Reliability improvements in 33 kv distribution lines in the coastal belt : a case study

Abstract

In Sri Lanka, majority of MV network runs through vegetation, hilly and polluted areas etc. Hence, it has been vulnerable to many faults caused by wayleaves, insulator flash over due to lightning, switching operations and the effect produced by pollution in the insulators etc. The insulator failure due to saline pollution in particular is a problem that increases failure significantly. The priority 33 kV feeder, Ratmalana Feeder -9 which feeds power from Ratmalana GSS to Angulana PSS and Moratuwa PSS causes flashover of insulators frequently. While analyzing the outage details in the Ratmalana Feeder - 9, it has been noted that the most of the tripping are due to insulator flashover and wayleaves. During the monsoon period, the tripping rate is very high. The routing maintenance including washing of insulators in this line is being done once a year during the monsoon period. In this case study four possible solutions were discussed to overcome this problem. The solutions are composed of introducing UG cable, LYNX line, CC line and increased frequency of maintenance. Analyzing the economic parameters, implementation of UG cable is not a viable solution. The other three solutions are viable and increasing of maintenance frequency is the most viable. The implementation of LYNX line as an alternative route is practically a difficult task to maintain safety clearance to buildings and other lines as per CEB safety standards. Replacing existing conductor by CC is a better approach in this specific case. RUBY SAX CC is newly introduced CC which is equivalent to LYNX conductor manufactured by locally. In this case study, most viable solution is increasing of maintenance frequency. To minimize the trippings, it is recommended that maintenance to be done periodically and efficiently with skilled field staff and proper maintenance schedule especially during monsoon period. Secondly, vegetation management system should be efficiently adopted. Finally, the public awareness programme is to be implemented on vegetation management along the RF – 9. Therefore, introduction of efficient and effective maintenance programme periodically with increased frequency is the most viable solution which could be recommended by the findings of this study.