Procedure to increase voltage rating of field installed 15 kV cable by replacement of nitrogen with sulfur hexafluoride

This paper presents the results of a study to establish the feasibility of increasing the operating voltage and MVA rating of an installed 15 kV cable system by replacing the nitrogen with sulfur hexafluoride gas. The results of laboratory and field studies indicate that such a conversion is feasible and can be accomplished in the field if the ionization starting potential of the cable is measured during conversion to prove the safe operation at the higher voltage. It is concluded that the ionization starting potential of a 15 kV cable system can be raised by a factor of approximately 1.5 at 15 psig (10.4 × 10⁴N/m²) after conversion to sulfur hexafluoride gas.