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Evaluating the electrostatic discharge risk between small radius objects and charged planar insulating materials

Evaluating the electrostatic discharge risk between small radius objects and charged planar insulating materials
Evaluating the electrostatic discharge risk between small radius objects and charged planar insulating materials
In some industrial situations such as web processes, charging of large planar insulating surfaces can give risk of electrostatic discharges that could ignite flammable process materials such as solvent vapours. Charging of the material has for some years been evaluated using electrostatic field measurements to estimate surface charge densities. In a planar system, the threshold risk of an electrostatic discharge has been equated with a surface charge density of about 25 μCm-2 required to produce a field strength exceeding about 3 MVm-1, the breakdown field strength of air. It is known that where a small radius earthed conducting object approaches a charged insulator, intensification of the field strength occurs at the surface of the object. Similarly, the field strength is increased by the presence of a field meter near the surface. This paper investigates the effect of field concentration by an object near the charged insulator and the conditions leading to electrostatic discharges using analysis, electrostatic field modelling and experiments. The results are applied to understanding and quantification of the effect on measurements and safety factor indicated for evaluation of electrostatic discharge risk introduced by the earthed conductor in this situation.

Initiation of a discharge to a spherical measurement electrode requires that the field strength at the surface of the electrode exceeds the breakdown field strength and other factors. This occurs at different induced charge levels on the electrode for different electrode diameter. Discharges could occur with electrode-target gap around 10–20 mm at lower charge density than with smaller gaps. The threshold of discharges occurring was reached at lower charge density for a smaller 16.6 mm diameter electrode, which might be important when evaluating ignition risk for Group IIC flammable materials. Conversely higher charge transfer was confirmed with 25.4 mm electrode above the threshold for discharges occurring.
Charge transfer, Electric field, Electrostatic discharge risk evaluation, Electrostatic field measurements, Modeling
0304-3886
Smallwood, Jeremy
4bf63fe3-e1c3-49b3-b787-6c66824ceccd
Green, Nicolas G.
d9b47269-c426-41fd-a41d-5f4579faa581
Robinson, Kelly
2b1727aa-6747-4be3-86d8-c5588b9e371b
Smallwood, Jeremy
4bf63fe3-e1c3-49b3-b787-6c66824ceccd
Green, Nicolas G.
d9b47269-c426-41fd-a41d-5f4579faa581
Robinson, Kelly
2b1727aa-6747-4be3-86d8-c5588b9e371b

Smallwood, Jeremy, Green, Nicolas G. and Robinson, Kelly (2022) Evaluating the electrostatic discharge risk between small radius objects and charged planar insulating materials. Journal of Electrostatics, 115, [103680]. (doi:10.1016/j.elstat.2022.103680).

Record type: Article

Abstract

In some industrial situations such as web processes, charging of large planar insulating surfaces can give risk of electrostatic discharges that could ignite flammable process materials such as solvent vapours. Charging of the material has for some years been evaluated using electrostatic field measurements to estimate surface charge densities. In a planar system, the threshold risk of an electrostatic discharge has been equated with a surface charge density of about 25 μCm-2 required to produce a field strength exceeding about 3 MVm-1, the breakdown field strength of air. It is known that where a small radius earthed conducting object approaches a charged insulator, intensification of the field strength occurs at the surface of the object. Similarly, the field strength is increased by the presence of a field meter near the surface. This paper investigates the effect of field concentration by an object near the charged insulator and the conditions leading to electrostatic discharges using analysis, electrostatic field modelling and experiments. The results are applied to understanding and quantification of the effect on measurements and safety factor indicated for evaluation of electrostatic discharge risk introduced by the earthed conductor in this situation.

Initiation of a discharge to a spherical measurement electrode requires that the field strength at the surface of the electrode exceeds the breakdown field strength and other factors. This occurs at different induced charge levels on the electrode for different electrode diameter. Discharges could occur with electrode-target gap around 10–20 mm at lower charge density than with smaller gaps. The threshold of discharges occurring was reached at lower charge density for a smaller 16.6 mm diameter electrode, which might be important when evaluating ignition risk for Group IIC flammable materials. Conversely higher charge transfer was confirmed with 25.4 mm electrode above the threshold for discharges occurring.

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More information

Accepted/In Press date: 27 January 2022
Published date: 3 February 2022
Additional Information: Publisher Copyright: © 2022 Copyright: Copyright 2022 Elsevier B.V., All rights reserved.
Keywords: Charge transfer, Electric field, Electrostatic discharge risk evaluation, Electrostatic field measurements, Modeling

Identifiers

Local EPrints ID: 454802
URI: http://eprints.soton.ac.uk/id/eprint/454802
ISSN: 0304-3886
PURE UUID: 07919343-c2d6-43a2-84e3-b5fa26b32e2b
ORCID for Nicolas G. Green: ORCID iD orcid.org/0000-0001-9230-4455

Catalogue record

Date deposited: 24 Feb 2022 17:30
Last modified: 28 Apr 2022 01:53

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Contributors

Author: Jeremy Smallwood
Author: Nicolas G. Green ORCID iD
Author: Kelly Robinson

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