US1716155A - Vacuum-responsive glow-tube control for rectifiers - Google Patents

Description

L. SMEDE VACUUI RESPONSIVE GLOW TUBE CONTROL FOR RECTIFIERS Filed Augr. 6, 1927 ATTORNEY Patented June 4,1929,

UN1TED STATES 1,716,155 PATENT OFFICE.

TBIC MANUFACTURING COMPANY,

A CORPORATION 0F PENNSYLVANIA.

VACUUM-RESPONSIVE GLOW-TUBE CONTROL FOB RECTIFIERS.

Application led `August: 6, 1927. Serial No. 211,104.

My invention relates to vacuum-responsive devices, and it has particular relation to means for obtaining an indication of an increase in gas pressure in an evacuated vessel.

The principal object of my invention is to provide means utilizing a glow-discharge dcvice which is responsive to the vacuum in question and which breaks down upon the attainment of a predetermined gaseous pressure, as a means for obtaining an automatic response to a change in the degree of vacuum existing in an evacuated vessel.

A further object of my invention is to provide an auxiliary means, associated with the means just mentioned, for the purpose of operating in response to still further increases in the gas pressure and before the glow-discharge device ceases to discharge as a result of said increased gas pressure.

With the foregoing and other objects in view, which will be readily understood from the following description and claims, my invention consists of the lovel features and' combinations hereinafter described and claimed and illustrated in the accompanying drawing, wherein Figure 1 is a diagrammatic view of circuits and apparatus embodying my invention in a preferred form, some parts of the device being indicated in section and other parts being indicated diagrammaticall Fig. 2 is a curve diagram which will be subsequently referred to;

Fig. 3 is a bottom plan view of the central portion of the bottom electrode of my improved glowedischarge device; and

Fig. 4 is a cross-sectional view of a differentform of glow-discharge device.

My invent-ion is particularly adapted to the automatic control of a metaLtank mercury-arc rectifier. which is indicated at 4 on the drawing. The rectifier is supplied with energy, in the usual way, from the secondary member of a main transformer 6 which is energized through a high-tension oil switch 8. The oil switch is provided with closing and opening coils 9 and 10, respectively. The rectifier tank is either continuously or intermittently evacuated by means of a pumping system which is connected at 11, so as to operate normally at a gas pressure no greater than a few microns of mercury. The pumping system is not shown in detail, as any known or desired mechanism Afier tank by means of a pipe 14.- The for such purpose may be utilized within the spirit lof my invention.

I have provided a novel glow-discharge mechanism 13 which is connected to the rectilow discharge device consists of upper and lower electrodes 15 and 16, each comprising a base portion 17 and .18 and a flat-topped central nob or projectlon 19 and 20, respectively, the two projections extending toward each other and separated by any desired distance such as an inch or less. For convenience in manufacture, the bottom electrode 16 is made in two pieces, the central knob portion 20 being made in the form of a separate plug having a depending projection 21 fitting into the pipe 14. The two electrodes 15 and 16 are held in spaced relation by a tubular insulating member 23, which may be of glass or porcelain, and which surrounds the knobs 19 and 2() with as close a fit as is mechanically feasible, for a purpose to be hereinafter mentioned. The tubular insulating member 23 is spaced from the base members 17 and 18 of the respective electrodes by means of rubber gaskets 24, or other means for effecting a vacuum-tight joint, said gaskets being compressed by means of insulated bolts 25. The problem of effecting a good vacuum-tight joint is very simple because the device always operates at room temperature.

An electromotive force of the order of 500 to 5000 or more volts is applied across the electrodes 15 and 16 by means of a step-up transformer 28 which may be provided with voltage-changingmeans 29 for the purpose of adjusting the pressure at which the glowdischarge device begins to operate. In the embodiment of my invention shown in the' drawings, the step-up transformer 28 is energized from the auxiliary 11G-volt alternating-current bus 3() of the rectifier station.

When a glow-discharge device operates under variable conditions of voltage, vacuum and electrode-spacing, different break-down voltages are obtained for different voltages, gas pressures and electrode spacings, according to the gaseous ionization in the space between the electrodes. If the vacuum is suiciently high, the electrons, in passing from one electrode to the other under the influence of the electrostatic field or applied voltage, do not encounter enough gas molecules to produce the ionization necessary to ization by collision. y

In Fig.2, I have plotted a curve 33 showinitiate the glow discharge. On the other hand, if the gas pressure, or number of gas molecules, is `too great, the electrons are stopped by collisions with gas molecules before the electrons have had an opportunity to attain a velocity necessary to produce 1oning the relation of the break-down voltage to the air pressure, in a particular gap device having electrodes spaced about one inch apart, although it will be understood that I am not limited to the specific values so indicated. It will be noted that, for the higher vacua, or low pressures, itl requires relatively high voltages to break down the gap. As the pressure increases, the breakdown voltage rapidly falls to a minimum break-down voltage which may be of the order of 360 volts, and as the air pressure still further increases, the break-down voltage again rises, but at a more gradual rate.

