Optimisation of existing right of ways in Transmission Network supplying Mega city of Mumbai- Challenges and Solutions
P MURUGAN U K MAHARAJA S S PATHAK S V SURANGE S.V. DESHMUKH
Tata Power Company Ltd.
Massive all round infrastructure development undertaken, in and around mega city of Mumbai had led to rapid increase in electricity requirement. This has necessitated augmentation of existing Transmission network for supplying electricity to various load centres.
The geography of the island city (three sides-sea and one side-mountain) has further compounded the challenges faced while augmenting the transmission capacities , due to restricted land access for developing new transmission line network. The creeks surrounding the island city and environmental regulations pose a great hindrance in establishing new lines through use of new Right of Ways. Due to heavy congestion within the city , the lines at the most could be brought and terminated at the periphery of the city, and transmit power to load centres , under ground cables is the obvious choice, but the cost is very high. It is therefore vitally important to electrically optimise the existing right of ways. TATA POWER have been exploring various options to optimise existing ROW based on the technological development . The solution may differ from case to case based on the system conditions , load growth , environmental constraints and availability of corridors for carrying out modifications planned, which may offer optimum techno- economic acceptable alternative.
This paper focuses on the challenges faced and the solutions adopted by TATA POWER for optimizing Right of ways to meet the load growth[u1].
TATA POWER has been operating 1218 circuit-kms of Transmission network in Mumbai area at various voltage levels , supplying Extra High Voltage substations .
Optimization of existing Right of Ways has been one of the key drivers of transmission planning process. The solution adopted to achieve this purpose, is based on the following three options. (Ref. sketch attached)
a) Enhance the ampacity of line by using higher size of conductor
b) Use of High Ampacity conductor on the same line towers
c) Upgrade line to next higher voltage level by replacing towers, conductors and insulators .
Option – a) , is relatively simpler to implement as compared to option – b), however , it requires a detailed study of the mechanical strength of existing line towers , insulator ageing , and condition of clamps and hardware before deciding the higher size of the conductor , that can be safely used on the line.
Use of High Temperature low sag conductor is another option (option -b) for up-rating existing lines . It is very effective in metropolitan areas where there is little scope for additional Right of Ways. This option can be implemented on parallel lines , when one circuit can be taken out for conductor replacement , while other line meets the load.
Option c) involves design of the new line using existing Right of Ways , keeping in view the critical locations where special measures to achieve safe clearances may be planned. Since most of the construction activities are carried out underneath the existing Right of Ways, frequent outages of the existing lines should be envisaged during planning. The other challenges faced include handling of sensitive environmental issues , protection of Flora and Fauna , Rehabilitation and Resettlement of Project affected Persons under Right of Ways, handling of probable litigation during land acquisition by means of up-gradation to next higher voltage with additional circuits, enhancement of capacity increase through new high ampacity conductor etc, wherever required.
This paper highlights the projects undertaken by TATA POWER for Transmission network augmentation through optimization of existing Right of Ways where different methodologies were implemented.
Up rating of 110 kV Lines Khopoli Mankhurd and Khopoli Chembur line (106 km)
This modification facilitated enhancement of line capacity from 105 MVA to 172 MVA by replacement of existing Panther conductor with Twin wolf conductor , maintaining the same line towers . This project was based on option (a) , it has facilitated connection of additional generating capacity of 40 MW at Lodhivali.[a2]
Uprating of 110 kV Borivali-Malad lines (D/C) and 110 kV Salestte -Saki lines (D/C) using High Temperature Low Sag conductor (8 km each)
This case highlights how the use of High Temperature Low Sag (HTLS) conductor in place of the existing conductor has led to enhancement of line capacity from 150MVA to 315MVA . Although tower design was retained the same , the stringing of conductor and other installation practices called for special precautions when compared to conventional conductor replacement. Study of different High Temperature Low Sag Conductors namely Gap type ( GZTACSR ) , INVAR-STACIR and ACCR (Aluminium conductor Core Reinforced ) was carried out . Based on the study , ACCR conductor was selected for replacing existing ACSR conductor. In addition to physical properties conforming with the existing tower strength and electrical clearances , the replacement called for specific considerations during actual installation [a3]. A different set of gadgets including tensioner -puller assembly , special rollers , was required to installation of ACCR conductor. Since the installation practices for ACCR are significantly different from those of conventional conductor , training of personnel involved in execution is utmost important . In sync with up-rating line using ACCR , up-rating of terminal equipment at both the ends was also carried out successfully .
Construction of 220 kV Trombay -Dharavi -Salsette line and Salsette Saki line using existing Right of Way of 110 kV line. (32 km)
This case highlights how quantum jump in transmission capacity could be achieved using the same Right of Way. 4 circuits of 220kV lines have been planned using Right of ways of existing 110 kV double circuit lines , to meet the load growth in Northern Mumbai . The scheme involved upgrading existing 110 kV Trombay- Dharavi line and Dharavi – Salsette line to 220 kV Trombay-Salsette and Trombay -Salsette Saki lines using existing Right of Way and installing 220 kV Towers . Since line- route traversed through thickly populated areas and mangroves in creek , a number of socio -environmental challenges have been faced during execution of the project.
In order to further optimize existing Right of Ways, installation of tubular pole in the existing foundation of the tower is also being explored, where lattice type four circuits, conventional tower can not be installed. This methodology will enable installation of 4 circuit lines in place of two circuits in addition to enhancing the voltage from 110 kV to 220 kV, with reduced footprints.
SKETCH SHOWING OPTIONS ADOPTED FOR OPTIMISATION OF EXISTING RoW
Bfbbbbb OPTION-(a) showing 110kV KHOPOLI-MANKHURD and KHOPOLI-CHEMBUR line by replacing Panther conductor 0.2 ACSR(200sq. mm Al) to Twin Wolf conductor 0.15 ACSR(2×150 sq. mm Al) using higher size of the conductor on existing line towers (106 Km).
OPTION-(b) showing 110kV BORIVALI-MALAD lines and SALSETTE-SAKI lines using High Temperature Low Sag Conductor (8km each).
OPTION- (c) showing 220kV TROMBAY-DHARAVI-SALSETTE line and SALSETTE- SAKI line using existing RoW of 110kV line (32Km).
[a2]Check the sentence