US2989664A - Excess voltage discharge device - Google Patents

Description

June 1961 w. ZOLLER 2,989,664

EXCESS VOLTAGE DISCHARGE DEVICE Filed Oct. 10, 1956 2 Sheets-Shoe? 1 1 I /0 w 350 /0 INVENTOR \d f/helm Zoller ATTORNEYS June 20, 1961 w. ZOLLER EXCESS VOLTAGE DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed Oct. 10, 1956 INVENTOR Wt helm Zol Le r BY mm, Mafia/v ATTORNEYS llnited States Patent ice 2,989,664 Patented June 20, 1961 2,989,664 EXCESS VOLTAGE DISCHARGE DEVICE Wilhelm Zoller, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland,

a joint-stock company Filed Oct. 10, 1956, Ser. No. 615,115 Claims priority, application Switzerland Oct. 13, 1955 '6 Claims. (Cl. 31770) This invention relates to excess voltage discharge devices for use on high voltage alternating current power transmission lines and which are often referred to as lightning arresters. It is common practice to make up such a lightning arrester from a plurality of sets of series connected spark gaps alternating with a plurality of series connected voltage dependent i.e. exponential, resistors, arranged in a vertical column. The upper end of the column of arrester elements i.e. the spark gaps and resistors, is electrically connected to the power transmission line and the lower end of the column is electrically connected to ground, i.e. earthed. It is also known to provide each of the spark gaps with a resistance control so that the arrester has, at the principal frequency of the transmission line, for example 50 cycles per second, a linear voltage distribution along the quenched spark gaps. Under shock stress, however, the voltage distribution is determined by the capacities, and is exponenial, due to the earth capacities. Consequently, the peak value of the sparkover voltage under shock conditions is smaller than that at the normal line frequency, e.g. 50 cycles per second. The sparkover voltage U,, as a function of the frequency f extends approximately according to the curve a in FIG 1. One can thus see that the curve drops in the region between about 250 and cycles per second from the response voltage of 50 cycles per second to the value of the shock stress. For protection against switching surges, it is necessary, however, that the sparkover voltage in the region above 250 cycles per second does not exceed the protective level for the protected apparatus. This desired result could be achieved by reducing the number of spark gaps, but this would impair the quenching safety of the arrester. Another possibility would be to reduce the control current so that the passage from the capacitative to the resistance control takes place at lower frequencies. This measure would increase, however, the influence of the weather conditions (rain, dryness, fog, contamination) on the sparkover voltage.

It is the object of the present invention to reach this desired result by different and simpler means in lightning arresters with a series of single elements connected between the transmission line and the ground, which consist of spark gaps and exponential resistors and where the spark gaps are provided with a resistance control. This is achieved according to the invention in that points of different potentials are connected with each other on the arrester by at least one frequency-dependent impedance in such a manner that only a part of the column is shunted by said impedance.

So as not to impair the quenching capacity of the arrester, this frequency-dependent impedance should be high at the frequency of the transmission line, e.g. 50 cycles per second, compared to the impedance of the bridged part of the arrester. If a condenser is used as an impedance, one obtains a dependence of the sparkover voltage on the frequency according to curve b (FIG. 1). In this case both the sparkover voltage at excessive voltages and that under shock condition are reduced coresponding to the ratio of the bridged part to the entire arrester column. At the transmission line frequency, however, the sparkover voltage is maintained. If a highly damped series-resonant circuit is used as a condenser, the sparkover voltage will only be reduced in the resonance region of the oscillatory circuit (curve c, FIG. 1).

For special purposes, it may also be convenient to reduce the sparkover voltage at low frequencies. In this case a choke must be connected parallel with the arrester column. The original curve a, FIG. 2, is then changed according to curve a, FIG. 2. It is also possible to use a parallel resonant circuit which increases the sparkover voltage for its resonant frequency (curve e, FIG. 2). These are only the most simple possibilities of a frequencydependent impedance, and it is possible to use any number of other possibilities, depending on the desired operating conditions.

FIG. 3 shows an embodiment of the subject matter of the invention in a longitudinal vertical central section. The arrester column is composed of various elements which consist of tubular insulators 1 and end fittings 2 in which are contained the active elements of the arrester, i.e. the spark gaps and voltage-dependent resistors. Each resistance block 3 of voltage dependent material is followed by a column of series connected spark gaps 4 which are spaced from each other by rings 5. These rings 5 are designed at the same time as high-ohmic resistances and efiect the resistance control of the spark gaps. Parallel to the bottom section of the arrester column, i.e. the lowermost three sets of spark gaps 4 and voltage-dependent resistors 3, is connected the frequencydependent parallel impedance 7 which has the desired influence on the sparkover voltage.

