The copyright of this report belongs to the author under the terms of the Copyright Act 1987 as set out in the Intellectual Property Policy of Universiti Tunku Abdul Rahman. The use of any material contained in or derived from this report must always be duly acknowledged. I would like to express my gratitude to my research supervisor, Dr. Chew, for his invaluable advice, guidance and his enormous patience during the development of the research.
The collected results of the earthing system performance were validated based on other reference documents. Df Reduction factor for the entire duration of the given fault h Depth of the ground grid conductor, m. Lc Total length of horizontal grid conductor, m Length Total length of grid preview, m Lp Length of conductor along the perimeter, m.
TCAP Thermal capacity per unit volume, J/cm3°C Tm Maximum allowed temperature in °C Width Total width of previous grid layout, m αr Conductor material resistance, Ohm-M.
General Introduction
Importance of the Study
Problem Statement
A case study written by (Sven & Driz, 2001) investigated several 10 kV lightning rods that exploded in three substations while an electrical system was being tested in a new installation.
Aims and Objectives
Scope and Limitation of the Study
Contribution of the Study
Outline of the Report
Introduction
Earthing Schemes
- IT System
- TN-S System
- TN-C System
- TN-C-S System
Separating the protective conductor will be expensive, but harmonics and voltage drops are unlikely. Installation of protective devices is sensitive and clear defect before serious damage occurs to the system. All enclosures or exposed metal parts of electrical equipment are connected to the earth conductor, which is then to a local connection of the earth electrode.
All enclosures or exposed metal parts of electrical equipment are connected to the grounding conductor, which is then connected to the grounding terminal of the power system. It was used for installation over a public low voltage distribution network (LV) and is considered the easiest solution to install and design. ii). It required a functional check of the residual current device (RCD) periodically and continuous monitoring is not required during operation. IV).
The main features of the IT system as below:. i) The operation of the IT system provides continuity in the service solution. ii) Supply interruptions systematic prevention by first insulation failure and then mandatory placement and clearing. iii). First fault will be the indication of insulation monitoring device (IMD) and other fault protection from overcurrent protection devices. The earth terminal and earth neutral between the transformer also become live, completing the circuit to the wire conductor and passing the electric company's insulator.
Due to the elimination of a conductor and device pole, it will be cheaper. ii). The installation of this system is not allowed for computer equipment due to the presence of harmonic currents in the neutral conductor and in places where there is a risk of fire. Is similar to the TN-C system, the only difference being the separate protective earth functions and the neutral conductor on the load side. ii).
Mesh Design Grounding System
- Earthing Grid Conductor Sizing
- Touch and Step Potential Voltage
- Earthing Grid Resistance
- Maximum Grid Current
- Maxim Ground Potential Rise (GPR)
- Earthing Grid Design Verification
Typical wet and dry surface layer material resistance values can be referred to IEEE Std 80 Table 7. Cs = Surface layer reduction factor ps = Surface layer reduction factor ts = Breakdown current duration of land, sec. The extended Sverak equation [B132] (51) provided by IEEE Std 80 for the calculation of earthing network resistance with respect to the effect of network depth.
LT = buried conductors and bars in the total length, m h = depth of the earth network conductor, m. Buried conductors and rods in total length as follows:. Length = total length of the preliminary network plan, m Width = total width of the preliminary network plan, m D = conductor spacing, m. First, the symmetrical earth fault current must be calculated and the primary side of the largest distribution transformer will be the highest relevant earth fault level.
Further design verification is the step voltages and maximum mesh calculation according to IEEE Std 80 Section 16.5. Grid voltage based on IEEE Std 80 Equation 80 as follows:. P = Earth resistance, Ohm − M IG= Maximum grid current, A. Km = Geometric Spacing Factor for grid voltage Ki = Correction factor for current irregularity LT1= Buried conductors in total length, m Lr = Length of earth rods, m. Lx= Maximum length of the conductor in the X − axis, m Ly = Maximum length of the conductor in the Y − axis, m LR= Total length of the ground rods, m. Buried conductors in total length as follows:. Length = Total length of grid preview, m Width = Total width of grid preview, m.
LT1= Buried conductors in total length, m Lp= Length of conductor along the perimeter, m nb = 1 for square grids. nc = 1 for square and rectangular meshes. nd = 1 for square, rectangular and L-shaped grids. The weighting correction factor emphasizing the depth of the grid as follows: h = Depth of ground grid conductor, m ho= Reference depth of grid, m. Geometric Spacing Factor for grid voltage based on IEEE Std 80 Equation 81 as follows:. h = Depth of earth grid conductor, m d = Conductor diameter, m. Ki = Correction factor for current irregularity P = Earth resistance, Ohm − M. LT1= Buried conductors in total length, m LR= Total length of earth rods, m. Geometric Spacing Factor based on IEEE Std 80 Equation 81 as follows:. h = Depth of Earth Grid, m D = Conductor Spacing, m.
Surge
LT1= Total length of buried conductors, m LR= Total length of ground rods, m. Geometric distance factor based on IEEE Std 80 equation 81 as follows:. h = Depth of the ground, m D = Conductor distance, m.
