Oral-History:Paolo Gazzana-Priaroggia

About Paolo Gazzana-Priaroggia

Paolo Gazzana Priaroggia, born in 1917, received his degree in Electrical Engineering in 1940 from the Polytechnic Institute of Milan. In 1945 he joined R&D Department of Pirelli Cables in Milan, initially in the telecommunication field and then in the power field. In 1950 he became manager of the Power Cables Laboratory. In 1958 he was appointed manager of the R&D Department of Pirelli Cables-Italy, and in 1966 Chief Engineer of the Cable Division-Italy. In 1972 he was given the responsibility of the whole Pirelli Cable International Sector as Chief Engineer and R&D Director. Retired in 1982, he served Pirelli SpA as Consulting Engineer until 1987.

In the interview he briefly recounts his wartime experience before discussing the research he conducted at Pirelli in the field of high-voltage cables. Early on, his group developed new types of paper insulation for oil-filled high-tension cables that strengthened their performance during impulse-testing. He also mentions advances in submarine power cables, the screening of cables, the prefabrication of cable joints, the production of extremely long cables, the use of computers in design, and DC underwater cables. He also describes Pirelli’s communications research, including pioneering fiber-optic work. He concludes by pointing out Pirelli’s truly international organization.

About the Interview

Paolo Gazzana-Priaroggia: An Interview Conducted by David L. Morton, IEEE History Center, 31 July, 1996

Interview #289 for the IEEE History Center, The Institute of Electrical and Electronics Engineers, Inc.

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It is recommended that this oral history be cited as follows:

Paolo Gazzana-Priaroggia, an oral history conducted in 1996 by David Morton, IEEE History Center, Piscataway, NJ, USA.

Interview

Interview: Paolo Gazzana-Priaroggia

Interviewer: David Morton

Place: Milan, Italy

Date: July 31, 1996

Background and World War II

Morton:

Would you tell us your name for the record?

Gazzana:

Yes. My name is Paolo Gazzana-Priaroggia. I have a double name. I was born in 1917. I became a Doctor of Electrical Engineering in 1940, just at the beginning of the war. I spent three years, 1941, ‘42, and ‘43, in the Italian Army as a Signal Corps Officer in the North African War against the British. During May 1943, I was captured by the British in Tunis and I spent one year in a prison camp in French Morocco.

Morton:

What was that experience like? Was it bad?

Gazzana:

No, not too bad. When Italy started their cooperation with the Allies at the end of 1943, I was asked to enlist in an American company, a signal company the 7287 Signal Construction Company. So with this company I reached Italy and I participated with the Fifth American Army in the invasion of Italy, and so I arrived in Milan slightly after the end of April of 1945. So all my experience during the war was with signal, both radio and telephone. In 1945, at the end of the war, I joined the Pirelli cable sector where I started as a research engineer.

Pirelli and Cable Research

Morton:

At that time, what kind of cable was there? What was Pirelli's market?

Gazzana:

You see, I was mainly involved with the oil filled high tension cables. Before the war, from 1926 to 1928, Pirelli had already manufactured and installed 138KV oil filled cables in New York and in Chicago (these were the first in the world) and licensed American manufacturers like General Electric. Subsequently, in 1935, ‘36, ‘37, Pirelli had already introduced in the Paris grid in France the 220 KV oil filled super tension cable, which was the first in the world at that time. But after the war, there were new specifications for the super tension cables, not only an AC-type test, but especially an impulse-type test, because the main concern at that time, immediately after the war, was the stability of a cable against lightning. There were difficulties at that time because whereas the existing super tension cables were very good at AC, they were not so good at impulse.

Audio File

MP3 Audio
(289 - gazzana-priroggia - clip 1.mp3)

So I was involved in a research team which was engaged to find out why the cables were so weak at impulse. This was a situation everywhere in the world, not only in Italy. We discovered, with my team, that the main reason of the weakness of cables against impulse was the presence of tiny wrinkles, which were produced in the cable in the butt spaces of the paper insulation during bending of the cable. Do you understand what I mean? During bending of the cable, when you have the two paper tapes butting each other, in the middle there were tiny wrinkles because the paper could not slip. So, first of all, we proved that this was the main reason, and then we started to investigate all the mechanical aspects of the bending of the cable, the internal stresses of the cable, the possibility of slipping one tape against the other one. We arrived — By doing this, we were able to build cables in which the tapes could slip very smoothly, one against the other, without producing wrinkles. I think we were the first in the world to discover this and to arrive at this point.

