BAUM: Long distance transmission

HIGH POTENTIAL, LONG DISTANCE TRANSMISSION AND CONTROL.

BY F. G. BAUM.

INTRODUCTORY.

In 1900, at the General Meeting of the American Institute of Electrical Engineers, I presented a paper entitled "Some Constants for Transmission Lines," based on measurements made on several transmission lines — the longest that had been built up to that time. Since then I have followed very closely the progress of transmission work, and in this paper I will give the practice and results on what is, and has been since 1900, the greatest transmission system in existence.

The system to which I refer is that of the California Gas & Electric Corporation, which has absorbed the Bay Counties Power Company, the Standard Electric Company of California, the Valley Counties Power Company, the Sacramento Electric, Gas & Railway Company, the Yuba Electric Power Company and the Nevada County Electric Power Company. The accompanying map will give some idea of the system.

Map of High-Tension Transmission Lines of California Gas & Electric Company. Line From Colgate to Oakland is in Duplicate.

The system has continuously in operation about 700 miles of line at 50,000 volts, 70 miles at 40,000 and a great many miles at 23,000, 16,000, 10,000 and 5,000 volts. The high-voltage lines extend from the Sierra Nevada Mountains of California to the Bay of San Francisco, and are thus exposed to all sorts and conditions of weather. In a short time some of these lines will be operating at 60,000 volts. The longest distance to which power is regularly transmitted is 200 miles, most of the power being transmitted 150 miles. The amount of power available on the system is 43,650 kw, and this will soon be increased by the addition of two 5000-kw generators at Electra. Owing to the large day motor load the peak on the system is not above 25 per cent of the average load.

In this paper. I will give as briefly as possible some simple methods of line calculations, and deal with the means of controlling the power at the high voltages.

Part I. LINE CALCULATIONS.

(Pages 33-44 have been omitted because it is too technical)

PART II. HIGH POTENTIAL CONTROL.

1. Insulators.-- We have on our lines practically every type of insulator manufactured. We have glass insulators, porcelain insulators and combinations of porcelain and glass having from one to four parts. In the mountains and away from the fog, a 7-inch glass does very well on 40,000 volts, but to go from 40,000 to 60,000 requires that the insulator be increased more than the proportionate increase in voltage. The insulator shown in Fig. 7 is used up to 50,000 volts, but at this voltage it gives trouble in the fog districts and during wet weather. Insulators of the types shown in Figs. 8 and 9 give very good results and are probably so good as can be obtained at present. Fig. 9 has been designed by the engineers of the California Gas & Electric Corporation.

Fig. 7. - 40,000-Volt, 11-Inch Porcelain Insulator

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Fig. 8. - 60,000-Volt, 14-Inch Porcelain Insulator

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Fig. 9. - 60,000-Volt, 14-Inch Porcelain Insulator

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As the time will probably come when 100,000 volts will be as common as 10,000 is today, we have not yet reached the limit of development in line insulation.

In testing the insulators, each part is subjected to more than the normal voltage from line to ground. The top is generally tested to 55,000 volts, the center to 45,000 and the middle petticoats to 40,000 volts. The test is made with salt water as electrodes.

2. Pins.— We are using iron pins on all our new work, and believe the idea of depending on the pin for insulation is wrong. Place the strain where it belongs — on the insulator. We are making our pins of pipe drawn down at one end. The pins are galvanized and a lead thread then cast to fit the insulator.

3. General Line Construction.—We are constructing our 60,000 volt lines with a 6 ft. spread, the wires being on the corners of a triangle. On our late work we are using tall poles and spreading about double the distance ordinarily used. In the mountains where we can take advantage of the hills and ravines, we use long spans, having some aluminum spans of 1000 to 1800 ft. in length.

A tower construction using a span of about 500 ft. would make an ideal line, and a line not much more expensive and much easier to care for than the ordinary pole line.

Our method of entering buildings is through a piece of plate glass about 24 inches square having a hole about 3 inches in diameter through which the wire passes. The glass is held by a simple wood frame. This construction is more satisfactory than the old method of passing through terra-cotta pipes.

4. Line Operation.— The lines are operated by keeping men at important points who patrol the lines from one to three times a week, depending on the condition of the line, these men being ready at all times to go out in case of emergency.

Our line troubles have been due to a few weak insulators; in some localities we have a good many insulators shot off. Some of our unexpected causes of trouble have been cranes or geese flying into the line; cats climbing up on the poles; green hay carried by wind dropped on the line; an engine starting up under the lines; a long tailed rat crossing temporary bus-bars.

