220kV Line TR1350, TR1351 Renovation of the Lines

Project Description:

1. Castasegna – Löbbia 220kV Transmission Line (Trasse 1350)

Connection and Purpose:The 220-kV transmission line Castasegna – Löbbia connects two important substations, Castasegna and Löbbia. This line plays a central role in the energy evacuation from the Castasegna power plant, ensuring the electrical power supply to the region.

Construction Year and Infrastructure:The line was constructed in the late 1950s and includes several 'Katzenkopfmasten' (cat-head towers). Some of these towers are difficult to access, which makes maintenance and repairs challenging. While the outdoor switchgear is in good condition, the insulators in the line have reached the end of their technical lifespan and require urgent replacement.

Problem and Urgency:As part of the "Transmission Line Rehabilitation Program," it has been determined that not only the cap insulators need to be replaced, but also that targeted adjustments to the line tensions need to be made in order to comply with the required ground clearance distances. Due to the project's high urgency, the development of a preliminary design (SIA 31) is skipped, and the project will proceed directly to the construction phase.

Planned Rehabilitation Measures for the Castasegna – Löbbia Line:

• Replacement of Insulators: At 34 towers, the existing insulator chains will be replaced with chains containing modern plastic insulators. These new insulators provide longer service life and increased operational safety for the transmission line.
• Installation of Double Insulator Chains: For 2 towers, double insulator chains will be installed to better withstand mechanical stress. Modifications to the arms and the middle suspension of the towers will be necessary.
• Adjustment of Tension in Conductors: Tension in the conductors will be adjusted across six spans along the line to ensure compliance with the required ground clearance.
• Inspection and Replacement of Vibration Dampers: All vibration dampers along the line will be inspected. If necessary, they will be replaced with new dampers that offer better performance and reduce mechanical stress on the line.

2. Löbbia – Tinzen 220kV Transmission Line (Trasse 1351)

Connection and Purpose:The 220-kV line Löbbia – Tinzen connects the Löbbia and Tinzen substations, securing the electrical power supply for the region. The line is approximately 12 km long and crosses the Septimer Pass, posing significant challenges regarding accessibility and maintenance.

Construction Year and Infrastructure:This line, also constructed in the 1950s, runs through difficult mountainous terrain. Similar to the Castasegna – Löbbia line, the cap insulators on this line are at the end of their service life and require urgent replacement.

Problem and Urgency:As with the Castasegna – Löbbia line, the insulators along the Löbbia – Tinzen line have been identified as needing replacement. Additionally, the earth wire (composed of either steel or bronze) needs to be replaced with an Optical Ground Wire (OPGW) to optimize communication within the grid. Failure to undertake this work could result in mechanical damage to the transmission elements, jeopardizing both personnel and equipment safety.

Decision:
Due to the project's high urgency, the development of a preliminary design is omitted, and the project will move directly into the construction phase to ensure network safety and stability.

Planned Rehabilitation Measures for the Löbbia – Tinzen Line:

• Replacement of Insulators: At 34 towers along the line, existing insulator chains will be replaced with chains containing plastic insulators to enhance the durability and longevity of the line.
• Installation of Double Insulator Chains: At 5 towers, double insulator chains will be installed to withstand increased mechanical stresses caused by environmental conditions such as wind and ice. Necessary adjustments to the arms and middle suspension will also be made.
• Adjustment of Tension in Conductors: The tension in the conductors will be checked and adjusted along the entire project perimeter to ensure compliance with required ground clearance.
• Earth Wire Replacement: One of the existing earth wires, composed partially of steel and bronze, will be removed and replaced with an OPGW (Optical Ground Wire) that includes 144 fibers. This will improve both telecommunications and grid monitoring.
• Inspection of Vibration Dampers: All vibration dampers along the line will be inspected and, if necessary, replaced with higher-performance dampers to reduce mechanical vibrations and extend the line's lifespan.
• Structural Integrity Check and Reinforcement Measures: The structural integrity of all 39 towers and the portal along the line will be thoroughly checked. If any weaknesses or instabilities are found, reinforcement measures will be defined and implemented to ensure the long-term safety of the line.

Objective of the Rehabilitation Measures:The primary goal of this project is to ensure the long-term operational reliability and stability of both the Castasegna – Löbbia and Löbbia – Tinzen 220-kV transmission lines. Through the planned rehabilitation measures, the insulators, earth wires, conductor tensions, and vibration dampers will be renewed, and the structural integrity of the towers will be assured. This will guarantee a reliable and safe power supply while preventing any potential mechanical damage to the transmission elements.