Morton:

What material did you use?

Gazzana:

We used special cellulose fiber tapes. You could call it paper, but it was not really normal paper. It was a special type of paper in which the impermeability, the density of the paper, the uniformity of the paper, the uniformity of the friction coefficient was extremely important. We also had to build new taping machines because the existing taping machines in the factory could not do such perfect work. So we had to build machines in which the calibration of the tension of the tapes was extremely precise. By doing this we were able to make super tension cables which could stand up to the impulse tests, and years later we published a book like this in England. If you want I can give you a copy. This was published several years later, when the subject was known. You know, at the first moment we were a little jealous of our finding, and so this book was published years later, when all the problems had already been solved.

Morton:

Could you describe the impulse-tests, the procedure and the equipment?

Gazzana:

Not here. Not in this book. There are other publications. Later on if you want I can show you other publications where we discuss the problem.

Morton:

So that became an important product?

Gazzana:

So this became an important product and we made 300 KV cables for Canada, 275 KV cables for England, 220 KV cables for Italy, and 330 KV cables for Australia. That was the result of all of this. We have several IEEE publications which I will show you later. I don’t know if I can give you some of them because I don’t have many copies. But in case, we can go downstairs and have a photostatic copy in the library, which is near my home. So later on I will show you all the material I have on this subject, if you like.

Alkyl-Benzenes & Submarine Power Cables

Gazzana:

I have always been in research, even when I was a boss in the company, but I was always in research because that was my favorite job. So another important thing that my research team did was the introduction in super tension oil filled cables of alkyl-benzenes instead of mineral oil. The reason for this is, first of all, you can have alkyl-benzenes with a very precise chemical composition. You have dodecyl-benzene, decyl-benzene, and nonyl-benzene. One great advantage of these oils is that they are very fluid, and so you can have much longer feeding distances for the cable. This was the reason which enabled us, in the years between 1950 and 1960, to start making longer submarine cables of this type.

Morton:

These were submarine power cables?

Gazzana:

Power cables, power cables. So for instance, we made the 138 KV cables across the Long Island Sound, for instance. We made a 300 KV DC oil filled cable in the Vancouver Strait. We made 138 KV oil-filled cables in the Mediterranean between the Baleares Islands. We made a 400 KV oil-filled cable across the Messina Strait. We made 550 KV oil filled cables across the Vancouver Strait again. So we made several of these cables around the world, utilizing these alkyl-benzenes which, besides their very good chemical and electrical properties, they had the great advantage of having a low viscosity.

Another development made for the first time about 30 years ago, were 400KV oil-filled cables installed in very deep vertical shafts with terminals inside the transformers. Here the main problem was the very high oil pressure at the bottom of the shafts.

Morton:

If I may ask a question, in these cases you mentioned with the submarine cables and other cases, did Pirelli install this equipment, or did they first sell it to a customer who installed it themselves?

Gazzana:

No, no, we installed it. In the past there were two Pirelli cable laying ships. One was destroyed by storm during the first World War, and the second one was destroyed by a war event during the last war. Now Pirelli has another very big laying ship which is very good for these jobs. Pirelli does everything, installation, survey, installation of terminals, all work that is required. They give a finer job.

Morton:

Is that an area that Pirelli really dominates, or are there other big competitors in submarine cables?

Gazzana:

Yes, Pirelli has several competitors today. Not many at the beginning, but later there was, first of all, Les Cables Lyon in France, then STK in Norway, then there is ASEA in Sweden, and also the Japanese. The three big Japanese factories make oil filled cables for submarine use. But I think we were the first for long lengths, of course, because for short lengths we were not the first. But for long lengths we have been the first in a certain moment.

