Lightning Arresters Research Articles

Interconnection of Primary Lightning Arrester Ground and the Grounded Neutral of the Secondary Main

This investigation of the relative merits of various possible transformer connections and protective devices was the result of statistical data secured, over a long period of years, by the Commonwealth Edison Company of Chicago regarding the number and types of distribution transformer failures during lightning storms.* It refers to standard, 60 cycle, overhead, power and lighting distribution systems having 4,000-volt, four-wire primaries and three-wire, 230-volt, three-phase power and 115-230-volt lighting secondary mains. Five spans of standard pole line construction were exposed to transient potentials of steep wave front, the latter being induced by the sudden charging of the well insulated artificial clould suspended over the line. The cloud was charged to potentials, up to 150 kv., by means of a surge generator. Measurements of potentials, ranging as high as 40 kv. in some instances which were induced upon various portions of the distribution system were made by means of ionized sphere gaps and the cathode-ray oscillograph. Some of the important conclusions reached as the result of this investigation are: 1. The value of an experimental wood pole distribution line with an insulated artificial cloud charged by means of a surge generator was definitely established for lightning protective investigations involving induced as well as direct stroke potentials. 2. The practicability and economy of studying, by means of such laboratory equipment, the operation of various transformer, lightning arrester and ground connections, when exposed to surges approximating those of lightning, were demonstrated. 3.

Lightning Protection for Distribution ransformers Field Studies of Lightning Arrester Protection, Including the Effect of Interconnection

A cooperative field study with portable impulse generator and cathode ray oscillograph was made of the lightning protection of transformers connected to a 4.45-mile 4,600-volt rural distribution circuit. The tests described were made with the pellet arrester. Some of the conclusions are: 1. Although the arrester discharge voltage is but a fraction of the strength of the transformer, yet for the usual connection to ground now commonly employed, arrester ground resistances may be high enough so that the transformer is not protected, resulting in either blownfuses or a windingfailure. 2. Interconnection of the primary arrester ground and secondary neutral gives a high degree of protection to the transformer from surges originating on either primary or secondary regardless of the arrester ground resistance. 3. The interconnection of primary arrester ground and secondary neutral does not increase the magnitude of voltages which appear between various grounded objects on the consumers' premises over that now experienced with exposed secondary conductors and possible bushing flashovers or transformer failure. The effect of the interconnection is to increase the number of impulses reaching the secondary circuits but not their magnitude.

Interconnection of primary lightning arrester ground and grounded neutral or the secondary main

VARIOUS possible transformer connections and protective devices on standard 60-cycle overhead power and lighting distribution systems having 4,000-volt four-wire primaries and power and lighting secondary mains have been investigated over a period of years. Considerable information was furnished by an experimental line with an insulated artificial cloud charged to potentials up to 150 kv. by means of a surge generator.

Field Tests on Thyrite Lightning Arresters Using Artificial Lightning of 1,500,000 Volts

The impulse characteristics of thyrite station type arresters of various ratings have been studied when connected to a 45-mile transmission line. The surges were supplied by a 1,500,000-volt impulse generator. The volt-timle curves for arresters of various ratings were obtained under the conditions corresponding to the arrester on each incoming circuit, on the bus with two incoming circuits and on the bus with one incoming and one outgoing circuit. The oscillograms were found to check the calculations closely. With the arrester 90 ft. from a nearby tower the effect of tying arrester and tower grounds together was studied, and also the effect on flashover at nearby towers. The effect of flashover at a tower 1,660 ft. away on the operation of the arrester was determined. Oscillograms are given comparing the protective characteristic of a single-stack arrester with that of a two-stack arrester of the same rating. There is no discernable difference between the two characteristics. It has been proposed that line insulation for a distance of one-half mile from the station should be limited. Oscillograms are given for two arrester ratings, showing that, for the waves used, no protection is offered by the arrester at a distance of 2,180 ft. and a large part is lost at 500 ft. It is concluaded that the insulation should be limited at the arrester if the arrester is to protect it safely. The effect of the length of arrester connections is given, showing that on the 69-kv. arrester a loop 30 ft.

