US3259780A - Electric gap device using porous material in the arc chamber - Google Patents

Description

E. W. STETSON July 5, 1966 ELECTRIC GAP DEVICE USING POROUS MATERIAL IN THE ARC CHAMBER Filed July 6, 1964 2 Sheets-Sheet 1.

E. W. STETSON July 5, 1966 ELECTRIC GAP DEVICE USING POROUS MATERIAL IN THE ARC CHAMBER Filed July 6, 1964 2 Sheets-Sheet 2 [22%"1225: Far/ P11515930, y VM/e 7224a;

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United States Patent 3,259,780 ELECTRIC GAP DEVICE USING POROUS MATERIAL IN THE ARC CHAMBER Earl W. Stetson, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed July 6, 1964, Ser. No. 380,421 3 Claims. (Cl. 313231) This invention relates to gap units for valve type lightning arresters and more particularly to non-current limiting series gap units for extra high voltage lightning arresters.

A lightning arrester is an electrical safety valve for protecting the insulation of a charged electrical conductor, such as a conductor of an electric cable power line or transformer winding, from the insulation rupturing effect of excess electrical pressure or voltage which can be caused by lightning or switching surges. However, in the electrical and mechanical arts the meaning of the terms open and closed is reversed when referring to a valve. Thus when an electrical valve or switch is said to be open it is non-conductive whereas when a mechanical valve is open it is conductive. Similarly when an electric valve or switch is said to be closed it is conductive whereas when a mechanical valve is closed it is nonconductive. Therefore, a lightning arrester is a normally open electrical safety valve and a mechanical safety valve is a normally closed valve. However, they both operate to prevent the escape of normal pressure while allowing the escape of excess pressure.

A typical power system lightning arrester comprises a so-called gap unit and a so-called valve resistance, usually of the negative-resistance-voltage characteristic type, connected in series between ground and the conductor whose insulation is to be protected against overvoltage by the arrester. At normal voltage no discharge current flows through the arrester and practically all the voltage is across the gap unit. On the occurrence of excess voltage the gap unit breaks down electrically (sparks over) allowing the flow of current through the arrester. As the initial electrical resistance of an are between gap electrodes is low, compared to the resistance of a gap when there is no are, most of the excess voltage will then be across the valve resistance whose resistance practically instantaneously falls to a low value because of its negative resistance-voltage characteristic. Consequently, the arrestercan conduct large voltage-surge-produced discharge currents to ground while holding the voltage down to a safe value. After the surge of excess voltage has been drained off through the arrester, the normal system voltage tries to maintain the flow of so-called power follow current through the arrester but as the voltage on the valve resistance is now very much reduced its resistance increases thus reducing the magnitude of the power follow current to a value which the gap unit can interrupt.

Two comparatively recent developments have greatly increased the energy absorbing duty imposed on the gap unit. One results from the deliberate conversion of the gap unit into a current limiting gap which, by the use of .a magnetic coil and other means, causes it rapidly greatly to increase its arc voltage or arc resistance. This permits reducing the amount of valve resistance material in the arrester because the current limiting gap also performs the function of a valve resistance. The other development is the increase in power system operating voltage to values where switching surges impose a greater energy absorbing duty on the arrester than lightning surges. The transition occurs at voltages of about 230 kv. (R.M.S. line-to-line) on a conventional open air line of a three phase power system and at lower voltages on a cable line because of the higher capacitance per unit Patented July 5, 1966 length of a cable operating at the same voltage. Switching surge energy is approximately proportional to both system capacitance and the square of the system operating voltage. In general, higher voltages mean longer lines and the combination of longer lines and bundling conductor means increased line capacity. Thus at 700 kv., for which systems are currently being designed and constructed, the switching surge energy can be many times the lightning surge energy.

Lightning arresters are rated in terms of the applied voltage at which they will interrupt power follow current. Thus the rating of a lightning arrester is proportional to the system operating voltages. For voltages above about 345 kv., it has been proposed to provide additional valve resistance material in the arrester to aid in absorbing the switching surge energy (which is proportional .to the square of the system operating voltage) and to shunt the added valve resistance material with a current switching gap which, like a current limiting gap, rapidly increases its arc voltage or resistance after sparkover so as to switch power follow current and switching surge current into the additional valve resistance material.

