Polyurethane foam application for high voltage insulation

In recent years, the improvement in optical technology has increased the use of optical instrument transformers (OIT). The active parts of many OITs are placed in SF₆ or N₂ filled insulating structures. The challenge with using these insulating gases initiated the replacement of them with polyurethane foam, which is frequently used in low-voltage switchgear. The insulation of an OIT was modeled by foam filled tubes: 61.0 cm (24") long, 20.3 cm (8") diameter and electrode gap 15.2 cm (6"), and electrode radius 1.27 cm (0.5"). The AC and lightning impulse breakdown voltages of these samples were determined by a large number of tests. The repeated lightning impulse test was conducted by using 600 impulses with a peak voltage of 120 kV. The partial discharge measurements were also investigated.