For the desired effect it is naturally immaterial whether the parallel impedance is connected parallel to the bottom section or to any other section. Likewise, the arrester column can consist of any desired number of elements or sections and the impedance 7 can bridge several elements, or parallel frequency-dependent impedances can be connected in parallel to several elements. The distribution of the exponential resistors and spark gaps in the individual elements can also vary. The same control effect is also obtained if the impedance 7 is arranged in the interior of the insulators 1. In this case they are connected with advantage parallel to the individual groups of exponential resistors and spark gaps.

In order to obtain lower voltages or to increase the absorption capacity of the arrester, it is known to design the arrester with at least two columns of arrester elements connected in series, these columns being connected with each other at the upper and lower ends. In this type of arrester, the above described frequency-dependent control impedance can be easily applied by connecting with each other at least at one point the arrester colurrms, which are connected in parallel, by a frequency-dependent impedance which is connected between points of different potentials. This way one obtains the above described etfect for both arrester columns with the advantage that one control impedance can be saved per pair of columns. At the same time, the impedance enforces the simultaneous ignition between the two columns and even with a weak but long-lasting current, such current is therefore distributed over both columns and the arrester can thus lead away twice as much current as a single arrester, or as two parallel arrester columns without a coupling element as provided by the present invention. To avoid having to design the control impedance at high nominal voltages of the arrester for very high voltages, it is advantageous to divide the arresters into several sections connected in parallel, which are connected each for itself, with a frequency-dependent control impedance between points of different potentials.

FIG. 4 shows an embodiment of the invention for a multi-column arrester. On a base plate 11 are atranged two upstanding arrester columns each containing sets of series connected spark gap elements 4' having resistance control rings 5 associated therewith, alternating with voltage dependent (exponential) resistance blocks 3. These spark gap elements, resistance control rings and resistance blocks are contained within superposed tubular insulator sections in basically the same manner as described with respect to the embodiment illustrated in FIG. 3. However, the heights of the insulator sections, and hence the number of spark gap elements with their resistance control rings and exponential resistance blocks are not uniform for all sections throughout the height of the arrester columns. The lower parts of each arrester column do contain the same number (three) of superposed tubular insulator sections 12 and these sections are all of the same length and hence contain the same number and arrangement of spark gaps and exponential resistance blocks. These insulator sections are supported by and separated from each other by electrically conductive metallic flanged end fittings 19 of the same construction as the fittings 2 shown in FIG. 3. The upper part of the left-hand arrester column is constituted by two superposed insulator sections 13, 14 of different lengths. The lowermost section 13 is seen to be about twice the length of the lower insulator sections 12 and hence contains about twice the number of spark gaps and exponential resistance blocks. The uppermost insulator section 14 mounted upon insulator section 13 by conductive fitting 19 is seen to be of substantially the same length as the lowermost insulator sections 12 and hence has a corresponding number of spark gaps and exponential resistance blocks. The upper part of the right-hand arrester column which is the same height as the upper part of the left-hand column is also constituted by two superposed insulator sections -15 and 16 separated by an end fitting 19 and these sections are of equal length. Consequently, each of the insulator sections 15 and 16 is longer than insulator section 14 but shorter than insulator section 13 and hence has a corresponding number of series connected spark gaps and exponential insulator blocks greater than that of insulator section 14, but less than that of insulator section 13. The two, parallel arrester columns are tied together at the top and middle by electrically conductive metallic bars 17.

The special control in accordance with the invention is effected by means of frequency-dependent impedances connected between the two arrester columns at points of different potentials. Thus, in the lower part of the two arrester columns, one frequency-dependent impedance 18 is anchored to and thereby electrically connected at one end thereof to the bottommost fitting 19 at the top of the lowermost insulator section 12 of the right-hand column. The other end of the frequency-dependent impedance 18 is anchored and electrically connected to the fitting 19 separating the top and middle insulator sections 12 of the lefthand column. In the upper part of the two arrester columns, one end of a frequency-dependent impedance 18' is anchored and electrically connected to the fitting 19 separating the insulator sections 13, 14 of the left-hand arrester column and the other end of impedance 18' is anchored and electrically connected to the fitting 19 separating insulator sections 15, 16 of the right-hand arrester column.

