US2279729A

US2279729A - Electric converting system

Info

Publication number: US2279729A
Application number: US139893A
Authority: US
Inventors: Burnice D Bedford
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1937-04-30
Filing date: 1937-04-30
Publication date: 1942-04-14
Anticipated expiration: 1959-04-14

Description

April 14, 1942. a. D. BEDFORD 2,279,729

ELECTRIC CONVERTING SYSTEM Filed April 30, 1937 Fig.1.

42 2 26 x y I 33 g ab cd e f gh k B \l" r c Inventor:

His Attorney.

Patented Apr. 14, 1942 ELECTRIC CONVERTING SYSTEM Burnlce D. Bedlord, Schenectady,

N. 1., alalgnor to General Electric Company, a corporation of New York I 5 Claims.

My invention relates to electric converting systems and more particularly to systems for eiIecting transfer of energy between circuits by means of switching apparatus and associated equipment.

In many applications where circuit interrupting means are used, it is desirable to control the currents of the associated circuits so that the circuit interrupting duty imposed is not excessive. It is advantageous to construct and arrange the associated circuits and equipment to effect a substantial reduction in the current to be interrupted.- By reducing the current immediately prior to and coincidentally with the circuit interrupting operation, it has been found that the size and rating of the switching or circuit interrupting means may be considerably reduced as compared with that which would be required if the apparatus were required to interrupt the maximum currents of the associated circuit, or circuits.

For example, in electric translating circuits such as rectifying and inverting circuits employing switching or mechanical interrupting means, it is desirable from an economic standpoint to reduce as much as possible the current to be interrupted so that the switching or interrupting apparatus may be correspondingly reduced in size and rating. Moreover, it has been found that it is highly desirable to relieve the cooperating contacts of the switching meansfrom all current establishing and interrupting functions so that the establishment of arcs at the contacts is entirely eliminated, thereby relieving the cooperating contacts of the most severe function in the cycle of operation.

It is an object of my invention to provide a new and improved electric converting system.

It is another object of my invention to provide a new and improved electric circuit.

It is a further object of my invention to provide a new and improved electric translating circult.

It is a still further object of my invention to provide a new and improved circuit interrupting means for use in electric converting systems.

The subject matter of this application is an improvement of the subject matter described and claimed in my copending application Serial No.

113,581, filed December 1, 1936, entitled Electric circuits and assigned to the assignee of the present application.

In accordance with the illustrated embodiment of my invention, I employ a switching means operated in electrical synchronism with the voltage of an alternating current circuit for transmitting energy between the alternating current circuit and a direct current circuit. saturable inductive devices are connected in series relation with the phase conductors of the alternating current circuit and the switching means for controlling the rate of change of current at the beginning and the end of the normal predetermined intervals of conduction of current from the alternating current circuit to the direct current circuit established by the cooperating contacts of the switching means. Each of the saturable inductive devices includes a main winding connected in series relation with one of of the phase conductors of the alternating current circuit, and a control winding connected in series relation with a different phase conductor oi the alternating current circuit for controlling the impedance of the associated main winding and for controlling the rate of change of current through the main winding at the beginning and at the end of the normal conductor intervals for that inductive device. Each of the saturable inductive devices may include an auxiliary winding for providing a-commutating voltage. Electric valve means is connected in parallel with the switching means periodically to establish and interrupt the flow of current through the various associated saturable inductive devices to prevent sparking at the contacts of the switching means. The conductivity of the electric valve means is controlled so that the electric valve means conducts or interrupts current of only small value at the beginning and the end of the conducting intervals,.permitting thereby the use of an electric valve means of relatively small rating compared with the amount of power which may be transmitted by the system.

For a better understanding of my invention. reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. trates an embodiment of my invention as applied to an electric converting system for transmitting energy between a three phase alternating current circuit and a direct current circuit, and Figs. 2a to 2e, inclusive, diagrammatically show an arrangement of one part of the switching means, while Fig. 3 represents certain operating characteristics of the arrangement shown in Fig. 1.

