US1770334A - Electrical-distribution system - Google Patents

Description

July 8, 1930.

ELECTRICAL DISTRIBUTION SYSTEM Filed Dec. 1925 A A A;

' WITN s E v INVENTOR Patented July 8, 1930 UNITED STATES PATENT OFFICE I EARL R. EVANS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK ELECTRICAL-DISTRIBUTION SYSTEM Application flledDecember 2, 1925. Serial No. 72,718.

My invention relates to electrical distribution systems and apparatus and particularly to systems embodying means for controlling or modifying the transmission characteristics thereof under predetermined conditions.

In general terms, it is one object of my invention to provide an electrical power distri- A still further object of my invention is to improve, the detailed construction of protective apparatus for electrical systems.

In accordance with my invention, as aplied to a power distribution circuit a reactor liaving a winding connected in series relation with the distribution circuit and a short-circuited secondary winding is employed. The secondary winding is short-circuited through a current-limiting device, such as a highlyevacuated thermionic tube or a gas or Vaporfilled tube. The tube is so constructed that its resistance is a minimum at normal fullload current or other desired condition. Un

der abnormal conditions, the resistance of the tube is greatl increased so that the secondary winding no longer functions as a short-circuited winding.

Under normal conditions, the effective impedance of the reactor is low because of the short-circuited secondary winding. When the resistance. of the secondary winding increases, however, the effective impedance of the reactor is increased, thereby modifying the transmission characteristics of the systems but may also be applied to other systems, in its application to power-transmission systems but may also be applied to other system, such as signalling or communication systems.

For ordinary applications, any electrical discharge, device having a current-limiting characteristic may be used in combination with the reactor. Thermionic tubes either of the highly evacuated type operating with a pure electron discharge or of the gas-tilled arc type utilizing ionization principles are examples of suitable current-limiting devices. For certain applications, either of these types of thermionic tubes may be used, but for the protection of long, high-voltage circuits, I prefer to use the gas-filled tube because this tube has a smaller resistance for normal currents than the highly evacuated tube and a higher resistance than normal for either small a plied voltages or over-voltage surges.

nder light-load conditions, such high-voltage circuits have a larger ratio of capacity voltage-drop to inductive voltage-drop than under full load conditions which tends to make the voltage regulation of the line poor. The use of an arc device in connection with such a line not only limits the excessive current flow resulting from a fault on the system, but also increase the effective induc tance of the circuit during light-load periods, thereby improving the inherent voltage regulation-of the circuit.

For a clearer understanding of my invention, reference should be had to the accompanying drawings, of which Figure 1 is a view of a portion of an elec trical distribution system embodying the same;

Fig. 2 is a detailed view of an improved current-limiting device applicable to the system shown in Fig. 1;

Fig. 3 is a similar view of another modification;

Fig. 4 is a schematic diagram of a highvoltage transmission line having reactors disposed therein at a plurality of points; and

Fig. 5 is a detailed view showing an arrangement of the reactor upon a tower or supporting structure of a high-voltage trans mission line.

Refzrring to Fig. 1, an electrical distribution system comprises an alternator l or other source of alternating current and a transmission circuit 2 having a reactor 3 in series therewith for controlling or modifying the load current under predetermined conditions. In accordance with my invention, the reactor 3 is so designed as to offer a minimum impedance to the load current at a predetermined value of current-for instance, that corresponding to full-load output of the generator 1, and a greater impedance to smaller or larger currents, or both.

The reactor 3 comprises a main winding or section 4; in series with the transmission circuit 2 and an auxiliary or secondary winding 5 inductively related to the winding 4. As the main winding 4 may be subjected, in the case of a short-circuit or overload on the transmission circuit, to a current many times larger than the normal full-load current, it comprises substantial conductors embedded in or supported by refractory insulating members 6 of porcelain or other suitable material. In this manner, the winding is braced against the magnetic forces produced by the excessive currents. Suitable spaces or openings 7 may be provided for ventilation purposes, if appreciable heat is developed in the winding in operation.

