US3519882A

US3519882A - Gas discharge tube with magnetic means for extinguishing the discharge

Info

Publication number: US3519882A
Application number: US770520A
Authority: US
Inventors: John Gowar; Kenneth George Cook
Original assignee: MO Valve Co Ltd
Current assignee: MO Valve Co Ltd
Priority date: 1967-11-03
Filing date: 1968-10-25
Publication date: 1970-07-07
Anticipated expiration: 1987-07-07
Also published as: GB1186453A

Description

t a i July 7, 1970 GQWAR ET AL 3 ,519,882

GAS DISCHARGE TUBE WITH MAGNETIC, MEANS FOR EXTINGUISHING THE DISCHARGE" Filed Oct. 25, 1968 2 Shets-Sheet' 1 l IIII 2Z\ 49 46 2g 2s- 1 5\: %?)47 @g 4 24 i' 2s 9 10 i8 5?; H l7 I: i2 q7 N 28 l8 8 F 8 I fl :1 W I I I I, V l Fig.1 1 v Q INVENTORS JOHN eowm KENNETH GEORGE COOK BY@M y Filed Oct. 25, 1968 July 7, 1970 I J. GOWAR ETAL GA S DISCHARGE TUBE WITH MAGNETIC MEANS FOR EXTINGUISHING THE DISCHARGE Load 2 Sheets-Sheet 2 Pulse Generaror INVENTORS J'OHN GIOWAR KENNETHEEORQE C OK United States Patent GAS DISCHARGE TUBE WITH MAGNETIC MEANS FOR EXTINGUISHING THE DISCHARGE John Gowar, Rickmansworth, and Kenneth George Cook, Northwood, England, assignors to The M-O Valve Company Limited, London, England, a British company Filed Oct. 25, 1968, Ser. No. 770,520

Claims priority, application Great Britain, Nov. 3, 1967,

Int. Cl. H01j17/14, 17/56 US. Cl. 315-340 11 Claims ABSTRACT OF THE DISCLOSURE A gas-filled device having an anode, a cathode and a battle structure, and means for producing a magnetic field. In the absence of the magnetic field a discharge may pass between the cathode and anode, but when the field is applied electrons emitted from the cathode are constrained by the magnetic field to follow paths obstructed by the baffle structure.

This invention relates to electric circuit interrupting devices.

Known electric circuit interruping devices operate relatively slowly and are therefore not suitable in applications where rapid operation is required, for example, for the protection of radio frequency oscillating valves in the event of the occurrence of a flash arc in the valve.

One way of overcoming this difficulty is to connect a so-called crow-bar device, typically a gas discharge device, in parallel with the device to be protected, which by-passes overload current around the device being protected until an associated interrupting device has had time to operate. However, this method has the disadvantage that the magnitude of the current to be by-passed may be very high, and where there are several devices to be protected operating from a common power supply, has the disadvantage that failure of one device results in all the other devices being by-passed as well.

Thus there is a need for an electric circuit interrupting device capable of operating at a higher speed than known devices, and it is an object of the present invention to provide such a device.

According to the present invention an electric circuit interrupting device includes an envelope containing a gas filling; an anode and a cathode housed Within the envelope; a battle disposed within the envelope between the anode and the cathode and allowing the passage of a discharge between the anode and the cathode; and means for producing a magnetic field whose lines of force extend Within the envelope in the region of and in the direction of the path of said discharge, the arrangement being such that with the magnetic field applied electrons emitted from the cathode are constrained to follow paths obstructed by the battle, thereby preventing the passage of a discharge between the anode and the cathode.

In the present specification the term gas filling is intended to include vapour filling.

-In a preferred arrangement in accordance with the invention the device further includes a grid electrode disposed between the anode and the bafile, adjacent the anode, which, when maintained at a negative potential with respect to the anode, allows the anode to be raised to a higher positive potential with respect to the cathode before a discharge between the anode and cathode occurs than would be the case in the absence of the grid electrode. With such an arrangement the grid electrode may cnveniently be utilsed to trigger a discharge between the anode and the cathode.

