Failure of polyester spacer at low voltage equipment

Arak Refinery plant of Iran confronted a number of failures of low voltage equipment. Our investigations after each event have shown that the phases of vertical busbars are connected together electrically and this caused flashover between them. Also, vertical busbars melted near the surface of spacers. Our inspections showed that degradation of polyester spacers left carbon on their surface and increased the surface conductivity between phases and neutral. So using general-purpose polyester in low voltage equipment at 50/spl deg/C for long duration or higher temperature will cause surface conductivity.