In Fig. l of the accompanying drawing, I have diagrammatically shown my invention as applied to an arrangement for transmitting energy between a direct current circuit I and an alternat- Fig. 1 diagrammatically illusdegrees.

ent phase conductor for controlling the saturation of the core member I and hence for controlling the impedance of the associated main winding H, and an auxiliary winding l3 for providing a commutating voltage, the function of. which will be explained hereinafter.

The switching means 5 and 6 include rotatable drum members l4 which are driven in electrical synchronism with the voltage of the alternating current circuit by any suitable means such as an alternating current motor I5 01' the synchronous winding II. The angular displacement of the I drums l4 relative to the voltage of the alternating current circuit may be adjusted by any suitable arrangement such as a rotary phase shifter l8. In order to control an electrical condition of one of the associated circuits, such as the voltage of the direct current circuit I, the angular displacement of the drums l4 may be automatically controlled in accordance with an electrical condition of one of the associated circuits, such as the current of the direct current circuit I, by any conventional arrangement l9 which may comprise a current responsive actuating coil 20, a spring biased plunger 2| for controlling the relative angular displacement by means of a phase shifting device 22 of the rotary type. The synchronous motor I5 may be energized from any suitable source of alternating current and in the arrangement shown, the motor I5 is energized from the alternating current circuit comprising Phase conductors 2, 3 and 4.

Switching device 5 includes a rotating contact 23 which extends completely around the periphery oi the drum l4 and a cooperating stationary contact or brush 24 which is connected to one terminal of the direct current circuit I. In order to control the period or interval during which current is transmitted from the phase conductors of the altemating-current circuit to the direct current circuit, I provide on the surface of the drum l4 of switching device 5 a contact 25, the length of which is determined by the desired electrical interval oi. conduction. In the particular arrangement shown in Fig. l, the arcuate length of the contact 25 corresponds to I electrical degrees. The cooperating stationary contacts or brushes 26, 2'! and 26 are connected to main windings II or difl'erent saturable

inductive devices

1, 8 and 9 respectively and are spaced at equal intervals around the periphery of the drum I4. In the particular arrangement shown, the

brushes

26, 21 and 28 ar displaced 120 electrical Electric valve means 29 is connected in shunt relation with the switching device 5 to periodical- I ly short circuit the switching device to eifect establishment and interruption of the current flow through the associated saturable inductive devices I, 8 and 9 and to thereby relieve the switching device 5 of this operation. The electric valve means 29 is preferably 0! the type employing an ionizable medium such as a gas or a vapor and includes an anode 39, a cathode 3| and a control member 32 for controlling the conductivity theretype having armature windings I6 and a field biasing potential.

employed to eflect this control and I'have chosen.

drum 14.

of. The-anode 39 is connected to brush 24 through a conductor 32' and,the cathode 3| is connected to the switching device 6 through a contact or brush 33 which cooperates with a rotatable contact 34 mounted on the surface of the The contact 34 extends completely around the drum l4 and is connected to control contacts 36, 39'; 31 and 33. Stationary control contacts orbrushes 39, 49, 4| and stationary control contacts or

brushes

42, 43 and 44 cooperate with

contacts

35, 31 and 36, 33, respectively.

Brushes

39 and 42 are associated with auxiliary winding l3 of ,inductive device I; brushes 40 and 43 are associated with auxiliary winding I3 01' inductive device 9 and brushes 4| and 44 are associated with auxiliary winding l3 of inductive device 3. The various auxiliary windings I3 are 1 connected to the electric valve 29 through the associated control brushes and control contacts to impress on the anode 30 of electric valve means 29 a commutating voltage to transfer the current from the main windings II to the electric valve 29 at the end of the various conducting intervals. Contacts 35 and 33 with the associated brushes serve to connect the anode-cathode circuit of electric valve means 29 to the auxiliary windings i3 in advance of the establishment of the circuit to the associated main windings. This is accomplished by positioning the contacts 35 and 36 to lead the contact 25. Electric valve 29 is rendered conductive by means of the contact 36 and the associated brushes immediately after the anodecathode circuit of the electric valve means 29 is established by contact 35 and the associated brushes. Electric valve means 29 is maintained nonconductive by impressing on the control member 32 thereof a negative uni-directional Any suitable means may be to represent the arrangement as comprising a battery 49 and a serially connected resistance 46 connected across the cathode 3| and the control member 32. A control circuit for the electric valve means 29 which cooperates with