The eifect of this arrangement is based upon the fact that a part of the control current, which flows through the short arrester section 14 of the left column, is taken over by the coupling condenser 18' and is conducted to the right column. Here it is added to the current of the arrester section 16 and the summation current flows off through the next below arrester section 15. The currents which traverse the arrester sections 14 and 15 are thus greater than the currents which flow through the arrester sections 13 and 16. Since the arrester sections all contain the same number of arrester units per unit of length, then the voltage drop at the arrester sections 14 and 15 will be correspondingly greater than the vo1tage drops at arrester sections 13 and 16. The arrester units of the sections 14' and 15 will therefore be the first to attain the operating voltage. When the arrester section 14 ignites, for example, the voltage is displaced from this section to the coupling capacity and the arrester sections 15 and 13, respectively. Since the arrester section 15 is closer to its operating voltage than is the arrester section 13, the former will ignite as the next section. The current flowing through the ignited sections 14 and 15 now charges the coupling capacity. Concurrently, the voltage at the long arrester sections increases until one of these sections, for example, section 13 ignites. If the voltage drop in the voltage-dependent resistances is less than the ignition voltage, the voltage drops suddenly at these sections. Since on the other hand, the voltage at condenser 18' cannot change suddenly the section 16 thus receives a higher voltage so that it also responds. In this manner, a successive ignition of the two columns is achieved.

I claim:

1. In a lightning arrester the combination comprisinga pair of columns of equal height each of which comprises the same number of identical series connected spark gap elements distributed uniformly throughout the length of the column and exponential resistor elements, said columns of arrester elements being adapted to be connected in parallel between a transmission line and ground, said spark gap elements being provided with resistance control means, and a frequency-dependent impedance interconnecting said columns of arrester elements at points on said columns which lie at different levels above ground.

2. A lightning arrester as defined in claim 1 wherein said columns of arrester elements are electrically connected with each other by metallic conductor means at least at one point between the upper and lower ends thereof.

3. A lightning arrester as defined in'claim 1 wherein said frequency-dependent impedance comprises condenser means.

4. A lightning arrester as defined in claim 1 wherein said frequency-dependent impedance comprises a parallel resonant circuit.

5. A lightning arrester as defined in claim 1 wherein said columns are each constituted by a plurality of arrester sections in tubular insulators connected end-to-end, and said frequency-dependent impedance extends between the junction lines of arrester sections which lie at different levels on the two columns.

6. A lightning arrester as defined in claim 1 wherein said columns are each constituted by a plurality of arrester sections of different length in tubular insulators connected end-to-end, and said frequency-dependent impedance extends between the junction lines of arrester sections which lie at different levels on the two columns.

References Cited in the file of this patent UNITED STATES PATENTS 1,902,510 McEachron et al Mar. 21, 1933 2,542,805 Fink Feb. 20, 1951 2,600,149 Yonkers June 10, 1952 2,608,600 Vorts et al Aug. 26, 1952 2,618,765 Vogelsanger Nov. 18, 1952 2,778,954 Perillard Jan. 22, 1954 FOREIGN PATENTS 847,379 France June 26, 1939 UNITED STATES PATENT OFFICE s CERTIFICATE OF CORRECTION Patent .Nq, 2,989,664 June 20, 1961 I I Wilhelm Zoller I I i I I I I It is Iiereby certified that error appears in the above n umbered patent requiring correction and that the-said Letters Patent. should read es corre cted below I Column 4, lines 29 and 30, strike out "distributed uniformly throughout the length ofthe column? and insert the same after "elements" and before the comma, in line 30, same column.

Signe d'and sealed this 7th 'day of November 1961.

I (SEAL) Attest: E I V v ERNEST W. SWIDER DAVID LADD Attesti lg Officer V Commissioner of Patents uscoMM-Dc UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Na 2,989,664 i June e0," 1951 Wilhelm Z ller i H i 4 l It is hereb certified that erroi' appears in the above numberedtpatent requiring correction. and that the-said Letters Patent' should, readfes I corrected below I Column 4, lines and 30, strike out 'idi stributed uni formly throughout the length. of .the column? and. insert the same after "elements" and before the. comma in line 30, same column. I

Signed and sealed this 'TthE'day of November 1961.

(SEAL) Attest: v T ERNEST W. SWIDER f DAVID L. LADD Attestil ag Officer Commissioner oflPatents -t I USCOMM-DC

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