Effectiveness of earth mat when jointing high voltage underground cables (33 kV and above)

Siddans, Ryan (2021) Effectiveness of earth mat when jointing high voltage underground cables (33 kV and above). [USQ Project]

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SIDDANS Ryan dissertation_redacted.pdf

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It should never be assumed that when undergoing jointing or sheath repairs on underground high voltage (HV) cables, that they are at ground potential. Induced voltages and currents may be present from nearby cables and require engineering controls to be applied in order to reduce the risk of shock, by way of working earthed, insulated or isolated. Further, since all HV cables are sheath bonded to at least one substation, hazardous voltages will transfer to the remote joint bay site whenever a fault is present at the substation. Risk of ventricular fibrillation of the heart through step and touch potential is possible depending on many factors such as, protection timing, soil conditions, body weight and application of working earths. While the application of earthing is better than none, questions arise as to how much is adequate. Under certain conditions a sheath connection to earth rod is enough however a worst case fault scenario at the source substation requires more attention.

Uncertainty around the effectiveness of an earth mat within a 33 kV cable joint bay in order to mitigate unsafe situations has presented a topic that was realised through this project. Modelling of three scenarios with the use of the Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis (CDEGS) software package has provided insight for a worst case substation fault situation. The results demonstrate that the application of an earth mat is effective in reducing both step and touch potentials for primary and backup protection timings. Analysis of results from remote earth injection testing indicated that only a portion of the fault current returns through the earth grid creating the transfer potential hazard. Further modelling with the reduced fault level has indicated that there may be situations that may not be hazardous without the use of earth mat.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Mechanical and Electrical Engineering (1 Jul 2013 - 31 Dec 2021)
Supervisors: Ahfock, Tony
Qualification: Bachelor of Engineering (Honours) (Electrical and Electronic)
Date Deposited: 03 Jan 2023 04:27
Last Modified: 26 Jun 2023 02:01
Uncontrolled Keywords: high voltage, underground, jointing, sheath, repair, earths, hazard, earth mat, current distribution, electromagnetic fields, grounding and soil structure analysis, protection
URI: https://sear.unisq.edu.au/id/eprint/51837

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