A monopole tower is a new type of electricity and WiûFi transmission tower which takes up less space as compared to the conventional lattice tower. With states like Uttar Pradesh, Bihar, Madhya Pradesh, Rajasthan, Karnataka and Haryana embarking more on monopoles, the demand for this neglected industry is likely to witness an upward trend.
Once widely used only in the US and European countries, monopoles are now becoming popular in India too. This is because monopoles have distinct advantages over the lattice towers with respect to space, speed of erection, short delivery time and more. The benefits of smaller base installation space, even while rising higher than 40 to 50 m, make monopoles an eco-friendly alternative as well.
Advantages of monopoles in comparison to conventional towers are: Lesser right of way (RoW), better appearance, less components resulting in faster installation, better reliability under extreme conditions, design flexibility, vandalism proof, reliable performance and longer service life.
A case in point is, recently, the Delhi Metro Rail Corporation (DMRC) for the first time, installed six monopole towers for Uttar Pradesh Power Transmission Corporation (UPPTCL) at Noida Sector 34 on its under-construction corridor from Noida Sector 34 to Electronic City. These towers are 61.2 mts high, the highest for any monopole tower in India.
The electricity transmission lines of UPPTCL were infringing the alignment of the corridor in Sector 34, hence DMRC decided to raise the height of these transmission lines. The area is heavily populated and also sees a great volume of traffic on a daily basis, hence raising the height of the towers was not an easy task.
The decision to install monopole towers was taken to reduce land requirement and save land cost. The space required by a conventional transmission tower was 245 sq mts per tower, whereas one monopole tower required only 33.26 sq mts land. Each monopole tower weighs around 40 tonnes. To further curtail the requirement of land, two transmission lines were clubbed into one monopole tower, it said.
The monopole towers were erected using heavy duty cranes of 400 tonnes capacity. Heavy machinery and trailers were also used in the erection of these towers, which was extremely difficult considering the densely populated area. DMRC took adequate safety precautions while erecting the towers and testing of the entire structure was done by experts from IIT Mumbai and IIT Roorkee. This completely elevated corridor from Noida Sector 34 to Electronic City is approximately 6.8 kms long and comprises six stations.
According to DC Bagde, Managing Director, Transrail Lighting, 'With increasing urbanisation and smart city, the requirement of monopoles is going to increase higher than ever.' He further adds: 'Cable laying or monopoles are the options and underground cabling for higher voltage is very expensive. Therefore the demand of monopoles will increase.'
Costly or cost effective
POWER TODY spoke to Sanjiv Bhandoh, General Manager - Projects, TLT EPC, Bajaj Electricals, and according to him the only thing which seems to be a disadvantage is the cost of monopole, which is not a factor, when you consider the complete solution it provides and the life-cycle cost of lines running through urban and suburban areas is comparatively less with use of poles. 'Monopoles are not only structures, but are solutions,' he said.
Bhandoh outlines how with the multi-purpose use of monopoles the implementing agencies can bring down the cost. Since space is a constraint in urban areas, monopole can be used as a smart pole and accommodate space for Wi-Fi infrastructure, surveillance systems, EV charging station, solar lighting to name a few.
According to him, the cost can further come down if the industry avoids sheet wastage and designs its monopoles accordingly. For example, with 92 monopoles to erect, Bajaj Electricals has done the foundation in just 45 days, which brings down the fixed cost erection. Considering that the entire erection is equipment oriented, there is minimal human intervention, which in turn saves labour cost.
It is expected that in the years to come, with better designing taking place, the cost of monopoles will likely to cost 1.25 times of the conventional tower than the earlier 2.5X charge. That being said, there is a major demand for understanding the concept of monopoles from states namely Uttar Pradesh, Bihar, Madhya Pradesh, Rajasthan, Karnataka, Haryana to name a few. These states have shown interest and have started adopting the concept of monopole as a solution and an alternative. In fact, said Devesh Bansal, Director, Skipper, 'PGCIL, too has come out with tenders for Monopoles installation and type testing of monopoles upto 765 kV.'
Deepak Lakhpati, Chief Design Officer, Sterlite Power is of the opinion that in recent times, monopoles are being installed very selectively for a very few road crossings and metro constructions in major cities. But for longer lines, it is still an expensive option, unless the market size improves and reduces the cost.
Lakhpati and Bandoh suggest that, once the Indian standard for designing and installation of monopoles is developed and released, there is a necessity to include it in the request for proposals by the authorities like how Bihar did. Only then will the market perception about monopoles change.