movable contacts

36 and 39 and

brushes

42, 43 and 44 serves to render the electric valve means 29 conductive at the beginning and at the end of the normal conducting intervals for each of said saturable inductive devices. The control circuit may comprise any conventional arrangement such as a source of voltage for rendering the valve 29 conductive at the desired time, and in the present arrangement I have chosen a battery 41 for impr essing on the control member 32 a positive voltage at times established by the position of the

contacts

36 and 34 on the drum l4. A current limiting resistance 49 may be connected in series relation with the battery 41. The ar rangement of the cooperating contacts of the switching device 5 of Fig. 1 may be better understood by referring to-Figs. 2a-2e, inclusive. The

- shaded portions of these figures represent the in inductive devices. The control circuit for the electric valve means I2 is similar to that for electric valve means 22.

The operation of the embodiment of my invention diagrammatically shown in Fig. i will be explained when the system is operating to transmit energy from the alternating current circuit comprising phase conductors 2-, 2 and 4 to the direct current circuit l. Switching devices I and 9 will operate. as'a full wave controlled rectiner to transmit energy through each of the phase conductors and the associated inductive devices during both the positive and negative half cycles of voltage of the alternating current circuit. The synchronous motor II will be assumed to rotate in the direction indicated by the arrow in Fig. l and the rotary phase shifter I! may be adjusted to effect the desired angular displacement between the voltages of the alternating current circuit and the contacts on the drums l4 of switching devices I and 9. Let it be assumed that at the particular instant indicated by the positions of the drums l4 of Fig. l, the voltage of the phase conductor 4 is positive-so that current will be conducted from phase conductor 4 through control winding l2 of inductive device 9, main winding ll of inductive device I, brush 22, contact 29. contact 22, brush 24, to the positive terminal of direct current circuit i, through switching device 2 to main winding I l of inductive device 9, control winding i2 of inductive device 2 and phase conductor 2. During the greater part of the conducting intervals for each of the main windings ll of inductive devices I, 2 and 9, the impedance of the main windings Ii will be relatively small due to the fact that the control windings I2 have efi'ected saturation of the associated core members l9. However, at the beginning and at the end of these conducting intervals, the core members I0 will not be saturated and the impedance of the main windings i I will be substantially greater to eifect a slow rate of change of current at the beginning and at the end ofthe intervals of conduction. By virtue of the leading relationship of the contact 29 relative to the contact 29, the anode-cathode circuit for the electric valve means 29 will be established prior to the establishment of the main power circuit through brush 29. Moreover, since the contact 29 leads contact 26, the electric valve means 29 will be rendered conductive by energization of the control circuit to permit electric valve means 29 to establish the flow of current through main winding ii of inductive device I to relieve brush 29 and the contact 25 of this circuit establishing operation and to thereby prevent sparking between the brush 22 and the contact 25 when the circuit connection is made. current to the electric valve means 29. will be accomplished by the operation which is commonly known as phase commutation; that is, the voltageof the inductive device I at this particular time in the cycle of operation is such as to cause this commutation of current.

