The paper presents investigation of the properties of the surface and the material stiffness – flexibility of series of samples taken from the sheds of the composite insulators. The insulators were previously subjected to wheel test. The wheel test and 1000 h salt fog test are regarded as alternative examination of the material resistance to the effects of electrical surface discharges. There were investigated two series of the samples of the composite insulators sheds. Examined specimens, made of HTV silicone rubber, were taken from the sheds of medium-voltage composite insulators of two different manufacturers. Insulators of both types passed the 1000 h salt fog test without reservation. Meanwhile, the wheel test can provide a basis for better distinguishing between physical properties of the tested materials. In the case of the insulators of one of the manufacturers the wheel test result was negative. Cross puncture effect of the sheds took place in several places. In addition, sheds were covered with dark coating of varying thicknesses. The results of the study indicated a significantly stronger influence of electrical and temperature factors on the sheds under investigations during the wheel test than in the case of the 1000 h salt fog test. It can be stated that these tests cannot be considered as alternative and it seems that wheel test enables better distinguishing between properties of the materials.
 IEC /TR 62730 HV polymeric insulators for indoor and outdoor use tracking and erosion testing by wheel test and 5000h test. Edition 1.0 2012-03.
 A.S. Krzma, M. Albano, R.T. Waters and A. Haddad, Comparative performance of 11 kV silicone rubber polymeric insulators with HVAC and HVDC excitations using the rotating wheel dip test, paper no. 653, Mat. 19th Int. Symp. on HV Engineering, Pilsen, Czech Republic, August 23-28, 2015.
 Standard IEC 62217:2012-09. Edition 2.0: Polymeric HV insulators for indoor and outdoor use – General definitions, test methods and acceptance criteria.
 M. Mackiewicz, Evaluation of the methods of examination of the resistance of insulator sheath and sheds to creep discharges and erosion. Report of the Institute of Power Engineering No. EWN/91/Stat/13 MMM, Part 1: Tests of the resistance of the composite insulators in the salt mist chamber and in the circular test, Warsaw, November 2013 (in Polish).
 Standard ISO 4287:1997: Geometrical Product Specifications (GPS) – Surface texture: Profile method – Terms, definitions and surface texture parameters.
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