Porcelain Insulators - The Wise Choice for Your Substation

For decades, glass was the predominate material used for manufacturing electric insulators, but today the porcelain insulator has become the standard for power substations due to its greater strength and surface resistance compared to glass and other non ceramic insulators (NCIs).

The advantages of porcelain insulators include superior electrical properties, good mechanical properties (especially tensile strength), good creep resistance at room temperature, high corrosion resistance, minimal leakage problems, and less adverse effects from changing temperatures.

While it is possible for a porcelain insulator to be damaged by rough handling, acts of vandalism, or from flashover, the glaze usually sustains only superficial damage. The electrical or mechanical strengths are usually not affected, so change-out is not required. In cases where vandal damage has occurred, the extent of damage can be spotted from the ground using binoculars, and the need for change-out is easily determined. Vandal-damaged porcelain insulators do not impose immediate operational risks, either mechanically or electrically.

NCIs are more easily damaged than porcelain insulators. Damage can occur during handling, shipping, and construction. Due to the fact that NCIs are smaller than porcelain insulators, close-range inspection is often required to determine the extent of vandal damage. To inspect the insulator, an outage may be necessary to safely assess the damage at close range. NCIs damaged by vandals may require change-out or monitoring.

During production, insulator manufacturers test porcelain products insulators to confirm both electrical and mechanical strengths. NCIs are only tested mechanically. Moreover, porcelain insulators can be installed live, while NCIs should not.
Various tests can determine the electrical integrity of a porcelain insulator, and mechanical integrity can be determined visually. A complete loss of the porcelain shell of an insulator will result in a reduced strength, but not low enough to jeopardize the insulator's ability to support the line.

Routine maintenance, such as water washing or dry cleaning, removes contamination and restores porcelain insulators to their original insulation strength, preventing flashover. Porcelain repairs and maintenance methods for porcelain electrical insulators are well developed, and various industry application guides are available.

Although NCIs' flashover performance is generally considered better than porcelain insulators, they cannot withstand the heat produced from leakage current and dry band arcing as well as porcelain. Therefore corrosion occurs, exposing the core to moisture and voltage, leading to tracking of the core and insulator failure.

The major drawback of glass is that moisture condenses easily on its surface, limiting its use to lower voltages. With the advent of electric power distribution in the 1880's, larger and more reliable electrical insulators were needed to carry the higher voltages of power lines, which reached into the tens of thousands of volts. Glass was simply not sufficient enough to handle that level of voltage.

A number of insulators manufacturers began producing porcelain insulators and, from around 1915 on, the porcelain insulator virtually replaced the glass insulator on all electrical distribution, even at low voltages, as porcelain's superiority was demonstrated in both insulation quality and strength.
Apart from acts of vandalism, and rare poor quality-control issues, porcelain insulators have served the industry well, and users have attained a significant level of confidence in their long-term reliability. Maintenance methods are well established, and porcelain insulators commonly outlive their 40- to 50-year life expectancy.

Glass and other non ceramic insulators, however, have not yet attained the same level of experience or standardization, and their weaknesses are still being discovered.

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