Since one object of my invention is to limit, to a greater extent than has heretofore been possible, the current traversing the reactor under abnormal conditions, the winding 4 and insulating members 6 may be smaller and less substantial and expensive than those commonly used. The auxiliary winding 5 carries only a limited current under all conditions. It does not require such careful insulation and bracing as the main winding, therefore, and it has been deemed unnecessary to illustrate the supporting elements thereof.

A plurality of current-limiting devices 8 are connected across the terminals of the secondary winding 5. As shown, these devices comprise a cathode 9 and an anode 1O enclosed in a sealed envelope 11. The cathode 9 may be of the filamentary type, as shown, and heated by any suitable source of current, such as the circuit 2. The envelope 11 may be highly evacuated or may contain a gas or vapor at such pressure as to produce an arc discharge between the electrodes of the desired characteristics depending upon the applied voltage. In the case of a highly evacuated tube, the current traversing the device is limited by the number of electrons emitted by the cathode and will not exceed a predetermined value irrespective of the applied voltage. In the case of the arc-discharge device, the cathode or other source of electrons serve as an ionizing means and the envelope may contain mercury vapor or argon or other inert gas at such pressure as to produce an arc of the desired characteristics, such as a low voltage drop.

Either of these devices will, therefore, serve as a current-limiting means if an excessive current traverses the main winding of the reactor 3. Furthermore, the gas-filled tube will present a high resistance to the passage of current when the applied voltage is less than the ionization potential of the gas or insuflicient. to strike the arc, and the reactor 3 will therefore possess a greater impedance for small values of current than for full-load current, when embodying an arc-discharge tube.

In the arc-discharge device, the current is only momentarily limited in value, as the current will build up in time until the voltage dro across the tube is of the same order as the initial drop. Accordingly, with this type of tube, a fuse 12 in series with the tube or a. quick-acting overload circuit-interrupter 13 in the main circuit is used, and the tube is only utilized to limit the current momentarily, or during the time required for the fuse or circuit-interrupter to become operative. \Vhile this time may be very short, it is often a critical period in the case of sudden large surges of current. It will be apparent therefore, that apparatus embodying the invention provides protection against surges not afforded by circuit-interrupters and the like.

A plurality of tubes may be connected in parallel, as indicated in Fig. 1, when the normal current in the secondary winding 5 is large. versed in order to equalize the resistance to the flow of current in either direction through the winding 5.

The use of oppositely connected tubes may be avoided by providing the tube with two cathodes, as shown in Fig. 2. The tube shown in Fig. 2 is similar to those shown in Fig. 1, except that two filamentary cathodes 15 and 16 are supported from opposite ends of the tube by the supporting leads 17, on which are disposed metal discs or plates 18. As shown, the leads 17 are connected to conductors 19 adapted to be connected to an auxiliary source of current for heating the oathode to incandescence. The disc members 18 serve to cool the cathodes by conduction and radiation, particularly when a gas filling is used andthe current in the arc is abnormally high. Certain of the disc members 18 may be disposed in such close proximity to the cathodes 15, 16 as to serve as anodes or terminals for the arc discharge or the electrons emitted by the opposite cathodes.

Another form of current-limiting device is illustrated in Fig. 3. The device comprises a filamentary cathode 25 centrally disposed in a cylindrical anode 26, both anode and cathode being contained in the sealed envelope 27. The electrodes 25 and 26 are connected to the terminals of the secondary winding 5 of the reactor 3. Preferably one or more opp0sitely-connected pairs of thermionic tubes are provided, as in Fig. 1, although only one is shown. A magnetic field transverse to the current flow between the electrodes is provided by a field winding 28 connected to a As shown, half of the tubes are recurrent transformer 29 in the line circuit. lVhen the current exceeds a predetermined value, the strengthened magnetic field increases the impedance of the current-limiting device, thereby increasing the impedance of the reactor 3. An auxiliary field winding 30' controlled by an under-current relay 31 in the circuit of the current transformer 29 may also be provided, if desired, to increase the impedance of the device when the -load current is less than a predetermined value. The devices shown in Figs. 1 and 2 may be similarly provided with a field winding or so disposed with respect to the reactor winding 4 as to control or extinguish the are under excessive current conditions.