In accordance with this invention, there is provided a new and improved arc quenching or arc interrupting but non-current limiting gap unit which is particularly adapted for use as a series or interrupting gap in extra high voltage lightning arresters such as for use on 700 kv. systems in which a substantial part of the valve resistance is shunted by a current switching gap or gaps. Among other things, the gap unit has porous ceramic insulating surfaces adjacent where an arc is formed between horn gap electrodes for absorbing and controlling the plasma of a high current arc to a size that the magnetic field of a horn gap can effectively act on and'move quickly. Another feature of the invention is a relatively high volume porous walled arc chamber extending between the tips of the horn gaps electrodes and provided with deionizing fins for providing rapid recovery voltage after normal current zero without producing substantial arc voltage. Another feature of the invention is a novel horn gap electrode configuration.

An object of the invention is to provide a new and improved spark gap unit.

Another object of the invention is to provide a new and improved are quenching current interrupter as distinguished from a current limiting gap unit for lightning arresters.

The invention will be better understood from the following description taken in connection with the accon1- panying drawings and its scope will be pointed out in the appended claims.

In the drawings,

FIG. 1 is a perspective view of an at present preferred embodiment of the invention,

FIG. 2 is an exploded view of the gap unit shown in FIG. 1,

FIG. 3 is a somewhat enlarged top view of one of the intermediate plates of the gap unit,

FIG. 4 is a cross sectional view of plates 2 and 3 taken on lines 44 of FIG. 2,

FIG. 5 is a diagrammatic view of the electrical connections of the gap unit.

' Referring now to the drawing and more particularly to FIG. 1, there is shown therein a gap unit 1 comprising a stack of five porous ceramic plates or discs 2, 3, 4, 5, and 6. These may be composed of small particles of aluminum oxide (A1 0 bonded together by glass so as to leave empty spaces representing about 15-20% of the over-all volume of the material.

Referring now to FIG. 2, the top plate 2 has a top side with a flat configuration as shown and the bottom plate 6 has a similar flat configuration. The underside of the plate 2 as well as the under side of the intermediate plates 3, 4, and 5 have configurations as shown in FIG. 2 for the top plate 2, while the upper sides of the intermediate plates 3, 4, and 5 and of the bottom plates 6 have the configuration shown in FIG. 2 and also in FIG. 3. Thus the top sides of plates 3, 4, 5, and 6 have horn gap electrodes 7 of any suitable material such as copper cemented thereto, these being roughly G-shaped but inverted with massive heat sink tips 8 connected to runners having a point of minimum spacing or confluence at 9 and then diverging again to terminals 10. Connected in shunt with each gap is a preionizer 11 of any suitable type and a grading resistor 12.

The vertical space between adjacent plates near the point of confluence 9 of the electrodes is shallow as shown in FIG. 4. By means of this construction, the plasma and hot gases of a heavy current arc formed at 9 are allowed to expand and permeate the porous plate structure so that the self-generated magnetic field of the horn gaps can produce initial arc motion more effectively; Thus the arc is moved relatively quickly away from the point 9 so as to prevent burning of the latter and so as to force the arc out along the runners to the relatively massive heat sink tips 8 which can withstand the long high current arcing without serious erosion and without changing the sparkover characteristics of the gaps which are determined by their spacings at 9.

Inserted within the plates 3, 4, 5, and 6 are arcuate porous members 13 which are slotted. As shown they are provided with five slots 14, the three intermediate ones being filled with deionizing fins 14 which extend into a relatively deep arcing chamber as is shown in the cross sectional view in FIG. 4. These deionizing fins are made of metal and break up the initial arc into shorter arcs, thus effecting a rapid deionization. Consequently at normal current zero the recovery voltage of the gap rises more than if the deionizing fins 15 were not present. The remaining two slots 14 serve to break up or provide a discontinuity in any conducting path which may be formed along the inner wall of the arcuate member 13 by the condensation of vaporizing metal or melting of the plate material. The likelihood of such a conducting path forming is, however, greatly reduced by reason of the porosity of the material from which the plates of the member 13 are made.

