Preface

After a trip to France in 1973, during which I recovered about fifty French insulators, I became interested in European insulator history. Language and distance made for significant handicaps; though I was able to obtain some data from a number of companies currently manufacturing European insulators after consulting the New York trade ministries of each country. They supplied me with the addresses of the manufacturers in their respective countries and, to each of these addresses, I wrote, in English, requesting catalogs, historical information, etc. 

The results varied. The reply rate was about fifty percent; though only half of these supplied data on pintype insulators. Of them, one company manufactures glass and five porcelain. All subsequent letters to these companies went unanswered. Still, in some cases, this information does illuminate some items which have previously appeared in Crown Jewels and with the seemingly increased interest in foreign insulators, will answer some questions which have yet to be published. 

This information was supplied in the first half of 1974, so that it is probably somewhat out of date. If anyone cares to follow up, as my personal interest in foreign insulators has waned, I would be most happy to supply them with the addresses of the companies and trade ministries. 

In this, and the following two issues, I will describe the items produced by companies operating in Germany, Spain and Italy. 

The German insulator industry is very much alive today. They are producing a number of unique EHV types, as well as more traditional designs, in porcelain. I received information from three companies producing pintype insulators, though only two provided catalog data. The following article provided by RWI outlines the early history of insulators in Germany:

DEVELOPMENT OF THE OVERHEAD-LINE-INSULATION IN GERMANY
by Ed. Diehl, Stuttgart and G. Reverey, Heidelberg 

The development of the overhead-line-insulation in Germany began in the middle of the last century. The first overhead lines were telegraph-lines on wooden poles and the first insulator was a porcelain pin-type insulator. This pin-type insulator was developed in the year 1850 by Werner von Siemens as a bell-shaped insulator (fig. 1). In the following years this insulator got an additional petticoat to improve the service reliability (fig. 2). 

A telegraph-line equipped with this kind of insulator was used by Oscar von Miller and Marcel Deprez in 1882 on the occasion of the world's fair in Munich to transmit a power of 1.5 hp from Miesbach to Munich over a distance of 57 km with a voltage of 2000 volts, This was the first German d. c. high voltage long distance transmission. 

The next stage of the bell-shaped insulator was the oil-groove insulator (fig. 3). The lower part of the bell-shaped coat was bent inside and in this way forming a groove which was to be filled with oil. The oil groove should prevent the formation of a coherent humidity film in rain and fog and thus to make a flow of current on the insulator surface impossible. Later on an improved type got some more such grooves. The oil-groove insulator can be regarded as the first anti-pollution insulator. 

With oil-groove insulators the wood pole overhead-line from Lauffen to Francfort was equipped over a distance of 178 km on which in 1891 a power of 210 kW at a voltage of 15000 volts was conveyed during the international electrical fair in Francfort (fig. 4). 

[This as the first type of insulator proposed for the Niagara Project in the early 1890's] 

This transmission line was the first one with three-phase a. c. over a great distance. The efficiency of the d. c. transmission from Miesbach to Munich compared with the three-phase a. c. one from Lauffen to Francfort had risen from about 23% to about 75%.

Conveying of energy with three-phase a. c. of high voltage made fast progress and the insulation had to meet the always growing requirements. Main problems became the puncture- and flash-over voltage of the insulators. 1897 arose the delta pin-insulator (fig. 5) and subsequently the wide-coat-insulator with greater flashover and puncture-path. For high voltages it was necessary to cement insulators of several parts. For the stability of the cementing could not be guaranteed a stronger delta-insulator was developed (fig. 6) which already could be produced as one piece. While one used with the first pin-type insulator the excellent compressive strength of the ceramic material the stronger delta insulator however had because of its short pinhole to withstand a cantilever strength. The delta-insulator was developed for transmission lines up to 30,000 volts. Three-phase a. c. grids with such rating voltages have already been in operation at the change of the century. 

The erection of big power stations at coal mines between 1910 and 1920 and conveying energy to the consumption centres far away required some more powerful transmission lines. For insulating such high voltages the pin-type insulator was no longer qualified. Also the stacking of pin-type insulators was not reliable enough and too expensive. The pin-type insulator therefore was superseded by the suspension insulator. 

