US3094648A - Nilsson - Google Patents

Description

June 18, 1963 Q ssoN 3,094,648

LIGHTNING ARRESTERS Filed Feb. 9, 1960 United States Patent 3,094,648 LIGHTNING ARRESTERS Erland Nilsson, Ludvika, Sweden, assignor to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a

corporation of Sweden Filed Feb. 9, 1960, Ser. No. 7,613 Claims priority, application Sweden Feb. 11, 1959 3 Claims. (Cl. 317-61) For special technical purposes, lightning arresters are needed with unusually large energy discharging capacity. It is then necessary to consider one or another form of parallel connection in Order to distribute the load over several lightning arrester elements in one lightning arrester. Each such lightning arrester element consists of piles of spark gaps and voltage dependent valve blocks. In special cases it would be conceivable merely to connect additional piles of valve blocks in parallel and, in series with the piles of valve blocks, connect a common spark gap pile, but in this case the safe current load for the spark gaps does not allow this when, for example, the dimensioning is such that the power follow current from the line would be too big for only one spark gap pile.

When both spark gaps and valve blocks are'integral parts of the parallel connected branches, one must ensure that all branches really work. Due to an unavoidable dispersion, the different spark gap piles will not be ignited at exactly the same time when an over-voltage higher than the flash-over voltage for the lightning arrester arises. One or more of the lightning arrester elements are ignited before the rest of the elements, and if the diverting voltage, eg the voltage over the valve block, is low after flash-over in the spark gap, which, from a protectional point of view, is favorable, it can happen that the over-voltage is limited to a value below the breakdown voltage for the lightning arrester before all parallel connected lightning arrester elements are brought into operation. Then the lightning arrester element which works first would be overloaded while on the other hand some of the elements would not come into service. It should be pointed out that one is often limited to a special relation between the breakdown voltage and the discharge voltage. If such is not the case, the problem would be most simply solved through a lower breakdown voltage in relation to the discharge voltage. In order to attain a so called forced breakdown for a lightning arrester element, which has a higher spark-over voltage than the parallel connected lightning arrester elements, there is described, in Swedish Patent No. 131,751, a device in which two or more parallel connected lightning arrester elements, at at least one point between the upper and the lower end of the element, are joined by a cross impedance. The function can be briefly described in that the chosen point in a lightning arrester element gets a distinct voltage jump when this lightning arrester element breaks down. The voltage jump is propagated through the cross impedance to the corresponding point of the adjacent lightning arrester element and causes a breakdown in this. Such a cross connection between corresponding points in the elements, however, takes up a great deal of space in the longitudinal direction, and it requires great distances between the elements. It is in practice impossible to use such a connection if one wishes to arrange several small lightning arrester elements within the same housing. Such a construction with all the elements in the same housing would be economical, space saving and, further, a simple mechanical construction allowing a simple grading of the voltages.

This invention shows a manner of realising the forced breakdown of a lightning arrester having at least two "ice lightning arrester elements consisting of valve blocks and spark gaps, in order to avoid the above mentioned inconveniences. The upper and lower ends respectively of the lightning arrester elements are usually electrically connected and, furthermore, a point on one of the lightning arrester elements is joined to a point on the other lightning arrester element by a cross impedance in such a way that said point, in the state of rest for the lightning arrester, has practically the same electrical potential. The invention is characterised in that the valve blocks are arranged in a pile in the middle of each lightning arrester element with spark gaps located towards the ends of the valve blocks and that said cross impedance is connected between the end of a valve block pile in a lightning arrester element and the opposite end of another valve block pile in another lightning arrester element. With a device according to the invention, a cross impedance can be fitted in a position geometrically in parallel with the valve blocks in the lightning arrester element. The cross impedances and the valve blocks each have a cylindrical shape with a diameter which is smaller than the length of the element, and a construction with the element located in vertical position gives a simple and space sav ing mechanical arrangement. Furthermore, the lightning arrester according to the invention has the advantage that the cross impedance, in spite of the impedance not being connected between corresponding points on the lightning arrester elements, is still connected between points which, in the state of rest of the lightning arrester, have practically the same electrical potential. Due to that fact, the

' cross impedance can be chosen with a high conductance,

however, which at the most, is the same as the conductance for a valve block pile since otherwise the cross impedance would take the main part of the load. For the same reason it is preferable that the cross impedance is a resistance and, for example, voltage dependent as are the valve blocks because the current distribution between the lightning arrester elements should not be distorted by an over-voltage with a steep wave front.

The accompanying drawings with the FIGURES l to 4 show schematically different embodiments of the invention.

FIGURE 1 shows a lightning arrester where each lightning arrester element consists of a valve block pile 2, in the middle of the lightning arrester element, with the spark gaps 1 and 4 located towards the ends of the valve block. The cross impedance is indicated by 3 and the lightning arrester consists of the lightning arrester elements A, B and C.

Before the breakdown of the lightning arrester the voltage over each lightning arrester element will be distributed over the spark gaps 1 and 4, which electrodes are spaced by pieces of insulating material or by grading resistors with high resistance in order to distribute the voltage over the electrodes of the spark gap. The voltage over the valve blocks 2 which are connected in series with the spark gaps is of no importance even if the spark gaps are supplied with grading resistances because the resistance of the valve blocks is low in proportion to the resistance of the grading resistor. Consequently both ends of the 'valve blocks in all lightning arrester elements have about the same voltage potential, for example, half the total voltage over the lightning arrester element. Suppose that an over-voltage arises, and that the lightning arrester element A breaks down first; the spark gaps 11a and 4a break down, while the spark gaps 1b and 4b still insulate. When the spark gaps 1a and 4a break down, the whole tension comes across the valve block pile 2a and the voltage potential at the upper end of a valve block pile 2a rapidly arises from about half the over-voltage potential to full over-voltage potential. The

voltage surge propagates through the cross impedance 3a to the lightning arrester element B and the voltage over the spark gap 412 will rise. The action propagates also in some degree to the spark gap 1]) (voltage reduction), 4c, (rising) and (reduction) dependent on the proportion between the resistance of the cross impedances 3 and other impedances.