The comparatively great depth or large volume of the arc chamber along the inner wall of the arcuate member 13 prevents pinching or restricting the arc and thus prevents the development of a high are voltage before normal current zero as is characteristic of current limiting gaps. Consequently, the gap unit of the present invention does not absorb much energy and does not act as a valve resistance element in the lightning arrester to any substantial extent.

The porosity of the material of which the plates are made and the undercut plate section at 16 also serve to inhibit the formation of a conducting path where the gap spacing is a minimum and where an are forms initially so as to preserve the initial gap setting which is, of course, fixed by the cementing of the electrodes of each gap to their common supportingplate.

FIG. 5 shows how the four similar gaps are serially connected by connectors extending through the plates.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

1. A series current interrupting gap unit for valve type lightning arresters comprising, in combination, a plurality of individual serially connected horn gaps sandwiched between stacked axially aligned body plates of porous ceramic material, each pair of contiguous plates forming between their facing surfaces a closed arc chamber having a relatively shallow portion at one side in which the part of its horn gap which has the minimum electrode spacing is located, said arc chamber having a relatively deep arc deionizing portion with a substantially larger ratio of volume to wall surface area than said relatively'shallow portion, the runners of said gap divergingly extending into said are chamber and terminating in tips at opposite ends of said relatively deep portion, said relatively deep portion having an arcuate wall extending between said tips and facing the point of minimum gap electrode spacing, the configuration of said horn gap electrodes providing the sole means for electromagnetically forcing an are initially struck between said electrodes at their point of minimum spacing into said are chamber along said runners to their tips and against said arcuate wall, said arcuate wall having a plurality of conductive deionizing grids inserted therein and extending radially inwardly therefrom across the path of an arc along said wall between said horns, the porosity of the walls of said relatively shallow portion of said are chamber serving to absorb and shrink a high current are struck across the point of minimum spacing of gap electrodes so as to preserve the automatic action of the horn gap in rapidly moving such high current arc away from such points, said relatively deep portion of said arc chamber serving to provide a rapid gap recovery voltage after normal current Zero without developing substantial arc voltage before current zero. 7

2. A series current interrupting gap unit for valve type lightning arresters comprising, in combination, a plurality of individual serially connected horn gaps sandwiched between stacked axially aligned body plates of porous ceramic material, each pair of contiguous plates forming between their facing surfaces a closed arc chamber having a relatively shallow portion at one side in which the part of its horn gap which has the minimum electrode spacing is located, said are chamber having a relatively deep arc deionizing portion with a substantially larger ratio of volume to wall surface area than said relatively shallow portion, the runners of said gap divergingly extending into said are chamber and terminating in tips at opposite ends of said relatively deep portion, said relatively deep portion having an arcuate wall extending between said horns and facing the point of minimum gap electrode spacing, the configuration of said horn gap electrodes providing the sole means for electromagnetically forcing an are initially struck between said electrodes at their point of minimum spacing into said are chamber along said runners to their horns and against said arcuate wall, said arcuate wall having a plurality of radially extending slots across whose mouths an are along said wall extends without entering said slots for breaking any conductive path formed on said wall as a result of prolonged high current arcs, the porosity of the walls of said relatively shallow portion of said are chamber serving to absorb and shrink a high current are struck across the point of minimum spacing of gap electrodes so as to preserve the automatic action of the horn gap in rapidly moving such high current are away from such points, said relatively deep portion of said are chamber serving to provide a rapid gap recovery voltage after normal current zero without developing substantial arc voltage before current zero.

