Sterlite Technologies Limited (STL) undertook the challenge of supplying and installing of Optical Ground Wires (OPGW) on GETCO’s old 220kV transmission line in Kangashiyali, Gujarat.
Critical attributes and challenges
The most critical attribute of this project was that the OPGW was to be strung on 30 years old towers, which were built in accordance to the old BIS standard. This placed emphasis on the OPGW to be of a very light and at the same time this was to be installed in one of India’s hottest regions, which meant the conductivity of the OPGW should be high enough to evacuate the fault even when the conductor was at a temperature of 50°C and still not to exceed 200°C even in the worst case scenario.
Parameters Considered for Design
• Fault current rating: 6.32 kA for 1 Sec.
• Temperature gradient: High Ambient Temp 50°C and up to 200°C
• Weight of the cable: Less than 350kg
• Isokeraunic Levels: 50 (Average lightning strike rates)
Design considerations
• Fibers should always be housed in hermetically sealed stainless steel tubes filled with hydrogen scavenging type of thixotropic jelly.
• Plastic/Polymer components for the optical units are clearly avoidable in Indian geographic conditions considering high ambient temperatures and temperature gradients during fault currents/ lightning strikes.
• High wind zones around 60% of Gujarat’s demography mandates use of higher UTS designs.
• Old towers as per IS:802 – 1977 forces to use an extremely low weight cable so that the towers withstand the forces.
Advantages of Design offered to GETCO
• High Strain Margin
• Low Diameter
• Designed to work in high Ambient temperatures (50°C)
• Very Low weight (< 350 kg / km)
• One full layer of Aluminium Alloy on the outer to handle current surges / faults.
Compliance with Sag & Tension Requirements of GETCO
The key considerations included:
• 220 kV Transmission Line
• Span Length: 350m
• Wind Loading: 45 Kg/m2
Sterlite’s OPGW solution
STL’s existing strengths in fiber optic cables and power conductors engineering, complemented with its domain knowledge in integrating the total solution, is in line with expectations from our customers to provide a data transfer solution in addition to a power transmission solution.
The company’s conductor, fiber & cable products and systems have been approved for quality, environment, safety and additionally our OPGW products have been approved by SABS (South Africa) and have been type tested at CPRI & DRDO in Bangalore.
Conclusion
Through STL’s OPGW solution offering, it has operationalised an extremely versatile set-up, considering all the design options mapped to geo-technical conditions applicable globally.