Analysis and design of high voltage transmission lines and substation earthing system

Abstract

The thesis covers numerous new findings for high voltage earthing system analysis and design including: soil resistivity structure, pole grid resistance measurements, soil voltage contour, overhead earth wire (OHEW) fault current distribution under finite and infinite conditions, and AC interference study using the superposition theorem. The importance of soil resistivity is highlighted when it comes to human safety, earth grid resistance and fault current distributions. Various approaches have been proposed to obtain accurate soil resistivity structure. The thesis defines the conditions for the use of single layer soil resistivity along with updated equations for the uniform soil structure computation. The thesis addresses issues with non-continuous OHEWs under finite and infinite conditions. The impact of non-continuous OHEW on fault current distribution under substation fault is analysed. The simplified equations are proposed to compute the pole grid current under substation fault. Furthermore, it introduces the "n" factor which helps to determine the number of poles required for earthing assessment under substation fault. The research work defines the new substation split factor under finite non-continuous OHEW condition. This definition allows for accurate computation of the fault current distribution in OHEW system. The new fall of potential (FOP) method arrangement for transmission line earth grid resistance measurements, especially within limited space areas, are also included. The new arrangement allows the tester to choose between different separations as suitable for the project. The works introduces the new equation to compute the soil voltage contour around the pole earth grid system. In addition, a modification to IEEE 80 earthing design diagram is proposed and presented in the thesis. The AC interference between transmission lines and parallel running pipelines are analysed using the OHEW section current. The AC interference study is divided into three sections depending on the location of the fault and the parallel segment. The effective length concept with the modified shielding factor is also introduced. The experimental and simulation results confirm the accuracy of proposed contributions in terms of the soil resistivity structure, pole grid resistance measurements, soil voltage contour, OHEW fault current distribution under finite and infinite conditions, and AC interference study using the OHEW section current. The experimental data are obtained from numerous sites including UWS ground. The UWS field test site is located at Werrington campus of UWS and has an area of more than 6000 m2. UWS site allowed for the installation of the mini transmission line and its relevant earth grid systems. Numerous field tests are completed at UWS to obtain the required data that confirm the proposed novel theory within the thesis. Furthermore, the outcomes of similar field tests, which are completed at different sites within NSW, also support the novel findings of the thesis.

Date of Award	2015
Original language	English