a website collaboration between Science Service and the Smithsonian Institution

TRANSCRIPTION

E&MP 44.138
Electricity - Lichtenberg Figures

FROM PUBLISHED MATERIAL

GENERAL ELECTRIC REVIEW
SCHENECTADY, NEW YORK

--- 135 ---

Measurement of Surge Voltages on Transmission Lines Due to Lightning*

History of Lichtenberg Figures--Application to Measuring Transmission Line Surges--Determination of Polarity, Magnitude of Voltage, and Wave Shape--Results Fulfil Practical Purposes--Combination of Directly and Oppositely Connected Recorders--Service Applications--Analysis of Typical Records

By EVERETT S. LEE and C. M. FOUST
General Engineering Laboratory, General Electric Company

The investigation of natural phenomena in the field is vastly more difficult than corresponding research conducted with artificial equivalent in the laboratory. The field determination of lightning surge voltages in transmission lines presents a particularly difficult problem because the transient may last for only millionths of a second and may take place most unexpectedly. However, a suitable instrument and technique have been developed.--Editor

The results of continued recent study and use of the photographic Lichtenberg figures as a means of measuring voltages of short duration, of the order of microseconds,(a microsecond is one-millionth of a second.) and particularly surge voltages on transmission lines due to lightning, are creating a confidence in these figures which is gratifying both to the engineer who is called upon to make such measurements and to the engineer who uses the results in design and application. It was in 1777 that Dr. G. C. Lichtenberg(1) first described the figures made in sulphur dust by means of a charged electrode. In 1888, Trouvelet(2) and Brown(3) showed that the same figures could be produced on a photographic plate. Several investigators(4) have since devoted much time to studying the nature of these figures although at the present time their exact mechanism is still an uncertainty.

But it remained for J. F. Peters(5) in 1924 to suggest the application of these figures to the measurement of surge voltages and based on this application he developed a suitable instrument which he called the Klydonograph. In June, 1925, Cox and Legg(6) gave the results of field tests with this instrument and described extended developments in the instrument design. In September, 1926, K. B. McEachron(7) made public the results of a detailed study of the calibration of the photographic Lichtenberg figures using the Dufour Cathode Ray Oscillograph as the means for determining with certainty the wave shape of the

________________________
*Delivered by the authors as a paper at the Winter Convention of the A.I.E.E., New York city, Feb. 7-11, 1927.
(1) Lichtenberg, G. C.: "Super nova methodo motum ac naturum fluidi electrici investigandi," Soc. Reg. Sc. Gottingensis, 1778, T8, pp. 168-180.
(2) Trouvleet, E. T.: "Sur la forme des decharges electriques sur les plaques photographics," La Lumiere Electrique, 1888, v. 30. pp. 269-273.
(3) Brown, J.: "On figures Produced by Electric Action on Photographic Dry Plates," Phil. Mag. 1888, Series 5, v. 26, pp. 502-505.
(4) Pedersen, P. O.: "On Lichtenberg Figures," Pamphlet, 2 parts, 1919-1922, Host & Son, Copenhagen.
Toepler, Max.: "Laws of Creepage Phenomena," Archiv fur Elektrotechnik, Sept. 10, 1921, v. 10, pp. 157-158.
Heymans, Paul, and Frank, N. H.: "Method of Measurement of Time Intervals of 10-7 to 6.7 X 10-11 Seconds," Physical Review, June, 1925, v. 25.
(5) Peters, J. F.: "The Klydonograph," Electrical World, Apr. 19, 1924, v. 183, pp. 769-773.
(6) Cox, J. H., and Legg, J. W.: :The Klydonograph," A.I.E.E. Journal, June, 1925, v. 44, pp. 857-871.
(7) McEachron, K. B.: "Measurement of Transients by Lichtenberg Figures," A.I.E.E. Journal, Oct., 1926, v. 45, pp. 934-939.

impressed voltage. Thus, the discovery of 150 years has recently been applied to advantage.
To the work previously described, this article contributes additional correlative data, describes an extension of instrument design, and shows that the art has advanced to a stage where transmission-line surge voltages of the order of 2,000,000 volts may be recorded with a reasonable degree of accuracy.

