Figure 2.1: Shielding arrangement of ground wires (Naidu & Kamaraju, 2006) earth surface, G is ground wire, P-P is phase wires and Os is shielding angle. impedance at low currents and during high lightning currents, it offers low impedance. Nonlinear elements are used in the hollow gap of protector tubes, which gives very high line conductor. Figure 2.2 shows the position of protector tubes on transmission lines. with a second gap enclosed with electrode in a fibre tube. Figure 2.3 shows the assembly of expulsion gaps, which consists of a rod gap in series Figure 2.4: Surge arrester on transmission and distribution lines (Woodworth, 2010) creepage distance to total length can be increased. ontinuous conductive layers from appearing on the surface. Therefore, the ratio of of inclination must follow IEC 60815 regulation. The alternating shed profile can prevent Figure 2.9 show an example of VI characteristice curve of a typical ZnO surge arrester over a wide range. Figure 2.10: Sintered microvaristors (Shinji Ishibe et al., 2014) in Figure 2.10 (Shinji Ishibe, Masafumi Mori, Masahiro Kozako, & Hikita, 2014). particles, which is also called microvaristors is between 50-100um in diameter as shown ZnO varistor is a semiconductor and represents the protective characteristics of the during low voltage. These grains will close when overvoltage happens and causes a rise can be discerned as shown in Figure 2.12. The grain junction looks like an open circuit is completely finished. The advantage of the varistor is the non-linear characteristics that Figure 2.14: Waveform of total, resistive and capacitive leakage current (Abdul- Malek et al., 2008) .1 Current compensation method (CCCM) Figure 2.15: IEEE model (Nafar, Gharehpetian, & Niknam, 2011) dynamic characteristics of the metal oxide surge arrester (Hosseini & Gharadaghi, 2017 voltage among its input terminals as Ao has a higher voltage than A; that agrees with the L; develops more current into the non-linear branch Ao. The model creates a greater numerical problems. In this model, only electrical data are required and there are no In 2002, Popov has proposed a model that is suitable for switching studies (M & G.C, 2002) as presented in Figure 2.19. An iterative trial and error was needed in order tc Figure 2.18, which is also originated from IEEE. The model is similar to Fernandez-Diaz estimate its parameters. The disadvantage of this model is it does not always obtain the compared to the manufacturer’s datasheet. Figure 2.20: Wide-range model (Mousavi et al., 2017) However, the most accurate model is IEEE because it provides the smallest deviation Table 2.2: Leakage current measuring techniques aluminum caps at both ends. The dimensions and parameters of the ZnO surge arrester Figure 3.1: 11kV zinc oxide surge arrester with silicone rubber housing respectively, a glassfibre between insulator and ZnO blocks, four silicone sheds and test standard. The arrester consists of two ZnOs with diameter, height of 47mm are imperialist competitive algorithm (ICA) and gravitational search algorithm (GSA). There are six parameters adjusted on the surge arrester. The parameters are the dimension of the aluminum block, aluminum base, curve of the housing shed, thickness of th Figure 3.2: Optimised parameters of 11kV surge arrester Table 3.2 Properties of each material in the electric current physic After the boundary and material of the model were assigned, the model was meshed. extremely fine because it is the important element of the model (BAKAR et al., 2016; used was normal for air, finer for all domains of the model except for ZnO, which is elements has substantial effect on the simulation time, the size of the triangular elements of higher order. In order to obtain accurate results, a finer or coarser mesh is required Table 3.4: Statistic of mesh elements of surge arrester model elements are specifies in Table 3.4. Figure 3.6: Experimental set up for leakage current measurement main company of energy provider, Tenaga Nasional Berhad (TNB) to measure leakage Figure 3.9: Leakage current equipment (SCAR10) of the arrester was prepared by adding water on the arrester surface in different quantit uncontaminated arrester was sprayed with water of 100Vm resistivity. Different wetness in Figure 3.11. The outer layer of the surge arrester was contaminated with dry sand, wet Figure 3.14: Colony move to a new position by x units toward its imperialist imperialist to endure revolution. Therefore, a random sum of deviation as shown in Figure 3.15 is added to the path of movement. This deviation from the original direction i: lower leakage current) than an imperialist (existing dimension/permittivity of parameter), the colony and the imperialist exchange their positions. In this step, the colony and imperialist will exchange their position if it reaches a lower leakage current Figure 3.16: Exchange position between