US1914350A - Control apparatus - Google Patents

Description

June 13, 1933. E. R. EVANS 1,914,350

CONTROL APPARATUS Filed June 13, 1930 NETWORK AND PHASE ROTATOR gwvento'o ZMMZZM Patented June 13, 1933 PATENT OFFICE EARL R. EVANS, OF WASHINGTON, DISTRICT OF COLUMBIA CONTROL APPARATUS Application filed June 13,

My invention relates to electric control apparatus utilizing electric discharge devices for controlling an electric device or circuit and more particularly to motor starting systems of this character embodying electric space discharge devices of the arc-discharge type or the type which is responsive to variations in the phase of the voltages supplied to its electrodes, and also to the potentials of such voltages.

An object of my invention is to provide an improved reactance control apparatus I embodying an electric discharge device for controlling an electrical condition of an electric translating device or electric circuit.

Another object of my invention is to provide an improved and simplified starting system for alternating-current motors, such system embodying a space discharge device of controllable impedance, such as a gaseous or vapor electric discharge device operating with an arc discharge, as distinguished from space discharge devices operating with substantially pure electronic discharge. An are discharge device of thetype referred to, em-

bodiments of which are described respectively in the patent to Langmuir No. 1,289,823, dated December 31, 1918, and the patent to Toulon No. 1,654,949, dated January 3, 1928,

has a large current-carrying capacity and a low internal voltage drop, and hence is adapted toio pera;te with'high efliciency on ordinary'low -volt'age power circuits.

When an'alternat-ing potential is applied to the anode and the cathode of an electric discharge device of the type referred to above current passes through tlie device as an arc whose starting may' be controlled by a control-electrode or grid.. After'starting the arc cannot be influenced by the grid but it can be stopped by removing the anode voltage.'- The operation of this type, of elec tric discharge device consists in periodically ,removingthe anode voltage, for example by the alternating current wave going through zero, tostop the discharge, and controlling the restarting ofthe are by controlling the grid potential. The device therefore operates with an, intermittent arc discharge -whose average value of-space current is con- 1930. Serial no. 460,970.

trolled by the grid. Control of, the grid may be efli'ected by varying the magnitude of the grid potential or by varying the phase relation of the potential applied to the control electrode with respect to the phase of the 55. potential applied to the anode. Thedetailed construction and theory of operation of vapor electric discharge devices of this type are set forth in the above-mentioned patents. Accordingly this specific discharge device is referred to herein, although the detailed construction of the arc-discharge device may be modified, the object of my invention being to provide a system embodying a device of this general character for use in the control of electric devices or circuits and particularly in the starting of a motor.

A further object of my invention is to provide an improved motor starter which re quires no relays or series of contactor switches.

A still further object of my invention is to provide a device of this character which is quick and positive in action, and in which the impedance is controlled in accordance with the counter electromotive force developed by the motor being started.

Other objects of my invention will appear from the following description when read in connection with the embodiment shown on the accompanying drawing, in which Fig. 1 is a diagrammatic view of an embodiment of my invention in one form of motor starting system including an induction motor of the squirrel-cage type controlled by 35 space discharge devices.

Fig.2 is a detailed viewshowing one form of circuit for one of the phases of the system illustrated in Fig. 1'.

Referring to Fig. 1 of the drawing, the embodiment of .my invention there shown comprises a polyphase induction motor 4, a source of alternating current shown as a distribution circuit, a control switch, a phaseshifting device and a plurality of arc-discharge devices. The motor 4:, as shown, comprises a squirrel-cage rotor 5 and a threephase primary or stator winding, the phases being designated 6, 7 and 8 respectively. Current may be supplied to the phase windings 6, 7 and 8 over wires 9, 10 and 11 of the distribution circuit, by closing a switch 12.

Connected between the stator windings of the motor 4 and the alternating-current source are a plurality of arc-discharge devices 13, which for example may be electric discharge devices of the type referred to. Each of these devices as shown comprises a hot cathode 14, a grid or control electrode 15, and an anode 16, the construction and arrangement of the electrodes and the pressure of the gas-filling in the tube being such that the starting of current through the device depends upon the potential of the control electrode. In order to make it possible to vary the potential applied to the control electrodes 15 with respect to the potentials applied to the anodes 16, a phase rotator 17 or suitable equivalent network may be connected between the control electrodes of the discharge devices 13 and the circuit.

