US1658746A - Lightning arrester - Google Patents

Description

Feb 7, 1928. 1,658,746

S. P. STEINMETZ LIGHTNING ARRESTER Filed Sept. 27, 192.1

Inventor: Charles PI Steinmetz,

His a tt ornqg.

Patented Feb. 7,1928.

UNITED STATES' PATENT ol-rlca- CHARLES I. STEINMETZ, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIC COMPANY, .A. CORPORATION OF NEW YORK.

LIGHTNING ARRESTER.

Application filed September 27, 1921. Serial No. 503,559.

This invention relates to ligl'itning arresters and in its preferred embodiment consists of an arrester formed of a plurality of discharge. gaps arranged in series, each of said gaps being enclosed by a wall which separates the discharge electrodes of the gap. Certain of the walls are formed of insulating material, while others of material havin electrical resistance, each of the latter walls thus forming a resistance shunt to a gap.

The discharge terminals of the gaps are preferably formed of metal discs or cup-shaped members and the walls are formed of rings against which the discs are adapted to be clamped, the discharge taking place inside of the rings. To facilitate manufacture and assembly, the rings as well as the discs are preferably of the same form and size. In the case of the resistance rings, however, the materials of which these are composed have different specific resistances. This enables each of the gaps to be shunted by a differentresistance, which being properly chosen, produces a more effective breaking down of the gaps during the high potential discharge as well as a more efiective subsequent sealing of the gaps to interrupt the dynamic current.

By enclosing each of the gaps in a separate chamber, the gas formed by the discharge at each gap is kept away from the other gaps and so it is impossible for the arc formedbetween any pair of opposing electrodes to extend to an electrode of some other pair. As so constructed, the arrester may be used on lines of higher normal voltage because when the arcs are maintained separate the dynamic current which flows under the influence of the normal voltage is more easily interrupted at the gaps. The enclosing walls of the gaps 4 as well as the electrodes act to cool the hot gases and so assist in eatinguishing the arcs.

By making the enclosing chambers sufficiently tight, the formation of heated gases within the chambers may be made to cause 5 an increase in pressure which likewise assists inextinguishing the arcs.

The multiga arrester constructed as above describe furnishes a substantially straight. line path for the discharge and therefore has a minimum inductance.

' Further advantages and objects will appear from the following description taken in connection with the accompanyin drawing which represents in section, partly in elevation, an arrester constructed in accordance serrated, studded or otherwise roughened diswith my invention. This arrester comprises a porcelain tube 10 adapted to be secured to a sultable support by means of a strap 11 and provided with a member 12 secured to its lower end and a cap 14 cemented to its other end. Interposed between the member and cap are a series of gaps 15-24. These are formed of g a plurality of dished brass or other non-arcing metal. disc electrodes 26 having central charge surfaces, the two opposing electrodes of each gap being separated by one of the rings 27 to 84. Rings 27 are of porcelain or otheninsulating material, while the remainmg rings are of resistance material, the resistance in shunt to one gap being different from that in shunt to any other gap. Ring 28, for example is a very high resistance, ring 29 of somewhat less resistance, ring 30 of still less resistance and so on until ring 34 is 7 reached which has the least resistance of any.

The rings 28 to 30 are preferably formed of clay, carborundum and graphite in varylng proportions which are first thoroughly mixed, moulded and baked. The rings are subsequently ground to exact length to insure a constant and accurate spacing of the electrodes of each gap and are coated at their ends with copper to provide a good contact surface. 4

The lower disc 26 of the series is connected to a grounded terminal conductor 36 which passes through an opening in the member 12.

The upper disc is in contact with the lower of a series of metal spacin plates 39 which are inserted to take care of slight variations which are apt to occur in the lengths of the outer porcelain tubes. Pressing upon the upper plate 39 and serving to maintain the discs 26 and spacing rings in close contact is a spring 40 which bears at its upper end against the contact cap 41, which cap surrounds the upper end of the tube 10. Surrounding thecap 41 is a metallic strap 42 which is connected to the line terminal 43. 100

The cap 41, strap 42 and connected end of the line terminal-are embedded in the cement which serves to secure the cap 14 to the tube.

