US2093310A - Electric circuit - Google Patents

Description

Sept. 14, 1937. M CURRIER 7 2,093,310

ELECTRI C G IRCUIT Filed Feb. 1, 1936 Inventor:

Qphilip M. Currier.

by A ttOTTW e g Patented Sept. 14, 1937 PATENT OFFICE ELECTRIC CIRCUIT Philip M. Currier, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York Application February 1, 1936, Serial No. 61,935

15 Claims.

My invention relates to electric circuits and more particularly to' a protective system for three-wire distribution circuits.

Three-wire circuits represent a relatively economical way of transmitting and distributing both alternating and direct current. It sometimes happens, however, that these circuits are provided with a relatively small amount of power supply equipment between the neutral conductor and the two outer conductors. As a result such circuits often have badly unbalanced voltages, as for example when a short circuit occurs between one of the outer conductors and the neutral.

In accordance with my invention I provide a novel system for automatically and without the use of moving parts preventing the occurrence of excessive voltages or voltage unbalance on a three-wire circuit. I wish it to be understood, however, that some of the features of my invention are not limited to three-wire circuits and are capable of general application. For example, one feature of my invention is a novel circuit for stopping the current flow through an arc discharge device. This is done by applying a high enough inverse potential to the device through a substantially discharged capacitor.

An object of my invention is to provide a novel automatic overvoltage protective system.

Another object of my invention is to provide a. new and improved vacuum tube control circuit.

A further object of my invention is to provide a novel vacuum tube type protective system.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, I have shown therein diagrammatically an embodiment of my invention applied by way of example, to a direct current three-wire circuit consisting of a positive outer conductor I, a negative outer conductor 2 and a neutral conductor 3. This circuit is shown as being energized by an ordinary constant voltage three-wire generator.

For preventing excessive voltage between the positive outer conductor l and the neutral conductor 3 there is connected between these conductors a vacuum tube 4. This tube may be of any of the several types well knownin the art, but I prefer to use a vapor or gas filled are discharge type tube because of its lower voltage drop at relatively high current. This tube is provided with a cathode 5 connected to the neutral conductor and an anode 6 which is connected to the positive conductor, preferably through a resistor l which serves to limit the current through the tube. Resistor I also performs another function to be described later in connection with the control of the tube for rendering it nonconductive after it has become conductive. The tube 4 is also preferably but not necessarily provided with a control element 8 which is shown by way of example in the form of a grid and suitable means such as a bias battery 9 is provided for applying a negative bias potential to the control element 8 with respect to the potential of the cathode 5 so as to control the proper starting or conductivity of the tube. In order to control the stopping or nonconductivity of the tube 4 there is provided a capacitor I0 connected between the negative outer conductor and the anode 6.

In operation and assuming that the three-wire circuit is energized by a suitable source of supply, the bias battery 9 is arranged to produce a negative potential on the grid 8 which is sufficient to prevent the tube 4 from breaking down and passing current at all voltages between the positive outer conductor I and the neutral conductor 3 up to a predetermined maximum voltage, which may be slightly above the normal voltage. However, if the potential between the positive outer conductor I and the neutral conductor 3 exceeds this maximum voltage the negative potential on the grid 8 will be insufficient to prevent the tube from breaking down and passing current. Assume now that this maximum voltage is exceeded as the result of a short circuit, indicated at X, between the negative outer conductor 2 and the neutral conductor 3. With a low resistance short circuit the potential of the neutral conductor 3 becomes substantially the same as the potential of the negative conductor 2 so that substantially double voltage is applied between the positive outer conductor l and the neutral conductor}. Consequently, the tube 4 breaks down and passes current and as the arc drop in the tube 4 is relatively small, the amount of current that passes through the tube will be controlled by the value of the resistor 1. The total resistance of the tube 4 and resistor I may be made so low that the amount of current passed through them puts such a load between the positive outer conductor I and the neutral 3 that the voltage between these conductors is prevented from rising very much above the normal value.