Abridgment of voltage oscillations in armature windings under lightning impulses — I

Experience has shown that rotating machinery connected directly to overhead lines is more vulnerable to surges than many other types of apparatus. This fact, together with a desire on the part of some to connect important units to the line in this manner, has necessitated a study of the protection problem. Such a study is here described, showing oscillograms taken when steep voltage surges were applied to machine windings measuring internal voltages to ground which are 200 per cent of the voltage allowed by the terminal lightning arrester. A simple traveling wave analysis of these oscillations is developed, which has successfully explained the pecularities of over 400 oscillograms taken under various terminal conditions. Practical methods of eliminating the oscillations with neutral impedance are outlined in the light of the theory developed, and oscillographic evidence supporting their reliability is given. A generalized theory of neutral protection is proposed. The importance of wave-front, surge impedance of incoming line, arrester resistance, and other factors is discussed. Methods for protection of the turn insulation and the insulation to ground of such machines are suggested, showing that the lightning arrester limits only the potential of waves entering the machine and cannot control oscillations which may take place within the machine. The advantages of thyrite as a neutral resistor are pointed out in connection with the short-circuit protection, telephone interference, and lightning protection problems of such machines. In Appendix A, the test circuits and methods used in the laboratory are discussed in relation to actual field conditions.

Recommendations on balancing transformer and line insulations on basis of impulse voltage strength

The danger of over-insulating transmission lines without a corresponding increase in the insulation of connected apparatus is pointed out. To avoid trouble from lightning reaching the apparatus, the Transformer Subcommittee of the Electrical Machinery Committee has prepared a set of proposed rules covering: (1) A practical method of defining the impulse strength of transformers, and (2) recommendation on coordinating the transformer and adjacent line insulation on the basis of impulse voltage strength. It is pointed out that commercial methods for determining the impulse strength of transformer windings by acceptance test in the factory are not feasible. However, investigations in the laboratory show that the impulse strengths of transformer insulation and of standard line insulators or of air-gaps vary similarly with different forms of waves; also that the impulse ratio of strings of line insulators of different lengths is approximately constant for the same impulse waves. The forms of impulse waves actually occurring on transmission lines have not been fully determined. For these reasons the impulse strength of transformers is expressed in terms of the 60-cycle dry flashover voltage of non-shielded suspension type insulators. If the transformer and line insulation are properly balanced with a given wave, it eliminates the necessity of having to consider the different shapes of waves encountered in practise. Three methods are recommended for coordinating the transformer and line insulation, namely, (1) the use of an effective lightning arrester; (2) the use of a horn-gap; and (3) the maintenance of average line insulation for a limited distance from the station.

Rationalization of Station Insulating Structures With Respect to Insulation of the Transmission Line

The purpose of this paper is to present a logical basis for the insulation of transmission lines and substations using as a basis the characteristics of traveling waves produced by lightning discharges. The method presented was formulated from the data obtained from the cathode ray oscillograms of actual line surges and upon the laboratory work in which the impulse flashover characteristics of insulating structuires was determined. 7' he breakdown volt-time characteristics of various forms of insulation are presented. Using these curves of various forms of gaps in the known characteristics of traveling waves, insulation of the transmission line at various distances from the gap is determined so that flashover will be znlikely to occur at these points. A similar method of analysis is made upon substations and lines protected by lightning arresters, but with the known characteristics of lightning arresters, the insulation on the line up to points 1000 to 5000 ft. away can be apportioned so that the lightning arrester will take the discharge, preventing the flashover of insulation. The system set forth in the paper enables the transmission engineer to design the line and stubstation in an economical manner and obtain adeqiuate protection for all points desired.

Coordination of Insulation as a Design Problem

The factors having influence on insulation design of transmission line and station are briefly reviewed, and it is pointed out that the progress of the art does not yet allow of close design of the insulation structure for insulation strength. The prominent part played by the lightning arrester is stressed, and the fact that it has a marked effect on the coordination of station insulation. Examples of a typical 110-kv. station where no coordination was made, and of a 220-kv. station where a deliberate coordination was attempted, are given, as well as the experience obtained with each.

Voltage oscillations in armature windings under lightning impulses-I

Experience has shown that rotating machinery connected directly to overhead lines is more vulnerable to surges than many other types of apparatus. This fact together with a desire on the part of some to connect important units to the line in this manner, has necessitated a study of the protection problem. Such a study is here described, showing oscillograms taken when steep voltage surges were applied to machine windings, measuring internal voltages to ground which are 200 per cent of the voltage allowed by the terminal lightning arrester. A simple traveling wave analysis of these oscillations is developed, which has successfully explained the peculiarities of over 400 oscillograms taken under various terminal conditions. Practical methods of eliminating th. e oscillations with neutral impedance are outlined in the light of the theory developed, and oscillographic evidence supporting their reliability is given. A generalized theory of neutral protection is proposed. The importance of wave-front, surge impedance of incoming line, arrester resistance, and other factors is discussed. Methods for protection of the turn insulation and the insulation to ground of such machines are suggested, showing that the lightning arrester only limits the potential of waves entering the machine and cannot control oscillations which may take place within the machine. The advantages of thyrite as a neutral resistor are pointed out in connection with the short-circuit protection, telephone interference, and lighting protection problems of such machines.

