Development of A Newton Raphson Symmetrical Component Based Technique for Fault Analysis on Nigerian 330 KV Transmission Lines

Abstract

Fault analysis is one of the basic problems of power system engineering. It plays a significant role in the power system security for supply of stable and economical operations of power systems. This study carried out fault analysis on Nigerian 330 kV, 28 bus system using Newton-Raphson analysis and symmetrical components method to determine the voltage magnitude and fault magnitude in the system. Newton-Raphson method was used to calculate the short circuit pre-fault voltages and currents on power system. This was used to check the weak buses that are out of acceptable voltage limit of ± 10%. After identifying the buses with problems, a three-phase fault on the power network was then calculated using symmetrical component analysis and was simulated using MATLAB to determine the post-fault voltage magnitudes, angles and fault magnitudes of the power network. The pre-fault result showed that buses 13 (New-Haven), 14 (Onitsha) 19 (Jos), 22 (Kano) and 25 (Markurdi) were the buses that fell out of tolerance range of ± 10% and were termed as weak buses. These buses with low voltage values were examined and post-fault calculations were carried out and the results of voltage magnitude and voltage angle were reduced to zeros.The results of pre-fault current magnitude showed that the selected weak buses namely; Makurdi, New-Haven, Kano, Onitsha and Jos have the current magnitude values of 10.4200 p.u, 9.4350 p.u, 8.4501 p.u, 7.5440 p.u and 5.3320 p.u respectively. The results also showed that Makurdi, had the highest fault magnitudes with a value of  25.1006 p.u followed by New-Haven with value of 23.9455, Kano with value of 22.4917, Jos with value of 21.4686 and Onitsha had the least fault magnitude value of 19.8765 p.u under post-fault condition. More so, it was observed that the voltage on the affected buses was reduced however current magnitudes of these buses when fault occurred were excessively high compared to the pre-fault currents.The result confirmed that symmetrical three phase fault is the most severe kind at the
transmission lines. The result also revealed the abnormally high magnitude of current that flows through the Nigerian power network to the point of fault. Therefore, the Nigeria power regulator and policies are required to determine the flow of current regularly during faults occurrences in the power system so as to ensuring improvements in the country power sector. The study therefore recommendations that additional lines should be introduced into the network to assist in the strengthening and reduction of long lines to improve the voltage profile of the network, especially New-Haven, Kano, Onitsha and Markurdi lines. The study will assist the power regulators for selection of circuit breakers and rating of protective switchgears installed in power system to enhance the efficiency of the power supply in Nigeria.

Keywords: Fault Analysis, Nigerian Power Network, Newton-Raphson, Symmetrical Components, Three-Phase Fault, Voltage Magnitude, Fault Magnitude.

DOI: 10.7176/JNSR/9-16-02

Publication date: August 31^st 2019