Screening of Cables

Gazzana:

Another thing which I can mention is that we had studied extensively the screening of cables. The carbon paper as a screen was introduced by Anaconda many years ago for solid-type, high viscosity oil cables. But I don’t think Anaconda made a very thorough study of the properties of carbon paper and what is the reason for the benefit. We discovered that the thin oil layer which is against the carbon paper screen has a higher dielectric strength than thin oil against a metal electrode. But on the other hand, this increases the losses of the cable, because what produces the benefit of dielectric strength is the movement of ions in the thin layer of oil. This movement of ions is beneficial for the dielectric strength because it’s like a glow which removes the possibility of having a stress concentration and subsequently a puncture of the dielectric. But on the other hand, this movement of ions produces losses. So to overcome these difficulties, we got a patent on what we called a Duplex Carbon Paper. Duplex is a paper in which one side is carbon paper and the other side is insulation. The same paper, not two different tapes. On one side is carbon black and the other one is insulation.

Morton:

Is it a coating?

Gazzana:

No, no. These are two layers of paper, one in which small carbon particles are introduced, and the other not. These are joined together and glued together in the same paper-making machine. They are glued without any glue. They just adhere, one to the other one. There are some fibers which are interweaved. So this was one important thing. Another thing which we introduced was the metal sheathing of the cable under oil pressure. Normally these cables are taped and then they are provided with a metal sheath, either lead or aluminum. Then a vacuum is produced inside the cable and de-gassified oil is introduced from one end in order to fill all the cable. But this process is not perfect, because it is not easy to produce a vacuum in a long length of cable. So we started a process in which the cable was impregnated in a tank in which the cable was connected to the press, either lead or aluminum press, directly. So the cable was sheathed with metal under oil pressure, so when you obtain the cable on the other side of the lead press or the aluminum press, the cable is already completely full of oil. You don’t need to make this difficult impregnation of the cable from one end. This made a substantial amelioration of the quality of the cable. This became as perfect as possible.

Prefabricated Accessories

Gazzana:

Another thing which I can mention. We introduced prefabricated accessories. By the way, I am only speaking of high voltage cables, because even though medium voltage cables are very important, but they are not at the forefront of technological development. We made prefabricated joints and terminals for high voltage cables, super tension cables, using epoxy resins. The technique was not easy. The epoxy resins had already been used to make insulators, but not joints in which you have screens imbedded in the joint. So the novelty was the possibility to embed the screens and electrodes in the epoxy resins with the guarantee that no air gap was present, no air bubble and so on. So this was a very important technique, for which we gave some licenses, even in Japan.

Morton:

When was this?

Gazzana:

That was about thirty years ago, I would say, around 1960s, 1970s. Another thing, we introduced the design of these accessories by means of numerical calculations and iterative computer processes. So we could make very precise field plots of the electric field in the joint by these techniques. And this enabled us to improve the design of the joint.

Use of Computers in Engineering

Morton:

Was this the first time that your group had used computers for engineering purposes?

Gazzana:

We used computers for the first time immediately after the war, when we received in the University of Milan a computer from America, because at that time only America had computers available. So we got this computer about 1948, ‘49, something like that. This computer was installed in the Polytechnic of Milan and Professor Dadda was involved in that at that time. I remember that because we had some collaboration with Professor Dadda, Professor Bottani especially, and Professor Biondi. So we made lots of these calculations with the computer, especially when we got more modern computers. The first computer we got was the old type. And then there was a tremendous progress in computers until we received much faster computers.

Morton:

In those days, did the computer replace people with calculators, or did the availability of a computer encourage types of engineering that had not been done before?

Gazzana:

Certainly.

Morton:

Could you tell me more about exactly what things were being done?

Gazzana:

Of course, when we started numerical calculations, we were approximately in the same position as Professor Southwell when he started relaxation methods in engineering. And so we used mechanical calculators at that time. But by using mechanical calculators, it took us months to make a design of a joint or a design of a terminal. When we got the electronic computer, we reduced the time to one-tenth, and then with more modern computers, to one-hundredths and to one-thousandths. So it increased the speed. It was not only due to the computer, but also because we improved the numerical calculation and the iterative processes. We used a more convergent type of calculation. So computers and more convergent methods enabled us to produce in very short times the results which we needed. Is that all right?

