System Planning Stage
The transmission system planning is done
considering the load demand and the projected additions in power
generation capacity at various places of the country. For effective
power transfer with good reliability, security and economy different
alternatives are studied at the system planning stage; for example,
different voltage level of transmission lines, different routes of
transmission lines, different connecting points etc. Therefore the
routing and the cost of transmission line projects depends on
factors like terrain conditions (plain, hilly), soil conditions,
river crossings, power line crossings, railway crossings, reserved
forests, agricultural fields etc through which the line traverses.
At present, general routing and estimation of cost of each
alternative at planning stage is done with reference to certain
empirical rules as well as forest and physical maps. As these maps
are not updated frequently, percentage error in assessment may be
large. Even though this may not largely affect the selection of
alternatives it will be prudent to identify more accurate and faster
methods of collecting details at planning stage itself so that a
large number of possible alternatives can be examined. The
requirement generally would be to have updated information on maps
so that the planning engineers can study various line routes and
then identify and recommend cost effective solutions.
Fig. 2: Flow Chart of the Methodology for Route
Identification
Project Feasibility Stage
After system planning studies and identifying suitable transmission system Feasibility Reports for the transmission line projects are to be submitted for techno-economic clearance from the CEA and investment approval from the Government. At the project feasibility stage, detailed elaboration of the project is done for the technical details, BOQ, cost and implementation schedules of the project.
Presently, reconnaissances involving the following types of studies/ surveys are carried out prior to submission of feasibility reports:
- Map study
- Walkover survey and / or
- Preliminary survey
The types of surveys adopted at feasibility stage are generally ruled by time constraints for fast track projects. Reconnaissance forms the most important aspect of transmission line survey as the cost of the transmission line is influenced to a great extent by the route chosen. Selecting the best possible route can derive the following benefits:
- Line construction cost can be brought to the minimum.
- Material Estimation and procurement can be done fairly on realistic basis.
- Any possible delay/hindrance likely to come during the execution of the work can be avoided after taking due care of various statutory provisions during the course of selecting route alignment.
- Proper planning can be done for termination of lines at switchyards keeping provision for future lines etc.
- Approvals from PTCC, Railways, Civil Aviation, Forest authorities etc. can be obtained faster.
- Preparation of Master Network and fixing construction/erection targets can be done on realistic basis, which will help in the judicious planning of materials flow, cash flow and manpower requirements.
- Appreciable time can be saved during
construction of line, if selection of River Xing points, route
along hill sections and power line xings etc., are properly made.
Map Study: After drawing various feasible alternative routes of transmission line within 10kms of the bee line on the topographical maps (1:50000 scale) of Survey of India, a comparative study is done on the basis of the following data:
- Route length.
- Nos. and type of angle points in each proposal indicating the angle of each deviation as measured on the map.
- Nature and number of major crossings.
- Deviation in the line due to civil/military aerodromes and other industrial installations.
- Approach to the line in general for construction.
- Reaches through protected or Reserved Forests
- Continuously long stretches in paddy fields.
- Close parallelism with telecom and
Railway block circuits.
Walk-over survey is carried out on these routes. Walk over survey means going over the area associated with the alternative routes proposed and collecting features observed other than those existing on the map. In addition the indication on following features are also checked :.
- Communication lines
- Power lines
- Expanding villages and towns
- Rich gardens and plantations
- Reserved forests and high tree areas
- National Parks & Wild life sanctuaries
- Archaeological monuments
- Aerodromes, radar centers etc.
- Steep sloping terrain, Areas prone to land slides, soil instability etc.
- Prohibited areas declared under statutory
regulations
Preliminary survey: On completion of walkover survey proposal of the most suited route is further studied before taking preliminary survey. The main objective of preliminary survey is to transfer the route to the ground with such deviations as may be necessary as per field constraints. It involves generally fixing of angle points of the towers, route alignment, identification of major crossings, general classifications of soils, measurement of route length etc. Conventional instruments like tapes and theodolites do these. Based on these results, the Bill of Quantities (BOQs) of a transmission line are estimated and cost estimates are prepared. The preliminary survey does not include detailed soil investigations for locations along the route.