# Investigations on the Performance of Various Horizontal Ground Electrodes

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## Abstract

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## 1. Introduction

_{DC}and impulse polarity, have also been demonstrated by several researchers [1,2,3,4,5,6]. Generally, it was observed in these publications [1,2,3,4,5,6] that, the higher the current magnitudes, the lower the impulse ground impedance values are. Many studies [3,6] have also demonstrated that, under a high impulse current, a smaller reduction of impulse impedance was observed for the grounding systems’ low R

_{DC}. While the impulse polarity effect has been known to affect the breakdown voltage and performance of dielectric materials [7,8], an obvious noticeable impulse polarity effect was also found to occur for some soil conditions, when grounding systems are subjected to an impulse current [2,3,6]; it was observed that with positive impulse polarity, lower impulse impedance values were noticed for some ground electrodes. Many other factors have been discovered from experimental and analytical expressions that have shown differences in the degree of the ionization process, or the percentage of the decrease in the ground impedance from its R

_{DC}. It has been highlighted in [4,5] that the percentage of the decrease in the ground impedance from its R

_{DC}would be important in predicting the lightning performance accurately and in obtaining an optimized design of grounding systems for many electrical installations. In [4,5], mathematical expressions consider the extended electrodes that are presented to provide a more accurate estimation of the degree of the decrease in impulse impedance from its R

_{DC}for various ground electrode designs. They [4,5] estimated the impulse impedance in Ω, Z

_{imp}, from the characteristic dimension of the electrode in m, S, the impulse current in A, I, the critical soil ionization strength in V/m, E

_{c}of an electrode. As for the value of E

_{c}, the values can be obtained experimentally, or by adjusting the E

_{c}until the Z

_{imp}obtained theoretically is achieved. This relation can also be seen in Equation (1), defined in [4], where I

_{g}is the ground current, E

_{c}is the critical electric field, ρ is the soil resistivity, and R is the resistance at a steady state.

_{DC}. For the performance of grounding systems subjected to high impulse conditions, it can be noticed from Equation (1) that the lower the R

_{DC}, the lower the E

_{c}. This can result in a lesser percentage of the decrease in the impulse impedance in relation to R

_{DC}. Similarly, from Equation (1), it can be seen that the low soil resistivity gives a low I

_{g}, and a higher critical electric field, E

_{c}, is required to cause ionization in soil.

## 2. Experimental and Simulation Arrangement

#### 2.1. Tested Ground Electrodes and Remote Ground Electrodes

^{o}. The gap from one shaft to another is 150 mm apart. The shaft is buried facing downward to provide a more effective dissipation of the current into the grounding systems.

_{DC}of all these electrodes, which found to be 82.9 Ω, 72.7 Ω and 101.9 Ω, respectively, for the spiked strip, linear array and conventional electrodes.

#### 2.2. Testing Sites

_{1}of 160.20 Ωm, while the lower layer was found to have a soil resistivity, ρ

_{2}of 359.63 Ωm. The former had ae thickness of 4.3 m, while the latter had an infinite thickness.

_{DC}, presented in Section 2.1, R

_{DC}values were calculated for all electrodes using the geometric and contact resistance equations presented in [10]. In these equations, only the effective upper layer was used to calculate for contact resistance, R

_{c}in Equation (2) and added to the geometric resistance, R

_{g}in Equation (3) to obtain the total measured resistance, R

_{DC}, where the ρ

_{1}is the upper soil resistivity in Ωm, defined as 160.2 Ωm for the calculation of all electrodes. L is electrode’s length in m, A is the cross-sectional area of the trench (π × length of the trench × width of the trench), in m

^{2}, A

_{wire}is the electrode’s cross-sectional area (2 × thickness × length of the electrode) in m

^{2}, g is the geometric sum of electrode radius r

_{xyz}in each direction from the center in m, defined in Equation (4). Table 1 lists the values defined for all parameters, for all three electrodes. It was observed from the table that the percentage difference was below a 10% difference for all electrodes, verifying and confirming both the measurement and calculation methods. This analysis also shows that for the electrodes installed at the upper layer, the formula from Conseil International des Grands Réseaux Électriques (CIGRE) [10] can be used and considered as highly correct, where only the soil resistivity of upper layer should be considered in the calculation. It was believed that the complexity of the configurations and geometries of the spiked strip and linear arrays contributed to slightly higher percentage differences between the measured and calculated values of R

_{DC}, in comparison to a direct forward geometry of the conventional electrode.

#### 2.3. FEM Simulation

## 3. Experimental and Simulated Results

#### 3.1. Experimental Test Results

_{DC}, and referring to Equation (1), other parameters (i.e., E

_{c}, ρ, I

_{g}) could become of a similar range. Another reason that may contribute to similar characteristics for all these ground electrodes, though they have significant differences in their electric field profiles, which will be presented in the next sub section, could be low soil resistivity, which has become a dominant factor in the measurements, making the electrode’s configurations less significant. The characteristics of these electrodes, where the discharged times and impulse impedance decrease with increasing currents, indicate a better conduction that can be associated with the ionization process at higher magnitudes of current. It was also noticed from the experimental work that the linear array electrode has the lowest impulse impedance, as shown in Figure 9, which could be due to its low R

_{DC}and high electric field values obtained from FEM, presented in the next section.

