Pre-commissioning testing of 720MW Mangdechhu Hydroelectric Project
The 720MW Mangdechhu Hydroelectric Project Authority (MHPA) will start to pre-commissioning testing units I, II, III and IV and also the testing of auxiliary equipment in the underground power house in October this year.
The above referred testing shall be carried out by slowly filling the pressure shafts by water from identified external source.
The testing will ensure the perfection of the unit alignment and also the response of the auxiliary equipment in the power house.
The diversion tunnel and head race tunnel (HRT) of Mangdechhu Project would be plugged by end of October 2018.
According to the status report as of June 30th 2018 of MHPA, the overall physical progress of C-1 package as on 30th June 2018 is 99.81 percent with an average progress of 0.25 percent per month during the second quarter of 2018.
The report states that the construction of 114 meters (m) high concrete gravity dam has been completed. The total concrete quantity 4, 83,140 Cum has been done during the second quarter of 2018. “All major works in dam complex including underground works have now been completed and cleaning works are in progress.”
The plugging of the diversion tunnel is planned from 15th September 2018 onwards when discharge in the Mangdechhu river will be manageable, states the report.
The report further stated that the various instruments installed in the dam body and its appurtenant structures showed deformation in the early stage of installation. However, deformations observed are insignificant during the quarter. All the instruments are functioning properly.
The contact and consolidation grouting works of the HRT was also being done in parallel so that plugging of the tunnel is achieved, soon after completion of overt and inverts lining. Out of 13,505.19m of proposed contact grouting in HRT, 5,617.7m has been completed. About 2,902m has been done in this quarter of which 78m, 1,174m, 286m, 250m and 1,114m has been done, stated the report.
About 1,208m of consolidation grouting has been completed in this quarter of which 28m, 129m and 1,051m has been done in face-2, face3 and face-9 respectively.
The balance works for HRT including plugging of tunnel shall be completed by September or October next month, stated the report.
The report also stated
that major civil works of the underground power house have been completed. The concrete lining of Tail Race Tunnel (TRT) and surge shaft have also been completed. Cleaning or finishing works of the underground power house including control room is under progress. Monitoring of underground power house and transformer hall caverns Geotechnical instruments installed in the caverns were monitored regularly. As such no significant deformation is observed in this quarter.
Status of electro-mechanical, transmission line and its works, the report states that out of four units 180 MW each, unit-1, 2 & 3 have been boxed up. The unit-4 is expected to be boxed up in this month. All four MIVs have also been installed. The erection of one Butterfly Valve in BVC has been completed and the erection of second Butterfly Valve is nearing completion. Laying of All Dielectric Self Supporting (ADSS) cables started from June month.
And installation of Unit Tap-off Transformer (UTT) for unit 1 & 2 has been completed and installation for unit 3 & 4 is in progress. Installation of Unit Auxiliary Board (UAB) is completed and installation Station Auxiliary Board (SAB) in control room is in progress. The installation works of 33/11kV switchgear is under progress. Finishing works of the control room is in advance stage and the control room shall be ready in all respect by September 2018.
The works for EM-2 package has been completed in all respect. Electro-Mechanical package EM-3 (420 kV GIS) by Hyosung Corporation. The works for EM-3 Package has been completed in all respect. The HV Test of 420 kV GIS completed on the month of May this year. Erection of Lightning Arresters (LAs) has been completed and vacuuming and gas filling is in progress.
Electro-Mechanical package EM-4 (400 kV XLPE Cables), the report states that the works for EM-4 package has been completed in all respect. Cable termination works completed at pothead yard end and is under progress at GIS end. The four numbers of 67 MVA ICT transformers have been placed in the ICT Building.
The construction of transmission lines within the Bhutan portion from the Mangdechhu Pothead Yard to Jigmelling substation has been completed. The line was test charged on 23rd June 2018 from Jigmelling substation to the Mangdechhu Pothead Yard.
The transmission line works in West Bengal portion is progressing smoothly and the line shall be commissioned matching the commissioning schedule of the Mangdechhu Project. However the report states that the transmission line in Assam portion has been delayed due to delayed wildlife clearance from Assam Government for about 47kms stretch near Indo-Bhutan border in Assam. “The Government of Assam has recently granted the Wildlife Board Clearance and now the final clearance is under process in the Ministry of Environment, Forest and Climate Change, Government of India (GoI).”
Report further states that the delay in completion of Assam portion of the transmission line, will not pose problem for evacuation of power from Mangdechhu Project, as the Mangdechhu Project power would be getting evacuated to India at 400kV Substation Alipurduar (West Bengal) through the transmission lines of Punatshangchhu–I & II Hydroelectric Projects which has already been commissioned.
The quality of work at site was maintained by supervision at batching plants, placement sites, checking of quality of materials and workmanship. The concrete poured in different structures was tested in its fresh and hardened state at batching plants. Fresh concrete properties like slump value, air content and temperature were determined before dispatch of concrete from batching plant. Hardened concrete was tested by casting cubes and tested at 7 & 28 days for compressive strength.
Total 1066 sets of cubes of concrete were cast and tested for compressive strength. The strength test results were statistically analyzed to assess their conformity with the acceptance criteria given in IS 456:2000.
Meanwhile, the first Revised Cost Estimate (RCE) was approved by the GoI for Nu./Rs. 40,206.30 Million(M) as on March 2014 price level, an increase of Nu./ Rs.11,243.30M from the initial approved cost of Nu./Rs.28,963.00M as on March 2008 price level.
While the second RCE for Nu./Rs.46,723.85M as on March 2016 price level has been approved by the GoI. As on 30th June 2018, the MHPA has received a total amount of Nu./Rs.45,668.50M.
Of the total receipts, Nu./Rs.44,697.60M has been spent till 30th June 2018 including advances for various activities, representing fund utilization of 97.8 percent against total fund receipt from GoI.
All set for go: The testing will ensure the perfection of the unit alignment and also the response of the auxiliary equipment in the power house