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Comparison of two simple high-frequency earthing electrodes

Comparison of two simple high-frequency earthing electrodes
Comparison of two simple high-frequency earthing electrodes
Lightning strikes on high-voltage transmission lines may create hazardous touch potentials on adjacent substation equipment and damage to control equipment. When designing suitable substation earthing electrodes to overcome this problem and safely dissipate the transient fault currents to ground, it is essential to consider the behaviour of the current flow. The steady-state frequency equivalent to a lightning strike is at least 0.25 MHz, which corresponds to a current skin depth d of about 10m in homogeneous soil of conductivity 0.01 Sm-1. This surface effect causes the impedance of an electrode system to be considerably larger than the power frequency resistance. Thus, a dedicated electrode is normally placed in parallel with the low-frequency earthing system, usually taking the form of a simple vertical rod of copper-coated steel about 5m long. However, the work presented in this paper suggests that a long rod is not ideal for the purpose. Using a relatively simple numerical finite-difference procedure it has been found that a flat disc electrode parallel to the surface of the ground achieves a significant improvement over the performance of a vertical rod. Both rod and disc have been solved in the frequency domain, but the rod has also been analysed in time-stepping form so that the peak voltage for a given imposed current can be compared with that deduced from the equivalent steady-state complex impedance.
Lightning strike, earthing, transient
1350-2360
219-224
Stoll, R.L.
4495b884-40aa-4e31-8514-2a77c9e0212c
Chen, G.
07deca35-2545-4548-9657-9fe3bb50d4e8
Pilling, N.
983115ee-5431-4698-a822-ad529ff7747f
Stoll, R.L.
4495b884-40aa-4e31-8514-2a77c9e0212c
Chen, G.
07deca35-2545-4548-9657-9fe3bb50d4e8
Pilling, N.
983115ee-5431-4698-a822-ad529ff7747f

Stoll, R.L., Chen, G. and Pilling, N. (2004) Comparison of two simple high-frequency earthing electrodes. IEE Proceedings - Generation, Transmission and Distribution, 151 (2), 219-224. (doi:10.1049/ip-gtd:20040013).

Record type: Article

Abstract

Lightning strikes on high-voltage transmission lines may create hazardous touch potentials on adjacent substation equipment and damage to control equipment. When designing suitable substation earthing electrodes to overcome this problem and safely dissipate the transient fault currents to ground, it is essential to consider the behaviour of the current flow. The steady-state frequency equivalent to a lightning strike is at least 0.25 MHz, which corresponds to a current skin depth d of about 10m in homogeneous soil of conductivity 0.01 Sm-1. This surface effect causes the impedance of an electrode system to be considerably larger than the power frequency resistance. Thus, a dedicated electrode is normally placed in parallel with the low-frequency earthing system, usually taking the form of a simple vertical rod of copper-coated steel about 5m long. However, the work presented in this paper suggests that a long rod is not ideal for the purpose. Using a relatively simple numerical finite-difference procedure it has been found that a flat disc electrode parallel to the surface of the ground achieves a significant improvement over the performance of a vertical rod. Both rod and disc have been solved in the frequency domain, but the rod has also been analysed in time-stepping form so that the peak voltage for a given imposed current can be compared with that deduced from the equivalent steady-state complex impedance.

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More information

Published date: 5 March 2004
Keywords: Lightning strike, earthing, transient
Organisations: Electronics & Computer Science

Identifiers

Local EPrints ID: 260163
URI: http://eprints.soton.ac.uk/id/eprint/260163
ISSN: 1350-2360
PURE UUID: 8e079775-81ef-4cf3-8e4e-08e061c70a7b

Catalogue record

Date deposited: 01 Dec 2004
Last modified: 06 Oct 2020 23:17

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