The considered arrester is of station class continuous operating voltage Uc = 345 kV) and is available for testing purposes at the TU Darmstadt [see Fig. 1(a)]. It contains a total
of 76 vertically piled zinc-oxide (ZnO) resistor blocks as well as several metallic spacers and flanges amounting to a total stack height of 420 cm. This so-called MO resistor column
is enclosed within a porcelain housing [Fig. 1(b)], forming an air gap with the width δ = 35 mm. The most important figure for arrester operation is the electrical characteristic of
its MO resistors. For the analyzed specimen, the U–I -curves for different temperatures were obtained by single MO resistor measurements, as shown in Fig. 1(c). The relative permittivity is assumed constant, εr = 700. The reader is referred to for further material specifications.