Energetica India Magazine: september 2020

POWER SECTOR 49 energetica INDIA- September_2020 help of DLR real time data brings in in- telligence and can also help to identify if there is a real need of CAPEX investment for new lines. Uprate or Reconductoring: While DLR provides a quick solution to increase the power flow on a line, a more permanent solution to increase capacity is by reconductoring the transmission line. A number of high performance con- ductors (HPC) are available, which have higher current limits and operating tem- peratures as compared to ACSR conduc- tor. The line capacity can be increased by 2 to 2.5 times using such conductors. HPC conductors can be chosen such that they have lower weight and better sag performance as compared to exist- ing conductor on the line. This allows the conductor to be changed without need of any modification in the existing tow - er and foundations of the transmission line. Figure-5 shows the comparative performance of these HPC conductors with respect to ACSR conductor. The conductors on the extreme right on the curve are from the HTLS (high tempera- ture low sag) subset of HPC conductors. They offer highest increase in ampacity with better efficiency in terms of A/sqmm of Aluminium. ACCC (or Aluminium con- ductor with carbon composite core) are the most efficient conductors with best performance in terms of increase in am- pacity, sag performance as well as bet- ter losses. Figure-4 compares the diameter, weight, resistance, ampacity and sag of various HPC conductors, equivalent to ACSR Zebra conductor. It is clear that ACCC conductor provides lowest sag and high- est ampacity and the best power loss for the same current. Its weight is also less as compared to corresponding ACSR conductor, thereby ensuring suitability to replace existing ACSR conductor on a line on the same tower. In many cas- es with old lines, due to growth of hab- itation, the available ground clearances below lines are no longer safe. Reduced sag achieved post reconductoring can help to improve these clearances, there- by improving the safety for the popula- tion near the line. Reconductoring of a line can be carried out much faster as compared to build- ing a new line for increasing the capac- ity. Reconductoring is done on existing corridor and does not call for additional ROW, thereby avoiding any related risk of execution delays. The reconductor- ing process requires few hours of shut- down daily and line can be temporarily charged (with due precautions) during remaining hours till work resumes the next day. Live line reconductoring: Uprate/upgrade is generally done by taking power shutdown of the existing line. Such shutdown schedule depends on power demand and varies with every day, causing variation in the execution plan. Hence project execution requires daily coordination with system operator. It is possible to uprate the Transmission line without power shutdown and ensure uninterrupted power to the consumers. This is possible using live line recon- ductoring techniques. The need for same arises where no ROW is available for building a new line, no parallel line is available for power diversion loads served are critical (such as Industry, Hospitals, other essential services etc.) where availing shutdown is practically ruled out. One such live-line reconductoring work was executed successfully by Sterlite Power Transmission, a first in India. In the city of Bengaluru, a 66 KV transmis- sion line, passing through the very con- gested corridor, was reconductored to double its power transfer capacity. Fig- ure-6 depicts the congested corridor of the line on which live line reconductoring was carried out. Protective tower coating: Reconductoring increases the power capacity of the corridor and makes the line good for increasing loads for many years, with generally no modification re - quired on the line towers. However, in few cases old towers might be suffering from corrosion (see figure-7) due to ex - posure to elements over long years. Continued corrosion deteriorates the health of the tower which may result in tower failure and consequent risk of dis- ruption in the power supply. When the galvanized structure loses its zinc coat- ing, the deterioration of the structure rap- idly enhances due to exposed surface to the atmosphere. The life of such struc- ture becomes unpredictable and prone to failures. In order to avoid such failures Figure 2: Line current measured & predicted by DLR Figure 5: Comparison of HPC & HTLS conductors wrt ACSR Figure 4: Conductor parameters com- parative wrt 220 kV ACSR Zebra Figure 3: DLR one day weather data