Cracked insulators create hazardous working conditions during restoration after extreme ice storm

On February 9 and 10, 1994, parts of the service territory of ENTERGY were subjected to an extreme ice storm that damaged over 2600 miles of overhead lines leaving more than 220,000 customers without power. Hundreds of linemen and support personnel were recruited from noneffected utilities in the surrounding territories and mobilized to make emergency restoration of power supply. While inventories of new materials were being brought in on an expedited basis, repair crews were encouraged to reuse components from damaged lines that appeared to still be in operational condition. Many porcelain insulators had been cracked internally by overloads resulting from heavy ice accretion. Such cracks can have subtle openings to the outside that are not visible from field inspection. Accordingly, some cracked insulators were contained in reinstalled dead-end strings. Subsequent rains filled the cracks with moisture. When it came time to reenergize restored lines, some of the dead-ended strings flashed over. Heat of the resulting power arc vaporized the moisture in the cracks creating tremendous pressures which, in turn, caused the insulator to explode. In some cases, the explosion expelled the pin, causing the conductor to drop and trip out the line. In all cases, the explosion sprayed sharp porcelain shrapnel over the surrounding area. The first contingency created delays in the quick restoration of power. The second, however, created a very dangerous hazard for repair personnel working in the area. This paper describes the design and deployment of a disciplined inspection program to locate and remove the dangerous insulators