This paper presents a capacitive measurement principle to detect the formation and accumulation of ice on an overhead power transmission line, for the use with an autonomous monitoring system. The proposed scheme can use either a linear or a circular type electrode geometry. Interelectrode capacitances are measured by a capacitance-to-digital converter for linear as well as circular type electrodes, mounted on the surface of the conductor. The icing and the thickness of the ice layer can be determined by measuring the capacitances formed by the electrodes that are kept in different distances, by exploiting the time signals and differences in the permittivities of air, ice and water. A prototype system has been developed in the laboratory and test results along with finite element simulations results are presented. The test results show good agreement with the finite element analysis and the developed system successfully senses the icing of a transmission line. © 2009 IEEE.