Abridgment of rationalization of station insulating structures with respect to insulation of the transmission line

The purpose of this paper is to present a logical basis for the insulation of transmission lines and substations using as a basis the characteristics of traveling waves produced by lightning discharges. The method presented was formulated from the data obtained from the cathode ray oscillograms of actual line surges and upon the laboratory work in which the impulse flashover characteristics of insulating structures was determined. The breakdown volt — time characteristics of various forms of insulation are presented. Using these curves of various forms of gaps in the known characteristics of traveling waves, insulation of the transmission line at various distances from the gap is determined so that flashover will be unlikely to occur at these points. A similar method of analysis is made upon substations and lines protected by lightning arresters, but with the known characteristics of lightning arresters, the insulation on the line up to points 1000 to 5000 ft. away can be apportioned so that the lightning arrester will take the discharge, preventing the flashover of insulation. The system set forth in the paper enables the transmission engineer to design the line and substation in an economical manner and obtain adequate protection for all points desired.

Lightning Investigation on the Ohio Power Company's 132-Kv. System

Description is given of the Lightning Field Investigation on the 132-kv, Philo-Canton, 73-mile, two-circuit line made during 1929 with surge recorders, cathode ray oscillograph, lightning stroke recorders, and a lightning generator. Data are presented on the magnitude of lightning voltage surges, the attenuation of these surges as they travel along the line, and the difference in attenuation between positive and negative lightning surges. The preponderance of positive lightning surges is indicated; but the fewer negative surges produce the highest voltage on the line. The lightning stroke recorders gave data on the polarity of the direct strokes, and the magnitude of the current in the lightning stroke. Lightning arrester performance on lightning and switching surges is analyzed, and typical surges obtained by the cathode ray oscillograph are given for both cases. The magnitude and shape of lightning waves occurring on the line are shown and these waves analyzed as to duration of front, tail, and total length. These data are discussed as they relate to the proximity and rate of discharge of clouds producing lightning surges. General conclusions are drawn based on the data obtained in the investigation.

Coordination of insulation as a design problem

The factors having influence on insulation design of transmission line and station are briefly reviewed, and it is pointed out that the progress of the art does not yet allow of close design of the insulation structure for insulation strength. The prominent part played by the lightning arrester is stressed, and the fact that it has a marked effect on the coordination of station insulation. Examples of a typical 110-kv. station where no coordination was made, and of a 220-kv. station where a deliberate coordination was attempted, are given, as well as the experience obtained with each.

Abridgment of development of the new autovalve arrester

This paper describes the development of a new autovalve lightning arrester operating on the principle of discharge in restricted passages. A brief resume is given of the improvements in performance and size desired in lightning arresters. Reference is made to laboratory tests on insulation protected with arresters to determine the limits of discharge voltage required for good local protection. Oscillograms show that the new autovalve arresters meet these requirements. Successful operating experience with these arresters is staled to give final verification of the results obtained in the laboratory investigations. The steps in the development of materials are described and the materials finally chosen and the design of arresters are considered. The performance is discussed and illustrated by oscillograms covering a wide range of currents, both with and without power voltage applied. The size of the new arresters is about one-half that of the present commercial autovalve arresters. One of the probable benefits resulting from this reduction in size is the possibility of making practicable the protection of high-voltage lines against lightning flashover.

Development of the New Autovalve Arrester

This paper describes the development of a new auto-valve lightning arrester operating on the principle of discharge in restricted passages. A brief resume is given of the improvements in performance and size desired in lightning arresters. Reference is made to laboratory tests on insulation protected with arresters to determine the limits of discharge voltage required for good local protection. Oscillograms show that the new autovalve arresters meet these requirements. Successful operating experience with these arresters is stated to give final verification of the results obtained in the laboratory investigations. The steps in the development of materials are described and the materials finally chosen and the design of arresters are considered. The performance is discussed and illustrated by oscillograms covering a wide range of currents, both with and without power voltage applied. The size of the new arresters is about one-half that of the present commercial autovalve arresters. One of the probable benefits resulting from this reduction in size is the possibility of making practicable the protection of high-voltage lines against lightning flashover.