My invention is especially adapted for the protection of long, high-potential transmission circuits against abnormal surges of current or short-circuits. Such a circuit is represented diagrammatically in Fig. 4, in which a generator 35 is connected, through a stepup transformer 36, to the circuit 37. At some distant point, a load 38 is connected to the transmission circuit through a step-down transformer 39. A plurality of reactors 3, similar to those shown in the preceding figures, are connected in the transmission circuit at suitable intervals. In some cases, a single reactor may be found sufficient, but it is believed that the use of distributed reactors will serve to confine surges of current to short portions of the circuit and thereby provide the maximum protection.

- The impedance devices 3 have a minimum impedance at a predetermined value,of current, for instance, that corresponding to the maximum load carried by the system under normal conditions, and a relatively large-impedance for currents in excess of said predetermined current. Excessive currents are therefore limited by the increased impedance of the circuit. The conductors and switching apparatus may be less rug" ed and designed with a smaller factor of saf aty, while the occurrence of faults on one portion of a complicated network will not disturb the-rest of the system to the same extent as heretofore.

The increased im edance is available instantaneously and t 'erefore provides more complete protection than is rovided by the circuit-interrupters common y employed to isolate faulty circuits, as the latter require an appreciable period of time for their operation. In some cases, it is even possible to omit the circuit-interrupters entirely where the impedance of the system is of sufficient magnitude to limit the current under all conditions to a safe value. Furthermore, when arc-discharge devices re uiring a definite initial potential are utilized, the system possesses a relatively large inductive impedance at light loads. A long transmission circuit which has a high capacitive reactance ordinarily has a poor voltage regulation at light loads. The use of impedance of such character as to increase the inductive reactance or resistance of the circuit in connection with such a system improves the inherent voltage regulation of the system.

As shown in Fig. 5, the impedance may be combined with the supporting structure of a transmission line. As an example of this construction, a tower 40, of which only the upper portion is shown, for supporting a line conductor 41 upon the insulators 42 and 43 is adapted to carry the secondary winding 5 upon the cross-bar 44 thereof. The main winding 4 in series relation with the line conductor is carried in the axis of the winding 5 by a strain insulator 45 of wood, for example, supported by and between the insulators 42 and 43. The winding 5, if supported in such manner that there is no possiility of accidental contact with the winding 4, need not be insulated for the line of the system.

Various modifications and other uses of apparatus embodying the general principles disclosed above will occur to those skilled in the art and, if within the scope of the appended claims, shall be considered within the scope of the present invention.

I claim as my invention:

1. An electrical distribution system comprising a circuit and a reactive impedance device in said circuit having a smaller impedance at a predetermined load current than for either smaller or larger currents.

2. An electrical distribution system comprising a transmission circuit of high capacity reactance and means for im roving the light-load regulation of the circuit, said means including an electrical discharge device coupled to the circuit.

3.-An electrical distribution system comprising a high-voltage circuit of such length that-its capacity reactance is relatively high and a plurality of spaced impedance devices therein, each of which has a variable impedance which is less at full-load current than when a relatively small current traverses the circuit, said impedance devices being so distributed along the circuit as to improve the li ht-load regulation of the system.

4. he combination of a two-electrode therpotential mionic device having a constantly energized cathode and connected to said secondary winding. I

6. A reactor-comprising a primary winding and a secondary winding so related thereto as to have a voltage induced therein in accordance with the current traversing said primary winding, and a continuously excited arc-discharge device connected to said secondary winding.

