A Labaratory Investigation of the Pollution Performance of Insulator String fro UHV Transmission Systems

This paper reports on a series of 50-cycle tests performed by ENEL at CESI laboratories on artificially polluted insulator strings of various lengths, up to 13 m, using steam wetting methods. Most of the tests were performed inside a plastic tent 24m x 24m x 30m high, installed in the HV test room. Different arrangements of steam generators were used. Test voltages as high as 1000 kV phase-to-ground were applied, using different connections of 350 kV-700 kVA and 800 kV-2500 kVA transformers. Test results for different types and lengths of string and different degrees of pollution were obtained. On the basis of these results, the effect of a number of test parameters (characteristics of the voltage source, steam rate, size of the test chamber, geometrical configuration of the string) is analyzed and the performance of long insulator strings is discussed. A few results on artificially polluted insulators exposed to natural fog are also given and compared with the results obtained inside the laboratory. The application of the results to the design of phase-to-ground and phase-to-phase insulation for UHV systems is also discussed.