For gaps which are spaced a. greater distance than that corresponding to the curve 33, or for points along the sides of the electrodes which are spaced a. greater distance apart, the ga breaks down at lower air pressures, as indicated by the dotted-line curve 34, because of the greater opportunitiesfor collision which are obtained by reason of the longer distance which an electron travels in passing from one electrode to another.' It is noted that the same minimum discharge voltage is obtained with the different spacingV of the electrodes, but that in every case any given break-down voltage is obtained at a lower air pressure for the more widely separated gap electrodes.

It is for the reason above explained that I have constructed my electrodes 15 and 16 with e'ective portions 19 and 20 which fit as closely as possible into the tubular insulating members 23, in order te prevent the break- .ing down of the gap by reason of the variable discharge distances of electrons attempting to pass from the sides ot' one electrode to the sides of the other.

In like manner,I have provided the central plug near 20 of my lower electrode with a slot 37 extending up to a point above the flange or base member 18 of the lower electrode, as shown in Figs. 1 and 3, in order to provide a restricted tortuous path connecting the gap space with the pipe 14, or, in general, a path within which no electrictield lexists and so shaped as to collect all ions and electrons, so that electrons cannot travel from the upper electrode 19 to points at various distances along the inside of the pipe 14.

In order Ato provide an indication of the' break-down of thedischarge gap, I have provided an electro-responsive relay 40, which may be a current relay or, as shown in the drawing, a watt-responsive relay,

only of the order of which closes a contact 41 in response to the small amount of energy which is consumed in .the glow-discharge device when a glowdischarge current is passing therethrough.

The relay is preferably placed in the primary circuit of the step-up transformer 28 because of the largercurrents therein available, the secondary discharge currents being a few milliamperes at some 5000 volts. The relay 40 is also pref- 75 erably of a sluggishly acting type because, when the glow discharge device begins to operate, the discharge lick'ers somewhat and it is desirable to prevent the relay from opening and closing a large number of times before it finally moves to its steady-state position.

The relay Contact 4 1, when closed, is utilized to energize the opening coil 10 of the main switch 8, to shut down the rectifier in S5 response to a predetermined rise in the gas pressure within the rectifier tank.

The closing of the contact member 41 also energizes a lock-out relay 42 which deenergizes the closing coil 9 of the main switch 8, said closing coil having a supply conductor 43 which leads to the control equipment (not shown) provided at the sub-station.

In operation, the rectilier may be shut down by the glow-responsive relay 40 if the 95 pressure increases to any predetermined value such as that corresponding to a mercury column of 15 or 20 microns.

It will be observed that the particular preferred form ofglow-discharge device which I have designed, is made of massive iron parts and a massive tubular insulator member such as the insulators used in the rectiier tank itself. It is evident, therefore, that I haveI provided a vacuum-measuring device 13 which is no more susceptible to breakage or injury than the anode holders oi the rectifier itself.

While I have shown my glow-discharge device as being located on a pipe which bends out from the tank, it will be understood that such illustration is only for convenience in showing the apparatus in as single ligure. In an actual rectifier tank, the glow-discharge device is located above the top plate of the tank, either between two of the anodes or within the circle of the anodes of the tank. v

It will be noted from. Fig. 2, that with nearly 5000 volts electrical pressure applied to the electrodes, my glow-discharge device will break down when the air pressure rises initiated, becomes higher than the applied discharge is discontinued.

If a rectifier is shut down by the operay tion of m relay 40, in response to poor vacuum con itions such las may be caused by a leak, it may be that during theinterval in which lthe cause of shut-down is being investigated by the attendants of the plant, the pressure may increase beyond the point 45, so that the relay 40 opens and either automatically starts the tank again or at least permits the tank to be started in case an attempt should be made thereafter to restart the rectifier.

In the actual installation, as I have designed it, the operation of the relay 4()l is utilized to trip out the trip coil of a master controller such that the plant cannot be a ain started without manual manipulation, ifg the vacuum is so poor as to cause the operation o the said relay 40, and it is expected that no operator will attempt to restart the rectifier without assuring himself as to the proper vacuum conditions.

However, to make the device absolutely fool-proof, it is possible to add an attachment which is responsive to pressures of the order of one-half millimeter ora millimeter of mercury, in order to operate at a point, as indicated at 46 in Fig. 2, while the glowdischarge device is still vfunctioning and before the glow is interrupted by an increase in pressure beyond the point in Fig. 2. Such a device may be a simple manometer or mercury switch, as indicated at 47 in Fig. 1,

in which a mercury column 48 spills over and makes contact with a second mercury1 column 49 in response to excessive increases in the gas pressure to be measured. By this means, a circuit 50 is established to the lockout relay 42 hereinabove described.

lVhile I have described a form of glowdischarge device 13 substantially as I have constructed it in actual practice, it may be found that it will have more constant operating characteristics by being constructed on the point-to-cylinder discharge principle, as indicated by way of example, in Fig. 4, wherein a cup-like metal electrode is provided instead of the solid electrode 20 of Fig. 1, the other electrode being an axially depending wire 61 which is tightly enclosed by an insulating sleeve 62, except for the extreme tip 63 ot the wire, which is exposed. A tip 64 of carbon or graphite is preferably pushed over the wire tip 63 in orderto'preserve its life. The glow-discharge space is connected to the pipe 14a by a tortuous path 37 It will be understood that the construction, in Fig. 4, is otherwise similar to that shown in Fig. 1.

