US1734208A - Lightning-arrester unit - Google Patents

Description

Nov. 5,- 1929.

Wwf-f" CROSS RFERENCE L.R. HDLLIH}AY LIGHTNING ARRESTERUNIT med Jan. 2o. 192s y mm mm Pig. 1.

\ MW@ mi@ EXAMINER INVENTOR I .wvence R .l Golladay AToRNEY Patented l Nov.4 5, 1929 UNITED 'STATES PATENT OFFICE LAWRENCE l. GCLLADAY, OF 'WILKINSBUBIL PENNSYLVANIA, ASSIGNOR T0 WEST- INGHOUSE ELECTRIC MANUFACTURING COMPANY, A CORPORATION F PENN- LIGHTNING-ARRESTEB UNIT Application med January 2o, 1923. serial nu. slaaas. n"

My invention relates to excess voltage pro- .tection devices, and -more particularly to lightning arresters of the type embodying a plurality of disks of high resistance material 5 spaced sli htly apart.

` The sa type of lightning arrester is made by assembling flat plates or disks of highresistance material comprising generally a hardened mixture of graphite, carborundum and clay. Discs of such composition, as used in lightning arresters, generally have a resistivity of the order of from one to several hundred ohms per centimeter cube, as against .0037 4ohm for carbon, and .0000017 ohm for copper. The lightning arrester is assembled by stacking alternate plates of high resistance material and washers or spacers of mica or other' suitable insulating materialof such thickness as to space adjacent plates a small 2o distance'apart, generally from 3 to 7 mils.

The significance of the 3-mil spacing between the discs is to space the discs about the distance of the cathode glow of a glow discharge. This spacing secures the yresult that the gap will break down at the minimum voltage at which any gap will break down, for any given gaseous medium, density or electrodematerial. vA closer spacing will require a higher voltage to initiate the discharge, be-

cause there is not sufficient distance between the electrodes to produce ionization by co1- lision except at higher voltages. A much wider spacing will introduce large extravoltage losses in the anode dark space which then begins to become evident. A 3-mil spacing is so small that tiny particles or grains of the electrode surfaces occasionally touch, which does no harm in view of the exceedingly high resistance of the material. V

The significance of using a high-resistance material of the compositionmentioned is to prevent the glow discharge, as soon as it is started, from immediately concentrating into as against 350 volts for a glow discharge.

go out when the voltage drops to a value an arc, which has a voltage of about 30 volts only slightly lower than the breakdown voltage, or about 350 volts per gap.

Considerable ditliculty and annoyance is experienced in keeping the several members of the lightning arrester in the proper spaced relation, before and during the assembling thereof in a suitable struct-ure for use as a lightnin arrester. The present invention is designe to overcome this ditliculty, it being among the objects thereof to provide a lightning arrester of the type above set forth., which shall comprise a unit of any desired number of spaced plates held together in xed relation.

It is a further object of `'this invention to simplifythe manufacture and assembly of lightning arresters of this type.

In practicing my inventlon, I assemble plates of high resistancev material with washers or spacers ofmica'h'aving a thickness of about three mils, in such manner that the mica spacers project beyond the edges of the high resistance plates. The several plates and spacers are 4concentric'ally arranged. This may be accomplished by assembling the members either by hand or in -a jig which accurately alines the various parts. Means are provided for holding the plates and washers in lixed relative positions, such meanscomprising generally an insulating cement or a 80 cement having a relatively high resistivity, either in a liquid or plastic form which is applied to the edges of the plates and spacers, thus forming an insulating layer on the outside of the assembled structure, binding the arts together, and which hardens in a1r or y being baked in an oven.

In the accompanying drawings constituting a part hereof, and in which like reference characters designate like parts,

Figure 1 is a vertical, partial cross-sectional view of a lightning arrester unit embodying my invention, and

Fig. 2 is a similar .view showing a slightly modified structure. 95

The lightning arrester or other excess voltage protection' device consists of a tall stack of a suitable number of discs or plates 1 of the above-described high resistance material spaced apart by thin washers 2 of mica, or 100 2 i I 1,734,203y

other suitable material, the edges of the mica extending' beyond the edges of the plates. A suitable insulating cement is then ap lied to all of the edges of the structure and) the same allowed to set. This provides a layer 3 of insulating material which adheres strongly to the edges of the plates and the extending portions of the mica washers. The end plates may be provided with coatlm ings 4 of metal to make good contact with waterlass has a binding agent and suitable isl'ztiaterial, such as a mixture of feldmr, asbestos fibers and man anese di-i'i'd '1s' adrfflffilamd for my purpose. Iliis cement sets Without the aid of heat or pressure and is, therefore, preferable, although other types of cements of an insulating' nature, such as those including henolic condensation roducts and the-like, may also 5e used. 3o `A lightning arrester unit, made in accord- A ance with my invention, h as numerous advantages in that a suitable number of units having a predetermined break-down voltage may be made into a standard unit and a suitablenumber of such complete units may be readily assembled therefrom with but little labor for high voltage lightning arresters which require a large numberv of plates.

The hardened coating of insulator material 40 constitutes a mechanical supporting means for the stack of discs constltuting a single lightningarrester unit, and it also makes it possible to stack a number of said units, one on top of another, without requiring an expensive external casing or sup ort for relieving the bottom discs of t 'e excessive weight of the entire stack, which would otherwise be crushed together with too many points in contact, notwithstanding the 3-mil spacers. 5o The rigid integral insulator coating performs another very important function, the

significance of which was not at first appreciated.- Notwithstanding the fact that the discs were tested thoroughly, individually and' in combination, prior to my invention, when the finished arresters were completed, .with their j costly porcelain housings and ,hardware (not shown), an undesirably large percentage of the arresters had to be thrown 00 out'on final test, sometimes even after ship- I believe that the mament to the customer. jority of these defective arresterswere the result of a sliding of the discs, one over theother, after they were stacked. My present invention prevents all this and insures that a condition throughout the necessa i subsequent handling and shipment, and will, moreover, materially reduce the cost of handling, '7oas well as reduce the, cost of the supportin porcelain housings therefor, as above pointed Furthermore, this structure reduces diiculties which may arise from the tendency of an excess voltage discharge to pass along the edges of the structure instead of across the gaps between the plates under high voltage stresses...

The insulating layer also revents the ac cess of moisture or dust, t ereby insuring perfect operation of the lightning arrester. In the modification shown in Fig. 1, wherein the mica separators extend beyond the edges of the plates, the cement layer maintains the same in concentric position.v

Although I have described two specific embodiments of my invention, it is ap arent that many forms of structure may be evised in accordance with this disclosure. Various materials other than those mentioned in connection withthis description -may be substituted, therefore, within the scope of this inventiOn.

I claim as my invention:

1. A lightning-arrester unit comprising a stack of discs of composition reslstor material spaced `about three mils and having a sufficient resistivity to prevent the concentration of the discharge into a low-voltage arc, characterized by having a hardened coating of insulator material, around the side walls of the stack, of suicient strength and rigidity to protect the stack against dislacement or crushing of its composite discs urinlg ordinary usage.

2. lightnin -arrester unit comprising a stack of discs vaving a resistivity of the order of about one to several hundred ohms per centimeter cube and having a mean spacing of about three mils, characterized by having a hardened coating of insulator material, around the side walls of the stack, of suicient Vstrength and rigidity to protect the stack against displacement or crushing of its composite discs during ordinary usage.

In testimony whereof, I have hereunto sub 'los scribed my name this 11th day of January,

LAWRENCE R. GOLLADAY.

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