History of the Electrical Glass Industry in France

The following material was sent to Mr. N. R. Woodward (Houston, Texas) from Sediver International of France, in answer to his request for information about French insulators. Valuable it was, to be sure, but hardly the thing to just sit down and pour over when one doesn't speak French!! After several attempts to find a translator, all of which ended up in failure, he learned that Jack Tod's daughter, Diane, speaks fluent French, and she agreed to translate the article into English. (It was a welcome diversion for her while she nursed a broken ankle.) 

The article gives no actual names of glass manufacturers, but without taxing our brains too much, I think we can safely conclude that the "several glass manufacturers specializing in blown glassware" were probably Isorex, S.A.V., Folembray, VM, L'Electro Verre, Verreries De Reims, etc. It goes on to say that these manufacturers existed between 1920 and 1940 and became interested in making insulators because they considered them "an excellent diversification of their products". 

"In the 1950's", it says, "only two glass manufacturers, having experienced the required successes in the field, remained in competition. The others, having had either technical or economic problems, bowed out". Sediver itself tells us that the two factories in question were L'Electro Verre and the Insulator Department of the Charbonneaux Glass Works, and that they merged in 1959 to form the new Sediver Company. 

"The most complete line of glass insulators to be offered by one organization today is that of Sediver International, a sales organization offering French made insulators to a world wide market" (quoting from The Glass Insulator in America 1973 Report, by N. R. Woodward). Sediver is actually a composite word made up of the following: Societe Europeene D' Isolataurs En Verre, or European Society of Glass Makers. Insulators marked E.I.V. are manufactured by the Saint Gobain Glass Works, a Sediver subsidiary and major shareholder, in St. Yarre, France. This firm exists today and makes many types of glassware.

Many thanks to Mr. Woodward and Diane Tod for their efforts to make this information available to us.

Read on:

THE ELECTRICAL GLASS INDUSTRY AND ITS APPLICATIONS 
FOR THE INSULATION OF OVERHEAD POWER LINES 

by M. G. Duverney
Director General of Sediver 

HISTORY

At the beginning of this century the glass industry became interested, for the first time, in insulators designed for overhead power lines. At this time, certain well-known glass manufacturers, along with the directors of the railroad companies, introduced the first glass telephone insulators on lines paralleling the railroads.

The industry developed very rapidly, and by the war of 1914-18, multi-part pin insulators were already being used on high tension lines of up to 60 Kv.

The period between the wars saw the gradual and widespread adoption in France of this new type of insulator on distribution lines of low and medium tension. Meanwhile, the network of high tension lines, greater than 60 Kv, continued to use ceramic insulators -- "cap-and-stem". motor, Hewlett, etc.

At the industrial level, between 1920 and 1940, several glass manufacturers specializing in blown glassware became interested in insulators, considering them, above all, as an excellent diversification of their products.

Between 1945 and 1950, two developments occurred that would give new encouragement to this industrial activity:

• the gradual mechanization of production, thanks to the perfecting of specialized equipment: 
• the adaptation of the tempering process, well-known in the production of sheet glass, to the manufacture of glass suspension discs. 

Given the small number of glass insulator manufacturers in France and abroad, none of the makers of glass manufacturing machines were interested, up to now, in designing mass production equipment. However, a few glass makers, having large development departments and a certain faith in the future of the idea, invested their own money into perfecting automatic equipment that would profoundly alter the methods of production, virtually unchanged since the beginning. 

About the same time, these companies succeeded in adapting the techniques for tempering glass in the complicated shapes presented by suspension discs (ceramic insulators having dominated overhead high tension lines up to that time). 

Although tempering had been used in the production of safety glass as far back as the '20's, it was not until much later that companies were able to adapt the technique for electrical insulators.

The first industrial success occurred in England at the start of the Second World War. Techniques developed there were brought to France around 1945, where they were adopted and developed further.