5. Transformers.— Our transformers have given us very little trouble and are really the most satisfactory part of the system. High primary insulation and care in the handling of the oil to keep it free from dirt and moisture are of prime importance. The windings should be dried out before adding the oil.

That the presence of the oil does not increase the fire risk was amply demonstrated by a fire at the Colgate station in March, 1903. The transformers were in the hottest part of the fire and were damaged but little, the oil acting as a protection to the winding. The transformers were not responsible for the fire, as was reported at the time.

On test, the primary of each transformer should stand a test about equal to double the star voltage for which the transformer is designed. That is, a transformer which is to be connected 30,000 star, giving 51,960 volts line pressure, should stand an insulation test of about 100,000. Some manufacturers put on a test voltage from two to three times the transformer voltage. Less than two and one-half is not a good test.

6. Switches.— We find it convenient to use two types of switches to handle the electrical energy, the oil type and the air type. That the oil type switch is the only one that will stand heavy duty has been amply demonstrated. As it has not been possible to purchase satisfactory switches in the market, I have designed a line of switches for our high potential work.

We are now using the switches shown in Fig. 10 at our power houses, designed to handle from 10,000 to 40,000 kw at 50,000 or 60,000 volts. Each pole is in a separate tank and mounted in a fire-proof compartment as shown in Fig. 11. The three poles are operated together. The switch as shown gives four breaks per leg.

(pages 48-58 omitted, not pertinent, discussion about arresters, disconnect switches, etc.)

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Mr. E. F. OGLE: I would like to ask a question in reference to the insulators in Fig. 7 and Fig. 8 of the paper. With the type of insulator shown in Fig. 7, have you any trouble with the snow freezing in between the petticoats, or don't you have any snow?

Prof. BAUM: We have practically no snow on our lines.

MR. OGLE: Do you have any trouble with the cement that holds them together freezing?

Prof. BAUM: No.

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DR. PERRINE: I think in catechizing Mr. Baum on the question of his horn-arresters, we are getting away from the point of this paper, which is practically stated by Mr. Baum when he says that on such a system of transmission as this, he would use the highest possible voltage. He is having less troublesome experience at 55,000 — which is about the voltage I understand he is running now — than he had at lower voltage, and he ascribes this largely to the relatively smaller value of the voltage when a-Surging current is interrupted. In consequence, he believes that it is advisable to keep down the current on the line, keeping up the voltage, for the reason that it makes these minor devices, such as lightning arresters, relatively unimportant. It is not the important point to catechize Mr. Baum on whether he has set his arresters at 3 1/2 inches, or used multiple gaps, or what. The point that he has made in his paper is, that by going to this high voltage and keeping his current down, he has made the minor difficulties, which have troubled us all so much, relatively unimportant. That, I think, is due not only to his high voltage on long lines; but also to the presence of multiple stations which feed into the line from all directions and which feed a very large amount of power, so that while in our discussion we may say that a short-circuit reduces the voltage on the line beyond it to nothing, we say that not knowing what actually happens. We may have a short circuit across an arrester or between lines, across a piece of bale-wire thrown on the line, which may, as Mr. Baum has stated, result in a relatively small current; so that beyond that point, if we have generating capacity enough behind us, we will still get voltage, and although we may have these minor interruptions, they will not interfere with the service. The paper of Mr. Baum is notable to me particularly in the fact that he does not discuss as difficulties many of the problems that we have been discussing in our transmission papers during the past year. For example, when the first of these lines began operation the question of the capacity effect became very important. Until Mr. Baum introduced the exciter device which he has already described to us, one long-distance transmission system could not operate a lighting load on account of troubles with capacity, and, in consequence of capacity troubles, we have often discussed the use of motor-compensators. You will notice that in Mr. Baum's paper there is not any mention of any necessity for these artificial regulating conveniences, except when the question arises of operating large street-railway plants with their variable load. So that on account of high voltage, keeping down current, and the great number of stations feeding the line from different directions and different points, a very satisfactory solution of the switching problems has been reached; as well us an apparently satisfactory approaching solution of the insulator problems. In this great system, operating a total of about 700 miles of high potential lines, and operating two stations in parallel, 325 miles apart, he gets rid of the troubles which some stations have when carrying relatively small amounts of concentrated load of one kind, operating lines. The success of this system is the success of a system which is operated as a whole, and it is not only the lightning-arrester difficulty which largely disappears, but it is also the capacity difficulty and the Induct alley difficulty and many other difficulties which also largely disappear. It is firmly my opinion that the great success of this long-distance transmission is due to its apparent complexity.