In operation, the glow-discharge device of Fig. 4 provides a very sharp breakdownv at, or near, the surface of the point or small electrode 64. By reason of the highly concentrated field in the region of the point electrode, the device may be found to be much more sensitive to changes in pressure than a device in'whioh the field is uniform, although the latterv device has proved to be successful in operation. A peculiarity of the operation of the point-discharge device, which may, in some respects, be considered disadvantagcous, is that it is a rectif ing device and hence, unless two oppositely conducting devices are utilized, re uires a somewhat more slowly acting, an hence more expensive, relay than the non-rectifying glow-discharge device 13 of Fig. 1, 1n order to prevent chattering upon the occurrence of a discharge.

While I have speciiically described and explained my invention in relation to a particular form of embodiment, I desire to be understood that such particular description and explanation is only suggestive and not intended by way of limitation. It is desired, therefore, that the appended claims shall be accorded the broadest interpretation consistent with their language and the prior art.

I claim as my invention:

1. A vacuum-responsive mechanism comprising a glow-discharge device having spaced electrodes operating in the vacuum in question, a source of electromotive force higher than the minimum glow-discharge breakdown voltage applied to said electrodes, the applied electromotive force and the electrode spacing being such that no glow discharge can take place during normal vacuum conditions, and electrical-energy responsive means for operating in response to the flow of a glow-discharge current in said glow-discharge device.

2. The combination with a vessel n ormally having a vacuum corresponding to a gas pressure no greater than a few microns of mercury, of a mechanism associated therewith and responsive to a predetermined in crease in the gas pressure therein, said mechanism comprising a glow-discharge device having spaced electrodes operating in the vacuum in question, a source of electromotive force higher than about 360 volts applied to said electrodes, the ap lied electromotive force and the electro e spacing being such that no glow discharge can take place during normal vacuum conditions, and electrical-energy responsive means for operating in response to the flow of a glowdischarge current in said glow-discharge device.

3. The combination with a vessel normally having a vacuum corresponding to a gas pressure no greaterthan a few microns of mercury, of a mechanism associated therewith and responsive to a predetermined increase in the gas pressure therein, said mechanism comprising a glow-discharge device having spaced electrodes operating in the vacuum in question, a source of electromo-` tive force higher than about 360 volts applied to said electrodes, the applied electromotive force and the electrode spacing being such that no glow discharge can take lplace during normal vacuum conditions, electrical-energy responsive means for operating in response to the flow of a glow-discharge current in said glow-discharge device, and additional means operating in response to still further increases in the gas pressure and before the glow-discharge device ceases to member,

discharge as a result of said pressure.

4. A vacuum-responsive mechanism adapted to operate in response to an increase in gas pressure above values corresponding to a relatively good vacuum, said mechanism being characterized by having two electrodes, a tubular insulating member separating said electrodes, a vacuum-tight joint between each electrode and said insulating and a pipe connected to the discharge gapv through a path within which substantially no electric field exists, said path being tortuously shaped whereby it will collect all ions and electrons.

5. A vacuum-responsive mechanism adaptincreased gas i ed to operate in response to a change in gas pressure, said mechanism being characterized by having two electrodes, each having a base portion and a fiat-topped central knob or projection extending toward the other electrode, a tubular insulating member separating the base portions of said electrodes and closely surrounding said knobs, a vacuum-tight joint between each electrode and said insulating member, and a pipe connected to the discharge gap through a restricted, tortuous path.

, 6. A vacuum-responsive mechanism 'comrprising a glow-discharge devicehavingr spaced electrodes operating in the vacuum a source of electromotive force' about 360 volts appliedto said slow acting 'electrical relay for f 1n question, higher than electrodes, a operating in response to the How of a glowdischarge current in said glow-discharge device, and apparatus arranged and adapted to be controlled in response to said relay.

A vacuum-responsive mechanism comprising a glow-discharge device having electrodes operating in the vacuum in question,

- a sourceof electromotive force higher than about 360 voltsl applied to said electrodes, a sluggishly responsive electrical relay for operating in response to the iow of a glowdischarge current in said glow-discharge'device, means for varying the electromotive force of the said source, and apparatus arranged and adapted to be controlledin response to said relay.

8. The method of utilizing a glow-discharge device which is connected to a highly evacuated vessel for the purpose of securing anfindication of poor vacuum in said vessel which comprises the application to said glow-discharge device of a voltage which is just sufficient to cause break-down'of the glow-discharge device at the poorest permissible vacuum in said vessel, and obtaining an indication of the occurrence of any glow discharge which takes place in case the vacuum' becomes poorer than said predetermined amount.

In testimony whereof, I have hereunto subscribed my naine this 3rd day of Au` gust, 1927. i

LLOYD SMEDE.

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