In operation if a high power static imv pulse occursall of the gaps will break down 105 thus forming a free discharge ath without appreciable resistance to groun This will Y prevent the building or backing. up of voltage on the line which would cause Injury to theapparatus which it is desired to-prono tect. In most cases the dynamic current will follow the static over the gaps and continue for the remainder of the half wave of the dynamic current, thus momentarily short circuiting the system. At the end of this first half wave the dynamic current dies, the reverse dynamic voltage rises and reverse current begins to flow; first through the resistance rings until the voltage drop across the rings is high enough to cause a breaking down at the gaps. In the case of the gap or gaps which are shunted by the lowest resistance rings the voltage drop is not snflicient to cause them to bebroken down with the result that the dynamic current continues to flow through this resistance through the next half cycle. The effect of the inclusion of this resistance in the circuit is to reduce the dynamic current and consequently to produce less ionization at. the gaps over which the current is flowing. This will prevent the breaking down of the gap which is shunted by the next higher resistance during the next halt wave and in this manner the gaps are successively cleared and the dynamic current finally interrupted.

In the case of a lower power discharge all of thegaps may not break down. The following dynamic current would therefore flow through the resistance of one or more of the rings and consequently be reduced with the result that there would be less ionization and the system would not be short circuited. The successive clearing of the gaps which had broken down would take place in the manner above described? By grading the resistance as above described, it is possible to interrupt the dynamic current with a less total number of gaps.

It will be seen, therefore, that in the lightning arrester of the invention the resistor elements which bridge the air gaps constitute means for automatically varying the number of air gaps crossed by. a discharge depending upon the volume of the discharge. In other words. the larger the volume the greater the number of air gaps that are crossed.

While I have shown the porcelain rings arranged at the top of: the series and the resistance shunts arranged in a series with each ringot a less resistance than the ring immediately above, I desire it to be understood. that this arrangement is not in all cases necessary. It may, intact, be advisable in certain cases to alternate high resistance or insulation rings with low resistance rings to separate the gaps at which the greater amounts of heat are produced so that the heat may be more effectively dissipated.

In case of a continued discharge through the arrester, such as might be brought about if the distribution system comes in contact with a, conductor carrying current at a voltage very much higher than the normal voltage of the distribution system, or if the unshunted gaps become bridged in some way the heat generated by the passage of the current through the arrester will break the porcelain tube 10. Some suitable means is provided for placing the upper end of the tube 10 under a stress which tends to separate it from the lower part so that when the tube breaks in two the upper end will automatically be moved some distance away from the lower end, thereby making a very large gap in the path from line to ground and interrupting any current which may be flowing through the arrester. The line terminal may be connected in such a way as to furnish the desired stress upon the upper end of the tube to pull it away from the lower end when the tube breaks.

While I have shown the gaps of constant lengths, it may be advisable in certain cases to vary the length of the gaps and to produce the successive breaking down of the gaps by this means as well as by graded shunts a one.

It is not necessary in all cases that the resistance of each shunt be difi'erent from the resistance of every other shunt. It is however, advisable to have a suflicient number of different resistances to permit the selection of a greater or less number of gaps depending upon the volume of the discharge. In my arrester as at present constructed, I provide one shunt at least of very low re sistance, such as 1 ohm, one of very high resistance, such as 200 ohms, and two or more other shunts having intermediate values.

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

1. A multigap lightning arrester comprising a plurality of pairs of electrodes forming discharge gaps, and a wall of resistance material enclosing each gap, the resistances of the successive. walls being graded in value.

2. In a lightning arrester. the combination with a plurality of conducting plates, of a series of resistors disposed-between plates aforesaid to form air gaps, resistors aforesaid differing from one another in rcsisti vity.

3. In a lightning arrester. the combination with a plurality of conducting plates, of an insulator disposed between and spacing plates aforesaid to form an air gap between them, a resistor of relatively low ohmic resistance disposed between and spacing other plates aforesaid to form an air gap between them, and a resistor of relatively high ohmic resistance disposed between and spacing other plates aforesaid to form an air gap between them.

In a lightning arrester, the combination in columnar relation of a plurality of weep/ac electrodes and a plurality of devices whereby electrodes aforesaid are connected between contiguous devices and electrodes engaging respective devices aforesaid are sepa rated to form air aps, one of said devices being formed of insulating material and other of said devices being formed of conducting materials of different resistivity adapted for providing respectively relatively high and low resistance to an electric discharge from one or more of said air gaps.

5. A multigap lightning arrester comprising a plurality of pairs of electrodes forming discharge gaps, and a spacer of resistanee material between each pair of electrodes, the resistances of the successive spacers being graded in value.

6. in a lightning arrester, a casing containing a plurality of electrodes forming a series of air gaps, pairs of electrodes forming air gaps aforesaid being connected with resistors of different rcsistivities which antomatically vary the number of air gaps crossed by a discharge proportionately to the volume of discharge.

In witness whereof, I have hereunto set my band this 26th day of September, 1921.

CHARLES P. STEENMETZ.

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