Distribution grid reliability depends heavily on
insulation coordination of medium voltage overhead lines (OHL).
Adequate knowledge of OHL insulators is needed to improve
distribution grid performance. This paper discusses the
distribution of electrical fields in 24 kV pin-type porcelain and
glass insulators. To visualize the electric fields affecting the
insulators, computer simulations were conducted. The
simulations results were compared to previously conducted
lightning impulse puncture withstand tests. The comparison
showed that the electric stress in the insulators was not sufficient
to cause puncturing, but in the laboratory tests, puncture did
occur in some insulators.