Dr. BELL: I think the whole profession owes a debt of gratitude to Mr. Baum for his practical researches on these problems that have been bothering us all more or less. But apropos of what I think Dr, Perrine has just said, I cannot help feeling that there is a phase of the matter that we are justified in presenting to Mr. Baum's attention. A great system like this, the greatest transmission system in the world, may not have immunity from all troubles. When you feed from half-a-dozen points and have thirty load points, trouble no longer embarrasses the system as a whole, so that many of the difficulties are simply minor local troubles. Nevertheless, this is not a normal transmission line. It is a wonderful and exceptional one, on which Mr. Baum has been privileged to experiment. If we had instead of such a system a straightaway system of 10,000 kw for 75 or 100 miles, and the same troubles, of short circuits over the arresters, etc., came upon it, it would not mean an incident in the system; it would probably mean losing the whole load, with all that this implies. So that while these difficulties can be passed over as minor in a splendid large system with a considerable number of feeding points; they become major difficulties, perhaps controlling difficulties, under almost precisely similar circumstances as regards construction, when we deal with a single line on which anything happening puts the whole business of the company out of commission for a longer or shorter period. That, I think, is why we pressed home some of these questions which are not intended as criticisms at all, but merely to get Mr. Baum's valuable experience on some of them. As respects the high-voltage proposition, I have always believed that when you passed over the moderate, and comparatively insignificant voltages of the past, the 10.000 volts or so which was used so extensively, the proper thing to do was to play the limit fairly, and it seems to me one of the great advantages of playing the limit is not only immunity from surging — I have seen the terrific effect of it at three or four thousand volts — but the fact that when you are insulating for 50,000 volts, you are planning the details of the line with a respectable factor of safety, to which most of the minor troubles, including all the minor lighting discharges, become insignificant. In other words, when you are insulating for 60,000 volts as thoroughly as Professor Baum is insulating out there, the ordinary induced lightning flash — what we generally know as lightning on the line— is merely an incident; it is merely what might as well be a part of a surge in voltage, a part of any extra rise in voltage, but cuts no figure there with respect to the margin of insulation of sixty or seventy-five thousand volts which you have left. I think the secret of these high voltages lies not only in the dimunition of the surging troubles, which of course takes place just in that way, but also the fact that you have a tremendous factor of safety, and it gives, all of us, I think, courage in attacking the problems of the future to know of the great success which Mr. Baum has had on this big system, and the extent to which the insulation precautions, which he has taken, overcome these minor difficulties.

MR. MORAN: I would like to ask one or two more questions from Dr. Perrine and Mr. Baum. As I am not thoroughly familiar with the systems, I wish to ask if you have one circuit on lighting and one circuit on rotary-converter power?

Prof. BAUM: All together.

MR. MORAN: What I was driving at is that I wish to try to find the relative trouble, if any, on a rotary load and a lighting load on such a long-distance system.

Prof. BAUM: The lines are operated altogether; everything is in parallel; the lighting load is taken off from the same line that the motor load is taken. Up to a year ago the Northern system was independent of the other system, and we supplied its load from one power house, which was a straightaway system, load of course being taken all along the various points. During that time we had very great success with the continuity of service. To give an instance, at one point there were two 800-hp motors driving machinery in a cement plant. We have a record of those running for 67 days without a single stop. I think that is as good as we can get in any steam plant. We have motors driving a street-railway load, and we run that very often thirty or sixty days; we sometimes get a sudden knock-out, but are back in five minutes. If they are out over half-an-hour we hear from the board of directors.

I will illustrate what we did about two weeks ago. The station at Electra entirely broke down. There was a load all along its line which made it necessary to carry everything from the other stations. The intermediate station was partly disabled. That makes a distance of 325 miles the line was put through. We started up one machine at the end, and ran it as a synchronous motor and varied its excitation, and the entire load was carried, one portion to a mine.; making a total of 350 miles of stretch. The service was just as good as when we were feeding from both ends, due to the fact that we had the synchronous voltage running at the terminal and we held the voltage just as though we had the power house there.

MR. BLACKWELL: I would like to ask Mr. Baum whether all the different plants of the California Gas and Electric Corporation are ordinarily operated in parallel; or whether they each supply a different portion of the system, and are only thrown in parallel to meet emergencies?

