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EVACUATION OF BBGS 250 MW UNIT #3

CESC COMMISSIONS FIRST 220 kV SUBSTATION

The 220 kV Eastern Metropolitan Substation of CESC is now ready to receive power from its 250

MW 3rd Unit of Budge-Budge Generating station. The first three 160 MVA, 220/132/33 kV

Transformers at the above substation have been commissioned. The project for evacuating power

from BBGS Unit #3 which is one of the major and critical part of the CESC’s integrated

transmission plan conceived in the year 2006 comprise of about 85 km long one 220 kV Double

Circuit Overhead line from BBGS and terminating at 220/132 kV Eastern Metropolitan Sub-station

at mouza Nonadanga adjacent to existing WBSETCL’s 220 kV Kasba sub-station.

The 220 kV EM Substation will ultimately have 4 nos. 160 MVA 220/132/33 kV transformers. The

above transformers will, on one hand, step down the power to 132 kV level for onward

transmission to various Load Centres and, on the other hand, will meet the local area load at 33 kV

through the 33 kV tertiary winding of these transformers. This will reduce the need for stepping

down from 132 kV to 33 kV level through another set of transformers but will also render the

existing 3 nos. 75 MVA 132/33 kV transformers at Kasba Receiving Station spare for utilisation

elsewhere in the network to meet load growth. The 220 kV Outdoor Yard will also have outlets for

two 220 kV underground cable circuits to NCGS to meet the area demand following closure of the

Station in future. Till now the Generating Stations, Power exchange and Load centre Substations

are interconnected at 132 kV, which is the highest Transmission Voltage in CESC system .With the

commissioning of EM Substation CESC takes first step towards upgrading its Transmission

Voltage to 220 kV.

View of the 220kV Outdoor Yard

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Following are the some salient features of the Eastern Metropolitan S/S.

• One & Half breaker scheme designed 220 kV switchyard comprising 5 nos. Diameters.

• State & Central grid interconnectivity with WBSETCL & PGCIL (through 220 kV Double

Circuit OH line in future) for better operational flexibility, reliability and maintaining stability

of supply.

• Installation of internationally reputed make latest state of the art :-

1. SF6 filled 220 kV CTs and Gapless 220 & 132 kV Lightning Arrestors with Composite

Insulator casings.

2. 17 Bay, 132 kV Gas Insulated Switchboard (GIS) with duplicate bus-bar arrangement for

integration with the existing132 kV transmission network.

3. Dry silicone bushing plug-in type 132 kV Outdoor Cable Sealing End Termination, 50%

lighter in weight, without fire hazard oil and first time used in India.

4. Numerical Technology based relays for 220 and 132 kV network including Bus-bar Zone

protections for faster clearance of faults to enhance system stability & reliability and

recording of disturbances.

5. OF & OPGW based SDH communication system to provide reliable SCADA, line

differential & tele-transfer trip protection for 220 kV O/H & 132 kV UG lines and voice

communication.

160MVA 220/132/33kV Auto Transformer 132kV Gas Insulated Switchgear

A view of Control Room 220kV SF6 gas filled CTs with

Composite Insulators

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For an urban utility like CESC, availability of suitable land for such a large infrastructural

requirement is often a dominant issue. Seventy percent of the land at EM S/S was of hazardous and

poor soil quality. The area therefore required extensive land treatment with soil consolidation.

Considering the constraints and difficulties, commissioning of EM sub-station, a major milestone is

achieved in record time of about 18 months for the BBGS evacuation project.

Unless a glimpse of the hurdles encountered is given, it would be difficult to conceive the

enormous task that has to be dealt with 220 kV Double Circuit BBGS – EMSS Over Head line

execution.

The various ROW issues that had to be addressed while executing the OH line are as under.

� Growth of Urban and semi-urban area on the earlier envisaged line route in the intervening

period and by-passing of the area in Baruipur earmarked for the proposed 24 Paraganas

Head Quarter and Barasat – Raichak Expressway as advised by the Govt. body, resulting

extensive de-touring a necessity.

The revised route alignment also falls under East Kolkata Wetlands area, a Ramsar site under

international guideline which required further adherence as under.

� Maintaining of alignment as fixed by the Institute of Environmental Studies and Wetland

Management (IESWM) / East Kolkata Wetland Management Authority (EKWMA) and

keeping aside the proposed area for Wetland Interpretation Centre (WIP) from alignment of

transmission line.

� Installation of transmission line on the embankment between two canals.

� Number of towers to be one instead of two i.e. only one tower to be installed in between the

two canals.

� A part of the transmission line about 3.5 KM also to be underground to avoid the settlement

and water area.

� Towers to be erected on land only and to be eco-friendly. No tower to be installed in the

water area.

� Arrangements to be made so that the line does not create obstructions to flying migratory

birds.

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Consequences vis-à-vis Technical Aspects for O/H line due to above Issues:

1. Requirement of renewed survey.

2. Transmission line needed further deviation. The total length of line as on today thus has

become 88.5 KM comprising 85 KM of O/H section and 3.5 KM of underground cable

section compared to original estimate of 70 KM.

3. Since de-touring resulted intrusion more to eastwards, the encountered soil conditions for

erecting transmission towers have become more and more hazardous and difficult. Most of

the soils are water logged paddy fields, marshy, filled with decomposed vegetation. In other

words the load bearing properties of the soil are so poor that foundation requirement

compared to that on normal soil has become much critical. At several places special narrow

based heavy duty towers are needed to avoid the water body and to accommodate in narrow

tower footing area available at various places.

4. Revised alignment also made the transmission route zigzag at many places to avoid various

obstacles in the semi-urban areas. Crossing over large nos. of EHV O/H line (10 Nos.) and

passing through unavoidable fruit orchards also have to be taken care off. Compared to earlier

estimate all these issues thus resulted in increase in total no. of towers and more nos. of heavy

duty angle towers instead of normal tangent towers, higher towers (50-75 m.) to traverse over

fruit orchards and other transmission lines along with installation of gantries wherever

deemed necessary.

5. The conditions of erecting only one tower compelled to go in for a stretch of about 14 KM of

O/H line with multi-circuit towers in the EKW area to take care also of the future connectivity

of EM S/S with PGCIL along with the present line to BBGS at one go. Since these multi-

A view of 220kV Multi Circuit Tower Conductor Stringing work in Progress

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circuit tower will carry 2 nos. D/C line i.e. 4 circuits, hence special design consideration with

respect to strength & reliability have to be taken for such towers. These special type towers

have not only given a considerable impact on steel structure design but also on massive

foundation requirement due to the poor EKW area soil property and availability of limited

tower footing area. In addition to the above, in order to comply with the requirement of the

State’s Irrigation & Waterways Dept., pile foundation designs with minimum number of piles

had to be adopted on the embankment between two canals towards east of Bantala to ensure

no impediment during eventual merger of two canals if takes place in future.

6. Being most part of the transmission line route falls in low lying water catchments & EKW

area, mechanised excavation or transportation of material is extremely difficult . The work of

foundation, erections including stringing for many of such towers required massive head

loading and special arrangement.

7. Since within the multi-circuit tower section, a part of the transmission line of about 3.5 KM

near Bamunghata area required to be underground to avoid the settlement and water area in

the EKW area, additional cable bridges at canal crossings, Gantry structures and Isolators &

Lightning arrestors thus also have become essential to establish UG-OH connectivity at

Bamunghata.

.

The execution of 220 kV Double Circuit OH line in-spite of various hurdles & ROW issues is

presently under execution in full swing and will be ready shortly to integrate the 3rd Unit of BBGS

into the system as scheduled.