an imperialist and a colony Step 4: Empire total cost calculation words, the value of the leakage current will be computed for all parameters using Figure 4.1: Electric potential distribution from the surge arrester FEA model during normal opertion. Figure 4.2: Current density distribution from the surge arrester FEA model Figure 4.3: Electric field distribution from the surge arrester FEA model Figure 4.4: Comparison of electric potential and current density distribution between FEA model and measurement at 50 Hz, 9k Vrms and 26°C height of the ZnO block is tougher in order to attain adequate homogeneity of the material. ZnO block is not observed in this study. Besides, manufacturing procedure for greater crushing the housing, whereas, if the width is smaller, the mechanical resistance may In addition, if the width of glassfibre is too large, a pressure will built-up which result in In a surge arrester configuration, an insulation layer that is silicone rubber house has Figure 4.7: Leakage current in the surge arrester for different silicone thickness lifespan of the surge arrester and at the same time reduces the electric field intensity of Figure 4.8: Leakage current in the glassfibre material for different relative permittivity values at 8, 10, 13 and 15. Figure 4.9: Leakage current in the silicone rubber for different relative permittivity Figure 4.10: Comparison of RMS value of total leakage current between measurement and FEA model under different applied voltage amplitudes of the FEA model. applied voltage amplitudes can be considered reasonable. capacitive leakage current and resistive leakage current with harmonic components of leakage current are 1.60%, 4.05% and 1.38% respectively, as shown in Table 4.1. This leakage current at 10kVims from the measurement is 44u.A while from the simulation, the measurement and simulation at 10k Vims, as shown in Figure 4.13 (a) and (b). The resistive current with harmonic components of the total leakage current were obtained from the Figure 4.13: Leakage current waveforms and harmonic components at 10kVrms applied voltage from the (a) measurement and (b) FEA model much variation in the capacitive current components under different wetness conditions. Figure 4.14: RMS value of the total leakage current between measurement and FEA model under different wetness conditions at 8kVims Figure 4.15: RMS value of the leakage current between measurement and FEA model under different wetness conditions at 8kVrms for (a) resistive and (b) capacitive leakage current Figure 4.17: Comparison of RMS value of total leakage current between measurement and FEA model under different artificial pollution conditions results using the FEA model is also shown in Figures 4.17 and Figure 4.18 arrester under different pollution conditions in this work can be considered acceptable with their harmonic components for measurement and FEA model. The total, capacitive 4.3. This shows that the measurement and simulation results are in good agreement with each other. Therefore, the proposed FEA model for leakage current modelling in surge temperature and therefore degrade the material that will possibly explode the surge Figure 4.20: Parameters adjusted on the surge arrester variables. From the parametric study of the surge arrester, these parameters were carefully .5.1 Optimised parameters value of surge arrester Table 4.9: Parameters obtained using GSA and ICA for Case 4 Figure 4.24: Optimised design of the surge arrester model 4.23 and Figure 4.24 illustrate the comparison between original design and optimised Figure 4.2 and Figure 4.3 in Section 4.2, the current density and electric field distribution Figure 4.25: Electric potential distribution from the surge arrester FEA model more contour lines for the electric field. By comparing Figure 4.26 and Figure 4.27 with Figure 4.26: Current density distribution from the surge arrester FEA model Figure 4.27: Electric field distribution from the surge arrester FEA model 1 Optimised surge arrester model under various applied voltage amplitudes Table 4.13: Average percentage of reduction by optimised design surge arrester under various applied voltages Figure 4.29: Total leakage current under different applied voltages for original and optimised surge arrester design Table 4.14: Average percentage of reduction by optimised design surge arrester under different wetness conditions The leakage current of the optimised surge arrester design developed using FEA Figure 4.31: Total leakage current under different wetness condition for original and optimised surge arrester design Table 4.15: Average percentage of reduction by optimised design surge arrester under polluted conditions arrester surface with salt water for the original and optimised surge arrester model. Figure 4.35: Harmonic components from the original and optimised surge arrester design under clean and polluted surface
