L150 Anchor Inspection and Repair

NTPC is currently planning an anchor degradation study for L150 transmission line. The initial inspection phase of the project will be conducted outside of the migratory bird nesting period from late July to the end of August, 2023. Excavation work will take place during the fall months. The L-150 is a 115 kV transmission line that forms the South Slave Power Grid, it comprises of approximately 800 Guyed-Y aluminum transmission towers. The length of the transmission line spans 285 km and is strung with single 3/0 ACSR Pigeon conductor. The tower line was constructed in the 1960s and is currently experiencing widespread issues with its anchors. The anchors are fastened to the ground with anchor rods that are buried 2-3m below ground surface (bgs). Additional geotechnical information is required to complete Engineering of the anchor solution, and ground level assessments of all the anchor structures is required to prioritize structure rehabilitation. A drilling program is planned to take place starting September 2023 between Fort Smith and Pine Point. A desktop study will be carried out in August to determine the location of the boreholes (estimating 20-30 boreholes within the Park). Based on the results of the borehole logs, recommendations will be made for 8 excavations at Towers along the distribution line to extract the anchors for corrosion assessment. Extracted anchors will be sent for testing, and new anchors will be installed in their place. Excavation depths are expected to be 8-10 feet, and carried out using small tracked excavator. NTPC is planning to investigate the anchors and identify the main cause(s) of anchor degradation along the Transmission Line (Corrosion, End of Life, etc.) and the extent of the degradation during the summer of 2023. Anchors deemed to be in unsuitable condition throughout the SSES system will be dug up using an excavator (bobcat style equipment with rubber tracks to minimize ground disturbance). Anchors removed will be replaced. Minor travel and transportation of equipment between spans will occur. Repairs and upgrades may be undertaken as necessary. The scope of work involves shallow subsurface excavation (0.6 m bgs) as well as deep subsurface excavation (2-3 m) to determine extent of surface & subsurface corrosion, for one anchor at several tower sites. Exact dates and locations will be submitted in project information updates. July 7, 2022  A detailed sediment and erosion control plan will be delivered prior to work commencement.