Discharge energy available to grounded spheres approaching charged ground-backed insulators

Programming a commercial electrostatic field solver has enabled the accurate calculation of the field distribution existing within the air gap between a charged insulating sheet with a grounded backing and a grounded conducting sphere. These data are input into a computer program which uses a breakdown criterion to determine if the field conditions are sufficient to initiate a discharge between the sphere and the insulator. The presence of the insulating sheet has the effect of significantly increasing the electrostatic field which can be sustained prior to electrostatic discharge (ESD) between the conductor and charged insulating sheet compared to that for a similar sphere and conducting sheet system. A further computer program enables the determination of the stored electrostatic energy due to the presence of charge on a ground-backed insulating sheet. Results show the maximum available energy calculated over a defined area of the charged surface to be significantly dependent on the insulator thickness, relative primitivity and surface voltage. The obtained data can be considered in terms of the posed ignition risk to a surrounding flammable atmosphere which is useful for the determination of potential electrostatic hazards for a given geometry and charge level.