US2194145A - Lightning arrester - Google Patents

Description

Patented Mar. 19, 1940 UNITED STATES PATENT OFFICE LIGHTNING ARRE STER poration of Delaware Application July 28, 1937, Serial No. 156,040

4 Claims.

This invention relates to an improved lightning arrester, and is a continuation in part of my copending appln. Ser. No, 27,677, led June 21, 1935, which has matured into U. S. Patent No. 2,123,333, dated July 12, 1938.

An object of this invention is to simplify and improve lightning arresters of the gaseous discharge type.

Another object of this invention is to provide a lightning arrester which is particularly adapted for the protection of direct current circuits wherein it is necessary to limit the voltage peaks to as little as possible above the normal values.

Lightning arresters of the gaseous discharge type are well-known in the prior art for use in the protection of telephone and small power circuits; also, for radio antennas. However, the lightning arresters known in the prior art depend upon the minimum voltage drop through them being substantially greater than the normal voltage of the circuit to be protected so that the glow will extinguish itself after the disturbance has passed since the voltage required to start an arc is much higher than the minimum voltage drop. The circuit will then be protected only against voltages which were very much higher than normal, there being no protection against moderate voltage peaks, not greatly above normal.

To overcome this defect, I propose to provide an improved lightning arrester employing the principles disclosed in my Pat. #2,022,465, issued November 26, 1935, for an improved type of electrical vacuum pump for evacuating electron discharge devices which utilize electrical forces for eiecting evacuation. The evacuation process is accomplished by producing a direct current discharge through a tube or orifice between a vessel to be exhausted and the inlet to a mechanical pump, the discharge consisting chiefly of a ow of electrons in one direction and a flow of gas ions and molecules in the other direction. By choosing the proper electrode materials, dimensions, gas and gas pressure, I am able to start a discharge in my improved lightning arrester at voltages slightly above the normal operating voltage. To extinguish the discharge after the disturbance is passed, the gas distribution in the arrester will be changed by providing two separate chambers joined by a suitable aperture. The direct current flowing through the aperture then pumps the gas out through the aperture and from one chamber into another. The hardening or increasing of the vacuum in the aperture and in one chamber, caused by the pumping action, then (Cl. Z50-27.5)

increases the voltage drop through the aperture to the electrode in another chamber to extinguish the discharge and to reduce the probability of immediate reignition.

This invention will be more clearly understood by referring to the accompanying drawing, in which:

Fig. 1 shows a longitudinal sectional view of one form of this invention;

Fig, 2 is an end view of Fig. l;

Fig. 3 is a longitudinal cross-section of another iorm of this invention, and

Fig. 4 is a cross-section of Fig. 3, the section being taken along lines 3 3.

Referring now in detail to Figs. 1 and 2 of the drawing, an hour glass shaped envelope I contains two spherical electrodes 2 and 3, to 1%, in diameter, which are connected to end ferrules 4 and 5 by means of relatively stiff wires 6 and 1. The glass envelope is further protected by an outer cylinder 8 which is cemented to the end ferrules by any suitable cement 9. The outer casing 8 provides suitable protection against mechanical injury to the relatively fragile hour glass I and the metallic end errules provide for clip mounting similar to the manner in which an ordinary fuse is retained. The spherical portions of the hour glass shaped envelope l are approximately to 1% in diameter and are connected together by a narrow neck which is from to in diameter and from 1s-S to 1/2 long. The envelope is filled with a suitable gas such as, for example, argon, neon, helium, etc., having a pressure of :from 2 to 200 microns; with a suitable gas pressure and a 1% diameter neck, the arrester may handle an instantaneous discharge current of from about 2 to 200 amps., the critical value of current being dependent upon the size and shape of the neck and electrodes and upon the gas pressure.

In order that a discharge may be started consistently, and relatively easily in the presence of an overvoltage across the device, provision is made for positively maintaining some continuous ionization within the low pressure gas inside the envelope. To accomplish this a small amount of radioactive material 15A is painted on the envelope and enclosed by the embedding cement l5. For this purpose any of the well known radioactive salts may be used. In practice the radioactive luminous paints, used for marking watch dials, and other instruments which are to be rendered visible in the dark7 are easily obtainable and may be used.

In the operation of this device the dimensions and gas pressure are so adjusted that a normal operating voltage will not be sufficient to break down the gas between the electrodes. There will be electrons and ions in the gas, produced by bombardment from the corpuscles ejected from the radio active salts, but the electrical field will not be great enough to cause an unstable accumulation of electrons and ions, by free electrons and ions accelerating and colliding with molecules at a faster rate than electrons and ions are absorbed. In other words the dielectric strength of the gas between electrodes will be great enough to prevent' a short circuiting arc.

It now, the voltage across the device is subject to a transient increase, due to lightning, circuit switching, or any other cause the ionization will become cumulative and almost instantly allow a current to ow which will absorb the energy causing the transient over-voltage.

The iiow of current, due to the transient and to power current from the circuit will cause electrical pumping of gas out of the constriction between the chambers and from one electrode chamber to the other causing a momentary lack ol to maintain ionization in the constriction and in the chamber containing one electrode. Therefore the arc will be extinguished.

