As discussed in Alberto Pigini’ s Column, India is enhancing its grid by expanding its 765 kV AC, ± 800 kV DC and 1200 kV AC transmission networks. Present installed capacity is 210 GW but strategic estimates suggest an incremental peak demand load of up to 500 GW by 2025 +, meaning required capacity will be about 700 GW. To handle power transfer linked to such rapid growth, the country’ s transmission network will have to effectively interconnect generating resources in eastern and north eastern states with distant key consumption centres.
Papers at CIGRE UHV Colloquium in India
Apart from the technical challenges developing and testing line components and substation equipment at UHV, there will also be separate considerations, such as right-of-way( ROW) and environmental restrictions. Since 1200 kV technology has been developed for the first time in India, it seemed only logical after the 2 nd IEC / CIGRE Symposium on Standards for UHV Transmission( Jan 2009), to invite international experts from CIGRE Study Committees A2( Transformers), A3( High Voltage Equipment), B2( Overhead Lines), B3( Substations) and D1( Materials & Emerging Test Techniques) to exchange experience in the field. The event included a visit to the 1200 kV test station in Bina, commissioned during the first quarter of 2012. Some 140 participants came, including 40 from overseas, and CIGRE President Prof. Klaus Fröhlich gave the keynote presentation. 40 papers were selected and four of these, accepted for the overhead line session, are summarized here:
A paper, Design & Optimization of India’ s First ± 800 kV HVDC Transmission Line, R. Gupta, A. Anand, G. Ji, G. Gupta, B. S. Pandey, documents Powergrid’ s ± 800 kV line design. Experience with HVDC transmission as well as back-to-back systems has been available in India for some time, with the first ± 500 kV transmission line, commissioned in 1991, running 815 km between Rihand and Dadri. Two more such lines were built and commissioned in 2002 and 2010( the 1370 km Talchar-Kolar and the 800 km Balia-Bhiwadi lines respectively). Construction of the 1750 km ± 800 kV line between Biswanath Chariyali and Agra is now underway and expected to be commissioned this year or next. As is well documented from service experience of DC lines, pollution dominates decisions on string length and therefore composite insulators are being installed in certain polluted sections.
420 AC D / C
Voltage( kV)
765 AC S / C
765 AC D / C ± DC 500
± 800 DC
1200 AC S / C
ROW( m) 46 64 70 52 70 90
Power Capacity( MW)
600- 700
2500- 3000
5000- 6000
2000- 2500
6000- 6400
6000- 8000
MW / m 15 45 65 48 90 90
Another paper, Design & Optimization of Upgradable 1200 kV Transmission Line by R. R. Patel, A. Anand, G. Ji, G. Gupta, B. S. Pandey, discusses studies to develop a line that can be upgraded to 1200 kV. Engineering proved complex in terms of such aspects as conductors and their configuration, insulator strings, tower design and foundations and selection of earthwire. Overall, design is determined by planned initial service at 420 kV, to be followed by 1200 kV when the network will be upgraded. The 420 kV double circuits will therefore have a quad conductor configuration( ACSR Moose), upgraded later to an octagonal conductor configuration for 1200 kV( same conductor). Apparently, the new Bina test station provided important practical and experimental data to support this project.
A third paper, Right Of Way: Challenges & Solutions for Transmission Lines in India by D. Lakhapati, deals with issues utilities worldwide face for new lines or voltage upgrades, including ROW, land acquisition, regulatory and environmental clearances. In India, transmission lines have long been erected without any major ROW restrictions but increased awareness by farmers and landowners as well as environmental restrictions relating to forest reserves, bird estuaries and religious sites has made it increasingly difficult to obtain timely ROW approvals as required by line construction. Possible solutions to overcome these constraints are described and a comparative analysis is presented that relates power intensity per meter of ROW( see Table).
Despite the fact that an absolute wider ROW is required at higher voltages, the relative increase in MW / m illustrates the increasingly effective utilization of this space. Higher values still are possible using compact lines, as discussed in the final paper summarized here: A 765 kV Braced Line Post Prototype With Composite Insulators: Materials, Design, Testing by K. O. Papailiou, A. Furrer, H. R. Gassmann, F. Schmuck.
Comparison of standard lattice & compact tower for 765 kV AC double circuit line.
Reporting from CIGRE
44 20
YEARS
Q2 2013
This presents the state-of-the-art of line compacting and describes steps to develop a 765 kV braced line post arrangement. Initially, mechanical simulations were conducted to deduce basic designs using solid core, double beam as well as hollow core insulators. Both concepts, including filler for the hollow core alternative, were then compared. The single post and the double post solutions( both with solid cores) were found more commercially favorable and corresponding finite element simulations were conducted of various load scenarios and post arrangements. From this simulation, the two most technically feasible designs were selected and full-scale specimens installed in a special test frame. Simulations showed that destructive testing was not possible using the forces of the loading tree and post deflection by buckling was therefore the main focus of mechanical testing. At the end, technical solutions became available that showed good correlation between results of the simulation and full-scale testing( with the final compact tower shown in the Figure).
Dr. Frank Schmuck frank. schmuck @ sefag. ch