In Fig. 2 I have shown one form of circuit arrangement by which the motor 4 may be controlled. In this figure I have illustrated the switch 12 as having a pair of contacts arranged to control the connection between one phase winding 6 of the motor and the source, the other phases being similar to that shown. This arrangement includes an impedance in the form of an auto-transformer having primary and secondary windings 28 and 22 respectively, and a magnetic core 30. In series with one end of the primary winding 28, and connected to line wire 21, a non-inductive resistance 29 may be connected, if necessary, to increase the impedance of the circuit to the desired value. One end of secondary winding 22 is connected to the stationary winding 23 of the phase rotator. Inasmuch as the phase rotator is well known in. the art, and its elements form no part of my invention it is merely indicated diagrammatically as being made up of a stationary winding 23 and a movable winding 24 inductively coupled to the winding The stationary winding 23 is connected to the respective phases of the supply circuit and the secondary winding 24 is connected to the control grids of the electric discharge devices 13 and 13'.

As shown, the switch 12 has a starting contact 18, and a running contact 27. The contact 18 is connected to a tap between the windings 22 and 28 of the auto-transformer, and also through line wire 19 to the cathode 14 of the electric discharge device 13 and anode 16 of the electric discharge device 13. Each of the two electric discharge devices 13 and 13 is adapted to control the passage of current in one direction only, and the impedance of these tubes is controlled by the potential of control electrodes 15 and 15, these electrodes being connected to the movable winding 24 of the phase rotator. Connected to line 21 between the winding 6 of motor 4, and the non-inductive resistance 29 by means of wire 20, are the anode 16 of the electric discharge device 13, and the cathode 14 of the electric discharge device 13.

The arrangement as shown is adapted to apply only a portion of line voltage to the primary of motor 4, and to limit this voltage to a safe value until the counter electromot-ive force of the motor builds up so that full line voltage may be supplied to the motor. lVhen it is desired to start the motor 4, the switch 12 is moved onto contact 18 thereby completing a circuit from the source over line wire 9, switch 12, contact 18, primary winding 28 of the auto-transformer, noninductive resistance 29, line wire 21, winding 6 of motor 4, and back to the source over the return circuit formed by one of the other phases of the system. The auto-transformer is so designed that the impedance of primary winding 28 and resistance 29, if employed, is sufiicient to limit the current to a safe value under these conditions. WVhen contact 18 is closed there is also completed a parallel circuit comprising line wire 19, space discharge circuits of the electric discharge devices 13 and 13, line wires 20 and 21, and winding 6 of the motor. Inasmuch as the electric discharge devices at this time should offer a high impedance to current flow through them, the parts are so arranged that the control electrodes 15 and 15 will have potentials impressed upon them of a value and phase relation to prevent the passage of an are through the tubes or limit the current therethrough to a certain extent. The potential applied to these control electrodes will be determined by the voltage drop across the secondary winding 22 of the auto-transformer, and the phase relation by the design of the circuits and the adjustment of the phase rotator 17. As the speed of the motor increases the potential impressed upon control electrodes 15 and 15 will become less negative or more positive, by reason of the change in voltage in the secondary winding 22 of the auto-transformer, thereby lowering the impedance of the tubes and permitting more current to pass through them. When the motor reaches substantially full speed, the switch 12 may be moved to contact 27, thereby connecting the motor directly in circuit and by-passing the auto-trans-. former and its associated apparatus.

Normally the phase rotator 23, 24 may not be necessary, because the are discharge across the electric discharge devices 13 and 13 will depend largely upon the potentials of the control electrodes which are varied by the auto-transformer. The purpose of the phase rotator is merely to insure proper phase relation of the control potentials. Whenever the control electrodes have potentials impressed upon them slightly less negative or more positive than their critical values, the impedance of the dischargev paths will be materially reduced permitting the arc discharge to take place thereby lowering the impedance of the circuit and maintaining a discharge until the anode voltage drops substantially to zero for a long enough period to permit de-ionization of the gas in the tube. The great advantage of this arrangement is that it functions automatically to control the impedance of the circuit which by-passes the auto-transformer, and this impedance is controlled directly in accordance with an electrical condition of the circuit or device such as the counter electromotive force generated by the motor. j

'Notonly is this arrangement simple and positive in operation but it requires the use of very little apparatus and entirely eliminates the use of numerous relays or contactors which are found in most starting systems of this character.

lVhile I have shown and described but one embodiment of my invention it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects 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.