Abridgment of lightning investigation on 132-kv. system of the Ohio power company

Description is given of the lightning field investigation on the 132-kv. Philo-Canton 73-mi., two-circuit line made during 1929 with surge recorders, cathode ray oscillograph, lightning stroke recorders, and a lightning generator. Data are presented on the magnitude of lightning voltage surges, the attenuation of these surges as they travel along the line, and the difference in attenuation between positive and negative lightning surges. The preponderance of positive lightning surges is indicated; but the fewer negative surges produce the highest voltage on the line. The lightning stroke recorders gave data on the polarity of the direct strokes, and the magnitude of the current in the lightning stroke. Lightning arrester performance on lightning and switching surges is analyzed, and typical surges obtained by the cathode ray oscillograph are given for both cases. The magnitude and shape of lightning waves occurring on the line are shown and these waves analyzed as to duration of front, tail, and total length. These data are discussed as they relate to the proximity and rate of discharge of clouds producing lightning surges. General conclusions are drawn based on the data obtained in the investigation.

On the Characteristics of Impulse Generators and the Impulse Test of Lightning Arresters

On the Characteristics of Impulse Generators and the Impulse Test of Lightning Arresters

Abridgment of klydonograph surge investigations

Since its recent development, the klydonograph has been used to investigate surge conditions on a number of transmission systems. Quantitative data, which show the characteristics of the actual surges present on transmission systems, are presented. In addition, these data are discussed in relation to various existing theories and practises regarding the production and the elimination of transient high voltages. The correctness of some of these ideas and the fallacy of others are indicated. The paper is subdivided, according to the nature of individual investigations, as follows: I. Open-wire Systems. II. Cable Systems. III. Lightning Arresters.

Klydonograph Surge Investigations

Since its recent development, the klydonograph has been used to investigate surge conditions on a number of transmission systems. Quantitative data, which show the characteristics of the actual surges present on transmission systems, are presented. In addition, these data are discussed in relation to various existing theories and practises regarding the production and the elimination of transient high voltages. The correctness of some of these ideas and the fallacy of others are indicated. The paper is subdivided, according to the nature of individual investigations, as follows: I. Open-wire Systems. II Cable Systems. III. Lightning Arresters.

Switchgear for Electric Power Control

THE electric power engineer will find much in this book that will be of value to him. As electrical stations increase in size, the amount and the cost of the requisite switchgear increase very rapidly. Devices are required for protecting the machines and for protecting the distributing mains. The question often arises whether it is worth while to instal a very expensive protection device in order to protect a main, thus paying a heavy annual insurance, or to run the small risk of having the main broken down. Cable manufacturers naturally favour the latter alternative, whilst manufacturers of protective switchgear favour the former. The authors rightly point out that the psychological device of calling a piece of apparatus a “lightning arrester” alone ensures a market for it, even without the accompaniment of a “publicity campaign.” Many English engineers have had the temerity not to use them. It has to be remembered, however, that in Great Britain we rarely have severe thunderstorms. The British Electrical and Allied Industries Research Association is carrying out valuable researches on switchgear, and Mr. Wedmore's official work keeps him in close touch with the most modern developments. The book discusses the latest practice.

Discussion at Spring convention: Lightning arrester application from the economic standpoint

K. B. McEachron: In the fourth paragraph in the first page, the statement is made that the relief voltage of the aluminum arrester for 6.6-kv. service is 18 kv., and for a certain distribution arrester is 28 kv. In the next paragraph is stated that the station type auto-valve has a relief voltage of 21 kv. instantaneous value. It is also stated that the comparison is well shown by the curves in Fig. 1. If the relief voltage is taken as that at which current first begins to flow then, according to the figure referred to, the distribution type (Curve 2) has a relief value of zero volts and the type S V and L V, 10 and 24 kv. respectively. From an examination of the curves, is it not true that these curves do not represent test results, but rather calculated curves based on theoretical considerations It is stated that the station type “closely parallels the electrolytic and therefore no curve is shown.” As shown, however, this cannot be the case, since as stated in Mr. Atherton's paper before the Institute in 1923, the arrester is designed for a so-called counter voltage of 25 per cent above the crest value of the rated voltage of the arrester. In this case, this gives about 13,000 volts, which is the value given in the paper. It should be remembered that this critical voltage is without the series line gap which adds materially to the voltage at which discharge begins.