While the short circuit is maintained, the capacitor I0 is in effect connected across the vacuum tube 4 through the short circuit and as the arc drop in the tube is relatively low the capacitor 4 will be substantially discharged during this time. If now the short circuit is removed the potential of the negative outer con- 5 ductor 2 will be more negative with respect to the neutral 3, than the potential of the anode 6 is positive, with respect to the neutral 3, because of the voltage drop in the resistor 1. Consequently, a sufficiently high inverse potential will 'be applied through the substantially discharged capacitor lll to the anode 6 to make this anode momentarily more negative than the cathode 5 and thereby extinguish the arc in the tube 4 and stop the flow of current there- 15 through. After the condenser 'Hl has become charged it prevents any further flow of current from the negative outer conductor 2 to the anode 6 or to the positive conductor I through the resistor 1. The circuit will then have re- 20 turned to its original condition and be ready for another operation in case of another short circuit betweenthe outer negative conductor 2 and the neutral conductor 3. r I As the function of capacitor I is to stop the conductivity of tube 4 it is only necessary in cases where tube 4 is of the type in which the grid 8 loses control once current flow has started.

It may be that in some cases the mere increase in anode potential of a tube with a fixed 30 negative grid bias is not a sufficiently reliable way to control the starting of the tube 4. In such cases an auxiliary electroresponsive device in the form of a voltage sensitive relay I I may be connected between the negative outer conductor 2 and neutral conductor 3 so as normally to maintain the grid circuit completed but When the voltage between the negative outer conductor and the neutral conductor falls to arelatively low value, as when a short circuit occurs, this 40 relay II will open its contacts thereby in effect increasing the potential of the control element 8 in a positive direction with respect to the oathode 5. This will therefore render the tube more easily conductive at any given anode voltage and possibly more reliable means for starting conductivity of thetube is assured.

A similar set of elements is provided for protecti ng against over-voltage between the negative outer conductor 2 and the neutral 3. As shown they comprise a second vacuum tube l2 whose anode I3 is connected to the neutral conductor 3 and whose cathode I4 is connected to the negative outer conductor through a resistor I 5. A control element l6 for the tube I2 is con nected to the cathode l4 through the negative bias battery I! and connected between the oathode l4 and the positive outer conductor is a capacitor IS. A voltage responsive bias controlling relay IQ is connected between the outer positive conductor and the neutral conductor of the three-wire circuit. I V

The operation of these elements is just the same as the operation of the previously described elements for' protecting against overvoltage between the positive outer conductor and the neutral 3 and should be obvious to those skilled in the art. Briefly it is such that when a' tube 12, now applies to the cathode M a potential which is more positive than the potential already applied to the cathode is negative so that momentarily the cathode [4 becomes positive with respect to the anode l3 thereby extinguishing the arc in the tube and allowing it to deionize so that it will be nonconductive at normal voltage.

While the particular circuit which I have shown and described above is only adapted for operation with direct current three-wire circuits, it should be obvious to those skilled in the art that essentially my circuit is not limited thereto and that it can also be applied to alternating current three-wire circuits in which case either one tube could be used to conduct alternate half cycles during an overvoltage condition or two tubes could be connected back to back between each outer conductor and the neutral so as to conduct both half cycles of current during overvoltage. While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled .in the art that changes and modifications may be made therein and therefore, I aim in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the'United States, is:

1. In a system of distribution, a three-wire circuit having a pair of outer conductors and a neutral conductor, and means responsive to a predetermined voltageunbalance on said threecircuit having a pair of outer conductors and a neutral conductor, separate variable'impedance conducting paths connected respectively between the neutral conductor and each of the outer cone ductors, means responsive to unbalanced voltage conditions on said circuit for increasing the conductivity of the conducting path between the neutral conductor and the outer conductor at the greater potential difierence from the neutral conductor, and means responsive to the restoration of substantially balanced voltage conditions on said three-wire circuit for interrupting the current flow through the conducting path whose conductivity has been increased.

4. In a system of distribution, a three-wire circuit having a pair of outer conductors and a neutral conductor, .and means including a normally nonconducting vacuum tube connected between one of said outer conductors and the neutral conductor for providing a relatively lowresistance 1 conducting path in response to an abnormally high voltage between the conductors between which said tube is connected. g

5. In combination, a three-wire circuit having a pair of outer conductors and a neutral conductor, means including a normally nonconductingvacuum tube for providing a relatively low resistance conducting path between one of said outer conductors and the neutral conductor inresponse to unbalanced voltage conditions on said circuit causing the voltage betweensaid neutral conductor and the outer conductor to which said tube is connected to be abnormally high, and means responsive to the restoration of balanced voltage conditions on said circuit for rendering said tube nonconducting.

6. In combination, a three-wire circuit having a pair of outer conductors and a neutral conductor, means including an arc discharge device having an anode, a cathode and a control element, said anode and cathode being connected between one of the outer conductors of said three-wire circuit and the neutral thereof, and means responsive to the efiect of a condition of said circult causing the voltage between the outer conductor and the neutral to which said anode and cathode are connected to be abnormally high for increasing the potential of said control element with respect to the cathode in a positive direction.

