Pollution flashover accidents are still happening in areas with severe environmental conditions, and the existing pollution flashover warning methods are still very simple. In this article, the space electric field characteristics of silicone rubber insulators during pollution flashover were revealed, and the application of the space electric field signal (SEFS) for pollution flashover prewarning was proposed for the first time. During the research, artificial pollution tests were conducted to obtain the SEFS waveform, and then its time-frequency characteristic parameters under different pollution flashover stages were extracted and analyzed. Research results indicate that, according to the SEFS amplitude variation, the development of pollution flashover can be divided into three zones: safe zone, dangerous zone, and critical zone. The four characteristic parameters, the rms increase factor, maximum value increase factor, peak factor, and third harmonic factor change obviously during different flashover stages. Combining the SEFS parameters and the pattern recognition algorithm, the recognition of pollution flashover zones is realized, which can be directly used to form the pollution flashover prewarning strategy.

Through spatial electric field monitoring, it is expected to realize insulator pollution condition monitoring and contamination flashover warning in a non-contact way. Therefore, in this paper, the spatial electric field distribution characteristics of 110 kV composite insulators are simulated, where the effects of different surface states and their discharge levels on the spatial electric field of insulators are analyzed. On this basis, a non-contact monitoring method for composite insulator pollution based on the spatial electric field is proposed. The results show that there are significant differences in the spatial electric field of the composite insulator among three conditions, namely cleaning, pollution layer wetting, and dry band arcing. Increases of pollution layer wetting and dry band arcing would lead to an increase of the amplitude of the spatial electric field of the insulator. Verification experiments well indicated that it is feasible to identify the degree of pollution layer wetting as well as dry band arcing of the insulator string by fixed-point monitoring, the spatial electric field signal at the cross-strand of d = 0.5 m and directly opposite the last three positions. Research results can provide references for the online monitoring of overhead line polluted insulators and its flashover warning.