Monopole is a latest advancement in the T&D sector, saving on space and time for the grid managers and discoms. However, the knowledge of it is yet to sink in among the powers that be before it can make a mark.
There is an emergent need to provide high voltage electric power transmission that minimises impact on the environment, agriculture and communities. Overhead transmission lines have been the normal, located on designated rights-of-way. Acquiring a new right of way (RoW) for overhead DC/AC transmission lines is usually challenging to permit and in some jurisdictions it is impossible to obtain.
Nowadays most of the transmission utilities are facing problems in laying transmission lines in urban areas due to severe RoW problems. This is in view of non-availability of adequate land for installation of conventional lattice type towers. To overcome these practical difficulties, a new concept of transmission lines is being used world-wide, called ´monopole´. Monopoles are the latest alternative to overhead transmission lines lattice type self- supporting towers, seeking only one-sixteenth the space sought by lattice towers for erection.
Monopoles are Tubular Structures with the uniform Taper throughout the length. Having a polygonal cross section (i.e. 8-sided, 12-sided and 16-sided), and shall be continuously tapered with longitudinal welding. There shall not be any circumferential welding. Monopoles shall be of two or more sections with telescopic joint as per the required height.
In India, the market for T&D monopoles is still at a very nascent stage, though the products are in use for over 50 years in the Gulf and European Countries. These steel monopoles can also be used for many applications including street lighting, high mast, for mounting CCTV cameras, stadium mast, as telecom monopoles, for unipole signage structures, swaged poles etc., along with luminaires.
´The monopoles were first introduced by Power Grid Corporation of India Limited (PGCIL) during the year 2008-û09. The current market size for monopoles in India would be roughly Rs 50 crore,-ö said Devesh Bansal, Director, Skipper Limited. Use of steel poles started in late 1960s in US, with extensive research, engineering and testing in early stages. It received wider acceptance in the´70s and ´80s. Today, steel poles are the dominant type structures for new age power transmission and are commonly used in many countries, gradually being adopted in more new markets.
There are a handful of monopole manufacturers in India by now. This is a latest advancement in transmission and distribution sector, saving on space and time for the grid managers and discoms.
There are four major integrated players in the country - Skipper Ltd, Bajaj Electrical Ltd, Valmont Structures Pvt Ltd, India, and Transrail Lighting Limited, a Gammon Group company. Almost all of them have facilities to design, manufacture and galvanise monopoles from 11 kV up to 400 kV.
Bajaj Electricals Ltd (BEL) had set-up the first world-class, state-of-the-art galvanised steel structure manufacturing unit in India at MIDC Ranjangaon, near Pune in 2002. Thereafter, BEL designed and successfully commissioned first 400-kV DC monopole for transmission application in India in 2007. BEL has pioneered monopoles in India by executing the India´s first monopole project, almost a decade ago, comprising of a 400-kV double circuit transmission line for Power Grid Corporation of India Ltd (PGCIL).
´After coming to India, Valmont successfully re-introduced monopoles in India in 2012 by co-partnering one of the local EPCs in construction of 11.2 km of 132 kV line near Ghaziabad under UPPTCL completely on monopoles,-ö Vamont claims. Here a 132-kV line was constructed successfully in the existing 33 kV corridor with expertise monopole solution from Valmont. ´With our rich international experience, we have also brought in world class galvanising solution to India, which provides much longer life,´ Valmont added.
Transrail Lighting claims that they are the only Indian pole manufacturing company which is certified for CE Marking (quality certification required in European Market), apart from being an ISO 9001:2008, 14001:2004 & OHSAS 18001:2007 certified company.
-´For monopoles, we are using ASCE 48-05 and ASCE 48-11. The software which we are using for design of these monopoles is PLS POLE SOFTWARE, which produces design in line with ASCE 48-05/ASCE 48-11. Manual on Transmission Tower from CBIP (Central board for Irrigation and Power) Manual is also providing details for fabrication and design requirements of transmission monopole,´ said Kailash K Agarwal, Chief Executive Officer - Pole Division, Transrail Lighting Limited.
Unlike US and Europe, in India, Bureau of Indian Standards (BIS) is yet to come out with a standard on manufacturing of monopoles, said Bansal of Skipper.
To minimise the adverse effects of high voltage electric power transmission lines, new technologies are forthcoming that when applied may be more acceptable. By judicious compacting of high voltage direct current (HVDC) and high voltage alternating current (HVAC) transmission systems, existing RoW can be utilised better.