The technical improvements made possible by the adaptation of the tempering process, combined with a decline in the cost price, led to the modernization of the production process. The glass industry had come of age.

Supported by a business-oriented government and by the principal utilities, it was not long before the effects of the industry's growth were seen. This was as true abroad, where sales continued to increase, as it was in France, where in less than ten years, use of this type of insulator was widespread. 

France is, in effect, one of the top suppliers of this type of equipment to importing countries lacking national glass or ceramic industries.

In the 1950's, only two glass makers, having experienced the required successes in the field, remained in competition. The others, having had either technical or economic problems, bowed out.

Finally, around 1958-1959, confronted with significant problems remaining to be solved (e.g., developing distribution channels in France and abroad that could handle the increased volume created by mass production, and perfecting the tempering process, through the use of a special glass, so that utilities could be guaranteed the quality of the product), the two remaining companies decided to merge. This merger allowed them to consolidate their technical abilities and improve their profit margin.

The merger had been approved beforehand by the government and, more importantly, by Electricité de France, the principal user. 

Thus, this particular application of the glass industry, begun in France at the beginning of the century, gradually came to dominate the insulation of overhead lines, regardless of the tension.

The single French company to remain in the business is now the leading producer of line insulators -- glass or ceramic -- worldwide. Its export business, combined with its manufacturing licenses issued to foreign companies, has made the foreign market several times larger than its French counterpart.

MANUFACTURING PROCESS

Standard glass insulators used on communication and distribution lines of low and medium tensions are practically identical to their ceramic counterparts, with the exception of the lower cost price. It is therefore preferable to spend time describing in detail the suspension disc using a tempered dielectric. 

Generally speaking, the process consists of using blasts of compressed air to re-cool the insulator, which has already been pressed to the desired form and then reheated. The outer surface of the insulator cools quickly during the blasting without substantially affecting the middle region where the moderate temperature slowly decreases. 

The middle zone, not having been directly exposed to the cold blasts, slowly releases its heat toward the outside, contracting itself in the process in function of the distension coefficient of the insulating glass. 

This glass tempering process has many similarities with the one used in pre-stressed concrete, where the pre-stressing does not appear until the release of the metal stays put in place beforehand.

This glass process is thus very different from the one used in metallurgy.

The manufacturing process includes:

• a glass furnace similar in design to the standard furnace and giving a glass of pure quality.
• a feeder specially adapted for delivering heavy glass globs at a slower rate than for other pieces of blown glass. The unit weight of the insulators can, in effect, vary from one to seven kilograms according to the type.
• a special type of press.
• an annealing lehr.
• a tempering machine for cooling the exterior zones of the insulator.
• a controlled re-cooling table where the pre-stressing process is completed. 
• a double arc designed to eliminate by a thermic process any insulator with a defect in the glass or in the pre-stressing. 

To the equipment and processes listed above should be added the assembly operation, which consists of attaching a medium-hard steel stem and a hood of malleable cast iron onto the piece of glass by means of a suitable cement. And so the complete insulator of the type in Figure 3 is formed.

The assembly operation in tempered suspension disc insulators is virtually the same as that used in the ceramic insulator industry. 

The assembly of the metal parts and the dielectric is done under mechanical vibration, and curing of cement is done by immersion in a tank of water maintained at a certain temperature. 

Next the insulators pass through a series of quality controls according to the regulations of France or of the foreign countries for which the product is destined. 

TECHNICAL CHARACTERISTICS OF HIGH-TENSION INSULATORS IN TEMPERED GLASS

Continuing our examination of high tension insulators of the suspension disc type in tempered glass, it is easy to isolate several factors favoring their technical and commercial development in France and their ultimate exportation abroad.

"Absence of fatigue effect of the insulator" 

The appearance of micro-fissures on the surface of the glass is called the fatigue effect. The fissures can occur under the combined or independent action of variable mechanical pressures or changes in temperature resulting from atmospheric conditions (the action of the wind on the conductors and its effect on the insulator chain, particularly insulators in anchor positions; the influence of the sun and rain during different seasons of the year). 