One circuit interrupting device in accordance with the invention will now be described by way of example, with reference to the accompanying drawing in which:

FIG. 1 is a sectional view of the device; and

FIG. 2 is a circuit diagram of a switching arrangement utilising the device shown in FIG. 1.

Referring to FIG. 1, the device has a generally cylindrical sealed glass envelope 1 containing a filling of hydrogen at a pressure of about 0.2 torr.

The envelope 1 houses an electrode structure including an anode 2, a grid 3, a cathode 4 and a bafile structure '5.

The cathode 4 is mounted on a metal base plate 6 which is disposed in a plane perpendicular to the axis of the envelope 1, near one end of the envelope 1. The base plate 6 is supported on six metal rods 7 which are sealed through the adjacent end of the envelope 1 and at their inner ends are sealed into tubular insulators 8 secured through the base plate 6. The cathode 4 of conventional form and comprised a hollow cylindrical impregnated body '9 which houses a spiral electrical resistance heater 10 and is coaxially surrounded by a tubular heat shield 11 having inwardly projecting fins 12 on its inner curved surface.

The anode 2 is in the form of a metal disc supported at one end of a metal rod 13 which is sealed through the end of the envelope 1 remote from the cathode 4, the rod 13 constituting a lead to the anode 2.

The grid 3 is in the form of a shallow circular cylindrical sheet metal box, the anode being housed within thegrid box 3 with the two planar ends 14 of the grid box 3 in parallel spaced relation with the anode 2, one on either side of the anode 2. The grid 3 is supported from a tubular glass sleeve '15 which forms part of the envelope 1 and coaxially surrounds parts of the rod 13.

In the planar end of the grid 3 nearer the cathode 4 there is formed an elongated rectangular slot 16, the axis of the envelope 1 passing through the centre of the slot 16.

The baffle structure 5 is made of mumetal sheet and is of hollow circular cylindrical form. The structure 5 is supported coaxial with the envelope 1, with one end closely adjacent the slotted end of the grid 3, by means of three metal rods 17 which extend perpendicularly between the cathode base plate 6 and the nearer end of the structure 5, the ends of the rods 17 being sealed into insulators 18 secured through the cathode base plate 6 and the relevant end of the baffle structure 5.

In each end of the baffle structure 5 there is formed a circular recess '19 or 20, the

recesses

19 and 20 being of the same depth and diameter.

In the side wall of the recess 19 there are formed eight equally spaced apart rectangular apertures 21, the lengths of the apertures 21 being parallel to the axis of the envelope 1. This end of the baflle structure 5 also carries a shallow, sheet metal cup-shaped member 22 having an aperture of somewhat larger diameter than the recess 13 formed in its base. The inner surface of the base of the member 22 is welded to the periphery of the outer surface of the anode end of the baflle structure 5, the side wall 23 of the member 22 extending towards the cathode 4 withits outer surface close to the inner surface of the adjacent part of the envelope 1. The purpose of the member 22 is to assist in the prevention of unwanted long path breakdown in operation.

In the base of the recess 20 there is formed a circular aperture 24 and between this aperture 24 and the cathode 4 there is disposed a circular metal plate 25 of slightly greater diameter than the aperture 24. This plate 25 is mounted from the adjacent end of the baffle structure 5 by means of metal brackets 26 so as to lie parallel to but spaced from the base of the recess 20, in register with the aperture 24. The plate 25 serves to inhibit contamination of the remainder of the electrode structure with material evaporated from the cathode 4 in operation.

The baffle structure 5 houses a coil of wire 27 which coaxially surrounds the space between the bases of the

recesses

19 and 20. The ends of the wire extend through apertures in the cathode end of the baffie structure 5 and the cathode base plate 6 and are connected to two of the rods 7 which serve as leads to the coil 27.

Others of the rods 7 serve as leads to the cathode heater 10.