Monopoles are advantageous due to visual impact and better suited where ROW is not available to install lattice towers. Monopole is much faster to install, comes in slip joint or flange joint for connections and hence does not contribute to shortages at site as commonly experienced in lattice towers. Monopole infrastructure is a single pile foundation and much faster to execute compared to four open foundations of a transmission tower.
However, the differences between monopoles and conventional towers are not so glaring except for shape and geometry. Monopoles can carry equal loads with ease and still can serve longer. Due to flexibility built in, monopoles are less susceptible to failure during severe wind storms, which is not the case with conventional towers.
'The load carrying capacity of a lattice tower is upto 1,200 kV and higher whereas for the monopoles it is upto 765 kV only, with no major difference in the frequency levels. Yes, they both can be adapted to both AC / DC lines,' said Bagde.
'There is no difference in power carrying capabilities between monopoles and lattice towers as long as the electrical clearance is maintained. They can be adopted by both AV & DC lines,' mentioned Lakhpati. However, Lakhpati demand a code of practice for design and installation of monopoles in India, which is currently off the radar when it comes to Indian standard for designing of monopoles.
There are a few differences between lattice towers and monopoles. 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 may require higher land base than a 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 lastly, monopole is costlier compared to the lattice tower.
To minimise the adverse effects of high voltage electric power transmission lines, new technologies are forthcoming which, when applied, may be more acceptable. By judicious compacting of high voltage direct current (HVDC) and high voltage alternating current (HVAC) transmission systems, existing right of way (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 at about 3.5 per cent per 1,000 km, which is 30 - 40 per cent lesser 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 was of DC or AC, they were being carried on overhead lattice towers till monopoles were introduced in India during the last decade.
Bajaj was the first to design, manufacture and erect steel monopoles in India, and now it continues to bring in an expertise of over 10 years to the table.
The Bajaj EPC Power Transmission segment was the first and the only one in India to design, type test, manufacture and install monopoles of 400 kV double-circuit line with a height of 42 m for Power Grid Corporation of India Limited for their project line from Dadri to Ballabhgarh. Apart from PGCIL, another notable project where BEL displayed its expertise is UPPTCL-132 kV 90-degree deviation monopole line at Agra. The steel monopole structures are designed as per ASCE/ASTM manual 72. Right now, Bajaj is executing 400 kV monopole project for UPPTCL at Noida, which is India's largest ever.
Certified by TUV NORD for ISO 9001: 2008, ISO 14001:2004 and BS OHSAS 18001: 2007, the BEL plant meets all the stringent quality standards. Moreover, all the 400 kV, 220 kV and 132 kV monopoles are type tested at a third party independent reputed lab for additional quality checks. Bajaj Electricals is equipped with a very strong in-house design and engineering team that offers complete solution from concept to commissioning.
Currently, BEL has an order book of around Rs 1.5 billion and Sanjiv Bhandoh, General Manager - Projects, TLT EPC expect another Rs 2 billion worth projects in the current FY.
Meanwhile, as a strategy to gain volumes in monopoles space, BEL is eyeing international projects which BEL claims to build a strong case study in domestic market. Bhandoh told PT that BEL is executing a 132 KV project in Zambia and in the process of bidding for Kenya, Nepal and Zambia.
I envisage, in the next two years at least 10 per cent of the total transmission segment will switch to monopoles,' Bhandoh suggests, 'And the demand would be primarily from urban areas rather than cross country lines.'
Availability of space: Space consumed by a monopole compared to a lattice structure of same capacity is almost 70 per cent less. Hence, monopole structures become suitable for heavily populated and congested areas like metros and other cities
Easy installation: As the number of components used in monopoles are much lesser than the lattice tower structure the installation times are much lower
Designing: Due to its built-in flexibility and lower aerodynamic coefficient poles are subjected to lesser wind load as compared to conventional tower structure
Aesthetically pleasing: Occupying lesser space makes Monopoles look aesthetically smarter Protection against vandalism: Since poles being more continuum type structures, they offer more resistance to vandalism
Difficulty in transportation: Monopoles require heavy cranes for their deployment and installation
Limits transmission of high voltage current: Manufacturing limitations for voltage higher than 765kV Monopole being cantilever type structures have higher overturning moments at the base which necessitates the use of heavy pile foundations
- RAHUL KAMAT
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