Prof. BAUM: Just at present we are not operating them in parallel. We intend to arrange, in the course of time, so that we can at any time parallel them. They are arranged now so that you can pass a load from one point to the other. The two systems are kept separate at present so that the services from one line will not affect the service on the other. But we may change that. I anticipate when we get some insulators replaced, which we are now doing, that we will not have an interruption once in two or three months, with the modern insulators, and in that case we might as well tie the whole thing together.

Prof. BAUM: Just at present we are not operating them in parallel. We intend to arrange, in the course of time, so that we can at any time parallel them. They are arranged now so that you can pass a load from one point to the other. The two systems are kept separate at present so that the services from one line will not affect the service on the other. But we may change that. I anticipate when we get some insulators replaced, which we are now doing, that we will not have an interruption once in two or three months, with the modern insulators, and in that case we might as well tie the whole thing together.

Mr. T. J. CREAGHEAD: I would like to ask Professor Baum about the line switch as shown on page 52. I have not dealt with the fifty and sixty thousand volt lines but on medium high-tension transmission lines. I have always had the greatest respect for any place up the pole anywhere near the cross-arm. Now, in the use of a line switch as indicated by Professor Baum. I would like to know whether it is the intent to climb the pole and turn the switch by hand.

Prof. BAUM: The switch is operated from the ground with a single lever. The three switches are connected here with a wooden cross-bar and they are operated from the ground with a lever.

Mr. P. H. THOMAS: I wish to ask the author for a point of information. As I understand his calculation, the possible voltage rise on a line due to the interruption of a short-circuit current is made as follows: The heavy current resulting from the short-circuit stores magnetically in the inductance of the line a considerable amount of energy. On interrupting this current, this energy, is discharged into the capacity of the line. The result is a certain rise of potential, depending on the inductance of the line, the resistance and capacity and some other factors. The numerical value of this equation is based upon the assumption that the interruption of current occurs near its maximum value. What I wish to ask, is whether any experimental evidence has been derived tending to show that actual interruption of current does occur near the maximum point? I wish to call attention to the distinction between the mathematical basis of the equation stated and the rise of potential which may occur due to a resonant circuit tuned to an oscillating source of electromotive force, the latter requiring evidently a number of alternations to establish maximum potential. As far as my observation and experience are concerned, which include a number of direct experiments, no positive evidence is obtained proving that a heavy current will actually be interrupted near its maximum point within the wave.

Prof. BAUM: Mr. Thomas has got the wrong impression from the article. The rise in voltage is two hundred times the interrupted current, as I said. Take the value of the current the moment you interrupt it, and you get the rise in voltage. If you have no current, you have no rise. In other words, the current is sinusoidal. If you interrupt it at the zero line, we don't get any rise in voltage. If we interrupt it at the crest, the maximum, we have the maximum disturbance. I do not think we have any more evidence that the current will be interrupted at the crest than we have that it will be interrupted at any other point. If you throw a wire over that line, you do not know whether the final burning out is going to be at one point of the current wave more than another.

DR. PERRINE: I think the real thing Mr. Thomas is trying to get at is, whether there is any direct evidence that there is any considerable rise in potential?

MR. THOMAS: That is the point exactly.

Prof. BAUM: When we performed these experiments by short-circuiting this line a hundred miles away, we short-circuited the switch, an oil switch; the line discharged over an arrester set for 41/2 inches. You can readily calculate your voltage in order to jump that air gap; about 90,000 volts; 41/2 inches to ground, 9 inches between lines; short-circuit to ground. That occurred repeatedly.

MR. THOMAS: At which end did that discharge occur?

Prof. BAUM: It occurred at the power house. It would undoubtedly have occurred elsewhere if we had other lightning arresters. It occurred at the power house because that is where we had lightning arresters. It was an oil-break switch.

MR. THOMAS: What do you conclude from that?

Prof. BAUM: I conclude from that that you get a rise in voltage somewhere approximating that formula, due to an interruption, a short-circuit.

DR. PERRINE: I think there is an unfortunate double meaning to the term " resonance" as employed in the discussion. Mr. Baum is using resonance to signify the discharge due to a resonant circuit, a circuit which may not be perfectly balanced against another circuit but which at the same time is a circuit which discharges because it has inductance and capacity in it and in which the current circulating is interrupted. What Mr. Baum is giving us is what actually occurs when we interrupt a definite circuit. What Mr. Thomas described is what might occur, if we had one circuit perfectly balanced against another circuit. If this were impressed with the same frequency and voltage that are used in Mr. Baum's calculations, it would result in a very much higher increase of potential.