The battle structure 5 and the grid 3 are provided with leads in the form of rods 28 and 29 :ealed through the side wall of the envelope 1.

In the absence of a current in the coil 27 the device operates in the manner of a conventional thyratron. With a suitable voltage applied between the anode 2 and the cathode 4 a discharge between the anode 2 and cathode 4 can be initiated by raising the grid 3 and the baffle structure 5 to positive potentials with respect to the cathode 4. Thereafter the potentials of the grid 3 and the bafile structure 5 have little control of the discharge and the discharge can only be extinguished by reducing the anode-to-cathode voltage.

However, when a suitable current is applied to the coil 27, the passage of the discharge between the anode 2 and the cathode 4 is prevented due to the electrons emitted by the cathode 4 being constrained to follow the lines of force of the magnetic field, produced by the current and therefore to be obstructed by the anode end of the baffle structure 5. In addition, the ions produced within the baflle structure are also constrained to follow the lines of force of the magentic field, and are therefore obstructed by the cathode end of the baffle structure 5 and the plate 25. As a result, insufficient ions are produced between the baffle structure 5 and the grid 3 to support a discharge. Since the balfie structure 5 is formed of mumetal, the magnetic field is substantially contained within'the bafile structure 5 and therefore does not extend to the region of the anode 2 where its presence would lead to long path breakdown.

One particular application of the device described above, by way of example, will now be described with reference to FIG. 2.

In this arrangement, the device 30 is connected in a circuit breaker arrangement for protecting a load 31 in the event of the load 31 drawing excess current from a power supply (not shown).

The anode 2 of the device is connected via the load 31 and a path through a pulse generator 32 to the positive terminal 33 of the power supply, the negative terminal 34 of the power supply being earthed. The pulse generator 32 is arranged to produce a pulse in the event of the current passing to the load 31 from the terminal 33 exceeding a predetermined value. This pulse is applied between the cathode and the grid of a conventional hydrogen thyratron valve 35, the cathode of the thyratron 35 being earthed.

The anode of the thyratron 35 is connected via an inductor 36 and two

resistors

37 and 38 in series to a suitable positive potential with respect to earth, and the junction between the

resistors

37 and 38 is connected via a capacitor 39 to one end of the coil 27 in the device 30. The other end of the coil 27 and the cathode 4 of the device 30 are earthed and the grid 3 and baffle structure -5 of the device are connected via

separate resistors

40 and 41 to one end of the secondary winding 42 of a transformer 43, the other end of the winding 42 being earthed.

In operation of the arrangement, after the power supply has been turned on, the supply of current to the load 31 from the power supply is initiated by the application of a pulse to the primary winding 44 thereby momentarily driving the grid 3 positive with respect to the cathode 4 and causing a discharge to pass between the anode 2 and the cathode 4. In the event of the current passing through the load 31 exceeding the predetermined value, the pulse produced by the generator 32 initiates a discharge in the thyratron 35. As a result, the capacitor 39 discharges via the coil 27, the anode-to-cathode path through the thyratron 35, the inductor 36 and the resistor 37, the discharge in the thyratron 35 extinguishing when the capacitor 39 has discharged. The resulting pulse of magnetic field produced in the device 30 caused the discharge in the device 30 to be extinguished so that current ceases to be supplied to the load 31. The supply of current to the load 31 may subsequently be re-established by the application of a further pulse to the primary 44 of the transformer 43.

In one arrangement which has been used in practice, the voltage provided between the

terminals

33 and 34 by the power supply is 7.5 kilovolts, and the pulse generator 32 is arranged to produce an output pulse when the current supplied to the load 31 exceeds 1 amp. The pulse supplied to the coil 27 is such as to produce a pulse of magnetic field in the coil 27 having a duration of 60 microseconds and a peak value of 1 kilogauss.

