and a transformer 33. this circuit, however, amplified variations are produced in the positive bias potential in response to variations in the load current. These variations are produced by means of a saturable reactance device 34 connected across the alternating current side of the rectifying bridge 30 and provided with saturating windings 35. A circuit having a non-linear volt ampere characteristic, such for example, as a parallel circuit comprising a resistor 36 and reactor 31 connected in parallel with a capacitor 38, is serially included in the circuit of the current transformer 32 so as to be traversed by a current proportional to the load current of the apparatus. The reactor 31 is selfsaturating and provided with an air gap, a structure well known in connection with non-linear circuits. The voltage across this non-linear circuit is rectified by any suitable means, such as a. contact rectifier bridge 39, and connected to energize the saturating winding of the reactance device 34. A. current limiting impedance, such as a capacitor 40, is preferably connected inseries with the transformer 33 to limit the current when the reactance device 34 is in a saturated state.

The mode of operation of the apparatus shown in Fig. 3 is similar to that of' Fig. 1,.with the exception of the variation of the positive bias potential in accordance with variations in current in the system to increase the sensitivity of The parallel non-linear circuit comprising the elements 36, 31 and 38 has a volt ampere characteristic similar to that illustrated in Fig. 4. This circuit per -se, is of a type well known in the art and comprises no part of my present invention. In brief, for relatively small variations in current flowing through the circuit, corresponding to variations in load current of the system, such for example, as variations from the value Ii to I2 of Fig. 4, relatively very large variations in the terminal voltage across the circuit occur, such as represented by the values E1 and E2, respectively, of Fig. 4. These amplified variations, rectified by means of the bridge 39, vary the saturation of the reactance device 34, which is effective to bypass current from the rectifier bridge 30 and thus decrease the value of the posi tive bias on the capacitor 26. Thus, an increase in load current on the system is amplified by the non-linear circuit 36, 31 and 38 to decrease the bias on the capacitor 26, as just described. The effect of a. decrease of the positive grid bias, it will be seen by reference to Fig. 2, is to delay the instant ii at which the alternating component of grid potential (is intersects the axis 0 and thus to effectively retard the phase of the grid potentials of the valves 2| and 22 and to decrease the average voltage impressed upon the load circuit and thereby regulate the current within narrow limits. This regulation, coupled to that previously described in connection with Fig. 1, produces an extremely sensitive regulating apparatus.

While I have described what I at present con-- sider the preferred embodiments of my invention it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from my invention, and I. therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. An electric regulating system comprising a source of alternating current, a load device having an arc discharge volt ampere characteristic,

.a pair of discontinuous control electric valves interconnecting said source and said load device to transmit the load current thereto, each of said valves being provided with a control electrode, and a control circuit for producing an alternating potential variable in magnitude in response to the load current of said system and connected to said control electrodes to stabilize said load circult'and maintain said current substantially constant.

2. An electric regulating system comprising a source of alternating current, a plurality of serially connected gaseous discharge lamps, a pair of discontinuous control electric valves connected to transmit the load current from said source to said lamps, each of said valves being provided with a control electrode, and a control circuit for said control electrodes including a source of unidirectional bias potential and a source of alternating potential variable in magnitude in 9.0-

cordance with the load current of said system to maintain the load current 01' the system substantially constant.

3. An electric regulating system comprising a source of alternating current, a load circuit, means including a pair of discontinuous control electric valves for controlling the transmission of energy from said source to said load circuit, each of said valves being provided with a control electrode, a control circuit for each of said valves including a source of unidirectional bias potential and a source of recurrent transients dependent in amplitude upon the load current of the sys-, tem and of opposite polarity to said bias potensubstantially constant.

4. An electric regulating system comprising a. source of alternating current, a load circuit, a pair of discontinuous control electric valves connected to supply rectified current from said source to said load circuit, a smoothing reactance device in said load circuit, a resistance element connected to carry a current proportional to the load current of said system, and a control circult for each of said valves including a source of positive bias potential and means for deriving from said resistance element an alternating po tential comprising a series of repeated transients.

5. An electric regulating system comprising a source of alternating current, a load circuit including a smoothing reactance device, a transformer winding energized from said source and provided with an electrical midpoint connected to one terminal of said load circuit, a pair of discontinuous control electric valves having corresponding main electrodes connected to the terminals of said winding, a resistance device interconnecting the other main electrodes of said valves and provided with an electrical midpoint connected to the other terminal of said load circult, and a control circuit for each of said valves including a source of positive bias potential and means for deriving an alternating potential from said resistance device.

6. An electric regulating system comprising a source of alternating current, a load circuit including a smoothing reactance device, a transformer winding energized from said source and provided with an electrical midpoint connected to one terminal of said load circuit, a pair of discontinuous control electric valves having corresponding main electrodes connected to the terminals of said winding, a resistance device interconnecting the other main electrodes of said valves and provided with an electrical midpoint connected to the other terminal of said load circuit, a control transformer connected across said resistance device, and a control circuit for each of said valves including a source of substantially constant positive bias potential and a winding of said transformer connected to supply a potential opposed to said bias potential.

7. An electric regulating system comprising a source of alternating current, a load circuit, means including a pair of electric valves for controlling the transmission of energy from said source to said load circuit, each of said valves being provided with a control electrode, a cow trol circuit for each of said valves including a source of alternating potential proportional to trol circuit for each oi. said valves including a source of alternating potential proportional to the load current of the system and including also a source of positive bias potential, an impedance device connected to bypass said source of bias potential, a circuit having a non-linear volt ampere characteristic connected to carry a current proportional to the load current of the system, and means for varying the impedance of said impedance device in response to variations in the potential across said non-linear circuit.

9. An electric regulating system comprising a source of alternating current, a load circuit including a reactance device, means including a pair of discontinuous control electric valves for controlling the transmission of energy from said source to said load circuit, each of said valves being provided with a control electrode, a control circuit for each of said valves including a source of alternating potential proportional to the load current of the system rectifying means for introducing into said control circuit a positive bias potential, a saturable reactor connected in parallel to said rectifying means and provided with a saturating winding, a circuit having a non-linear volt ampere characteristic comprising a parallel connected capacitor and self saturating reactor and connected to carry a current proportional to the load current of the system, and a circuit for energizing said saturating winding in accordance with the potential across said nonlinear circuit.

WILLEM I". WESTENDORP.

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