US1620506A

US1620506A - System of distribution

Info

Publication number: US1620506A
Application number: US747394A
Authority: US
Inventors: Ernst F W Alexanderson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1924-11-01
Filing date: 1924-11-01
Publication date: 1927-03-08
Anticipated expiration: 1944-03-08
Also published as: DE493810C

Description

Patented Mar. 8, 1927.

UNITED STATES PA ERNST F. W. ALEXANDERSON, F SCHENECTADY, NEW YORK,

ASSIGNOR TO GElVERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

.SYSTEM on DISTRIBUTION.

Application filed November 1, 1924. Serial No. 747,394.

My present invention relates to systems of electrical distribution, and more particularly to systems for converting direct cur,- rent to polyphase alternating current.

One of the'objects of my invention is to provide a system of the class described which will not require for its operation any device having moving parts. A further object of my invention is to provide an ap-.

paratus for the purpose mentioned, which will be especially adapted for high voltage direct current distribution systems.

- In carrying my invention into efi'ect, 1 provide a plurality of single phase transformers, and supply current from the direct current source to each primary winding through a pair of electric valves. In order that these valves should operate at the best efficiency they should be controlled in such a way that current will flow only when the potential difference between the terminals is comparatively small and substantially the maximum current carried by the valve should be permitted to flow therein duiing the entire period during'which the val e is rendered conductive. These valves may be of the pure electron discharge type, or may be of the type which operate byreason of gas ionization. In either case, the action of the,valve is controlled by means of a third electrode or grid of some convenient form.

In the-case of the valve operating by gas ionization, it is important in order to secure good commutation of the current in trans fer-ring current from one valve to another that the'current through one valve should be reduced to zero at the time it is made non-conducting and current starts in the other valve of each'pair. In the case of the valve operatingby a pure electron discharge, this feature is not so important, but unless the current through each valve is reduced to a small amount at the time the valve is rendered non-conducting surges may be set up in. the system which will cause the insulation at some point to break b down. In order to meet this requirement,

I provide means whereby the potential ap' plied to a valve is reversed at the instant that the valve is rendered non-conducting by the application of a negative potential to its grid. we

The novel features which I believe to be characteristic of my invention are ,set forth with particularity'in the appended claims,

10 and 11.

my invention itself however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the accompanying drawmg m which I have shown diagrammatically a system for converting direct current to three-phase alternating current.

have indicated in the drawing three pairs of valves, 1 and 2, 3 and 4, 5 and 6, of the thermionic type for supplying current from direct current mains 7 and 8, to the primary Windings9, 10 and 11, of three single-

phase transformers

12, 13 and 14. The positive side 7 of the direct current system is connected to the middle point of each primary winding 9, 10 and 11, through inductive windings 15 to 20, inclusive. These windings may all be entirel independent of one another, but prefera ly will be wound upon a three legged closed magnetic core, windings 15 and being placed on one leg, windings 16 and 17 on the second leg, and windings Hand 19 on the third leg of the magnetic core. The windings are so connected that when equal currents are applied to the three primary windings f, 10 and 11, the magnetomotive forces of the different windings oppose each other, thus producing no flux in the core upon which they are wound except for a slight leakage flux.

The

secondary windings

21,22 and 23 are connected in delta to the three-phase distribution mains 24, .25 and 26.

Condensers

27, 28 and 29 are connected across each phase of the distribution system through

transformers

30, 31 and 32. These condensers may be connected directly across the secondaries of the

transformers

12, 13 and 14 or acros the primary windings 9, In case the valves operate by means of gas ionization the latter connection is probablypreferable. The excitation for the grids of the valves ,1 to 6 is obtained y means of transformers 33, 34 and 35, which are connected to the

distribution mains

24, and 26. The terminals of the secondaries of transformers 33, 34 and 35 are connected to the grids-of the valves 1 to 6. through resistances 36. .The mid points of the secondary windings are connected to the cathodes of valves 1 to 6 through resistances 37 and reactances 38. Current forheating the cathodes of valves 1 to 6, which are all connected in parallel, may be sup plied by a source of direct current 39 or from any other convenient source of current as desired.

In the operation of a system of the type described, it is necessary for satisfactory operation that one valve of each pair should be made conducting by the application of a positive potential to the grid before current has been interrupted in the other pair. This requires that the positive voltages applied to the grids of the valves should lead the voltages induced in the and 23. The desired lead in voltage may be secured by including condensers 40 in the circuit of the primary windings of transtential is supplie formers 33, 34 and 35. In the arrangement shown, these condensers are connecte through transformers 41 for the purpose of stepping down the current, and thus permitting the use of a smaller condenser.

The use of phase control means for the purpose of causing the current to start through one anode before itisinterrupted in the other is broadly claimed in a copending application of mine, Serial No. 651,409, filed July 13, 1923, and assigned to the same assignee as the present application.

In the operation of the system described, I have found that although the current wave flowing through each valve is ofsubstantial rectangular form, the potential set up in the secondary windings of the transformers is of substantially sine wave form.

" A substantially sine wave-potential is also primary windings 9, 10,

current is flowing throng one valve the potential upon the anode of the other valve is negative and of ahigh value, whereasthe potential set up across the across the-valve which is conducting is com- The difier'ence between the paratively low.

positive potential of the supply main 7 and the potential of the anode of the valve which is conducting is taken up by the inductive windings 15 to 20.

When the potential of the valve which is non-conducting has been reduced to zero or has become as current is permitted to flow through the valve the

condensers

27, 28 and 29., which have previously become charged, discharge, and as a result the potential across the valve which had previously been carrying the current is momentarily reversed. This causes a sudden interruption in the current through that valve and at the same time'the potential of. the grid is made negative. I have found therefore that the system operates in.

windings 21, 22'

. supplying current supplying current positive, a positive poto its grid. As soon by Letters Patent of the United States, is:' 1.. The combination in a system'ofdistrtbution of a source of direct current, a polyphase system of transformers, having their secondaries connected to a polyphase distribution system, individual connections for supplying current from saidvsource to each of the primar windings of said transformers, an in uctive winding included in 'apair of electric each of said connections, valves for controlling the fiow of current to each of said primary windings, and means for controlling the action of said valves in such away that when current is permitted to start in one of each pair of said valves the potential applied to the other valve of the pair will be'momentarily reversed.

2. bution of a source of direct current, a polyphase system of transformers, having their The combination in a system of distri-' secondaries connected to a polyphase distribution system, individual connections for of the primawindings of said transformers, an in uctive winding included in each of sai connections, all of said inductive windin being wound upona common core, a pair of electric valves for controlling the flow of current to each of said primary windings, and means for controlling the action of said valves in such a way that when current is permitted to start in one of each pair of said valves the potential applied to the other valve of the pair will be momentarily reversed;

3. The combination in a system of distribution of a source of direct current, a polyphase system of transformers having their secondaries connected to a polyphase'distribution system, individual connections for from said source to each of the prima windings of said transformers, an in uctive winding included in each of said'connect1ons,-a pair of electric valves for controlling the flow of current from said source to each' to eachof said primary windings, and .a

capacityassociated with each of said windings in such a way that when current starts to flow through one of each pair of valves the potential applied to the other valve of the pair will be momentarily reversed by the action of the capacity. In witness whereof, I my hand this 30th day of October, 1924.

ERNST'F. W. ALEXANDERSON.

have hereunto set 4'