General
As now used the klydonograph or surge-voltage recorder consists of an electrode bearing upon the emulsion side of a photographic film or plate which rests on the smooth surface of a piece of homogenous insulating material, as shown in Fig. 1. If the electrode is connected to the line side of a circuit, and the insulation connected to the ground side through a metal plate, and a positive surge voltage of say 20 kv. maximum is impressed from line to ground, a positive figure, as shown in Fig. 2, will be found on the photographic film after development. If with the same connections a negative surge voltage of say 20 kv. maximum is impressed from line to ground, a negative figure, as shown in Fig. 2, will be found.

It has been discovered that figures will be produced even though the time duration of the impressed voltage is only a fraction of a microsecond. Also that the size (radius) of the figure is a function of the magnitude of the maximum value of the impressed voltage, while the shape and configuration of the figure is a function of the wave shape of the impressed voltage. The problem of the instrument engineer therefore becomes one of deciphering the figures in terms of voltage and wave shape.

Magnitude of Voltage
The calibration of Lichtenberg figures for a given instrument to determine magnitude of voltage is obtained by impressing voltages of different values and

--- 136 ---

March, 1927 GENERAL ELECTRIC REVIEW Vol. 30, No. 3

observing the size of the resulting figures. This can be done for as wide a range of wave shapes as are available.

Table I and Fig. 3 give results of the authors' calibrations obtained on a film-type instrument with varnished paper insulation and a spherically rounded brass electrode 1/8 in. in diameter. The wave shapes

Fig. 1. Arrangement of Elements in a Directly-connected Recorder for Producing Photographic Lichtenberg Figures

varied from one-half cycle of a sine wave at 60 cycles (wave shape No. 1), to surge voltages rising to their maximum value in 2 microseconds (wave shape

CALIBRATION OF POSITIVE PHOTOGRAPHIC LICHTENBERG FIGURES
TABLE 1

No. 2), and in 4 microseconds (wave shape No. 3). The surge voltages were impressed from sections of a 500-kv. rectifying-type lightning generator, the circuit for wave shape No. 2 being as shown in Fig. 4 and for wave shape No. 3 as shown in Fig. 5. The wave shapes were determined by the Dufour Cathode Ray Oscillograph. Wave shape No. 2 is shown in Fig. 6 and wave shape No. 3 in Fig. 7.

When calibrating the surge-voltage recorder or when photographing the wave shapes with the cathode ray oscillograph, these instruments were connected between ground and the various voltage taps as shown in Figs. 4 and 5. The magnitude of the voltage was measured by a sphere spark gap similarly connected.

Fig. 8 shows a set of positive and negative figures for 5, 10, 15, and 20 kv. taken with wave shape No. 2. It is from such figures as these that the calibration curves are obtained. The radius of a positive figure is measured from the figure center to the most distant streamer tip.
Referring to Table I, it is seen that the average deviation from the mean for 100 figures resulting from the three wave shapes investigated at the different

Fig. 2. Appearance of Positive and Negative Lichtenberg Figures as Produced with a Directly-connected Recorder by Positive and Negative Surge Voltages of the Same Magnitude and Wave Shape

voltages is within + or - 30 per cent.
These results are shown graphically in Fig. 3. For any voltage, all figures obtained in 100 tests were within the extreme limits as shown.

--- 137 ---

MEASUREMENT OF SURGE VOLTAGES DUE TO LIGHTNING

These limits are determined by one figure out of one hundred, and are quite outside of the values which may be reasonably expected from the average values shown. It appears that an accuracy of 25 per cent can be reasonably expected from any single test made with these figures. Where several figures of somewhat the same size are obtained under similar conditions, the agreement of these among themselves permits of a more exact interpretation.