These micro-fissures grow with time, slowly decreasing the effectiveness of the insulators.

The lessening of some of the electro-mechanical qualities due to this fatigue effect can cause an interruption in the service of suspension disc insulators and can be responsible for serious accidents if stress on the line occurs (collapse of the line, for example, by release of the stem if the ceramic insulator is damaged in the head).

Tempering effectively protects the glass insulator against the above possibilities, thanks to the pre-stressed surface several millimeters thick and under strong compression.

After more than 20 years use on power lines, suspension disc insulators made of tempered glass have been shown to retain completely the same electro-mechanical characteristics promised when they left the factory.

"Improvement of mechanical properties"

Thanks to the strengthening from tempering, the insulator's mechanical resistance is greatly improved.

The mechanical characteristics of the insulator itself are at least twice as good as those of the iron fittings which, in the final analysis, represent the weak point of the insulator.

"Behavior of power arcs"

To simplify the explanation, a power arc caused, for example, by an accidental over-voltage or by a lightning strike, acts on the insulator like a shock wave followed immediately by a thermal shock. 

Now, thanks to the pre-stressing creating a strong compression on the surface of the tempered glass, the power arc should, in the first place, calcine the protective layer before destroying the insulator's skirt. 

It is thus possible to produce power arcs of 15,000 amperes during 50/100 of a second without causing the destruction of the insulator -- and that is without the protective rims which would have considerably modified the action of the arc.

COMMERCIAL ACTIVITIES

Better than any discussion, the following statistics show both the glass insulator industry's position in France (on power lines of all tensions) and the industry's position in the world market for equipment on high-tension lines.

French production is about 13,000 tons of electro-technical glass each year, with production divided into two principal areas.

The 5,000 tons sold in France represent practically the entire national market for insulators. 

The export business in annealed glass insulators is limited by the costs of packing and long-distance shipping. In addition, tempered glass insulators for low and medium tension lines have little advantage over their ceramic competitors. Only their price advantage has permitted their generalized use in France, whereas foreign countries lacking a glass industry have adopted the ceramic insulator.

The 2,500 tons sold in France represent practically the entire French market for insulators used on middle and high tension lines from 15 Kv to 380 Kv inclusive. 

The export business is principally concerned with high tension lines (of either direct or alternating current), including some experimental lines of up to a million volts.

From these figures we can conclude that the export market in suspension insulators is twice as large as the market for the product in France (4,500 tons versus 2,500 tons).

French insulators in tempered glass represent more than 30 per cent of the international market in high tension glass or ceramic insulators. This commercial activity establishes a near record in the exportation of electrical equipment.

In addition, the French industry has agreements with six foreign countries permitting the licensed production of insulators in tempered glass. These licensed industries occupy an important position in their respective countries, despite the competition in most countries of the ceramic industry.

License for manufacture of complete insulators:

• Italy -- 75% of the national market.
• Spain -- 70% of the national market.
• Brazil -- 80% of the national market. 

License for assembly, requiring the importation of dielectrics from France:

• Norway -- 80% of the national market.
• Australia -- 60% of the national market.
• South Africa -- 40% of the national market. 

Just recently, the French insulator industry concluded a seventh production and sale agreement with one of the principal porcelain companies in the United States. The American company, after numerous laboratory tests and a user survey, decided to end its porcelain suspension disc operation and to replace it with insulators in tempered glass.

The success of the French manufacturing process reinforces, if it is necessary to do so at this point, the position of French industry in the forefront of insulator manufacturers.

- - - - - - - - - - 

English translation by Diane Tod
Edited by N. R. Woodward 

NOTICE: In last month's issue (April 1982) there should be a caption under the picture on page 17. It should read: Figures 1, 2, 3 and 4. Sorry this caption got lost during production, Marilyn. You can just write it in, if you like.