The first suspension insulator was invented by Hewlett in 1907 in the USA (fig. 7). Two types of this insulator -- a suspension and a dead end type -- have been developed. The porcelain was only stressed by compression. The single units were connected by metallic rope U-Iinks which were threaded through curved tunnels in the porcelain disc. Thus the application of high voltages and the erection of towers with greater spans have become possible. 

The Hewlett insulator stood the test in Germany, too. Detrimental, however, was the metal loop which frequently lead to rupture by corrosion. After the Hewlett insulator followed several other types of suspension insulators which were developed as cap and pin type insulators simultaneously in America and Europe. For an insulator string the units were connected by caps and pins. The first type of them appeared in 1908 (fig. 8). For taking up the pinball a cylindrical or conical hole was used in America while in Europe a relieved pinhole was preferred (fig. 9). Within the insulator the ceramic material was stressed by compressive, cantilever, and transverse strength. In Germany many different ways were tried to construct the pin hole and the pin ball fastening. 

Increasing industrial contamination and salt deposit at the sea coasts led to numerous types of cap and pin-type insulators. Long creepage distances and good self cleaning properties became the basic requirements for the construction. In Germany in areas with industrial contamination the deep shed insulator has stood test well (fig. 10). 

An intermediate stage of the normally with an outer cap provided suspension insulator was the insulator with the cap inside (fig. 11). 

By inserting the cap into the insulating part the flashover voltage should be improved. With chains of such suspension insulators the first German 110 kV transmission line with three phases a. c. from Lauchhammer to Riesa was insulated. The overhead line with a length of 56 km was also the first overhead line of this rating voltage with towers in steel lattice construction in the kind of the suspension-wide-span-length-system in Germany. With two circuits 40,000 kW were transmitted. Later on instead of the cemented-in-cap, a pin ball was used. Both kinds of inside cementing were left soon afterwards. 

The impetuous extension of the German high voltage grid after World War I resulted in requirements of a greater reliability as for power transmitting. Referring to German experiences the crucial shortcoming of all types of suspension insulators was that they were not puncture proof. Cracks in the thin walled head part of the insulating material by mechanical stress led to electrical punctures. The constant control of single units under service and the replacement of the defect insulators on dead lines were very disadvantageous for operation and led to the search of a puncture proof insulator. 

As a first kind of a puncture proof insulator appeared in 1910 the double cap insulator with one disc (fig. 12). Further development presents the solid core insulator with two sheds (fig. 13), from which the Motor-insulator was created in the year 1917 by Motor-Columbus AG in Switzerland. 

In the beginning the upper disc has been made from tin as a protection against rain, later on however it was manufactured from porcelain, too. This two-shed-insulator could be regarded as a puncture proof insulator because of its long stretched solid core. The porcelain being stressed on tensile strength was very exacting to the manufacturing process at that time. The two-sheds-solid core insulator is from 1925 on favoured for insulating overhead high voltage lines with chains of several units. Besides these types the cap-and-pin insulator has been used up to 1945. 

1929 in Germany the first 220 kV-transmission-line was put in operation, the first one in 380 kV followed 1957. On account of the good experiences with the puncture proof solid core insulators one strived for always longer units of insulators, for the high and highest voltage lines. 1938 one succeeded by means of the de-airing pug-mill and automatic trimming machines to manufacture homogeneous clay rods free of defects. By exactly controlled firing one could produce a long rod insulator which length was sufficient to insulate 110 kV overhead lines (fig. 14). 220 kV lines could be equipped with two units, 380 kV lines with three such units. For areas of extreme pollution appropriate types of long rod insulators have been developed, which are up to all standards after investigating the contamination flash over during the last twenty years. 

The long rod insulator being puncture proof therefore the aspect of the mechanical strength is well in the fare. With the development of super strong ceramic material this problem has been solved. 

A special advantage by using of long rod insulators also can be seen in the fact that compared with the cap and pin type insulators, as the case may be, a great number of intermediate connecting hardware can be omitted which represents end points of cascading arcs. All the long rod insulators are provided with arcing devices which guarantee a nearly complete protection against power arcs. 

