Porcelain has a long tradition of use as a high-voltage insulator. As early as 1849, Werner von Siemens used the first porcelain insulators on telegraph cables from Frankfurt to Berlin. Porcelain’s properties—such as hardness, mechanical strength, partial electric discharge with glowing discharge base points, and resistance to corrosion, chemicals, heat, and weather—have made it indispensable in insulation engineering.

Siegfried Krämer is a key figure in the history of high-voltage insulators. Almost 50 years ago, as a manager of Wessel Isolatoren GmbH (Bonn, Germany), Krämer helped develop a new composition, then called “test batch No. 73,” (Figure 1) that replaced the conventional quartz in porcelain with alumina and petalite, a lithium aluminosilicate. Postwar saturation of the high-voltage insulator market, largely because of the electrification of Federal Railways, spurred the innovation. Intense competition but high failure rates prompted the search to improve the inherent strength of porcelain. Test batch No. 73 achieved this by replacing porcelain’s standard 25 wt% feldspar with 12 wt% petalite, leaving room for 13 wt% alumina. The revolutionary new alumina-enriched porcelain insulators were so strong that they were an instant sensation at their introduction at the 1963 Hannover Fair.