The Afghanistan Engineering Support Program: Conductor for 150 MW Upgrade of Pul-e-Khumri to Chimtala Transmission Line

A question has arisen regarding the use of high-temperature, shaped conductors for this upgrade. The answer to this question is yes, provided the current structures can accommodate the new conductors and the electrical grid can accept the additional power flow. The current conductors are made up of multiple strands of aluminum and steel, while the high-temperature conductors will be made up of a different material with each strand compressed into a trapezoidal shape. The characteristics of the high-temperature conductor will differ from those of the current in-service conductor, including allowable tension and sag characteristics. To assess the feasibility of increasing the power flow, a study of the existing transmission line is needed. The study must determine the existing conductor characteristics, including present sag and tension, as well as the existing tower structural details, such as materials, spacing, and strength. A model of the subject line must be created using the current conductor spacing and characteristics, and the current Afghanistan electrical grid for power flow and stability. The model must determine the proper size for the Pul-e-Khumri to Chimtala transmission line conductor and whether additional mitigation is required to maintain the Afghanistan electrical grid when increasing power flow from 300 MW to 450 MW. The design of the re-conducted line must consider the thermal capacity of the conductor, the overall impedance characteristics of the line, and the system stability characteristics. The inductance of the line has a greater impact than the line resistance, and changing the inductance will affect the system stability. The capability of the present towers to handle the larger conductor(s) is a significant question, and structural competence is of paramount importance, especially during extreme conditions such as wind and ice loading. The line in question was designed by PowerGrid of India, and the design documents or design criteria are not available. A suggested back-up is to take a short ground survey to determine the present attachment levels on the structures and the present conductor sag. This information would allow for a portion of the design criteria to be defined, and the system power/load flow studies could be performed to determine if the present electrical system can operate successfully when transporting an additional 150 MW.