Epoxy Insulation and Long Cables

Morton:

Yes. I interrupted when you were telling me about the later use of computers for design work on the joint. When we started talking about computers you were in the middle of a story about the special epoxy.

Gazzana:

Oh, yes, yes. It was especially important with epoxy resin terminals and joints just because we had electrodes imbedded in the epoxy insulation. It was not a simple insulator with nothing special. We had these electrodes imbedded in the middle of the insulation, and that required a more careful investigation.

Another thing which I would like to mention is that for long submarine cables we built, in one of the factories that we have near Naples, a very big impregnating tank, which has about twenty meters in diameter. It’s very big and can rotate about its axis. In a tank like this we were able to make one hundred kilometers of cable in one piece, for instance. Not of the biggest size, but for instance, a 132 KV cable could be made in one piece of one hundred kilometers. This was an important achievement. We reduced the number of joints either before laying the cable or during laying. So for instance, we made the crossing between Italy and Corsica in one piece. We made the same thing in Vancouver strait with the 550 KV cable, for instance, with this enormous tank, this big tank. Also, with this big tank we could sheath the cable after impregnation, keeping the cable under pressure. So we did not risk having a poor impregnation of the cable, because the cable was introduced into the lead press under a certain oil pressure.

EPR Insulated Cables

Gazzana:

Another thing which I would like to mention is that we developed EPR insulated cables up to 150 KV. EPR, you know, is ethylene propylene rubber. Whereas other people concentrated in a cross-link polyethylene, we preferred to concentrate in EPR, which is a flexible material. It’s not as hard as cross-link polyethylene. It is true that with polyethylene you can reach a higher tension, but for higher tensions we preferred to continue with our oil filled cable rather than to use cross-link polyethylene. We did not find a great advantage to abandon oil filled cables in favor of cross-link polyethylene. But when you need a good flexibility of the cable for cable inside the power station, inside the plant, and so on, we developed, and I think we were one of the first in the world to develop, an EPR insulated cable up to 150 KV.

DC Solid-type Submarine Cables

Gazzana:

Another thing which we made, we developed was DC solid-type submarine cables.

Morton:

When did that begin?

Gazzana:

We were not the first to do this, but I think we were the first to make the cables in such long lengths in one piece. DC solid-type submarine cables are cables impregnated with a very viscous compound not operating under oil feeding.

Morton:

Are there special considerations for DC? Are they very different than AC cables?

Gazzana:

It depends on where you have to lay the cables. For instance, for very long crossings it is necessary to use DC because of the reactive power of the cable. If the crossing is not too long, you can easily use an oil filled cable for AC. You can use an oil filled cable for DC also. There is no difficulty. But here I’m speaking only of DC against AC. Generally, DC is used for long crossings. AC is used for not too long crossings where the reactive power of the cable is not of great importance. Is it clear? Whereas reactive power is a limitation for the length of an AC submarine cable of any type, oil-feeding distance, even with the most fluid oil, is also a limitation for the length of an oil-filled submaring cable, either AC or DC. Therefore, very long submarine connections could be made only with DC solid-type cables.

Morton:

Yes. I know that DC was used very early, but this is much later. This is in the ‘70s?

Gazzana:

I am speaking of cables installed between 1965 and 1980, something like that. So we installed such cables in the Mediterranean. We installed such cables across the British Channel. As I said, we were not the first one, and we’re not the only ones, but we are certainly the ones who can make the longest cable in one piece. I will show you later that one of the main problems of DC solid-type cables was to understand the breakdown phenomenon of the cable, which was not at all clear because this cable, as you know, is not completely impregnated as an oil filled cable. It is impregnated with a viscous compound, but then it has some tiny voids. The presence of these tiny voids is a great problem, not because of ionization. Ionization in DC is not as important as in AC, but it is important for other phenomenon which we explained in a paper which we published not many years ago. I will give you a copy of that if you would like to have it.

