US2226025A - Voltage regulator for lighting systems - Google Patents

Description

Dec. 24, 1940.

C. STANSBURY VOLTAGE REGULATOR FOR LIGHTING SYSTEMS Filed May 27, 1939 LAMP CURRE TIME Patented Dec. 24, 1940 PATENT OFFICE I VOLTAGE REGULATOR FOR LIGHTING SYSTEMS Carroll Stansbury, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application May 27, 1939, Serial No. 276,041

12 Claims.

This invention relates to voltage regulators and while not limited thereto is particularly adapted to regulators for illumination control systems of the distant control type wherein the mechanical and electrical inertia of various elements of the system combine with the time delay in the variation of lamp resistance with changes in lamp circuit to produce temporary over-regulation or overshooting of the lamp current with resultant hunting of the control apparatus.

An object of the invention is to provide a system of the aforementioned type which is free from overshooting due to the time delay between variations in lamp current and lamp resistance.

Another object is to provide an illumination control system in which the lamp current at all times bears a definite relation to the position of a pilot control sender device, such as a potentiometer resistor or other source of adjustable voltage.

Another object is to provide a voltage control system for lamps having a temperature coefiicient of resistance and a time lag in the response of their resistance to variations in current, wherein overshooting of the current in the lamp circuit or circuits is prevented.

Another object is to provide a system in which the lamp current is independent of changes in load of the lamp circuit.

Other objects and advantages will hereinafter appear.

The accompanying drawing is illustrative of several forms of a system embodying the invention, but the appended'claims are not intended to be limited thereto but are to be interpreted to 30 cover all modifications within the scope of the present disclosure.

In the drawing, Figure 1 is a schematic diagram of an illumination control system embodying the invention in which both the lamp and the control circuits are operated from an alternating current source.

Fig. 2 is a modification of the system in which the source for the control circuits is direct current and that for the lamp circuit is alternating current, while Fig. 3 is a diagram serving to explain the functioning of the system illustrated in Fig. 2, as will be discussed more in detail hereinafter.

Referring to Fig. l, a generator I or .other source of alternating current supplies the lines L L with energy which is in turn supplied to a bank of lamps 2 whose brilliancy is to be controlled by the system. The current of the lamps is controlled by means of a variable voltage autotransformer 3 which is connected across the lines L L A sliding contact brush 4 of thetransformer also makes contact with a conducting bar 5 which in turn is connected to one lamp circuit terminal, the other terminal of the lamp circuit being connected to line L The contact 5 4 is moved along the winding of the transformer 3 and the bar 5 by a reversible motor 6 which is connected by suitable means to a screw 1 which engages the brush 4 to move it in one direction or the other and thus increase or decrease the 10 voltage impressed upon the lamp circuit.

A balanced relay 8 has a centrally pivoted armature 9 forming in efiect a horseshoe magnet the two limbs of which are provided with magnetizing coils l0 and II respectively, which coils are con- 15 nected in series with each other across the lines L L The coilsv exert pulls on the armature which are equal and opposite, so that the latter normally remains in the central position. Adjacent to the coils l0 and H are two further coils l2 and 13, respectively, which are connected in series with each other and wound in such a manner, that a current flowing therein produces a magnetizing force which is added to the magnetizing forcelof one of the coils [0 or II and subtracted from the other, the effect reversing with the reversal of the current flow in the coils I2 and I3 with respect to the direction of current flow in coils l0 and IL, Thus with current flowing in the coils l2 and [3 the armature-9 is ro- 3O tated in one direction or another to make contact with, stationary contacts 14 and I5, respectively,'of the relay 8. The coils l2 and I3 are connected between the bar 5 and a sliding con-' tact I 6 of a sender potentiometer rheostat l! which in turn is connected across the lines L and L Hence the current flowing in the coils l2 and I3 is a function of the position. of the contact l6, and the brush 4, and no current flows therethrough if the lamp voltage is equal to the voltage between brush l6 and line L It will be observed that as long as the lamp voltage balances the sender voltage, the relay 8.is in its neutral position, the motor' 6 is at rest and the brush 4 remains stationary. If now the rheostat contact [6 is moved, for instance, toward the line L a'current flows in-coils l2 and I3 in a direction from contact It to the contact 4 which causes the armature 9 to contact with stationary contact l4 and to connect motor 6 across 50 the supply lines to move brush 4 toward line L and thereby increase the potential which is impressed upon the lamps 2. The motor and brush 4 continue to move'until the current in coils l2 and. I3 is again zero. It will be noted that by 55 the employment of an auto-transformer, the secondary voltage of which is substantially constant within a wide range of loads, it is possible to directly balance the lamp voltage against the sender voltage without any tendency of the system to hunt due to the time lag of the resistance variation of the lamps in response to variations of the impressed voltage. The system described is much simpler than systems which have been employed heretofore, as it makes unnecessary a potentiometer rheostat at the receiving end which cooperates with the sender rheostat to determine the desired position of the lamp regulator brush. This simplification is obtained simultaneously with the aforedescribed more accurate and more stable control.