7. A reactor comprising a winding and a thermionic device in circuit therewith, means for altering the im edance of said reactor comprising means Ior establishing a magnetic field through said thermionic device.

8. Electrical controlling apparatus of the character described comprising a winding and a magnetically controlled thermionic device so related to said winding as to alter the impedance thereof depending upon the current traversing the said winding.

9. A reactor having an arc-discharge device operatively associated therewith and disposed in such relation thereto that the magnetic field of the reactor influences the impedance of said device.

10. In an alternatin -current circuit, a device including two indirctively related windings, one connected to said circuit, and a continuously excited electrical discharge device of the ionization type which breaks down and commences to discharge at a certain critical potential connected in series relation with the other winding.

11. In combination with a power line conductor, current-controlling apparatus embodying an electric discharge device spaced from but so disposed in relation to the line conductor that the impedance of the device is influenced by the magnetic field surrounding said conductor.

12. A variable-impedance device comprising two inductively related windings and an arc-discharge device embodying a heated cathode element, said arc-discharge device being connected to one of said windings.

13. A variable-impedance device comprising two inductively related windings, an arcdischarge device associated therewith and means for limiting the current traversing said arc-discharge device.

14. In an alternating-current circuit, a device including two inductively related windings, one connected to said circuit, and an electrical discharge device of the ionization type in which the discharge takes the form of an arc and which breaks down and commences to discharge at a certain critical potential connected in shunt relation with the other winding, said discharge device embody ing a heated cathode.

15. In combination with a power line conductor, current-controlling apparatus em-.

bodying an electric discharge device spaced from but so disposed in relation to the line conductor that the impedance of the device is influenced by the magnetic field surrounding said conductor, said device embodying a heated cathode.

16. Electrical controlling apparatus of the character described comprising a main winding, a secondary winding inductively related thereto and an arc-discharge device connected to said secondary winding, said device embodying a discharge ath and a heated cathodehfor ionizing at east a portion of said pat 17. Electrical controlling apparatus of the character described, comprising two inductively related windings and an arc-discharge device embodying a. solid ionizing cathode maintained at an elevated temperature, said device being connected in shunt to one of said windings.

18. In an electrical circuit, controlling means embodying a. space-discharge device comprising a heated cathode and arranged to interact on the circuit to affect the current flowing therein, said discharge device being of the type which has substantially infinite impedance for applied voltages below av predetermined value and a low impedance for a greater applied voltage.

19. In combination, an electric circuit, a reactor connected in said circuit, an electric discharge device connected in circuit with said reactor, means energized in accordance with the current in said circuit for establishing a magnetic field through said electric discharge device, additional means for establishing a magnetic field through said electric discharge device, and means for establishing an energizing circuit for said additional means when the current in said circuit is below a predetermined value.

20. In combination, an electric circuit, a reactor connected in said circuit, an electric discharge device connected in circuit with said reactor, means energized in accordance with the current in said circuit for establishing a magnetic field through said electric discharge device, additional means for establishing a magnetic field throu h said electric discharge device, a source of current independent of said electric circuit for energizing said additional means, and current responsive means in said circuit for connecting said additional means to said source of current when the current in said circuit is below a predetermined value.

In testimony whereof, I have hereunto subscribed my name this 25th day of November,

EARL R. EVANS.

CERTIFICATE OF CORRECTION.

Patent No. 1,770,334. I Granted July 3, 1930', m

' EARL R. EVANS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 46, beginning with the word "systems" strike out all to .and including the word "system" end of line 49, and insert instead system. Obviously the invention is not limited in its application to power-transmission systems but may also be applied to other systems; same page, line 75, for the word "increase" read increases; page 2, line 58, for the word "serve" read serves, and line 117, for "cathodes" read cathode; and that the I'said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 23rd day of September, A. D. 1930.

' M. J. Moore, (Seal) 1 Acting Commissioner of Patents.

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