The operation experiences with puncture proof solid core and long rod insulators gathered during several decades have led to the result that this kind of insulation is today the only insulation of overhead lines. On secondary lines non puncture proof pin-type and suspension insulators have been displaced by puncture proof solid post and rod types. On the high and highest voltage overhead lines the long rod insulator is the only kind of insulation. The long rod type had its way also in other countries of Middle Europe and the other part of the world is increasingly interested in it. 

The advantage of the one-piece-long-rod-insulator, especially its short nominal length by omission of the intermediate connecting hardware and thus suppression of cascading arcs, incited to develop a one-piece insulator for 220 kV. Such insulators are in a great number in operation since more than 15 years, with good success. It is intended to start in 1973 in Germany with a two-piece insulation for 380 kV Lines, also it will be the year of birth of the one-piece-insulator for 380 kV. 

The following are the companies that are producing pintype insulators today, along with a description of their insulators:

Rheinisch-Westfalische Isolatoren-Werke began producing porcelain insulators in 1949, on the site of the Royal Ammunition Factory. Their production consists of a full line of porcelain insulators: long-rod, station post, conductor-rail, bushings, pintypes, egg and shackle. Apparently the bulk of their production is devoted to transmission line insulators, most notably the "Langstab" or long-rod insulator. These consist of a solid porcelain post with metal fittings as shown in figure 14. 

All information I have on their insulator line is related to the long rod and station type insulators. The catalog I have shows only these two varieties, though it has dividers for all of the aforementioned types. A photograph in the catalog shows brown long-rods marked with their trademark (shown above left) in what appears to be white underglaze. I would assume this trademark is used, in some form, on their pintypes as well. 

Rosenthal Stemag Technische Keramik manufacturers a wide range of industrial ceramics including: insulators, grinding balls, laboratory ware and electronic ceramics. They produce a full line of insulators: power, railway, telephone, telegraph, and porcelain terminal blocks, sockets, and knobs. Rosenthal is one of the world's largest industrial ceramic manufacturers and is a daughter company of Rosenthal; who, among other products, produces high quality porcelain (china) dinnerware. Their shops are located throughout Europe. 

Rosenthal Stemag was founded in 1971, through the merger of three separate divisions: Steatit Magnesia, Rosenthal Isolatoren and Rosenthal Technische Werke. Rosenthal Isolatoren is the division which manufacturers pintypes. 

The catalogs I have show long-rod and pintype insulators (figures A and B). 

Figure A shows low voltage pintypes. Numbers one through four show typically European styles, though I have never seen an insulator (transposition) similar to the one shown in four. Perhaps these were produced for export. Numbers five through eight are designed to British specifications and can be "screwed directly on the pins." The sizes in which these are cataloged are tabulated in Table 1. 

Figure B shows the typical pintype insulators (Stutzen-Isolatoren) for voltages up to 35 Kv. The sizes in which these are cataloged are shown in Table 2. Note that these are essentially the same as the Delta insulator first designed in 1897. The marking they employ is most likely some variation of the trademark shown at right. 

Kronacher Porzellanfabrick, Division of Stockhardt and Schmidt-Eckert was the final company to supply me with information. The catalog sheets I have show long-rod, pintype, guy-strain and line-post insulators. I have no historical information regarding Kronacher. 

Their pintypes are shown in figures C, D, and E. 

Figure C shows the N-95 which is similar to the N-95 cataloged by Rosenthal (Dimensions, Table 3). except it has a cable top designed for a special form of tie wire (figure D). 

They also catalog a traditional ST insulator (figure B) in exactly the sizes shown in Table 2. Apparently, this is a European standard design.

Their type ST-RK insulator (figure E, dimensions table 4) is modeled after the traditional ST insulator but has a special "RK" cable top. They also catalog two variations of the ST-RK with cemented in bolts similar to American style line-posts. The standard German glaze, brown, appears to be used on these insulators. 

The markings employed are most likely variations of the trademark to the right.

Next Month: Glass insulators of E.S.A. (Spain)

Table 3. Kronacher N-95-RK

Table 2. Type ST and HD Pintypes

* All supplied with lead thimble
+ To Din 48004

Table 4. Kronacher Type ST-RK