1000 KV Oil Filled Cables

Gazzana:

Well, one of the last things which I would like to mention is the development of 1000 KV oil filled cables. This is certainly the first in the world. We installed a length of this cable in Italy years ago, after a long testing, a long research, but more recently we also installed a short line in Italy. This cable is energized today and is connected to an overhead line. This is certainly the first in the world. In no other country have 1000 KV cables been laid. I would like to say that it is certainly a prototype, and it is the first time in which a cable like that has been installed.

Morton:

I’m going to turn the tape over.

[End of Tape 1, Side A]

Development of Italian Power Grid

Gazzana:

If you like, I mentioned a booklet. This is in Italian, but this will tell you everything which has been done in the Pirelli Company during my responsibility. It starts from 1945 and it ends in 1982.

Morton:

That would be very nice.

Gazzana:

It is not a diary because it is very short, but if you have difficulty for a translation, let me know and I will send you a translation.

Morton:

Oh, okay. This is nice. Thank you very much.

Gazzana:

You can have the whole story in this, except for the last few years.

Morton:

What was the general development of power transmission in Italy during this period, from 1945 until the ‘80s? Of course, comparing it to the United States where there were longer and longer lines and higher and higher voltages, was that the trend here?

Gazzana:

132 KV transmission or 150 KV transmission was already done before the war in Italy. 220 KV transmission started in Italy after the war. In later years, about thirty years ago, also 400 KV transmission was installed in Italy. This 1000 KV transmission, which I mentioned, is just a small project which is more a prototype than a real installation. So 150 before the war all over Italy, then 220 after the war, and 400 KV again.

Morton:

Were these high voltage lines used mainly to form a grid, or to connect sources of power?

Gazzana:

Mainly to form a grid, but you also understand that in Italy we had many hydraulic stations in the Alps, and also in the Apennines. So there are long lines which are transmitting power from the Alps to the center and south of Italy. But we also have thermal stations, gas stations in Italy. There is a complete interconnection of the grid. Before the war we had many electric companies, but now we have a single electric company which is like EDF in France.

Morton:

So this interconnection and formation of the grid came after the war?

Gazzana:

After the war.

Morton:

Before that they were separate systems?

Gazzana:

Yes.

Morton:

So was it the case that the existing separate companies could be interconnected easily, or did everything have to be scrapped and started over?

Gazzana:

No, I think it was rather easy. It was not too difficult. Of course, first of all, we had a change from 42 hertz frequency to 50 hertz frequency. Before the war, practically we had only 42. After the war, we started with 50 hertz. But this did not require many modifications.

Morton:

Why 42?

Gazzana:

Forty-two was the minimum frequency which does not give oscillations of the light, the minimum. But then 50 was introduced all over Italy. In the U.S. you have 60, but in Europe we found that 50 was enough.

Morton:

Was there a particular manufacturer of generators associated with the 42, somebody who was really promoting that?

Gazzana:

Well, I don't really know. From this point of view I am a user. Perhaps you have to talk with some people of Enel, too. But of course, in Enel today there are only young people, so they don’t know very much of what was existing before.

DC Systems

Morton:

Do you happen to know if there were any DC systems in Italy before the War?

Gazzana:

No. In Italy there is now a DC system between Italy and Sardinia.

Morton:

But that was made more recently.

Gazzana:

That was made between 1960 and 1970. We installed two 200 KV cables, DC, and the French people, two other 200 KV DC cables. These cables go from Italy to Corsica, and from Corsica to Sardinia.

Morton:

Is that because those areas don’t have or can’t generate their own electricity?

Gazzana:

Yes. Well, the reason to make the crossing first to Corsica was also the depth of the sea. At that time a direct crossing between Italy and Sardinia I think it presented some difficulties due to the depth of the sea. Today it probably would not, but at that time. We had to reach Corsica. Corsica was just a point of landing. There was no power which would go to Corsica. I am not sure, but today I think the French people are trying to interconnect this cable with the Corsican grid, but I am not sure, not well informed.

Pirelli’s International Sales

Morton:

During the time that you were there, it sounds like Pirelli Cable had quite a few contacts with other countries. How important was that? Were they mainly selling in Italy?