Lightning
Summary
Introduction
Requirement/ Specification/ Standards
- Site Assessment on Grounding Resistance
- Site Assessment on GEM
- Site Assessment on Earth Grid System Design
- Simulation on Surges
This is the procedure mentioned in the 'Guidance for the Measurement of Earth Resistivity, Earth Impedance and Earth Surface Potentials for an Earth System'. Ground electrode disconnection from the building's electrical service must be performed for this method. The digital earth tester Kyoritsu, KEW4105A is used and connection as below:. i) E (green) connected to the ground electrode under test. ii) P (Yellow) as potential auxiliary electrode, connected to a stake driven into the ground at some distance between the electrodes. iii) C (Yellow) as current auxiliary electrode, connected to a pole driven into the ground further away.
Finding a ground grid configuration system means grid design optimization in the field of substation ground grid system design. The ground grid's basic design quantities are grid potential rise (GPR), grid resistance (Rg), step potential (Vs), touch potential (Vt) and the ground grid system design cost. The design of a grounding system can be done via commercially available software such as Electric Power System Analysis Software (ETAP) and SafeGrid grounding software.
The flowchart shown in Figure 3.3 is the design flow performed for substation earth grid. The changes of the values are much easier linked to Excel file formula to get the correct design for substation earthing grid. Initialize the decrement factor for conductor spacing. a) Touch and step potential voltage (b) Earth grid resistance.
The lightning block model will inject current into the system with an associated grounding system.
Summary
Introduction
Ground Resistance Finding
The earth electrode resistance was in the range of 17 to 18 Ohms shown in Table 4.1 and Figure 4.3, this case is considered as failed to meet the IEEE 142 requirement where the resistance range between 1 ohm and 5 ohms for industrial plant substation . Therefore, it is recommended to add more ground electrode to reduce the resistance value and archive the standard. It was also discovered that the incorrect schematic diagram that led to the finding of the lightning rod shared the same ground rod as the 11 kV switchgear.
Lightning related to voltage causes current to flow from lightning rod to general earth through copper tape and copper rod. Some of the current will escape and enter the electrical system through the shared ground connections due to high voltage. Second, it also means that the configuration of the grounding system is below a single point on the earth where it will prevent differential potential differences between different grounds.
Lightning flashes cannot dissipate properly because the common ground electrode has a high impedance.
Ground Enhance Material as Solution
Fall of Potential Plot
- Earth Grid System Design Method
- Step 1: Soil Resistivity Measurement and Conductor Resistivity
- Step 2: Length and Width of Earth Grid Dimension
- Step 3: Earthing Grid Conductor Sizing
- Step 4a: Touch and Step Potential Voltage
- Step 4b: Earthing Grid Resistance
- Step 4c: Maximum Grid Current and GPR The calculation of maximum grid current as follows
- Step 4d: Buried Conductors in Total Length The calculation of maximum grid current as follows
- Surge Simulation
- Summary
- Conclusions
- Recommendations for future work
In this section, we will go through the calculation and parameters that are considered when designing a ground grid system. The Estep and Etouch stress calculation is based on 70 kg as the average size of a human being as work and maintenance staff. The calculation of the resistance reflection factors of different materials follows:. i) Resistivity of the earth below the surface of the material, ρ = 70 Ohm-M. The calculation of the reduction factor of the surface layer is as follows: i) Resistivity of the soil below the surface of the material, ρ = 70 Ohm-M (ii) Resistivity of the surface material, ρs = 2500.
Ohm-M. The calculation of walking and contact stresses for body weights of 70 kg as follows:. The calculation of total length for buried conductors and bars as follows:. i) Total length of the preliminary grid layout, Length = 18.5 m. The calculation of weighting factors for earth electrodes or bars on the corner mesh as follows:.
Calculation of the geometric space factor for grid voltage as follows: iv) Weight factor for electrodes or ground rods in corner grid, Kii = 0.59. v) Correction factor for weighting the grid, Kh = 1.22 (vi) Number of parallel conductors, n = 12. A grounding system should provide lower ground potential rise voltages by providing a low resistance path and not just low resistance. Together with the case of the study carried out in 'Catchment 4 Water Treatment Plant' that the grounding system does not meet the resistance standard.
This study proposed a suitable grounding system design that should be designed for New Catchment 4 Water Treatment Plant relevant to IEEE standards and best practices adopted internationally. An ideal grounding system should have multiple grounding points connected together with different types of electrodes and grounding within the building to form a low-impedance ground path. The inspection of the grounding system should be performed at least once a year using a suitable grounding instrument for testing electrical continuity and resistance.
This is to ensure that the electrical system works continuously and properly with the effective earthing system. I would like to recommend the study of the possibility and effect of building steel structure as earth connection as well as the earth connection with water pipes as part of the earthing system. 2009) 'Modelling and simulation of a grounding system using simulink', 2009 Brazilian Power Electronics Conference, COBEP2009, (m), p.