MR. THOMAS: The information I desire is, which is the actual explanation of our troubles?

Prof. BAUM: I think that is given here.

MR. THOMAS: I was asking what the evidence was for that; that was the point I was starting out; and if that is clear then I am through. What is the evidence of that? You assume it is so?

Prof. BAUM: There is nothing theoretical that can be shown, but I have never heard the thing questioned before.

DR. BELL: As a matter of fact, when we have a circuit such as Professor Baum has indicated we have a perfectly straightforward clear case of simple resonance in a simple circuit and under those circumstances we get that rise. You can call it by any name you please. It is simply one form of resonance. The last speaker was referring to what you might call complex resonance, which I believe actually does take place on lines oftener than we think.

MR. NEALL: I wish to add to Dr. Bell's remarks that I do not wish to criticise Professor Baum for his lightning arrester, but to call attention to the importance of the lightning arrester situation in general. Abroad, where the horn-type arrester has been used very generally, there seems to be no data to show its efficiency at 50,000 volts. This system of protection has not until recently met with favor in this country, and its present employment, which is confined to very high voltages, indicates a degree of protection lacking in our regular types. For this reason we can appreciate the desirability of all possible information as to the operation of Professor Baum's 50,000-volt horn-type arrester. My question has for its object more to learn what happened to these arresters than to criticise any individual for installing them. In continuation of my series of questions, I should like to ask Professor Baum if he has lost any poles directly from lightning.

Prof. BAUM: I do not think we have lost any poles due to lightning. We may have lost an insulator here and there, but I cannot trace and absolutely prove a single thing on our lines due to lightning.

Me. NEALL: Don't you think you could have taken a record of the operation of your arresters wherever they have been installed, by putting in supplementary gaps and having your men watch them regularly, thus knowing very closely what your arresters were doing and when they did it?

Prof. BAUM: Of course, we try to get all the information we can from our system. You are no more eager for information than we are. We do not get the information primarily to present to a meeting of this kind. We get it primarily for ourselves.

MR. NEALL: I do not want to appear prejudiced, but it does seem to me that the usefulness of the horn-type arrester has not been brought out prominently. The only thing that has been brought out is that it does not do any harm to the system, but there is a very grave question whether it does any good.

Prof. BAUM: Well, I consider it a safety. It may not operate more than once in a year, may not operate more than once in two years, but even if it shuts down your system once in two years absolutely, I consider it a safety to the system.

Mr. NEALL: Do you think it is any better in that respect than other forms of arresters which will discharge at lower voltage?

Prof. BAUM: The trouble is that they discharge too often. We do not want them to discharge that way. When they discharge once they are entirely out of business; you have got to buy a new set, and you know how many there are in multiple; it is expensive to put in lightning arresters of the ordinary type. Here we just put up a lot of copper wire and there is the end of it. We could keep one freight car from the East loaded with lightning arresters of the ordinary type busy all the time. Of this kind we can buy ordinary copper wire in stock and put it up.

Mr. NEALL: Is that a matter of experience or just a matter of belief?

Prof. BAUM: That is experience. I have had lightning arresters out there by the hundreds.

Mr. NEALL: Have you tried all types of arresters?

Prof. BAUM: All types that we could get hold of.

Mr. NEALL: Then I am to infer from your remarks that you believe for the future protection of high-voltage lines that some simple form of horn arrester is the solution?

Prof. BAum: I don't profess to have any particular prophetic vision in the matter at all. At present we are using the horn arrester. As far as I am concerned I would just as soon take them all off; but I keep them there for safety.

Mr. MORAN: I have had no experience with the horn arresters and have had some with the multiple-gap arrester; a test of forty thousand volts did not prove satisfactory to the multiple-gap arrester. If you will notice 30,000-volt lightning arresters in working condition, closed upon the line there will be seen a number of sparks constantly plying between the gap half way down the arrester, and as the surges in the line increase they will go to ground, opening the circuit if you have any automatic arrangement in the line, so that Mr. Baum's answers indicate to me that 50,000 volts is the limit for such arresters.