A high-voltage, direct current (HVDC) electric power transmission system (also called a power super highway or an electrical super highway) uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems adopted at the distribution level in India. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. However, for shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links.
HVDC allows power transmission between unsynchronised AC transmission systems. Depending on voltage level and construction details, HVDC transmission losses are quoted as about 3.5 per cent per 1,000 km, which is 30 - 40 per cent less than with AC lines, at the same voltage levels. This is because direct current transfers only active power and thus, causes lower losses than alternating current, which transfers both active and reactive power.
The combined economic and technical benefits of HVDC transmission can make it a suitable choice for connecting electricity sources that are located far away from the main users.
The disadvantages of HVDC are in conversion, switching, control, availability and maintenance.
Whether the transmission line is of DC/AC, they were being carried on overhead lattice towers till monopoles were introduced in India during the last decade.
´Shape and geometry are the only differences between monopole and conventional tower. Monopole can carry equal loads with ease and still can serve longer. This is same for AC and DC lines. Due to flexibility built in, monopoles are very less susceptible to failure during severe wind storms. This is not the case with conventional towers,´ said Viswanath Devarajan, Managing Director, Valmont Structures Pvt Ltd, India.
There are a few differences between lattice towers and monopoles. Monopoles are of a pole type while lattice towers as the name denotes is a cantilever tower made up of angular steel pieces. As such, lattice tower calls for four foundations, while monopole may require only one.
For a typical 220 kV double circuit monopole of 300 metres with a ZEBRA conductor the differences in the structure will be as follows: Lattice type may require higher land base than monopole, weight of the monopoles is higher compared to that of the tower, RCC work for the monopole will be seven times that of the tower, steel required for monopole is at least five times more than that of the tower and ultimately cost wise monopole is costlier compared to the lattice tower (See Comparative table).
Transmission monopoles are pole structure used as replacement of lattice type towers. This structure helps countering the constraints as RoW or corridor width. Also for hilly terrains, a monopole can be conveniently used against a lattice tower. The monopole adds to the aesthetics of the city too. The transmission line using a monopole can be accommodated on highway curbs.
Monopoles reduce space requirement by 70 per cent when compared to angular transmission towers. Thus, it is more beneficial in urban areas as huge transmission towers of yore can occupy large amount of space. Due to lower number of components, its installation is quicker.
Sanjay Bhagat - Vice President & Head - TLT BU, Bajaj Electrical Ltd., lists out the advantages and disadvantages of monopoles. They are as follows:
Following are the major advantages:
1.Shorter project delivery period
2.Minimum space requirement
3.Faster & safer mechanised tower erection
4.Smaller footprint and hence lesser environment impact
5.Protection against vandalism
6.Aesthetically pleasing designs
7.Better inventory management as lesser components need to be handled
Disadvantages are as follows:
1.Higher weight and cost as compared to angular lattice tower
2.Difficulty in transportation & installation especially in hilly areas
for voltage range of 765 kV and above
Solutions: These monopole-based lines can give handy solutions to RoW-based problems, a few of them are mentioned below:
Up gradation of line within the existing Corridor can be done using the transmission line monopole
With varied applications and advantages, Monopoles are gaining popularity among the consumers, mainly grid and distribution companies, of late. However, lack of awareness and higher cost of monopoles seem to be major obstacles in growth of monopoles. ´At present, major obstacle is lack of awareness about monopoles and expertise with Indian utilities. As the market for monopoles has not yet fully evolved, there is no standardisation of specifications, designs or installation methodologies. With more monopole projects coming up in recent years, we can expect better standardisation in the years to come,´says Sanjay Bhagat.
However Bansal identified cost as a major obstacle. The main obstacle in spreading the use of monopoles in the current scenario is typically the higher cost which prevents its application, he says.
Nonetheless, some argue that if one considers the life cycle cost of the pj\roject then monopoles will work out cheaper. ´If we consider the factors like faster installation time and lesser space requirement reducing RoW constraints, it may turn out to be economical,´ says Agarwal of TLL.
Valmont thinks that the understanding is growing among the customers about the concept of steel poles and few of the prestigious utilities like UPPTCL, MPPTCL, RRVPNL, KPTCL, HVPNL, MSETCL etc., have shown interest in monopoles.
´Present prices of monopoles are much higher than that of angular lattice structures mainly due to smaller market size and non-standardisation. With increase in market size, better availability of raw materials and manufacturing optimisation, prices of monopoles will surely get reduced, making it more attractive,´ feels Bhagat.
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