1i the over voltage persists the arrester will. break down repeatedly and then extinguishthe arc through itself. It will then carry an average current tending to lower the over-voltage. On the other hand, if theV over-voltage is only momentary, as is usually the case, the intermittent arcing through the arrester will cease as soon as the over-voltage has passed.

in the other embodiment shown. by Figs. 3 and t, the outer casing i2 is provided with a metal plug I3 for separating the two chambers, the pumping between the two chambers being accomplished by means of an aperture M of a suitable size, the electrodes 2 and 3 being connected to the end ferrules i and 5 in a similar manner to that mentioned above, and the spaces iii and I6 being filled with any suitable cementing compound.

This latter modication is suitable for protecting circuits where the strength and duration of the excess voltage is normally greater than the voltage in the arrester, as shown in Figs. l and 2, for the reason that the metal plug I3 will withstand a much heavier voltage discharge without being damaged or destroyed than will the glass neck ifi. It might seem that the metal plug i3 would tend to divide the arrester into two separate discharge tubes; and that no voltage discharge would go through the aperture lll. However, I have Afound that this is not the case. Also as explained in connection with Fig. 2 of the above-mentioned patent application wherein a hole through the metal will also function as an orlcc for my vacuum pump, if desired, more than one orihce, in series, may be used in the arrester of Figs. l and 2 in order to increase the arc-quenching effect. Likewise, more than one plug and orifice may be used in the arrester of Figs. 3 and Il in order to obtain a greater ratio of quenching voltage to break down voltage and greater heat storage capacity in the arrester.

In applying the arrester to electrical circuits it is fundamentally only necessary to connect the arrester between two points in a circuit which are to be protected from over-voltages. However, in each case, a choice must be made of arrester dimensions, kind and pressure of inert gas and electrode materials in order to obtain optimum circuit protection.

In manufacturing the arrester a series of dimensions may be standardized and the arresters of any one size may be adjusted for voltage breakdown by first pumping a very high vacuum in the Vessel, While the electrodes and envelope are heated to drive out occluded gas-es. Then, after cooling, the desired breakdown voltage between electrodes is applied and the inert gas such as argon, neon, helium, nitrogen, etc., slowly admitted until a breakdown occurs between electrodes. The arrester is then sealed oil at this pressure, and is assembled in the protective covering after which it is ready for use.

In service the operation of the arrester may be improved by paralleling it with a condenser. The condenser itself helps to absorb very short transient over-voltages and it bypasses or short circuits the alternating current component of current through the arrester when the arrester is forced to carry current for an appreciable time so that it res and cuts oiT rapidly. Due to the condenser the arrester itsel is prevented from setting up transient voltages in the circuits. I have also found that the presence of a condenser makes the cut-off of current through the arrester more positive. This may be because the condenser discharge adds to the current through the arrester to increase the pumping and then holds down the arrester voltage at the instant the arc is extinguished.

Although only two exemplified embodiments ci' this improved lightning arrester have been disclosed, it is to be distinctly understood that other modifications will readily suggest themselves to those skilled in the art; therefore, this invention should not be limited except in accordance with such limitations as are clearly imposed by the appended claims.

What is claimed is:

l. A direct current lightning arrester having operating means to start a discharge at a voltage surge which is slightly above the normal operating voltage of a circuit and to extinguish said discharge when the voltage surge is passed, said operating means comprising a sealed insulating casing i'llled with a gas under pressure, two spherical electrodes located within and supported by said casing, said casing following the contour of said electrodes and being divided into two separate chambers with a narrow neck between said chambers to provide uid communication between each chamber so that the gas distribution in said chamber will be changed by the direct current discharge flow which pumps said gas through said neck from one chamber to another and increases the vacuum to extinguish said discharge.

2. A direct current lightning arrester having operating means to start a discharge at a voltage surge which is slightly above the normal operating voltage of a circuit and to extinguish said discharge when the voltage surge is passed, said operating means comprising a sealed insulating casing lled with a gas under pressure, two spherical electrodes located within and supported by said casing., said casing following the contour of saidk electrodes and being divided into two separate chambers with a narrow neck between said chambers to provide luid communication between each chamber so that the gas distribution in said chamber will be changed by the direct current discharge flow which pumps said gas-through said neck from one chamber to another and increases the vacuum to extinguish said discharge.

3. A direct current lightning arrester having operating means to start a discharge at a voltage surge which is slightly above the normal operating voltage of a circuit and to extinguish said discharge when the Voltage surge is passed, said operating means comprising a sealed insulating casing iilled with a gas under pressure, two spherical electrodes located within and supported by said casing, said casing following the contour of said electrodes and being divided into two separate chambers with a narrow neck between said chambers to provide fluid communication between each chamber so that the gas distribution in said chamber will be changed by the direct current discharge flow which pumps said gas through said neck from one chamber to another and increases the vacuum to extinguish said discharge, and a second insulating casing enclosing said first mentioned casing having an aperture located adjacent the narrow neck in said iirst mentioned case.

4. A lightning arrester comprising an envelope containing two spherically shaped discharge electrodes, means providing constricted gaseous communication between two chambers within said envelope, said means being interposed between said electrodes, and a quantity of gas within the envelope, the pressure of said gas being such as to initiate electrical discharge at a Voltage surge winch is measurably above a normal operating voltage diierence between said electrodes due to the circuit connections thereof, the first said means being further characterized in reizt-tion to said quantity of gas so that the gas pressures in the two chambers are unbalanced by a direct current discharge between said electrodes, whereby an increase in the resistance per unit length of the discharge path in one of the chambers becomes effective to extinguish said discharge.

CLARENCE W. HANSELL.

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