Cox and Legg in Fig. 39 of their paper(6) show a calibration curve for an experimental model of a film-type klydonograph. The wave shapes impressed

Fig. 3. Calibration Curves for Surge-voltage Recorder
Insulation--Varnished paper, 1/8 in. thick
Electrode--Brass, 1/8 in. dia., rounded spherically
Film--Eastman, No. 152
Curve 1--Wave shape No. 1
Curve 2--Wave shape No. 2
Curve 3--Wave shape No. 3
Curve 4--Average of data fore curves 1, 2 and 3
Curve 5--Extreme limits of data for curves 1, 2 and 3

varied from 25- and 60-cycle alternating-current, sine wave, to a surge voltage which attained its maximum value in 5 microseconds, the latter surges being obtained from a given network and their shape determined by calculation. The magnitude of the voltage was determined by a sphere spark gap.

McEachron in Fig. 7 of his paper(7) shows calibration curves of Lichtenberg figures obtained with Eastman's super-speed portrait films, placed on a glass plate, and using a cylindrical brass electrode 1 cm. in diameter with square edges. The shape of the impressed voltage was determined by a Dufour cathode ray oscillograph and the magnitude by a sphere spark gap. The range of wave shape was from a long wave wherein 22 minutes were required to reach a maximum value of 25 kv., to a short wave where the time to reach maximum value was 0.1 microsecond.

Fig. 4. Arrangement for Producing Wave Shape No. 2. The capacitors of the lightning generator discharge through the inductance and resistance in the external discharge circuit. The balance of the circuit constants with respect to the grounded point eliminates local oscillations.

Fig. 5. Arrangement for Producing Wave Shape No. 3. The capacitors of the lightning generator at the left discharge into capacitors at the right through the resistor in the external discharge circuit

The results of the calibrations reported by Cox and Legg, and the McEachron, are shown combined with the authors' in Fig. 9. These results show remarkable agreement for the work of different observers in different laboratories with different instruments and

--- 138 ---

March, 1927 GENERAL ELECTRIC REVIEW Vol. 30, No. 3

circuits, and give added weight and certainty to the calibration of the Lichtenberg figures with respect to magnitude of voltage.

Wave Shape of Impressed Voltage
In studying surge voltages, the wave shape as well as the magnitude is of importance, for on this depends the duration of the voltage. At the present time, the

Fig. 6. Upper--Cathode Ray Oscillogram of Wave Shape No. 2.
Lower--Cathode Ray Oscillogram of Wave Shape No. 2 Transcribed to Rectangular Co-ordinates

determination of the wave shape from the Lichtenberg figure characteristics is not as definite or as certain as the determination of the magnitude from the figure size and herein there is room for added study. At the present time the figures recorded with unknown wave shapes can be compared with figures recorded with known wave shapes as determined by the cathode ray oscillograph. This allows a prediction of the time duration to within a general order, but not with the

Fig. 7. Upper--Cathode Ray Oscillogram of Wave Shape No. 3.
Lower--Cathode Ray Oscillogram of Wave Shape No. 3 Transcribed to Rectangular Co-ordinates

Fig. 8. Positive and Negative Figures for Different Voltages Taken with Wave Shape No. 2

exactness required. The work by McEachron in this regard, as shown in Fig. 5 of his paper,(7) wherein he designates the figures as Type I, Type II, and Type III, is to be commended. Further study along these lines tending toward greater exactness

--- 139 ---

MEASUREMENT OF SURGE VOLTAGES DUE TO LIGHTNING

in the interpretation of figure characteristics is desirable.

Directly and Oppositely Connected Recorders
Form Fig. 89 it is clearly evident that the negative figures are quite inferior to the positive figures for purposes of voltage measurement since for a given voltage they are less than half the size of the positive figure; also McEachron has shown(7) that the negative figures present a greater deviation for differing wave shapes. There is also another serious objection: when the instrument with a moving film is connected to a

Fig. 9 Calibration Curves of Surge-voltage Recorders for Positive Lichtenberg Figures
Dotted Curve--Cox and Legg, Fig 39, referred to in footnote (6).
Dash Curve--McEachron, Fig. 7, referred to in footnote (7).
Full Curve--Aughor's, average curve Fig. 3 of this article.

