Design of grounding system to protect against lightning and fault is important for both safety and reliability especially for Metropolitan Electricity Authority (MEA) as mostly Metropolitan Electricity Authority operates on overhead networks. This thesis assesses lightning performance for 69 kV 115 kV overhead subtransmission lines 24 kV distribution line using case study from Metropolitan Electricity Authority. Because of the limitation of the right of way distribution feeders are regularly installed together with subtransmission lines in a single concrete pole. Overhead Ground Wire (OHGW) installed at top of the pole and grounding system in concrete pole protects fault current or direct lightning surge to ground. Metropolitan Electricity Authority has developed lightning protection based on an IEEE standard which uses international data for insulation coordination. As a result reliability of the system is lower than the designed value. This thesis suggests a methodology to improve the performance in order to increase the reliability of subtransmission and distribution lines feeding distribution substations. This thesis recommends installation of addition external ground wire on the outer surface of the concrete pole to reduce top pole voltage and back flashover rate or installation of bundle overhead ground wires to protect shielding failure. As all the case studies presented in the thesis which constitute this thesis are applied to existing systems of Metropolitan Electricity Authority it is expected that the proposed methodologies can be served as useful practical guidelines for lightning performance assessment subtransmission lines and distribution lines of Metropolitan Electricity Authority.

This paper presents a program developed for calculating magnetic field intensity of high voltage transmission line and high voltage distribution lines. This program was developed with Microsoft Visual Basic and Microsoft Access program was used to store the database of the peak ratings current height and space of transmission lines. The developed program was able to calculate magnetic field intensity of high voltage transmission line and high voltage distribution lines according to 2 standards of Provincial Electricity (PEA): “A 22 kV Single Conductor Circuit High Voltage Distribution System” and “115 kV Single Conductor Circuit High Voltage Transmission System”. The program was able to select structure of the electrical system to be calculated as well as types and specification of Transmission line from the stored database that corresponded with the structure. The calculated output waveforms were displayed on computer monitor. Results from the developed program enable more convenient and faster calculations of magnetic field intensity of high voltage transmission line and high voltage distribution lines and are useful for analysis of possible impacts on electric and electronic devices.