Fig. 2 is another example of a system embodying the invention which differs from the system of Fig. 1 in that the lamp circuit is in series with an impedance which affords a lamp voltage varying with the lamp load. Means are therefore provided which compensate for such variation as will be explained hereinafter. The lamps 22 are supplied with energy from an alternating current source 2| in series with a variable resistor 23 which may be varied by a sliding brush 24 which also makes contact with a conducting bar 25. The brush 24 is driven by a motor 6 through a screw 2'! as has been described in connection with Fig. 1. The current for the motor and control circuits is derived from a direct current line L L The sender potentiometer H, the motor 6 and the relay 8 are similar to the corresponding elements in the system Fig. 1 except that they are adapted to operate on direct current.

In series with one ofthe lamps 22 is the primary winding 28 of a current transformer 29 having a secondary winding 30. The winding 30 has therefore induced in it a voltage which is proportional to the lamp current. The voltage of winding 38 is rectified by a rectifier 3| of any suitable type and the rectified voltage is impressed on a circuit including the coils I 2 and I3 and that part of the potentiometer ll between the brush i6 and line L Hence when the voltage corresponding to a certain lamp current balances the sender voltage of the potentiometer, no current flows in coils l2 and [3, while said coils carry a current in one direction or another depending upon'whether the lamp current is lower or higher than the value corresponding to a given position of the brush it. The operation of the relay 8 in controlling the motor 6 and thus the brilliancy of the lamps 22 is obvious from the description of Fig. 1.

In the drawing is shown an inductance 32 which is connected in series with a resistance 33 across the direct current terminals of the rectifier Si to smooth out any ripples which might appear in the rectified voltage of the lamp circuit. The inductance 32 and the resistance 33 are however not required if the rectified volt= age is sufiiciently smooth.

The effect of the transformer 29 in series with one of the lamps .is as follows: If the contact 16 is moved rapidly through a great distance and in any event on-account of the fact that the temperature and resistance of the lamp filaments attain their new value with a time delay, the usual regulating systems overrun. This is ob- Viaxted in the system of Fig. 2 by balancing a sender voltage not against the lamp voltage but against the lamp current, which obviates overrunning. The diagram Fig. 3 illustrates the operation. If the lampfilament had no heat storage capacity, that is, it the lamp resistance varied instantaneously corresponding to the lamp current, the lamp current would always instantly correspond to the sender voltage, irrespective of the rapidity with which it is varied by changing of the position of the sender rheostat brush. In other words, the lamp current would vary as per curve A B. However, the lamp resistance does not instantaneously follow the lamp current and if the sender voltage is raised rapidly, the lamp current rises, for instance, as per curve A C. However, when the desired new current I2 ,fiows in the lamp circuit, the movement of the motor is stopped and the lamp current gradually decreases to the value I: at which value 15 the relay current is again sufficient to close the motor circuit to again permit the lamp current to reach the value I2. This action is repeated until the lamp resistance corresponds to the desired lamp current. 20

It is important that the time lag of the resistance change of the lamp in series with the coil 28 be no less than [that of the other lamps to be regulated but it may be greater. It is obvious that any other means which simulates 27 the time lag in the variation of resistance with current changes of the lamps to be regulated maybe inserted in series with the winding 28.

The relay 8 may also be of any other suitable known type. It is further apparent that the I rheostat 23 may be replaced by any other type of variable impedance, such as a transformer or a saturable reactor, while potentiometer I l may be replaced by any other known means for producing an adjustable potential against which 3:.) the potential of the transformer 29 is balanced.

It is further pointed out that the relation between the voltage impressed upon the lamp circuit and the position of the brush of the sender rheostat in the systems shown in Figs. 4c 1 and 2 is independent of the number of lamps in the circuit. Hence the number of lamps may be varied without changing the brilliancy of the remaining lamps for a given position of the sender potentiometer.

The system shown in Fig. 1 may be modified by insertion of a rectifier in the circuit of the coils l2 and I3 to rectify the current passing therethrough. In this case the coils Ill and H are supplied with current from a direct current source or the current from the alternating current source is also rectified.

What I claim as new and desire to secure by Letters Patent is:

1. A control system for dimming apparatus comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage and adapted to be connected to a source of constant voltag a voltage in circuit with said circuit for varying voltage impressed upon the latter, a motor drive for operating said adjuster, a source of variable control voltage, means aifording a voltage which is proportional to the lamp current, and a relay affording control of said motor in response to the resultant of said last named and said variable voltage to prevent over-shooting of the lamp current upon variation of said control voltage.

2. A control system for dimming apparatus, comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage and adapted to be connected to a source of constant voltage, a voltage adjuster in said circuit for varying the voltage impressed upon the latter, amotor drive for operating said adjuster, a source of variable-con trol voltagefanbrmally balanced relay having a control winding, means affording a voltage which is proportional to the lamp current, means to impress the resultant of the last named voltage and the control voltage upon said control winding to cause response of said relay in accordance with the current flowing in saidwinding, and means to control said motor in accordance with the response of said relay to prevent overshooting of the lamp current upon variation of said control voltage.

