The development of smart energy management systems is the need of the hour and is aimed at alleviating the burgeoning demands from today’s power infrastructures. Optical Fiber Composite Ground Wire (OPGW) is a revolutionary solution that enables synergies between efficient power distribution grids and high-speed optical fiber-based SCADA networks, giving power utility companies the unique capabilities of a telecom carrier or service provider.
The functional aspects
OPGW replaces a conventional ground wire (or earth wire) to protect the transmission system from lightning strikes and serves as a conductive medium for carrying fault currents to ground. It also acts as a medium for real-time monitoring and security of the transmission system over which it is installed – doubling up for SCADA controls and network.
Such cable combines the functions of grounding and communications. An OPGW cable contains a tubular structure with one or more optical fibers in it, surrounded by layers of steel and aluminum wire.
The OPGW cable is run between the tops of high-voltage electricity pylons. The conductive part of the cable serves to bond adjacent towers to earth ground, and shields the high-voltage conductors from lightning strikes. The optical fibers within the cable can be used for high-speed transmission of data, either for the electrical utility’s own purposes of protection and control of the transmission line, for the utility’s own voice and data communication, or may be leased or sold to third parties to serve as a high-speed fiber interconnection between cities.
The optical fiber itself is an insulator and protects against power transmission line and lightning induction, external noise and cross talk. Typically OPGW cables contain single-mode optical fibers with low transmission loss, allowing long distance transmission at high speeds.
Sterlite’s OPGW cables
Sterlite integrates its core expertise in fiber optic cables and bare overhead power conductors. Since the past two decades, Sterlite has developed technical expertise in fiber optic cables and proven its capabilities in manufacture of energy efficient bare overhead power conductors. Sterlite has integrated these core strengths in its comprehensive OPGW solution that includes Optical Fiber Composite Ground Wire and related hardware.
Sterlite’s OPGW cables are made up of optical fibers contained in one or more protective fiber optic units combined with concentric lay stranded metallic wires in single or multiple layers. Advanced technology is applied to produce stainless steel tubes which are then filled with a special hydrogen absorbent, thixotropic filling compound and made resistant to hydrogen perme-ability due to the same laser welded, hermetically sealed construction.
The cable is of compact structure reducing both the ice load and wind load and ensures quick dissipation of heat generated by short circuit. The cable is designed to match the existing ground wires in more or less equal diameter and pulling force-to-weight ratio. Hence, the cable can replace the existing ground wire with no need to change the route or towers. Sterlite’s OPGW cable is produced strictly according to IEEE1138 and relevant international standards pertaining to its constituents.
Design considerations for OPGW cables
OPGW cables are required to withstand the effects from installation and long-term in-service exposure to mechanical, electrical and environmental loads without allowing any significant degradation in its performance. OPGW cables would need to fulfill basic performance criteria to enable selection of an appropriate design.
(a) Electrical performance:
• Fault current performance to overcome the line-to-tower short circuits or system unbalances.
• Lighting performance so that lighting arcs do not impair the long-term functionality of the cable
(b) Mechanical performance
• Sag and tension
• Vibration
• Galloping and Sheave
(c) Environmental performance
• Range of temperatures & wind zones
• Corrosion levels at the installation sites including the pollution level (1-4)
• Salinity levels
(d) Packing
• The end-user needs to determine the length per reel depending on:
• The terrain of the installation site
• The type of installation to be carried out (‘Live Line’ or ‘On Outage’)
• Capacity of unreeling facility with installer
Sterlite’s OPGW hardware
The portfolio includes customized suspension sets, tension set assemblies, vibration dampers, joint boxes and bonding clamps.
In conclusion
OPGW as a communication medium has some advantages over buried optical fiber cable. Installation cost per kilometre is lower than a buried cable. Effectively, the optical circuits are protected from accidental contact by the high voltage cables below (and by the elevation of the OPGW from ground). A communications circuit carried by an overhead OPGW cable benefits from the lower likelihood of accidental damage due to excavation work, for example road expansion or by any kind of repairing work of underground drainage system or water supply system.
About Sterlite Technologies Ltd.
Sterlite Technologies is a leading global provider of connectivity solutions for the power and telecom industries. Equipped with a product portfolio that includes power conductors, optical fibers, telecommunication cables and a comprehensive telecom systems / solutions portfolio, Sterlite’s vision is to ‘Connect every home on the planet’. Sterlite is also executing multi-million dollar power transmission system projects, pan-India.