In alternative circuit breaker arrangements utilising switching devices in accordance with the invention, the magnetic field producing means in the switching device may be arranged to be energised by the current passing through the load protected by the circuit breaker arrangement, instead of by current derived from a separate power supply. With such and arrangement the magnetic field produced in the switching device is arranged to attain a sufficiently high value to extinguish the discharge in the switching device only when the the current through the load exceeds the maximum permissible value.

One particular application envisaged for circuit breaker arrangements utilising devices in accordance with the invention is for protecting loads constituted by electric discharge devices, for example, radio frequency oscillator valves.

We claim:

1. An electric circuit interrupting device including an envelope containing a gas filling; an anode and a cathode housed within the envelope; a bafile disposed within the envelope between the anode and the cathode and allowing the passage of a discharge between the anode and the cathode; and means for producing a magnetic field whose lines of force extend within the envelope in the region of and in the direction of the path of said discharge so as to constrain electrons emitted from the cathode to follow paths obstructed by the battle and thereby prevent the passage of a discharge between the anode and the cathode.

2. An electric circuit interrupting device as claimed in claim 1 wherein said baflle is of a material of high magnetic permeability.

3. An elelectric circuit interrupting device as claimed in claim 2 wherein said baffle surround said means for producing a magnetic field.

4. An electric circuit interrupting device as claimed in claim 3 wherein said bafile is of hollow cylindrical form with at least one aperture formed in each end wall thereof.

5. An electric circuit interrupting device as claimed in claim 4 wherein the end wall of the baffie nearer the anode has a recess formed therein, and the side wall of the recess has a plurality of apertures formed therein.

6. An electric circuit interrupting device as claimed in claim 5 wherein a plate of slightly greater dimensions than the aperture formed in the end wall of the bafile nearer the cathode is mounted parallel to but spaced from this end wall and in register with this aperture.

7. An electric circuit interrupting device as claimed in claim 1 wherein a grid electrode is provided, disposed between the anode and the baflle and adjacent to the anode which, when maintained at a negative potential with respect to the anode, allows the anode to be raised to a higher positive potential with respect to the cathode before a discharge between the anode and the cathode occurs than would be in the case in the absence of the grid electrode.

8. An electric circuit interrupting device as claimed in claim 7 wherein the grid electrode partially surrounds the anode.

9. An electric circuit interrupting device as claimed in claim 1 wherein the means for applying a magnetic field comprise a coil.

10. On electric circuit interrupting device including an envelope containing a gas filling; an anode and a cathode housed within the envelope; a 'bafile of hollow cylindrical form with at least one aperture formed in each end wall thereof, disposed within the envelope beween the anode and the cathode and allowing the passage of a discharge between the anode and the cathode; a grid electrode, disposed between the anode and the bafile and adjacent to the anode which, maintained at a negative potential with respect to the anode, allows the anode to be raised to a higher positive potential with respect to the cathode before a discharge between the anode and the cathode occurs than would be the case in the absence of the grid electrode; and means, comprising a coil housed within said baflle, for producing a magnetic field whose lines of force extend within the envelope in the region of and in the direction of the path of said discharge so as to constrain electrons emitted from the cathode to follow paths obstructed by the baffie and 6 thereby prevent the passage of a. discharge between the anode and the cathode.

11. A circuit breaker arrangement for protecting a load, comprising an electric circuit interrupting device as claimed in claim 1 connected in series with the load and with a power supply; and means for controlling said means for producing a magnetic field to produce a pulse of the magnetic field in the event of the current passing to the load exceeding a predetermined value, which pulse is of suflicient magnitude to extinguish a discharge in the device.

References Cited UNITED STATES PATENTS 1,962,158 6/1934 Smith 313161 X 2,217,186 10/1940 Smith 313l61 X 2,458,861 1/1949 Kohler 3l3161 X 2,497,911 2/1950 Reilly et a1 3l3204 X 2,543,227 2/1951 Buckingham 313-161 X 2,951,960 9/1960 Watrous 313204 X 3,435,287 3/1969 Jacobson 313-161 X JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R.