The manner in which the electric valve means 29 eflects the establishment and interruption 'of currentthrough the various main windings ll may be better understood by considering the operating characteristics represented in Fig. 3. Curve A represents the voltage of phase conductor 4 and curve B represents the current conducted by main winding ll of inductive device I during a specific portion of one half cycle of voltage of the alternating current circuit. By

Of course, the transfer ofthe proper adjustment of the position of the rotary phase shifter II, it is possible to control the time during each half cycle of voltage of the phase conductors 2, 2 and 4 at which the respective associated contacts are established by the switching devices I and l and to control thereby an electrical condition such as the voltage of the direct current circuit I. Considering the events which occur prior to the time corresponding to the relative positions of the contacts shown in Fig. l, the line it corresponds to the time when contact 24 engages brush 22. Since the electric valve means 22 is not conductive at this time, no current will be transmitted through main winding ll. At a later time corresponding to the position of line b, contact 29 engages brush 42 to render electric valve means 29 conductive by means of the positive voltage impressed on control member 22 thereof by battery 41. During the interval b-c, the electric valve means 29 completes the circuit through the main winding H and auxiliary winding [2 and conducts current during the corresponding interval. At time c, movable contact 25 engages brush 29 to connect main winding ii directly through

contacts

29 and 22 and brush 24 to the direct current circuit I. By virtue'of the lower resistance of this path relative to the resistance of the path including the electric valve means 29, current will be commutated from the electric valve means 22 to the path including the main contact 25 and the associated brush 24. At time d, the impedance of the main winding ii becomes substantially less due to the saturation of the core member l0 and the current will now increase to a'substantially greater value.

The circuits to electric valve 29 controlled by contacts 25 and 29 and brushes 29 and 42 are interrupted at some time after the time 0. At about the time e the current conducted by main winding ll of inductive device 1 begins to decrease due to the build-up of current in the next succeeding phase in the order of phase rotation. At time I inductive device 9 becomes saturated permitting a rapid rise in the current in main winding ii thereof. At time 0, the contact 21 engages brush 29 to establish the anodecathode circuit of electric valve means 29. And at time h, contact 29 engages brush 42 to render electric valve means 29 conductive. The current is commutated from main contact 25 and brush 29 to electric valve means 29 at time it due to -the commutating voltage provided by auxiliary winding i2 of inductive device 1. Within the interval h-j, the contact 25 and brush 29 are disengaged without being required to interrupt current. And at time k the circuits to electric valve means 29, controlled by

contacts

21 and 29 and brushes 29 and 42, are opened. The dotted curve C represents the current conducted by main winding ll of inductive device 9. It is to be noted that the switching device 5', more particularly contact 29 and brush 26, conduct current during the interval ch and that as concerns phase conductor 4, the electric valve means 29 conducts current during the interval b-c as represented by curve D and that electric valve means 29 also conducts current during the interval h-4 as represented by curve E. It is to be understood that the electric valve means 29 also conducts current in a similar manner for phase conductors 2 and 2; that is, it serves to establish the current and interrupt the current conducted by main windings ll of inductive devices 2 and 9 and the associated main contact 25 and brushes 2! and 28. Electric valve means 28 and electric valve means 50 each conduct current six times during each cycle of the alternating voltage of the alternating current circuit iiicluding phase conductors 2, 3 and I.

The relative rates at which the current increases and decreases at the beginning and at the end of the normal conducting intervals may be adjusted by the design of the saturable inductive devices I, 8 and 9. More particularly, the rate of rise of current through the main windings H at the beginning of the conducting intervals may be decreased by decreasing the number of turns of the control windings I2 relative to the main windings ll. Furthermore, by decreasing the number of turns of control windings l2 relative to the main windings I, the rate of change of current at the end of the conducting intervals will be increased.

One of the principal advantages of my invention is the arrangement whereby the switching means associated with an electric converting system is relieved of the functions of establishing and interrupting the current through the various inductive devices 7, 8 and 9. Because of this feature, the cooperating main or power contacts of the switching devices 5 and 6 are not required to establish or interrupt currents and are, therefore, not subject to the deterioration incident to apparatus performing these functions and maybe materially reduced in size and rating relative to the amount of energy which can be transmitted and controlled by the system.

