Thoubal Multipurpose Project (7.5 MW)

INTRODUCTION:

             The Thoubal Multipurpose Project on river Thoubal, a tributary of Manipur river, is located near the village Phayang at 35 km from Imphal town in Manipur. The Thoubal Multipurpose Project estimated to cost Rs.47.25 Crores was sanctioned for implementation by the Planning Commission during May’1980. The sanctioned project envisaged construction of 1120 m long earth dam across the river Thoubal, intercepting catchment area of 620 sq. kms. To form a reservoir with alive storage capacity of 124.58 million cum. (1.01 lakh accre feet). Water supply to Imphal town is proposed to be carried out through an RCC intake on the upstream of the dam. The irrigation outlet is through a separate tower type intake on the upstream of the dam which would run under the dam and trifurcate downstream to feed three generating units, after which the waters would be led back into the river to be picked up at a barrage 17 km downstream of the dam on the river Thoubal. Two irrigation canals are proposed on the either side of the barrage for irrigation 21862 Ha. of cultivatable land.

             The power generation proposals at Thoubal Multipurpose Project were received from the Govt. of Manipur during 1978. As per this report, installation of 3 units of 5 MW each was primarily envisaged utilizing the irrigation releases for incidental power generation at dam toe surface power house.

 HYDROLOGY AND POWER POTENTIAL:

             Daily discharge data at the dam site was made available from May’1972 to December, 1977. Besides this, rainfall data is also available at two sites viz. Ukhrul from 1961 to 1977 and Phayang dam site from 1972 to 1977. The working table prepared by the Govt. of Manipur indicated that run-off series have been worked out with the rainfall data at Ukhrul from 1961 to 1971 was not indicated in the Project report. Hydrological studies were examined by the C.W.C. and discussions were held with the project authorities, as a consequence of which the hydrology of the project was modified. The accepted hydrology of the Project was modified. The accepted hydrological series from the year 1961 to 1977 have been utilized for assessing the power generation from the Project. Continuous working table for the above period has been prepared and it is found that the energy generation from the project works out to 17.98 GWH on a 75% dependable basis. The output from the project would vary from a minimum of 1300 KW to a maximum of 3700 KW.

             It is proposed to install 3 units of 2500 KW each to economically exploit the energy potential afforded by the scheme.

 SCOPE OF WORKS AND CIVIL DESIGNS:

             While sanctioning the multipurpose project in May’1980, the Planning Commission stipulated certain conditions regarding the foundation of the dam and spill way and the water conductor systems. Subsequently officials of the C.W.C. Geological Survey of India, Govt. of Manipur and other inspected the site during 1982 and suggested for shifting of the pen-stock alignment and location of the power house to the left side of the dam on geological considerations. Accordingly, the location of the power house and penstock was proposed on the left hand side of the dam.

             The major items of works of modified Thoubal Hydro-Electric Project are given below:

 i)     460 m long & 2 m dia. conduit placed under earthen dam and trifurcating into 0.8 m dia. conduits to connect three machines             in the power house.

ii)    A 6.0 m dia. gate shaft in the earthen dam for installing emergency gate on 2.00 m dia. conduits.

iii)    A by- pass arrangement for meeting downstream irrigation requirement during the period of shut down of power house.

iv)   A surface power house with an installation of three units of 2500 KW each.

v)     A tail race channel to carry waters from power house to river Thoubal.

PROJECT PROFILE OF THOUBAL HEP (3X2.5MW), MANIPUR

 1.0       Implementation of the Project and Contract Package

The scope of  Electrical-Mechanical Works consist of design, manufacture, supply, erection, testing, commissioning and handing over to Employer 3 X  2.5 MW Hydroelectricproject consisting of  horizontal shaft Francis Turbine including Digital type Governing system, 2778 KVA Synchronous direct driven suspended type  horizontal shaft Generator alongwith Static Excitation system and DVR including associated auxiliaries and accessories, MainInlet Valves of Spherical type, 2.5 m diameter designed for rated net head of 50 m & rated unit discharge of 6.0 m³/sec. It will be a Hydroelectric power generation system consisting of 6.6/33Kv,  3150 KvA  three phase, 50 Hz Generator step-up transformer, 11kV Bus duct,  6.6 KV XLPE Cable, 33Kv outdoor switchyard computer based control, Protection and Monitoring equipment and all other electrical and mechanical auxiliaries.

2.0       Location and Access

2.1       Location

The Thoubal Hydroelectric Scheme is located in district Ukhrul of State of Manipur in North Eastern region. Project Headquarter is proposed at Imphal, which is about 35km from project site.  The nearest railhead is at Dimapur of State Nagaland, which is about 210 km from Imphal. The nearest Airport is located at Imphal, Manipur.

2.3      Principal Access Road to the Site

The existing bridge over spillway and existing earthen dam body will provide access from project road on right bank to various structures on the left bank of the river.

3.         Transport Facilities available in the area

3.1       Goods Transport

The nearest railhead for the project is Dimapur, Nagaland. The materials and equipments can be transported by rail up to railway siding and then transported from Dimapur, Nagaland siding to the project site.

4.         Transport limit

The capacity of the Road is 30R. The maximum permitted size of bulkiest package for transportation upto project site is as under:

Width                                                  –           3.0 m

Height on a normal trailer bed       –           4.0 m

 5.         HYDROLOGY OF THE PROJECT

5.1       Precipitation Characteristics

Summer prevail from the month of March till May, when temperature reaches to the max of 32°C. Monsoon formally arrives in the month of June and drenches the state with heavy rain showers up to September. Manipur receives an annual rainfall of 1500mm. The months of October and November, more or less, remain dry. The winter seasons extends from December to February, when the temperature usually drops down to 0°C.

5.3       Temperature

The maximum temperature of the region reaches to about +36 ⁰C during the month of May while minimum varies from -3^o C to zero levels in the month of January.