Quantitative Analysis and Verification on the Contribution of CaSO_4 to Equivalent Salt Deposit Density

The contribution of CaSO 4 in insulator surface dirt to equivalent salt deposit density (ESDD) is quantitatively calculated and verified by comparing measured flashover voltages with calculated ones. For suspension insulator in type of X-4.5, the contribution of CaSO 4 to the ESDD under operation or test conditions, which is called "actual ESDD" in this paper, is less than or equal to 9.4μg/cm 2. The range of the ESDD value determined by solution of CaSO 4 in 300 mL deioned water, which is called “apparent ESDD”, is 0～31 mg/ cm 2. The apparent ESDD will be larger than the actual ESDD if CaSO 4 in surface is more than 18.32 mg. The calculated flashover voltage can be consistent with the measured ones if the apparent ESDD is corrected by actual ESDD. For tests carried out with blend salts of NaCl and CaSO 4 in the surface dirt and with a fixed apparent ESDD, the flashover voltages will increase with increasing the ratio of CaSO 4 to NaCl, the main reason is the decrease in actual ESDD with increasing the ratio. The important reason why the flashover voltages of the environmental-dirt insulator is larger than those of artificial-dirt one is that the environmental dirt contains more CaSO 4, which makes the actual ESDD obviously less than apparent ESDD. The above results are helpful to the research on the on-line detection of salt density by optical fiber sensor and optic spectrum.