Comparison of various insulator contamination measurement methods

There are many methods to measure the degree of insulator pollution, such as equivalent salt density, conductivity of pollution layer, surface conductivity, leakage current, pollution flashover voltage and pollution flashover gradient. This paper chooses to measure the degree of insulator pollution by measuring the equivalent salt density of insulators for the following reasons:

a. The conductivity of the pollution layer is defined as the conductivity value of the pollution layer per unit surface of the insulation. In fact, it is obtained by multiplying the conductivity obtained by the ratio of the current and voltage applied to the pollution layer and the shape factor of the insulator. In order to measure the surface conductivity of the pollution layer, an appropriately high power frequency voltage should be applied to the insulator under the condition of saturated moisture in the pollution layer, and its leakage current should be measured to obtain the conductivity G=I/U. However, the above measurement has a large dispersion and is greatly affected by the uneven distribution of pollution. In addition, a power supply with a large capacity should be used for measurement, which is more troublesome.

b. In physical terms, the local surface conductivity and surface conductivity of the pollution layer are the same parameter, and their physical meanings are the same. The only difference is the measurement method. Although the measurement method is the same as the equivalent salt density, the conductivity is greatly affected by temperature changes.

c. There are many parameters used in leakage current test to indicate the degree of pollution: the maximum pulse amplitude of leakage current under operating voltage; the number of leakage current pulses exceeding a certain amplitude; the maximum leakage current value before flashover. Measuring these parameters requires applying a certain voltage to the insulator, which is inconvenient for on-site testing.

d. Pollution flashover voltage and pollution flashover gradient are the most direct and ideal pollution parameters to characterize the performance of insulators. On-site pollution tests can also truly measure the pollution flashover performance of insulators. However, since the critical state of natural pollution and pollution accumulation levels does not necessarily exist at the same time as the meteorological conditions that cause pollution flashover, it is often the case that the pollution has reached a critical level but there is no sufficient humid condition and the critical pollution flashover voltage cannot be measured. Therefore, the measurement of flashover voltage should also be combined with the measurement of other pollution degree parameters. The test equipment has a large capacity, the test is inconvenient, and the conditions are not available on site.

e. The method for measuring the equivalent salt density of insulators (the equivalent amount of salt per unit surface area of ​​external insulation) is to use a certain amount of distilled water to clean all the dirt on a certain area of ​​porcelain surface, and use an equivalent salt density tester to measure the salt density value ESDD of the pollution solution. YM3200 direct-reading salt density meter can directly measure and read ESDD value. Equivalent salt density can directly measure the degree of pollution, and is not limited by temperature, voltage, test equipment capacity and test site.

In terms of existing technology, equipment and feasibility of operation, the equivalent salt density of insulators is generally measured on site to measure the degree of insulator pollution. Equivalent salt density is an objective reflection of the pollution flashover of insulators and is one of the criteria for judging insulation performance. It can directly measure the degree of pollution, is not
limited by temperature, voltage, test equipment capacity and test site, and is easy to operate on site. (end)