7. In combination, an arc discharge device provided with an anode and a cathode, a source of direct potential connected in circuit with said anode and said cathode for maintaining a current flow therebetween, and means for stopping said current flow comprising a source of inverse potential which is higher than the potential between the anode and cathode which maintains said current flow and a substantially discharged capacitor through which said inverse potential is applied between said anode and cathode.

8. In combination, an arc discharge device provided with an anode and a cathode, a source of direct potential connected in circuit with said anode and cathode for maintaining a current flow therebetween, and means for stopping said current flow comprising a source of inverse direct potential which is higher than the potential between said anode and cathode which maintains said current flow and a substantially discharged capacitor through which said inverse potential is applied between said anode and cathode.

9. In a system of distribution, a three-wire direct current circuit, a vacuum tube and a resistance connected in series between the neutral and one of the outer conductors of said circuit, and a capacitor connected between the other outer conductor of said circuit and a point between said resistance and said vacuum tube.

10. In a system of distribution, a three-wire direct current circuit, an arc discharge device having electrodes including an anode and a cathode, a resistor, said vacuum tube and resistor being connected in series between the neutral and one of the outer conductors of said circuit in such a way that one of said electrodes is connected to the neutral and another of said electrodes is connected to said resistor and said anode is positive with respect to said cathode, and a capacitor connected between the other outer conductor of said circuit and the electrode connected to said resistor.

11. In a system of distribution, a three-wire direct current circuit, an arc discharge device having an anode, a cathode and a control element, a resistor, said vacuum tube and resistor being connected in series between the neutral and one of the outer conductors of said circuit in such a way that one of said electrodes is connected to the neutral and another of said electrodes is connected to said resistor and said anode is positive with respect to said cathode, a capacitor connected between the other outer conductor of said circuit and the electrode connected to said reresistor, said vacuum tube and resistor being connected in series between the neutral and one of the outer conductors of said circuit in such a way that one of said electrodes is connected to the neutral and another of said electrodes is connected to said resistor and said anode is positive with respect to said cathode, a capacitor connected between the other outer conductor of said circuit and the electrode connected to said resistor, and electroresponsive means responsive to an eflfect of an unbalanced voltage condition on said three-wire circuit which causes the potential between the neutral and the outer conductor to which said resistor is connected to be abnormally high for increasing the potential of said control element with respect to said cathode in a positive direction.

13. In a system of distribution, a three-wire direct current circuit having positive and negative outer conductors and a neutral conductor, a pair of parallel circuits each including a resistor and a capacitor in series connected between said outer conductors in such a manner that the resistors are connected respectively to the positive and negative outer conductors and the capacitors are connected respectively to the negative and positive outer conductors, and a pair of arc discharge devices connected respectively between intermediate points of said parallel circuits and said neutral conductor in such a manner that their anodes are normally positive with respect to their cathodes.

14. In a system of distribution, a three-wire direct current circuit having positive and negative outer conductors and a neutral conductor, an arc discharge device having an anode, a cathode and a control element, a resistor for connecting said anode to said positive outer conductor, said cathode being connected to said neutral conductor, a capacitor connected between said anode and said negative outer conductor, a second arc discharge device having an anode, a cathode and a control element, a second resistor for connecting the cathode of said second device and said negative outer conductor, the anode of said second device being connected to said neutral, a second capacitor connected between the cathode of said second device and said positive outer conductor, and means for applying negative potentials to said control elements with respect to their associated cathodes which are sufliciently high to prevent starting and conduction through said devices at normal potentials between said neutral and said outer conductors but which permits the starting of said conduction at potentials substantially higher than said normal potentials.

15. In a system of distribution, a three-wire direct current circuit having a positive and a negative outer conductor and a neutral conductor, an arc discharge device having an anode, a cathode and a control element, a resistor for connecting said anode to said positive outer conductor, said cathode being connected to said neutral, a capacitor connected between said anode and said negative outer conductor, a second arc discharge device having an anode, a cathode and a control element, a second resistor for connecting the cathode of said second device to said negative outer conductonthe anode of said second device being connected to said neutral, a

second capacitor connected between the cathode of said second devi'ce and said positive outer conductor, and'means for varying the bias potential applied to one of said control elements in accordance with changes in voltage between one of said outer conductors and the neutral conductori 1 PHILIP M. CURRI ER."

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