Fig. 10. Arrangement of Elements in an Oppositely-connected Recorder for Producing Photographic Lichtenberg Figures

transmission line having normal voltage continuously impressed, the width of the band produced by the line voltage (see Figs. 14 and 15) is great enough to hide negative surges of values as high as 2.3 times normal line voltage and to give uncertainty to higher values. This would result in erroneous conclusions as to the number of negative surges recorded.
To overcome these objections, C. M. Foust conceived the idea of connecting two recorders in parallel with the polarity connections of one opposite to those of the other, thus insuring a large positive figure for every surge. Referring again to Figs. 1 and 1, the results of directly connecting the recorder to the line are shown. However, if as in Fig. 10, the recorder is connected oppositely, that is, the electrode to ground and the metal plate to the line, the positive surge will record a negative figure and the negative surge will record a positive figure as in Fig. 11.

Fig. 11. Appearance of Negative and Positive Lichtenberg Figures as Produced with an Oppositely-connected Recorder by Positive and Negative Surge Voltages of the Same Magnitude and Wave Shape

Fig. 12. Arrangement of Recorder Elements for Producing Both Positive and Negative Figures for Surge Voltages of Either Polarity

If an instrument is made up with two recorders, one connected directly and one connected oppositely, as shown in Fig. 12, then all surges, positive and negative, can be measured from the positive figure. In addition, oscillatory surges will be more clearly recorded, and

--- 140 ---

March, 1927 GENERAL ELECTRIC REVIEW Vol. 30, No. 3

Fig. 13. Photographic Lichtenberg Figures Obtained with Two-recorder Type Instrument
Fig. A--Positive surge voltage, 20 kv. maximum.
Fig. B--Negative surge voltage, 20 kv. maximum.
Fig. C--Oscillatory surge voltage, 20 kv., highly damped.
Fig. D--Oscillatory surge voltage, 20 kv., slightly damped.

Fig. 14. Figures Obtained with a Two-recorder Type Instrument, Showing Line Voltage Band
Fig. A--Positive surge voltage, 13 kv. maximum.
Fig. B--Negative surge voltage, 14 kv. maximum.
Fig. C--Positive surge voltage, 17 kv. maximum.

The circles are drawn with the figure center as the center, and with the circumference touching the most distant streamer tip. The radius of the circle is the measure of the magnitude of the voltage.
The line voltage band records a 60-cycle service voltage of 2.84 kv. maximum value.

Fig. 15. Figures Obtained with a Two-recorder Type Instrument Showing How the Negative Figure May be Hidden

The negative figure, of 9 kv. maximum surge voltage, is hidden under the line voltage band. Its presence is indicated by the full-size positive figure on the oppositely-connected recorded.
The line voltage band records a 60-cycle service voltage of 3 kv. maximum value.

--- 141 ---

MEASUREMENT OF SURGE VOLTAGES DUE TO LIGHTNING

negative surges completely hidden by the line-voltage band will be distinctly shown as positive figures. These features are shown in Figs. 13, 14, and 15.

Fig. 16 shows and instrument of the two-recorder type. It uses an Eastman film eight feet long and eight inches wide as standard with Cirkut outfits. A clock mechanism drives it at the rate of 1/2 in. per hour, and so gives a continuous record for 8 days. Timing is obtained by photographing the hour numbers on the film.

This construction largely excludes polyphase instruments because of constructional difficulties, but the obvious advantages of having all figures available as positive figures is so great as to accept this condition. It is felt that the application of this idea represents a real extension of the use of Lichtenberg figures, and results already obtained in the field show its merits. For example, out of 103 surges measured on three different transmission systems, 31 were of positive polarity, 26 were of negative polarity, and 46 were oscillatory.

