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Manufacturing Technology Insights | Saturday, September 03, 2022
Cooling tower pollution impacts the insulations of thermal power plants causing equipment failure and flashovers.
FREMONT, CA: Substations near thermal power plants are significant sources of pollution due to cooling towers. Their effect can be even more critical when prevailing winds blow toward the substation from towers. Located near a thermal power plant, the Francisco Villa Power Substation in Mexico experienced a critical impact. Several transmission lines were affected by power outages caused by leakage current levels in the insulation at the substation. Failure of equipment insulation led to flashovers, notably that of a surge arrester protecting a transmission line adjacent to the plant's cooling towers.
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External insulation is prone to failure due to pollution. Therefore, a proper insulation design must consider all pollution sources potentially affecting insulation over time. External factors can alter pollution severity dramatically, affecting scheduled preventive maintenance effectiveness. Service interruptions caused by pollution can last hours, unlike other causes of outages.
Cooling towers of thermal power plants (TPPs) are pollution sources in many electrical systems. When steam is generated during extraction from cooling towers, it can also become a severe pollution source if steam conductivity is high. Several mechanisms cause insulation wetting. Condensation can occur if the insulator surface and the environment have different temperatures. Whenever a breeze comes from the cooling towers in the afternoon, vapor emissions cover and completely saturate insulators.
Francisco Villa Power Substation is a 115 kV/230 kV electrical substation located in northern Mexico next to Francisco Villa Thermal Power Plant. Insulators at this site are glass and porcelain, with some having been in service for more than 40 years. Various profiles and manufacturers of insulators have been installed on insulator strings and in primary equipment during this period.
Maintenance tasks such as cleaning and applying hydrophobic coatings have maintained insulation coordination. The system assesses pollution flashover risk by measuring leakage current. A risk determines whether maintenance is necessary. The climate is semi-arid, with 300 to 400 mm of rainfall annually and less than 50% percent relative humidity. Agricultural pollution surrounds the substation, so the leakage distance at the substation is set at 20 mm/kV for insulation design. Some substation equipment failed due to contamination caused by nearby cooling towers. This forced the CFE to replace failed insulators with others with a different profile to increase specific leakage distance. This has resulted in diverse insulator profiles with leakage distances ranging from 20 mm/kV to 39 mm/kV.
A dominant easterly or south-southeasterly wind causes vapor from nearby cooling towers to spray on insulators at Francisco Villa Substation, causing pollution. In the afternoon, it's most common. A cooling tower can be contaminated by condensation, settling of non-soluble materials, or wetting. When there is a temperature difference between an insulator's surface and ambient, condensation occurs before sunrise. When vapor covers insulators, condensation can occur because of the high temperature of the vapor. A cooling tower's vapor can also cover and saturate insulation, causing contaminants to accumulate.
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