3. A control system for dimming apparatus, comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage and adapted to be connected to a source of constant voltage, a voltage adjuster in circuit with said lamp circuit for varying the voltage impressed upon the latter, a motor drive for operating said adjuster, a potentiometer adapted to be supplied with a constant voltage and provided with means to supply a variable control voltage, means afiording a voltage which is proportional to the lamp current, a normally balanced relay having a control winding, means to impress the resultant of the last named voltage and said control voltage upon said control winding to cause response of said relay in accordance with the current flowing in said winding, and means to control said motor in accordance with the response of said relay to prevent overshooting of the lamp current upon variation of said control voltage.

4. A control system for dimming apparatus comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage, a variable voltage transformer adapted to be connected to a constant voltage source and to impress a variable Voltage upon said circuit, a motor drive for actuating a voltage varying element of said transformer, a source of variable control voltage, and a relay affording control of said motor in response to the resultant of said impressed and control voltage.

5. A control system for dimming apparatus, comprising, a lamp circuit whose resistance Variations tend to lag behind variations of the impressed voltage, a Variable voltage transformer adapted to be connected to a constant voltage source and to impress a variable voltage upon said circuit, a motor drive for actuating a voltage varying element of said transformer, a source of variable control voltage, a normally balanced relay having a control winding, means to impress the resultant of the lamp circuit voltage and the control voltage upon said control winding to cause response of said relay in accordance with the current flowing in said winding, and means to control said motor in accordance with the response of said. relay.

6. A control system for dimming apparatus, comprising, a lamp circuit whose resistance Variations tend to lag behind variations of the impressed voltage, a variable voltage transformer adapted to be connected to a constant voltage source and to impress a variable voltage upon said circuit, a motor drive for actuating a voltage varying element of said transformer, a potentiometer adapted to be supplied with a constant voltage and provided with means to supply a variable control voltage, a normally balanced relay having a control winding, means to impress the resultant of the lamp circuit voltage and said control voltage upon said control winding to cause response of said relay 'in accordance with the current flowing in said winding, and means to control said motor in accordance with the response of said relay.

7. A control system for dimming apparatus, comprising, alamp circuit whose resistance variations tend to lag behind variations of the impressed voltage, an auto-transformer having a primary circuit adapted to be connected to a constant voltage source and a secondary circuit adapted to-impress a variable voltage upon said lamp circuit, said secondary circuit/including a voltage Varying element, a potentiometer adapted to be supplied with a constant voltage and provided with means to supply a variable control voltage, and a reversible motor to actuate said element and including means responsive to a resultant of said control voltage and the lamp circuit voltage to energize said motor.

8. A control system for dimming apparatus, comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage and adapted to be connected to a source of constant voltage, a voltage adjuster in circuit with said lamp circuit for varying the voltage impressed upon the latter, a reversible motor operatively connected to said adjuster for varying the lamp circuit voltage, a source of variable control voltage, an electromagnetic reversing relay normally biased to an inoperative position and provided with a winding for selectively moving it to one of two circuit closing positions for selectively energizing said motor to cause it to rotate in a corresponding direction, means affording a voltage which is proportional to the lamp current, and means to impress the resultant of said last named and said control voltage upon said winding, to prevent overshooting of the lamp current upon variations of said control voltage.

9. A control system for dimming apparatus comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage, a variable voltage transformer adapted to be connected to a constant voltage source and having an element to vary its output voltage and to impress the latter upon said circuit, a motor drive for actuating said element,

a control element providing for a variable control Voltage, and a relay affording control of said motor in response to the resultant of said impressed and said control voltage.

10. A control system for dimming apparatus comprising, a lamp circuit whose resistance variations tend to lag behind variations of the impressed voltage and adapted to be connected to a source of constant voltage, a voltage adjuster in circuit with said lamp circuit for varying the voltage impressed upon the latter, a motor drive for operating said adjuster, a source of variable control voltage, means to derive a voltage from said lamp circuit which is proportional to the lamp current, and a relay affording control of said motor in response to the resultant of said control and said derived voltage.

11. A control system for dimming apparatus comprising, a lamp circuit, including a plurality of parallel lamps, a voltage adjuster adapted to be connected in circuit with said lamp circuit to a source of constant alternating current voltage to vary the voltage impressed upon said lamp circuit, a motor drive for operating said adjuster, a source of Variable control voltage, a current transformer having a primary winding connected cuit, a motor drive for operating said adjuster, a source of variable direct current control voltage, a current transformer having a primary winding connected in series with certain of said lamps and a secondary winding for supplying a voltage proportional to the current in said primary winding, a rectifier connected to said secondary winding to rectify said last named voltage, and a relay afiording control of said motor in response to the resultant of said control and said rectified volt- 10 a ge.

CARROLL STANSBURY.

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