Connection to Transmission Line
The voltage range of the instrument shown in Fig. 16 is from 2.8 to 25 kv. maximum. Above 25 kv. maximum, so called "slips" occur in the figures as shown in Fig. 17 for which condition the calibration curves do not apply. The arcover of this instrument on a 2-microsecond wave, wave shape No. 2, Fig. 6, is 35 kv. maximum. Thus, some provision must be made for connecting the instrument to transmission lines up to values where the normal maximum voltage to ground is 180 kv. maximum for a 220 kv. 3-phase line, and where the maximum values of surges may be ten times this value.

Cox and Legg(6) describe an electrostatic potentiometer and antenna coupling. The authors have investigated and used insulator coupling. Of the various schemes proposed for such connection, that

Fig. 16. Surge-voltage Recorder of the Two-recorder Type

shown in Fig. 18 has been recently used in 27 installations and has been found to be simple, reliable, and easy to calibrate. The instrument is connected in parallel across several insulators of an insulator string with added protection over the line insulation as

Fig. 17. Photographic Lichtenberg Figures of a Positive Surge Voltage (33 kv. max.) which Exceeds the Instrument Range

The black lines in the positive figure (lower) are commonly called "slips" and their presence indicates the figure to be of uncertain calibration. However, such figures can be stated with certainty to be above a given voltage value depending upon the instrument design.
The negative figure (upper) though symmetrical and appearing to be suitable for voltage measurement is nevertheless not usable because of the great variation in figure size with wave shape.

desired. The instrument is placed in a sheet metal housing equipped with a suitable entrance bushing and automatic device for grounding the outfit when the door is opened. This housing protects the

Fig. 18. Arrangement for Connecting Surge-voltage Recorder to Transmission Line

--- 142 ---

March, 1927 GENERAL ELECTRIC REVIEW Vol. 30, No. 3

instrument from the weather and insures safety against tampering. It also acts as an electrostatic shield to eliminate stray field effects.
It is important to have the instrument connecting leads short, preferably not longer than five feet. From Fig. 19 it is seen that the figure size decreases considerably with a longer lead; and if the instrument is used with leads of different length than that with which it is calibrated, the resulting error is large.

Adjustment of Insulator String Potentiometer
The adjustment of the insulator string potentiometer is made by adding a sufficient number of insulator units in series to the normal line insulators to give adequate protection, and to provide enough insulator units across which the surge voltage recorder instrument may be paralleled to obtain a satisfactory

Fig. 19. Calibration of Surge-voltage Recorder and Potentiometer to Show the Effect of the Length of Lead from the Instrument to the Potentiometer line voltage band. This procedure may be accomplished in the laboratory by impressing normal voltage at normal frequency across the entire insulator string with the surge-voltage recorder in position.

Table II gives the number of insulators which have been used successfully in the insulator string for different line voltages.

TABLE II

Calibration of Insulator String Potentiometer
The multiplying factor of the potentiometer can be calculated for normal voltage and frequency from the data obtained when adjusting the potentiometer string. For example, a 110-kv. line has a maximum value of voltage to ground of 90 kv. If the line-voltage band is 3 kv., then the potentiometer multiplying factor is 30.

The question then arises: Does this ratio hold for surge voltages? To answer this question, surge voltages were impressed across an insulator string potentiometer whose 60-cycle multiplying factor was 60. This string of 20 insulators, four of which were in parallel with the surge-voltage recorder. The source of the surge voltages was a lightning generator of the non-rectifying type discharging into an external circuit as shown in Fig. 20. This circuit had to be used rather than the circuits shown in Figs. 4 and 5 in order to attain the requisite voltage. The magnitude of the voltage was determined by a sphere spark gap. The time of rise of the surge voltage to its maximum value was calculated to be of the order of a fraction of a microsecond.