3. A series current interrupting gap unit for extra high voltage valve type lightning arresters comprising, in combination, a plurality of individual serially connected horn gaps sandwiched between stacked axially aligned body plates of porous ceramic material, each pair of contiguous plates forming between their facing surfaces a closed arc chamber having a relatively shallow portion at one side in which the part of a horn gap which has the minimum electrode spacing is located, said are chamber having a relatively deep arc deionizing portion with a substantially 'iarger ratio of volume to wall surface area than said relatively shallow portion, the runners of said gap divergingly extending into said are chamber and terminating in relatively massive erodable heat sink horns at opposite ends of said relatively deep portion, said relatively deep portion having an arcuate wall extending between said horns and facing the point of minimum gap electrode spacing, the configuration of said horn gap electrodes providing the sole means for electromagnetically forcing an are initially struck between said electrodes at their point of minimum spacing into said are chamber along said runners to their horns and against said arcuate wall, said arcuate wall having a plurality 'of conductive deionizing grids inserted therein and extending radially inwardly therefrom across the path of an are along said wall between said horns, said arcuate wall having a plurality of radially extending slots across whose mouths an arc along said wall extends without entering said slots for breaking any conductive path formed on said wall as a result of prolonged high current arcs characteristic of switching surges on extra high voltage lines, the porosity of the walls of said relatively shallow portion of said are chamber serving to absorb and shrink a high current arc struck across the point of minimum spacing of gap electrodes so as to preserve the automatic action of the horn gap in rapidly moving such high current are away from such points, said relatively deep portion of said are chamber serving to provide a rapid gap recovery voltage after normal current zero without developing substantial arc voltage before current zero.

GEORGE N. WESTBY, Primary Examiner. s. D. SCHLOSSER, Assistant Examiner.

Claims (1)

1. A SERIES CURRENT INTERRUPTING GAP UNIT FOR VALVE TYPE LIGHTNING ARRESTERS COMPRISING, IN COMBINATION, A PLURALITY OF INDIVIDUAL SERIALLY CONNECTED HORN GAPS SANDWICHED BETWEEN STACKED AXIALLY ALIGNED BODY PLATES OF POROUS CERAMIC MATERIAL, EACH PAIR OF CONTIGUOUS PLATES FORMING BETWEEN THEIR FACING SURFACES A CLOSED ARC CHAMBER HAVING A RELATIVELY SHALLOW PORTION AT ONE SIDE IN WHICH THE PART OF ITS HORN GAP WHICH HAS THE MINIMUM ELECTRODE SPACING IS LOCATED, SAID ARC CHAMBER HAVING A RELATIVELY DEEP ARC DEIONIZING PORTION WITH A SUBSTANTIALLY LARGER RATIO OF VOLUME TO WALL SURFACE OF SAID THAN SAID RELATIVELY SHALLOW PORTION, THE RUNNERS OF SAID GAP DIVERGINGLY EXTENDING INTO SAID ARC CHAMBER AND TERMINATING IN TIPS AT OPPOSITE ENDS OF SAID RELATIVELY DEEP PORTION, SAID RELATIVELY DEEP PORTION HAVING AN ARCUATE WALL EXTENDING BETWEEN SAID TIPS AND FACING THE POINT OF MINIMUM GAP ELECTRODE SPACING, THE CONFIGURATION OF SAID HORN GAP ELECTRODES PROVIDING THE SOLE MEANS FOR ELECTROMAGNETICALLY FORCING AN ARC INITIALLY STRUCK BETWEEN SAID ELECTRODES AT THEIR POINT OF MINIMUM SPACING INTO SAID ARC CHAMBER ALONG SAID RUNNERS TO THEIR TIPS AND AGAINST SAID ARCUATE WALL, SAID ARCUATE WALL HAVING A PLURALITY OF CONDUCTIVE DEIONIZING GRIDS INSERTED THEREIN AND EXTENDING RADIALLY INWARDLY THEREFROM ACROSS THE PATH OF AN ARC ALONG SAID WALL BETWEEN SAID HORNS, THE POROSITY OF THE WALLS OF SAID RELATIVELY SHALLOW PORTION OF SAID ARC CHAMBER SERVING TO ABSORB AND SHRINK A HIGH CURRENT ARC STRUCK ACROSS THE POINT OF MINIMUM SPACING OF GAP ELECTRODES SO AS TO PRESERVE THE AUTOMATIC ACTION OF THE HORN GAP IN RAPIDLY MOVING SUCH HIGH CURRENT ARC AWAY FROM SUCH POINTS, SAID RELATIVELY DEEP PORTION OF SAID ARC CHAMBER SERVING TO PROVIDE A RAPID GAP RECOVERY VOLTAGE AFTER NORMAL CURRENT ZERO WITHOUT DEVELOPING SUBSTANTIAL ARC VOLTAGE BEFORE CURRENT ZERO.

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