Experience with the merry-go-round test

Studies of the merry-go-round test (MGR), using a newly built apparatus, and the influence of the test procedure on the performance of different HV polymeric outdoor insulation housing materials are presented. In the test, the surface leakage currents, mass and wettability changes of the studied samples were monitored. The materials investigated were bisphenolic and cycloaliphatic epoxies, HTV and RTV silicone rubbers, and EPDM rubbers. Results show that epoxies containing a silane-treated filler perform very well in the test. The performance of the silicone rubbers, except for preservation of their hydrophobic properties, was comparable to that of the EPDM rubbers. This is contradictory to the materials' field performance and indicates that there are still problems with interpretation of the MGR test results and their correlation with actual service experience.>