Insulator fouling law and equivalent salt density measurement time

The dirt accumulated on the surface of insulators in power lines can be divided into soluble dirt and insoluble dirt, that is, inert dirt. Dissolvable contaminants are characterized by equivalent salt density (ESDD), which has been widely used in pollution tests, analysis of pollution flashover mechanism and classification of power system pollution grades; insoluble contaminants are characterized by gray density (NSDD).
Under the condition that the salt density ρESDD is constant, the pollution flashover voltage Uf of the contaminated insulator decreases with the increase of the ash density ρNSDD.The reason is that although the insoluble dirt in the pollution layer itself is not conductive, it retains moisture But it can dissolve the electrolyte and increase the conductivity. At the same time, with the increase of the insoluble matter attached to the surface of the insulator, the more water absorbed by the surface of the insulator, a thicker water film is formed, which reduces the surface resistance of the contaminated insulator, resulting in increased leakage current.
A large number of data analysis results show that the pollution flashover voltage Uf of the contaminated insulator has a three-dimensional curved relationship between the salt density ρESDD and the gray density ρNSDD. As ρESDD and ρNSDD increase, Uf gradually decreases; when ρESDD and ρNSDD are small, Uf decreases Faster, with the increase of ρESDD and ρNSDD, the downward trend of Uf slows down, which is similar to the effect on Uf when the effects of ρESDD and ρNSDD are considered separately.
In general, both ash density and salt density have an effect on the insulator flashover voltage. Taking XP-160 porcelain insulator as an example, the gray density influence characteristic index is 0.14, the salt density influence characteristic index is 0.24, the salt density influence is 1.71 times of the gray density influence, that is, the salt density influence is greater than the gray density influence .
The relationship between ρNSDD and the pollution flashover voltage Uf was tested at the equivalent salt density ρESDD of 0.026 mg / cm2, 0.068 mg / cm2, and 0.14 mg / cm2. XP-160 suspended porcelain insulator pollution flashover voltage was tested The relationship between Uf and the change of ash density ρNSDD. The test results are shown in Table 3. The standard deviation of Uf obtained by the test is within 7%. By curve fitting the test results in Table 3, the relationship between Uf and ρNSDD under the same ρESDD can be obtained, as shown in Figure 3.

It can be seen from Table 3 that the Uf of the 7 strings of artificially contaminated insulator strings under different ρESDD all decrease with the increase of ρNSDD; and when ρNSDD is smaller, Uf decreases faster with the increase of ρNSDD. This trend is consistent with the relationship between the flashover voltage of insulator strings and ρESDD.

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