Surface potential decay of DC-corona-charged PET films on humid electrodes

• Aim: evaluate the effect of humid electrode on surface potential decay of PET films.
• Experiments performed on 1-mm thick samples of PET films in ambient air.
• Samples placed on a grounded humid electrode and charged by negative DC corona.
• The humid electrode influences surface potential evolution after corona charging.
• Charge injection is the main physical mechanism that explains this potential decay.

Surface potential decay measurement is a widely used tool to test the electrical properties of insulation materials. The aim of the present paper is to evaluate the effect of a humid electrode on the surface potential decay process. The experiments are performed on 1-mm thick samples of PET films (50 mm × 50 mm) in ambient air (temperature: 25 °C–29 °C; relative humidity: 42%–48%). The samples are placed on a grounded humid electrode (aluminum plate covered by a humid textile: 52 mm × 52 mm), and are charged by exposing them for 10 s to the negative DC corona discharge generated by a high-voltage wire-type dual electrode.The results show that the humid electrode has a significant influence on the surface potential evolution during the first moments after corona charging. Bipolar charge injection is the main physical mechanism that explains this potential decay.