Fig. 20. Arrangement for Producing Surge Voltages for Calibration of Insulator String Potentiometer

The results of the calibration of the potentiometer up to 1,4000,000 volts are shown in Fig. 21.

These results show a generally decreasing multiplying factor from the higher to the lower voltages. At the higher voltages the multiplying factor is practically that obtained with 60-cycle voltage.
The results of tests with the rectifying type of lightning generator circuit arrangement (Fig. 4) to give a wave similar to that shown in Fig. 6 are also shown in Fig. 21. Tests were made with the insulator string potentiometer both dry and wet with spray. These were at the highest voltage that could be obtained with this generator for this type of work. The results seem to agree quite well with the non-rectifying type of lightning generator at the same voltage. The tests made with the insulator string when dry and also when wet show that for surge voltages the voltage distribution is practically alike under these two conditions. This is not the case at 60 cycles where, at least at the lower voltages, the difference between the distribution wet and dry is appreciable.
From the calibration of Fig. 21, for figures showing an instrument voltage of 25 kv., the surge voltage on

--- 143 ---

MEASUREMENT OF SURGE VOLTAGES DUE TO LIGHTNING

the line is 1500 kv. Figures with slips would indicate surge voltages from 1500 kv. to 2100 kv. Film arcover at 35 kv. on the instrument would indicate surge voltages on the line of 2100 kv. or over.

The results of these calibrations indicate that the magnitude of surge voltages up to ten times normal maximum value, line to ground on a 220-kv. line can be measured with considerable certainty.

Specimen Field Records
In Fig. 22 are shown some Lichtenberg figures obtained from a transmission line installation. The surge record is from 3 p.m. until 10 a.m. of the next day. During this time there were lightning storms in the vicinity of the line. It is clearly seen that these

Fig 21. Surge-voltage Calibration of Instrument String Potentiometer for 220-kv., 3-phase Line
20 insulators in the string.
4 insulators in parallel with surge-voltage recorder.
Instrument as shown in Fig. 16, housed and set up as in Fig. 18.
Circle plotting points obtained with circuit shown in fig. 20.
Cross plotting points obtained with circuit shown in fig. 4.

figures have the same characteristics as those produced with laboratory equipment. (The circles are drawn for voltage measurement as in Fig. 14.) The figures at the left and right are interpreted to be from oscillatory surges of highly damped nature, such as shown in Fig. 13 C which is known to be from an oscillatory surge voltage. The oscillatory nature of these surges is derived from the presence of both positive and negative Lichtenberg figures on both recorders. The middle figure indicates a unidirectional surge voltage of negative polarity, such as shown in Fig. 13 B.
It is noted that there is no line-voltage band upon the film. This sometimes occurs and it is thought that this is due to the variation in voltage distribution across the insulator string potentiometer at normal line voltage and frequency.

Fig. 23 shows a photographic record of surge voltages obtained on a 220-kv., 3-phase transmission line, using a surge voltage recorder of the two-recorder type (Fig. 16) with an insulator string potentiometer as has been described. The normal maximum value of the voltage to ground is 180 kv. and the multiplying factor of the potentiometer was 60. The record shown is from 11 a.m. on one day to 2 p.m. the day following. The line-voltage bands show when the line voltage was "on" and "off" during this period.

The record shows a high-surge voltage at 4:20 p.m. on Friday and the weather reports indicate severe lightning in the vicinity of the installation at this time. The loss of the line-voltage band some 30 min. before this surge shows that the line was de-energized at 3:50 p.m. A close examination of the original film reveals a surge at 4:03 p.m. but this is not distinguishable from the print. The figure obtained at 4:20 p.m. on the oppositely connected recorder is a positive "slip" (see Fig. 17) and therefore represents a voltage of negative polarity on the instrument of between 25 and 35 kv. Using a potentiometer multiplying factor of 60, this figure represents a line surge of some value between 1500 to 2100 kv. The corresponding figure on the directly connected recorder is predominantly negative. However, since some positive figure characteristics are discernible on the directly connected recorder, the surge must have been oscillatory and of a highly damped nature (see Fig. 13) with a first half cycle of negative polarity and a second of positive polarity and very much lower voltage.

