The minimum bushing creepage required for the areas with different contamination levels is well defined in IEEE Std C57.19.100.
The areas with contamination levels light, medium, heavy and extra heavy are defined in Table 1 of the above document as follows:
Light:
Areas without industries and with a low density of emission-producing residential heating systems. Areas with some industrial or residential density but subject to frequent winds and/or precipitation. Agricultural areas (exposure to wind-borne fertilizer spray or crop-burning residues can lead to higher contamination levels).Mountainous areas.
These areas are not exposed to sea winds or located near the sea. Typical measured equivalent salt deposit density (ESDD) levels are 0.03 mg/cm2 to 0.08 mg/cm2.
Medium:
Areas with industries not producing highly polluting smoke and/or with an average density of emission-producing residential heating systems. Areas with high industrial and/or residential density but subject to frequent winds and/or precipitation. Areas exposed to sea winds but not located directly on the coast. Typical measured ESDD levels are 0.08 mg/cm2 to 0.25 mg/cm2.
Heavy:
Areas with high industrial density and large city suburbs with a high density of emission-producing residential heating systems. Areas close to the sea or exposed to strong sea winds. Typical measured ESDD levels are 0.25 mg/cm2 to 0.6 mg/cm2.
Extra heavy:
Small areas subject to industrial smoke-producing thick conductive deposits. Small coastal areas exposed to very strong and polluting sea winds. Typical measured ESDD levels are above 0.6 mg/cm2.
The minimum creep values based on the nominal line to ground kV rating are recommended in the clause 9.1.5 of IEEE Std C57.19.100 as follows:
Contamination Creep distance
Light 28 mm/kV
Medium 35 mm/kV
Heavy 44 mm/kV
Extra heavy 54 mm/kV or greater
Below is a list of other measures recommended in the IEEE document to mitigate the risk of flashover in the contaminated areas:
· Application of protective coating to improve dielectric performance.
· Installation of conductive glaze bushings.
· Installation of contamination-resistant composite insulated bushings.
· Periodic Cleaning of the bushing surface.
· Design change to minimize the number of outdoor bushings.
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Masoud Kashani
Substation Engineer – New York, Brightline BES Program AVANGRID Networks Inc. | |
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