Upgrading Power Transmission Lines To Higher Voltage With Existing Infrastructure

Due to increasing urbanization and industrial growth, energy consumption has gone up in Tier I and Tier II cities in India. The rising population, along with the government’s focus to provide uninterrupted electricity to all homes by 2019, is projected to increase electricity consumption five to six times between 2014 and 2030. Over the last few decades, India has witnessed a steep rise in generation capacity. With government’s efforts, even if half of the planned renewable capacity gets installed by 2022, the generation would certainly match the nation’s requirement.

However, the key to this fulfillment will be to match generation capacity addition with adequate power transmission and more importantly, intrastate transmission and the sub-transmission network. This network must be made available to enable the downstream to the load centres around densely populated urban areas of important states and industrial areas. Under the 13th five-year plan, high capacity transmission corridors comprising 765 kV AC and 800 kV High Voltage Direct Current (HVDC) system have been planned to strengthen the national grid. It is estimated that 13,000 MW of HVDC systems will be required for grid expansion, but with growing demand, this itself is projected to grow to 15,000 MW under the 13th five-year plan. Most transmission networks in India had been built to handle specific amount of power flow. With increasing load, they’re ill-equipped for higher power flow, and now need upgradation to better transmission capabilities.

This transition traditionally requires building additional transmission capacity by reinforcing the existing infrastructure, which is currently being done in the one or more of the following ways:

  • Building additional circuits or towers
    • Most of the current structures, however, aren’t designed to accommodate additional circuits.
  • Constructing new parallel transmission lines
    • However, rapid urbanization, escalating land costs and right-of-way (ROW) challenges make this option prohibitively expensive. A right-of-way, that involves permission for additional ground space, can take several years to negotiate in addition to the time needed to upgrade to higher voltage transmission. Additionally, approvals for adding lines are difficult with today’s environmental concerns due to depreciating forest and agriculture cover.
  • Replacing existing conductors with conventional conductors of higher size
    • This would require tower replacements because of the additional structural loading and relative condition of the existing structures. Thermal sag associated with the conventional conductors is a concern too.
  • Uprating the existing transmission lines with reconductoring
    • This method is a quick-fix arrangement and applicable to only short stretches within the network to enable decongestioning.
    • The method also leads to high losses in the stretches thereby creating voltage drops and system imbalances which is why, a wide scale adoption is not possible by transmission planners.

The challenge today is to reduce the footprint of transmission corridor upgradation while increasing the transmission capacity multifold. Increased capacity without the need to reinforce existing infrastructure translates to greater profitability and lower transmission losses, therefore improving life-cycle costs compared with conventional line upgradation projects that often overrun, thereby increasing costs.

Fortunately, it is possible to upgrade transmission lines and substations to higher voltages without having to replace or reinforce the existing tower structures. The upgradation challenges can be overcome with a modern cost-effective approach that provides an ideal solution with respect to grid stability and widespread adoption for getting up to 12 times the existing power throughput. Let’s understand this approach in detail.

  • Use of compact towers to maintain the same corridor footprint
    • Using narrow base tower which has lower height, narrower base, as well as lower weight as compared to a standard tower maintains the tower footprint within the existing ROW requirements and saves significant costs and time.
    • For example, upgrading a line from 66KV to 132 KV requires ROW to be increased from 18 m to 27 m. With compact towers, this effective 33% reduction in ROW typically results in cost- savings of up to Rs. 1cr/Km and saves a timeframe of 6 months to 1 year since no additional ROW approval or forest clearance is required.
  • Lowering the corridor footprint by using monopoles and micropiles
    • Monopoles (single poles) can mitigate space constraints related to traditional poles that stand on 3-4 poles.
    • Use of Micropiles reduce excavation effort and time as well as tower foundation footprint (by 10-20%) and adds to tower stability.
  • Replacing existing ACSR conductors with high performance HTLS conductors
    • HTLS (High Temperature-Low Sag) conductors can carry more current per sq.mm than conventional ACSR (Aluminum Conductor- Steel Reinforced) conductor.
    • The power losses of the HTLS conductor are 20% to 25% lower as compared with the conventional conductor.
    • HTLS operate at much higher temperature ranges (150-2500C) than ACSR (1000C), which increases the power transmission throughput to almost twice the current capacity.
    • Additionally, HTLS conductors have low thermal expansion in the temperature range.
    • The low sag feature also facilitates reduction in tower height, which helps overcome ROW issues, as explained before.
  • Use of Mobile Substations during upgradation for minimum shutdowns
    • Usage of mobile substation at suitable strategic locations results in zero/minimal shutdown during the time upgradation is being carried out, thus resulting in higher grid reliability.

Sterlite Power is India’s leading integrated power transmission developer and solutions provider, which has been able to demonstrate this approach that tackles the key constraints of time, space and capital in voltage upgradation. Sterlite power has carried out comprehensive feasibility studies for voltage upgradation across numerous states in India and has proposed cost-effective solutions with the approach mentioned above.

India is the third largest producer of electricity in Asia, and its generating capacity is continuously growing. The distance between generating stations and load centers is increasing day by day. Huge transfer of power from generating plants to load centres at long distance will require significant line upgradation and adding additional infrastructure will not be a feasible solution to go forward. Access to power has the potential to change the lives of millions, by bringing about a transformation in the local economy, and with it, the country as a whole. The country wide power transmission upgradation, however, will require a co-ordinated effort by government and various power transmission solution providers to solve the toughest challenges of energy delivery.

Siraj Bhattacharya
AVP – Business Acquisition and Sales, Solutions BU at Sterlite Power

Disclaimer: The views and opinions expressed in this article are those of the author(s/) and do not necessarily reflect the official policy or position of Sterlite Power.


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