Controlling means l9 automatically controls the angular position of the synchronously driven switching devices 5 and 6 with respect to the voltage of the alternating current circuit to control the voltage of direct current circuit l in accordance with the current of the direct current circuit or in accordance with the amount of power transmitted between the alternating current circuit and the direct current circuit. This arrangement automatically controls the time of transfer of current among the various phase conductors in accordance with a load condition of one of the circuits.

While I have shown and described my inven tion as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes 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 asfall within the true spirit and scope of my inphase conductors, a control winding connected in series relation with a predeterm ned different one of said phase conductors for controlling the inductance of the associated main winding and an auxiliary winding, and electric valve means for periodically short circuiting said switching means to establish and interrupt the current through said main winding, said auxiliary winding providing the commutating voltage to effect transfer of current from said switching means to said electric valve means immediately preceding the end of the normal intervals of conduction by said main winding.

2. In combination, an alternating current circuit comprising a plurality of phase conductors, a direct current circuit, a plurality of saturable inductive devices each associated with a different one of said phase conductors and each comprising a core member, a main winding connected in series relation with one of said phase conductors, a winding connected in series relation with a different phase conductor for controlling the inductance of said associated main winding and an auxiliary winding for producing a commutating voltage, a switching means interposed between said inductive devices and said direct current circuit for selectively connecting said inductive devices to said direct current circuit to transmit energy between said alternating current circuit and said direct current circuit through said inductive devices during different predetermined intervals, and electric valve means connected in shunt relation with said switching means and connected with said auxiliary winding for establishing and interrupting the flow of current through said inductive devices.

3. In combination, an alternating current circuit comprising a plurality of phase conductors, a direct current circuit, a plurality of saturable inductive devices each associated with a different one of said phase conductors and each including a core member, a main winding connected in a control winding for controlling the inductance of the associated main winding and an auxiliary winding, switching means interposed between said main windings and said direct current circnit for selectively connecting said main windings to said direct current circuit to effect energy transfer between said alternating current circuit and said direct current circuit and comprising a plurality of cooperating contacts each associated with a different one of said inductive devices. and an electric valve means connected in shunt relation with said contacts and controlled by said auxiliary windings for establishing and interrupting the flow of current through said cooperating contacts to prevent sparking at said contacts.

4. In combination, an alternating current circuit comprising a plurality of phase conductors, a

plurality of saturable inductive devices each associated with a different one of said phase conductors and each comprising a core member, a main winding connected in series relation with one of said phase conductors, a control winding connected in series relation with a different one of said phase conductors for controlling the magnitude andthe rate of change of current through the associated main winding at the beginning and the end of the normal conducting intervals therefor and an auxiliary winding for providing a commutating voltage, switching means interposed between said inductive devices and said direct current circuit and comprising a plurality of cooperating contacts each associated with a different one of said main windings for effecting current transfer between said alternating current circuit and said direct current circuit during predetermined intervals, an electric valve means connected across said switching means and connected to be controlled by said auxiliary windings, and a control circuit for said electric valve means for rendering said electric valve means conductive to establish and interrupt the flow of current through said main windings.

5. In combination, an alternating current circuit comprising a plurality of phase conductors, a direct current circuit, a switching means operated in electrical synchronism with the voltage of said alternating current circuit for efiecting transfer of energy between said alternating current circuit and said direct current circuit and comprising a plurality of cooperating main conin: a core member, a main winding connected in series relation with a predetermined different phase conductor, a control winding connected in seriesrelation with another phase conductor for controlling the magnitude and the rate of change of current through the associated main winding at the beginning and at the end of the normal conducting intervals and an auxiliary winding for providing a commutating voltage, an electric valve means connected across said main contacts of said switching device to establish and interrupt the flow of current through said main windings, and a circuit for said electric valve means controlled by said control contacts for controlling the conductivity of said electric valve means.

BURNICE D. BEDFORD.