At 10:30 p.m. on the same day another surge was recorded. A lightning storm was in progress at this time and the line excitation had been removed about 15 min. before this surge. Positive figures were obtained on both recorders. The figure on the oppositely connected recorder indicates an initial half cycle of negative polarity of 780 kv. The figure on the directly connected recorder indicates the second half cycle to be of positive polarity of 270 kv.
The weather records for Saturday morning show another lightning storm in progress. The surge record reveals two surges, one at 8:11 a.m. and one at 8:18 a.m., the line having been de-energized at 8:11 a.m. These two surges are not so clearly distinguished from the print, though in the original film the record is

--- 144 ---

March, 1927 GENERAL ELECTRIC REVIEW Vol. 30, No. 3

Fig. 22 Lichtenberg Figures Obtained on a Transmission Line Installation During a Lightning Storm

Fig. 23. Specimen Record of Surge Voltages on a Transmission Line During Lightning Storms

--- 145 ---

MEASUREMENT OF SURGE VOLTAGES DUE TO LIGHTNING

clear. The figure obtained at 8:11 a.m. on the directly connected recorder is of positive characteristics and on the oppositely connected recorder of negative characteristics. The line surge was therefore unidirectional and positive in polarity. The figure on the directly connected recorder is a positive "slip" and therefore indicates a line voltage surge between 1500 and 2100 kv. in magnitude.

The figure obtained at 8:18 a.m. is positive on the oppositely connected recorder. The instrument voltage corresponding to this figure is 21.5 kv. and this gives a line voltage of 1290 kv. of negative polarity.

This specimen record shows how the figures may overlap on the slowly moving film when the surges occur in quick succession. However, even under these conditions, it is generally possible to analyze the figures with considerable accuracy when the original film is used and when the figures from the two recorders are available.

Practically all figures obtained on transmission lines have been of the Type II class,(7) and may be placed therefore within the wide range of wave fronts which vary roughly from that of a slow 60-cycle wave to a surge which comes to its maximum value in a fraction of a microsecond.
In connection with the surge voltage-values obtained from the figures shown in Fig. 23, it is interesting to note that they compare favorably with the laboratory results of insulator flashover tests.

The value 1800 kv. for the lightning sparkover of a 14-unit insulator string given by Peek(8) seems to be close to the upper limit of voltages actually measured on the line by means of the recorders.

Summary
Surge-voltage recorders using the positive photographic Lichtenberg figures have given essentially the same calibration data under a variety of conditions; also the accuracy of such an instrument is of the order of 25 per cent with a somewhat better value possible for those measurements wherein several similar observations may be obtained.

An extension of the instrument design incorporates two recorders and this combination allows the use of the positive figure as a voltage measure of all surge voltages thus insuring greater certainty in the results. A more comprehensive analysis of the figure characteristics is also made possible by this means since both positive and negative figures are available.

A means of connecting the surge-voltage recorder to a transmission line of higher than instrument voltage has been developed and has proved to be simple, reliable, and easy to calibrate. Calibration data show that with such a connection reasonable accuracy may be obtained in recording voltages up to values of the order of 2000 kv.

The records which can be obtained from surge-voltage recorder instruments located along a transmission line will allow the facts regarding surge voltages on these lines to be determined with reasonable exactness.
_______
(8) Peek, F. W.: "High-voltage Phenomena," Journal Franklin Institute, Jan. 1924, v. 197, No. 1, pp. 1-44.


General Electric Review
Vol. 30, No. 3 March 1927

Transcription BY Gary Horton

Document
Transcription

Origination Files
49 pages 4.4MB
Requires Acrobat Reader 7

Larger View
Images



National Museum of American History

Home

Search - Site Map - Subjects to Choose From - Numbering Format

Credits - Copyright - Comments