FIGURE 2 shows cross impedances 3 connected in zig-zag from lightning arrester element to lightning arrester element so that, at least with respect to some lightning arrester elements, two cross impedances are connected to one and the same point. The advantage of a device according to FIGURE 2 is perceived if we suppose that the lightning arrester elements A and C have broken down 'While the lightning arrester element B has not yet broken down. In a device according to FIGURE 1 the applied voltages would work against each other across the lightning arrester element B, through the cross impedances 3a and 3b, and therefore the breakdown of the lightning arrester element B would be more difficult.

In a device according to FIGURE 2 on the other hand, the applied voltages cooperate through the cross impedances 3a and 3b on the lightning arrester element B.

If the lightning arrester consists of an even number of lightning arrester elements, one may preferably connect the elements in a closed chain in accordance with FIG- URE 3. The arrester elements are composed of spark gaps 1 and 4 and valve blocks 2 connected by cross impedances 3. A voltage impulse from the first breakdown 7 element vvould be propagated in both directions around the chain and in this manner reach all the other lightning arrester elements faster.

Further, as shown in FIGURE 4, in which the arrester elements are composed of spark gaps -1 and 4 and valve blocks 2 connected by cross impedances 3 a prescribed series of breakdowns may be attained for the device when the lightning arrester element 1c, 2c, 4c, which is shown in the middle of the figure is the first element which breaks down. This is attained by making the other lightning arrester elements with a spark-over voltage which is a little increased, for instance 10-20%, in relation to the first mentioned element. The spark over impulse through the cross impedances is still sufficient to attain spark over in the gaps with increased spark over the voltage.

I claim:

1. Lightning arrester having at least two lightning arrester elements each comprising valve blocks and spark gaps, each of said lightning arrester elements being arranged as a pile with said valve blocks arranged as a resistive pile in the middle of said element and with all of said spark gaps divided into two substantially equal groups, one of said groups being located at the upper end of the element above the valve blocks, the other group located in the lower end of the element below the valve blocks, both spark gap groups being in electric contact with the ends of said resistive pile, means connecting all of said lightning arrester elements in parallel, comprising means electrically connecting all the upper ends of the lightning arrester elements and other means electrically connecting all the lower ends of said elements, a cross impedance element connecting a point on one of the lightning arrester elements to a point on another lightning arrester element, said points in the state of rest of the lightning arrester having practically the same electrical potential, said cross impedance element being substantially resistive and being connected between the upper end of said resistive pile in one lightning arrester element and the lower end ofrthe resistive pile in another lightning arrester element.

2. Lightning arrester according to claim 1 in which said impedance element is a resistance having a conductance, at the most, equal to the conductance of a valve block.

3. Lightning arrester according to claim 1, in which said impedance element is a voltage dependent resistance.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,085 Ludwig Nov. 1, 1938 2,608,600 Vorts et a1 Aug. 26, 1952 FOREIGN PATENTS 1,158,340 France Jan. 20, 1958

Claims (1)

1. LIGHTNING ARRESTER HAVING AT LEAST TWO LIGHTNING ARRESTER ELEMENTS EACH COMPRISING VALVE BLOCKS AND SPARK GAPS, EACH OF SAID LIGHTNING ARRESTER ELEMENTS BEING ARRANGED AS A PILE WITH SAID VALVE BLOCKS ARRANGED AS A RESISTIVE PILE IN THE MIDDLE OF SAID ELEMENT AND WITH ALL OF SAID SPARK GAPS DIVIDED INTO TWO SUBSTANTIALLY EQUAL GROUPS, ONE OF SAID GROUPS BEING LOCATED AT THE UPPER END OF THE ELEMENT ABOVE THE VALVE BLOCKS, THE OTHER GROUP LOCATED IN THE LOWER END OF THE ELEMENT BELOW THE VALVE BLOCKS, BOTH SPARK GAP GROUPS BEING IN ELECTRIC CONTACT WITH THE ENDS OF SAID RESISTIVE PILE, MEANS CONNECTING ALL OF SAID LIGHTNING ARRESTER ELEMENTS IN PARALLEL, COMPRISING MEANS ELECTRICALLY CONNECTING ALL THE UPPER ENDS OF THE LIGHTNING ARRESTER ELEMENTS AND OTHER MEANS ELECTRICALLY CONNECTING ALL THE LOWER ENDS OF SAID ELEMENTS, A CROSS IMPEDANCE ELEMENT CONNECTING A POINT ON ONE OF THE LIGHTNING ARRESTER HAVING PRACTICALLY THE SAME ELECTRICAL PORESTER ELEMENT, SAID POINTS IN THE STATE OF REST OF THE LIGHTNING ARRESTER HAVING PRATICALLY THE SAME ELECTRIC PO TENTIAL, SAID CROSS IMPEDANCE ELEMENT BEING SUBSTANTIALLY RESISTIVE AND BEING CONNECTED BETWEEN THE UPPER END OF SAID RESISTIVE PILE IN ONE LIGHTNING ARRESTER ELEMENT AND THE LOWER END OF THE RESISTIVE PILE IN ANOTHER LIGHTNING ARRESTER ELEMENT.

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