Evaluation of sustainability of microgrid grounding grid design under varying soil conditions through estimation of touch, step voltages and novel methods of earthing

• Published in: IET science, measurement & technology measurement & technology, 2020-07, Vol.14 (5), p.621-632
• Main Authors: Bhatia, Krishnav, Darji, Pranav B, Jariwala, Hitesh R
• Format: Article
• Language: English
• Subjects: bottom layer variations; distributed power generation; earthing; IEEE standard; IEEE standards; microgrid grounding grid design sustainability; middle layer variations; optimal compression ratio; power distribution protection; power grids; Research Article; soil; step voltages; top layer variations; touch estimation; touch voltage; varying soil conditions
• ISSN: 1751-8822; 1751-8830; 1751-8830
• DOI: 10.1049/iet-smt.2019.0168

This study examines the sustainability of uniform as well as an optimal grounding grid (GG) design for the microgrid (MG), in terms of variations in the top layer (TL), middle layer (ML), and bottom layer (BL) soil resistivities ($\rho _1$ρ1, $\rho _2$ρ2, and $\rho _3$ρ3, respectively) along with change in a thickness of TL and ML. GG design is highly dependent on $\rho _2$ρ2, as it helps in determining the density of conductors at grid extremities. With an increase in $\rho _2$ρ2, touch voltage (TV) crosses its tolerable limit, but step voltage (SV) remains within its limit. However, with a simultaneous increase in the thickness of ML (MLT), SV also crosses its limit. For $\rho _2$ρ2 higher than $\rho _3$ρ3, with an increase in MLT, TV, and SV increase, while in the reverse case, they decrease. For the given MLT, $\rho _3$ρ3 is crucial in determining GG burial depth. Validation of results is done by comparing them with the IEEE standard. Also, the optimal compression ratio of GG with an increase in MLT is analysed. TVs can be reduced to a great extent, with the application of distinctive methods of earthing (TT-GG system, TN-S-GG system, and TN-C-S-GG system) in MG. This study also reveals that an increase in GG resistance leads to a reduction in TV.