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

Abstract

On February 9 and IO, 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 [I]. Hundreds of linemen and support personnel were recruited from non-eff ected 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 those danger insulators.

Design of booster shed parameters for improving the electrical performance of post insulators under icing conditions /

“…This includes icing test methods, icing flashover performance, mitigation options. Several parameters and factors affect the dielectric strength of ice-covered insulators, such as the type and density of ice, length of icicles, freezing water conductivity, altitude, profile and type of insulator, and the position and length of ice-free zones (often called air gaps) [1], [21], [23], [24], [28], [29].…”

“…Outdoor insulators are widely used in power networks, but ice accretion may cause a drastic reduction in their electrical insulating performance in high altitudes and cold climate regions in many countries, such as Canada [21], [22], the USA [23], China [5], [24]- [27], Norway [28], Japan [29], and Iran [30]. In fact, in many cold regions of the world, atmospheric icing is a severe problem in electrical power systems.…”

Acoustic and HF Detection of Defects on Porcelain Pin Insulators

“…Lightning impulses may also cause rapid expansion of the trapped air in the insulation defects. This results in forces that either damage or completely shatter the insulators resulting in safety risks and power outages [4].…”

“…This involves measurement of the electric field distribution on the insulator surface or along a string of the insulators and compare with that of defect free conditions. Electric field probes of various forms are used in this regard [4] [9] [10]. viii.…”

Design of booster shed parameters for post insulators under heavy icing conditions using geometric modelling and the Taguchi method

“…Outdoor insulators are widely used in power networks. Nevertheless, ice accretion may cause a drastic reduction in their electrical insulating performance as reported from many countries, such as Canada [1][2][3][4], the USA [5], China [6][7][8][9], Norway [10], Japan [11] and Iran [12].…”