#### 3.2. FEM Simulation Results

## 4. Conclusions

_{DC}values for all three electrodes were firstly performed and compared with the measured R

_{DC}. Close results were seen for the calculated and measured R

_{DC}, confirming each other’s method. It was observed that for the experimental work, little variation was seen in terms of the time to peak current, current discharged time and impulse impedance values for all three electrodes, which could be due to the low R

_{DC}, and the results are influenced by the soil resistivity, rather than the configuration of the ground electrodes. The current discharged times and impulse impedance were found to decrease with increasing magnitudes of current for all electrodes, indicating a better conduction at higher current levels.

_{DC}used in the work, the simulated results suggest that the new design of ground electrode can still be considered, considering the right geometry and electrode configuration, particularly by having sharp edges, which can enhance ionization process, hence provide better conduction in soil.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Conflicts of Interest

## References

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**Figure 16.**Electric field values at corresponding areas of “a”, “b”, “c” and “d” of the spiked strip ground electrode, shown in Figure 13.

**Figure 17.**Electric field values at corresponding areas of “a”, “b” and“c” of the linear array ground electrode, shown in Figure 14.

Ground Electrodes | Spiked Strip | Linear Array | Conventional |
---|---|---|---|

r_{x} (m) | 0.75 | 0.75 | 0.75 |

r_{y} (m) | 0.02 | 0.1 | 0.01 |

r_{z} (m) | 0.35 | 0.3 | 0.3 |

g (m) | 0.827 | 0.814 | 0.81 |

Length of the trench (mm) | 1500 | 1500 | 1500 |

Width of the trench (mm) | 200 | 200 | 200 |

Area of the trench for main electrode (m^{2}) | 0.942 | 0.942 | 0.942 |

Area of the spiked strip/sharp spike, in contact with soil (m^{2}) | 0.05 m depth × 1.5 m × 2 (for each side of the trench) = 0.15 | 0.2 m width × 1.5 m length larger than 0.942) = 0.283 and extra exposed area at both ends (0.5 m × 2 (two sides)) = 0.1 | - |

Area of the trench, A (m^{2}) | 1.09 | 1.33 | 0.942 |

Thickness of the electrode (mm) | 20 | 20 | 20 |

Length of the main strip (m) | 1.5 | 1.5 | 1.5 |

Length of other electrodes/strips (m) | 0.45 | 4.2 | - |

Total length of the conductor, L (m) | 1.95 | 5.7 | 1.5 |

Cylindrical/shaft surface area (2 × π × r × l) (m^{2}) | 0.057 | 0.0066 | - |

Area of the main strip (m^{2}) | 0.06 | 0.06 | 0.06 |

Area of other strip (2 × thickness × length) (m^{2}) | 0.0027 | - | - |

Area of all the geometric conductor, A_{wire} (m^{2}) | 0.12 | 0.067 | 0.06 |

R_{c} (Ω) | 19.79 | 10.3 | 34.2 |

R_{g} (Ω) | 61.72 | 55.5 | 67.7 |

Total calculated R_{DC} (Ω) | 81.51 | 65.8 | 101.2 |

Measured R_{DC} (Ω) | 82.9 | 72.7 | 101.9 |

Percentage difference between the measured and calculated R_{DC} (%) | 1.68 | 9.5 | 0.69 |

Boundary (m) | 5 | 10 | 15 | 20 | 50 |
---|---|---|---|---|---|

x-axis (kV) | 27.516 | 28.097 | 28.857 | 28.961 | 29.518 |

y-axis (kV) | 27.514 | 28.097 | 28.858 | 28.961 | 29.518 |

z-axis (kV) | 26.492 | 27.409 | 28.313 | 28.572 | 29.423 |

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**MDPI and ACS Style**

Hizamul-Din, H.H.; Nor, N.M.; Ahmad, N.N.; Idris, N.F.; Mahmud, A.
Investigations on the Performance of Various Horizontal Ground Electrodes. *Energies* **2021**, *14*, 1036.
https://doi.org/10.3390/en14041036

**AMA Style**

Hizamul-Din HH, Nor NM, Ahmad NN, Idris NF, Mahmud A.
Investigations on the Performance of Various Horizontal Ground Electrodes. *Energies*. 2021; 14(4):1036.
https://doi.org/10.3390/en14041036

**Chicago/Turabian Style**

Hizamul-Din, Hanis Hamizah, Normiza Mohamad Nor, Nurul Nadia Ahmad, Nur Farahi Idris, and Azwan Mahmud.
2021. "Investigations on the Performance of Various Horizontal Ground Electrodes" *Energies* 14, no. 4: 1036.
https://doi.org/10.3390/en14041036