I claim:

1. A motor starting system comprising a source of power; an alternating-current mo tor connected therewith; an impedance con nected in series relation with a winding of said motor, an electric space discharge device connected in a circuit with said impedance for varying the effective impedance in circuit with said motor winding, and means for controlling the current transmit ted by said discharge device in accordance with the counter electromotive force of said motor.

2. A motor starting system comprising an alternating-current mot-or; a power circuit; a current limiting impedance connected between said motor and said power circuit; a space discharge device connected to by-pass current around said impedance for varying the How of current from said circuit to said motor; and means including a phase shifting circuit connected between the power circuit and the space discharge device for controlling the impedance of said device in accordance with the current traversing said imepdance.

3. A motor starting system comprising an alternating-current motor having a primary winding; means for supplying current to said motor; an electric discharge device connected between said motor and said source; an impedance connected in parallel relation with said discharge device for limiting the current suppliedto the motor while it'is coming up to speed; and means connected to be responsive to an electrical condition of said primary circuit for controlling the impedance of said discharge device in accordance with the counter electromotive force developed by said motor.

4. A motor starting system comprising an alternating-current motor having a primary winding; a source of power for energizing said motor; a reactor connected in series relation with said primary winding; an arcdischarge device connected in. parallel relation with said reactor and having a cathode, an anode and a control electrode; and means for gradually varying the energization of said controlelectrode to vary the resultant impedance of said reactor and said device in accordance with the current supplied to the primary winding of said motor.

5. A motor starting system comprising an alternating-current motor; a source of powerfor energizing said motor, a space discharge device for controlling the current supplied to said motor from said source in starting; and means connected to the circuit of the motor for controlling said device in accordance with the counter electromotive force developed by said motor.

6. A motor starting system comprising an alternating-current motor; a source of" current for said motor; a non-inductive resistance between said motor and said source; and a variable impedance circuit in parallel with said resistance, said circuit including a vapor electric discharge device having its control electrode energized in accordance with the counter electromotive force of said motor.

-7. In combination, a source of alternating current, an alternating current circuit connected to be energized therefrom, an impedance connected in series relation with said circuit, an electric discharge device connected in parallel relation with said impedance and provided with a control electrode for varying the conductivity of said discharge device, and means operative in accordance with an electrical condition of said impedance for varying the energization of said control electrode in a manner to vary the conductivity of said discharge device inversely with variations in the electrical condition of said impedance.

8. In combination, a source of alternating current, an alternating current device connected to be energized therefrom, a reactor connected in series relation with said device, an electric discharge device connected in parallel relation with said reactor and provided with a control electrode for controlling the conductivity of said discharge device, and means operative in accordance with the potential across said reactor for varying the encrgization of said control electrode in a manner to vary the conductivity of said discharge device inversely with variations in the potential across said reactor.

9. In combination, a source of alternating current, an alternating current device connected to be energized therefrom, an autotransformer having a primary winding connected in series relation with said device and being provided with a secondary winding, an electric discharge device connected in parallel relation with said primary winding and provided with a control electrode for controlling the conductivity of said discharge device, and means for controlling the energization of said control electrode in accordance with the voltage of said secondary winding.

10. A motor starting system comprising an induction motor having a primary winding, a source of power for energizing said motor, an auto-transformer having a primary winding connected in series relation with said motor primary winding and being provided with a secondary winding, a pair of oppositely connected vapor electric discharge devices connected in parallel relation with said auto-transformer primary winding and each provided with a grid for controlling the conductivity of said devices, and a phase shifting circuit connected to be energized from the secondary winding of said autotransformer for controlling the potential of said control grid to vary the conductivity of said discharge devices in accordance with the change in speed of said motor during its starting cycle.

In testimony whereof I afiix my signature.

EARL R. EVANS.

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