Gazzana:

No. Of course, it was more important to have contracts abroad. So certainly, when we had the contracts in North America it was very interesting and important for us. We had a very good collaboration with the American companies for the Long Island crossing. Also, recently we installed a 350 KV cable across the Long Island Strait. We started with 138 KV thirty years ago, and two years ago we made a new cable again across the Long Island Strait. And for Vancouver Strait we made three cables, 132, 300, and 500 KV as I already said.

Morton:

Has Pirelli been involved or were they involved in any of the African power developments?

Gazzana:

African? No, no, no African. Except a 350 KV oil-filled cable which was installed in Zambia near the Kariba dam more than 20 years ago.

Telephone Cables and Fiber Optics

Gazzana:

Of course, I did not speak to you about the telephone cables, because I have also been involved in telephone cables. But whereas in power cable we have always been in the first row, in telecommunications we were not one of the first.

Morton:

Why is that? Not as much research?

Gazzana:

No, because we have never produced the apparatus for telephones. We did not produce amplifiers. We did not produce terminals. And it was extremely important that all the telecommunications be produced as both cable and electronic equipment. Only recently, with the advance of optical fiber, Pirelli started to produce amplifiers by using an erbium-doped fiber. Pirelli developed amplifiers by doping a piece of fiber with Erbium. Erbium has the property of amplifying the message, the telephone transmission, provided you can use a laser pump to pump energy into the joint. So by using an independent line, you can start a laser. This laser is pumping energy into the erbium fiber, and by doing this the erbium fiber is acting as an amplifier. This is not our invention. This is an invention made by many people, including Pirelli, if you want, but Pirelli are not the only ones.

Morton:

Was that a difficult transition to make for Pirelli, to go from copper cables to fiber optics?

Gazzana:

No, no. Of course, today copper cables are decaying in their importance enormously. But we started early with optical fibers. We made the first collaboration with the University of Southhampton just at the beginning of this technique.

Morton:

Do you know when?

Gazzana:

That was the last years of the 1970s, about ‘77, ‘78, or something like that. We made this collaboration. But then there was the new development of Corning Glass in the United States, which was much better than any other idea in the world. So we had the license from Corning Glass to produce optical fibers. We installed a factory near Naples, in the south of Italy, to produce optical fibers. And so, Pirelli have made submarine optical fibers also across the Atlantic. For instance, Pirelli participated in a cable from Africa to Brazil. Then Pirelli laid very long submarine optical cables in Malay, and several cables in the Mediterranean, around Italy. So this was certainly a very important job for Pirelli. But as I say, Pirelli are not the only one. Whereas, in super tension cables Pirelli have always been the first, of course today Pirelli does not maintain this position. If Pirelli are not the first, they are the second or the third, but always in the first row. So that is the reason why I have spoken to you of power cables, because at that time these were really new achievements, whereas in telephone we were a very good producer, but not the first.

Pirelli as International Company

Morton:

You could also tell me something about Pirelli cables. Pirelli is a French company, is it not?

Gazzana:

Pirelli is not a French company. It is an international company. Oh, I would say it is perhaps in part a Swiss company.

Morton:

A Swiss company?

Gazzana:

A Swiss company, mainly financially. International Pirelli Company is located in Switzerland. In France we have factories, we have Pirelli plants, but it is not the main thing of Pirelli.

Morton:

Okay.

Gazzana:

Pirelli has several factories in England, several factories in France, in Spain, in Canada, in the United States, in Brazil, in Argentina, and in Australia. It also has some factories in Germany, but not with cables, but other products. Financially speaking, Pirelli is perhaps mainly Swiss. But I don’t know by certainty, because you know capitals are going here and there, causing too many influences which I do not know.

Morton:

But the cable section has always been in Italy, mainly.

Gazzana:

No, the cable sector is in all these countries which I mentioned.

Morton:

But research is here?

Gazzana:

For research, the main research is in Italy. Then we also have some other research in Great Britain. We have a little research in the United States, and we have a certain amount of research in Brazil. Also in France we have some research. But the main research is in Italy, with small subsidiaries in England, France, the United States, and Brazil.

Morton:

Those are all the questions I have. Thank you very much.