Mr. GERRY: Mr. Baum remarked that the limit of transmission tension rested with the insulator. I think it does not rest with the insulator, but with the transformers and secondary apparatus, such as the lightning arresters, switches, etc. Many of the difficulties have been worked out by Mr. Baum, and he has shown that we may go with safety to somewhat higher pressures, but it seems to me that the limiting condition is still in the apparatus even more than in the line insulation. The horn type of arrester will undoubtedly do good work under certain conditions, but as Mr. Baum will concede, if the gap be adjusted so that it will discharge only occasionally, a number of small difficulties such as occur with multiple-gap arresters, will be overcome but they will then be concentrated in one considerable difficulty, perhaps an interruption of the service, which may occur but once a month or once a year, depending upon the climatic conditions. In regions where there is a great deal of lightning it may readily be seen that a horn arrester might produce most unsatisfactory results, in the way of frequent shut-downs, while in other localities the results from a practical standpoint might be acceptable. I brought up the lightning arrester question, not because I disagreed with Mr. Baum, but to bring out the facts, and having done this I wish simply to reiterate the statement that I believe the limitations of working pressure for transmission purposes to be in the lightning arresters, switches, and secondary apparatus, as well as in the transformers. These limitations are not permanent, and the difficulties they present will be overcome, but at the present time the limiting conditions are there rather than in the line insulation.

Prof. BAUM: I do not agree with Mr. Gerry on most of those points. The transformers are not limited to the present voltages for which they are now being built. We are willing to build oil switches for 100,000 volts if we want them. The lightning arrester I think will take care of itself when you are operating at 100,000 volts and over; that is, if you insulate the line properly. There is nothing left, in my mind, but the line insulator, and I consider that the weak point of the transmission — the only one at which we see any very great difficulty in going to a higher voltage, say 100,000 volts. In other words, I believe if it were not for the line insulator we could go to 100,000 volts to-day.

Chairman SCOTT: We have had a very interesting discussion on the matter of lightning arresters, even though it be but an incidental part of the paper. I fear that some of the things Mr. Baum has said are susceptible of misinterpretation by others. If the simple statement goes forth that in operating his line he has found the simple horn arrester to be ample, and since his lines constitute the most extensive system in existence, then others may conclude, that because their lines are shorter and voltage lower, the horn arrester will be ample for them. I do not believe Prof. Baum quite intends that interpretation. In fact, he has said that he has but little lightning, and that he would not regret very much leaving them off entirely, but it was rather a matter of conscience and sentiment that the arresters were put on, so that they might feel a little safer. The absence of severe lightning is shown by the fact that they have lost no poles by lightning. On another plant a gentleman told me a while ago that in one storm forty-seven consecutive poles were more or less affected, and that he had had large poles from which, after one good disturbance, there wasn't enough left to make a fence post. Now Prof. Baum is not talking about conditions of that kind. He has said, moreover, that something happens on the lines from time to time, and he does not know whether it is caused by the lightning arrester or not; and he suggests that these disturbances, due to lightning arresters or something else, may be eliminated so that they occur only occasionally. Perhaps in the large system there is less likelihood of shutting down due to a disturbance at one place; but there are plants in which the mere fact of a temporary shut-down once or twice a season, of perhaps only a few minutes, and involving little or nothing in the way of cost and repairs, would lead to a very grave criticism of the protective devices. So I think, in line with what Mr. Gerry has said, we must feel that the lightning arrester problem is not at all solved because there have not been more difficulties on the Bay Counties line. If the operating engineers are satisfied with a horn arrester; if that will do all that they want, the manufacturers of lightning arresters have been entirely off the track in spending thousands of dollars and the time of experts in trying to solve the problem. Some may say it is because they want to sell something; but primarily it is because of the fundamental need of something of that kind, and because they have felt there is such a need. In fact I rather think that some of those who manufacture lightning aresters would possibly be glad to be relieved of the whole problem, but it is a necessary element, and one of the most difficult in the preparation of the apparatus for transmission systems, and I rather feel that operating engineers do not want to express a sentiment which will lead to the idea that efforts in this line by those who are doing the work of investigation, and trying to prepare apparatus of this kind should be lessened. Do I state it properly, Prof. Baum?

Prof. BAUM: That is correct. I do not want to give out the impression that if I were operating in a different part of the country and I were operating at a different voltage that I would not put on the multiple-gap lightning arrester.

Chairman SCOTT: Probably put on everything you could get?

Prof. BAUM: Tried everything I could get. We have tried this here and it has gone out of service and we have tried something else.