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The tracking wheel test specified in IEC/TR 62730:2012 provides a method that can be used to evaluate the resistance of composite insulators to tracking and erosion for rejecting inadequate materials or designs. Currently, most of the tests have been conducted on composite line insulators and some other insulator types with relatively small diameters. As the usage of large-diameter composite insulators, such as composite station insulators and composite cross-arms, increases rapidly, it is urgent to investigate if the tracking wheel test method is also suitable for their evaluation. In this study, a tracking wheel device for composite insulators with different diameters, designed and constructed in accordance with the IEC standard, is presented. The relationships between the leakage current and NaCl content as well as the average diameter of the specimen are investigated. It is shown that the test parameters specified in the IEC standard are not suitable for specimens of relatively large diameters. Accordingly, a relevant modification of test parameters has been introduced and verified, showing similar phenomena during the verified test as those observed during previous studies on composite line insulators. It is thus claimed that the modified test procedure is feasible for being applied on large-diameter insulators. [ABSTRACT FROM AUTHOR]