Contamination effects on charge distribution measurement of high voltage glass insulator string

•A new approach to measure the charge distribution on the surface of glass insulator is introduced.•The proposed method show an ability to capture charge distribution online.•The experimental results is validated by simulation using Finite Element software.•A negative charge distribution pattern was found in both experimental and simulation results. It is certain that accumulated charge greatly enhances the local electric field distribution of insulator and may lead to breakdown even under nominal voltage. Although research on charge distribution has gained worldwide attention for the past few decades, yet the study of charge distribution on its surface is still insufficient. Therefore, this paper presents the charge distributions measurement on the surfaces of glass insulators string without grading ring subject to clean and contaminated conditions. The experimental results revealed that the distribution of charge for glass insulator recently removed from service has negative distribution pattern and this is further supported by the simulation work results. Charge injection and extraction occurring at the metal-dielectric interface greatly affects the charge amplitude of the adjacent insulators. This study also revealed that the presence of contamination affect the charge distribution of the insulator located near to ground electrode.