Every year flash floods, during monsoon, bring loads of silt posing grave threat to the three run of river projects, hampering generation of 3,000 MW and resultant supply to northern grid states including Delhi. One of the projects is a storage water scheme operated by NTPC Limited and is not much impacted by <g data-gr-id="185">silt</g>.
In order to know the flash floods preparedness and measures to thwart the impending danger, this reporter had discussions with heads of these power stations.
How are you prepared to tackle the problem of flash floods and high <g data-gr-id="207">silt</g> this year, this reporter asked Sanjeev Sood, Head of India’s largest 1,500 MW Nathpa Jhakri Power Station, owned and operated by public sector SJVN Limited. He said that the generating turbines of the Nathpa Station were designed to operate upto 4,000 ppm of silt in the river. To reduce the impact of <g data-gr-id="210">silt</g>, he said, sufficient measures have been implemented. The measures, he said, are related to silt management, water management and machine management.
River Satluj, Sanjeev Sood informed, was formed with the joining of river Spiti with Satluj at Khab confluence, some 200 kms upstream of the Nathpa Jhakri Power Station. River Spiti, he said,
carried more silt and had higher inflows comparatively. While currently, the inflow at the confluence was 350 cubic metre per second (cumecs), the discharge available at the Nathpa Dam increases to 900 cumecs as many as small rivulets merge with Satluj in between Khab and Nathpa. With the onset of summer in mid April, the snow starts melting and the discharge tends to increase every day, he said. But with the onset of monsoon, the discharge increases manifolds, <g data-gr-id="189">posing</g> problems of higher inflows and of excessive <g data-gr-id="199">silt</g>, he added. As far as the threat of Parechu lake is concerned, Sood informed that the project had already experienced the breaching of the lake way back in 2005 when the <g data-gr-id="201">silt</g> levels in the river had crossed 1,00,000 ppm and the inflow had reached over 6,000 cumecs. The flash flood had resulted in heavy losses to the roads and bridges along the river, but
fortunately, the Nathpa Jhakri Power Station had been prepared well before hand and the impact on the project was not much, he said.
Every year, well before the onset of monsoons, we also take proactive measures related to smooth operations of the gates and hoists, he said. For water management, he said, we regularly share silt and <g data-gr-id="180">flow related</g> data with upstream 1,000 MW Karcham Wangtu Hydro Power Station. The company, he said, had also provided two advance warning stations upstream of the river at <g data-gr-id="195">Khab</g> and at Powari. These monitoring stations, he said, undertake regular monitoring of the river and thus in the eventualities of alarming rise in river discharge or silt content, the power station gets warning at least four to five hours in advance.
This advance warning, he said, provide sufficient preparation time for the closure of the project and also to send warning signals to the residents. He added that the project was providing information about discharge and high flows in the river by SMS to the general public.
The dam height had also been raised by five metres to increase the poundage of dam which reduces the speed of flow and helps in settling of silt in the river bed. Thus, the levels of silt in the intakes are also reduced. Further, the flow of silt is arrested in the world's largest <g data-gr-id="170">desilting</g> chambers by gravitation before water enters the 27.4 km long head race tunnel. We have also provided blanking panels at the trash racks of the intakes so that the silt near the river bed does not enter the <g data-gr-id="159">desilting</g> chambers, he said.
Sood informed that the main constituent mineral of silt is quartz which constituted more than 65 <g data-gr-id="178">per cent</g> of the mass and other constituents being biotite, feldspar and muscovite. Silt size during <g data-gr-id="192">monsoon</g> season, he said, is up to 1,000 microns while most of the silt mass belonged to fine silt as suspended material in water.
With a head of 425 metres, the silt particles shoot onto the turbine parts thus inflicting severe damages to the machines, which can render the turbine parts non repairable over a period of time, he said. Sood further informed that the management of silt abrasion starts from the design stage with various provisions of silt sedimentation and exclusion from its flowing into the head race tunnel and further into generation turbines. Various measures, he said, had been incorporated at the civil and hydro-mechanical design stage of the project itself.
Other measures adopted for the power station included regular monitoring of silt in the upstream of the river, <g data-gr-id="177">increase</g> of dam height, <g data-gr-id="168">blank</g> panelling of trash racks as well as scientific water and machine management. Further, coating of underwater turbine parts with tungsten Carbide also gave desired and effective <g data-gr-id="176">results,</g> said Sood.
The machine management, he said, was effected by providing tungsten coating plant for periodically coating the underwater parts thus increasing their life manifolds. Through these measures, we have been able to reduce the excessive silt related shut downs to less than ten days in a year against upto one month earlier, he said. And the annual machine maintenance time, too, had been reduced to just ten days now, he added.
The measures, he said, had resulted in record generations from the plant year after year. During FY 2014-2015, a total 6,838 million units had been generated from the plant, <g data-gr-id="151">while</g> during FY 2015-2016, we have targeted to generate 6,980 MUs, he said.
The 1,500 MW Nathpa Jhakri Hydro Power Station, he said, had six turbine units of 250 MW each which had the potential to generate 36 million units of electricity every day. Presently, the power plant, he said, was generating 38.5 million units every day, while during the current financial year till 25 June, 2015, it had already generated 2,450 million units. Annually, the plant had been targeted to generate more than 6,980 million units of energy by the Union Ministry of Power, he said. The Plant, he added, had been running successfully since 2003 and had so far generated more than 74,450 million units of electricity for the northern region states.
The power generated at the Plant, he said, was distributed among the beneficiary states including Delhi as per the Central government Gadgil formula. About the utilisation of the generation capacity of the machines, Sanjeev Sood said that the discharge in the river varied between 60 cumecs in peak winters and above 2,000 cumecs during monsoon season. For <g data-gr-id="421">operation</g> of the six francis generating machines, they needed about 400 cumecs of water. While during the months of winter, when the discharge is below 400 cumecs the power station cannot be operated at full capacity, while any discharge above 400 cumecs was of no use for the plant as higher flows tended to bring more silt in the river, he added. Thus the plant produces 70 per cent of total targeted generation in five months and the remaining 30 <g data-gr-id="386">per cent</g> during seven months of the year. The peak generating period, he informed was from <g data-gr-id="417">mid April</g> to <g data-gr-id="418">mid September</g> every year. If the availability of water is higher in early April and in late September, the generation is more, Sanjeev Sood said. Upstream of the Nathpa Jhakri Power Station, is located in the 1,000 MW Karcham Wangtoo Power Station, owned and operated by Jaiprakash Power Ventures Limited. This plant, Sanjeev Sood informed, has to bear the onslaught of excessive silt and high discharge in the river ahead of our Nathpa Jhakri Plant. After the commencement of operations of this plant, he said, they had been benefitted by the reduced speed of river flow thus providing more settling time for <g data-gr-id="415">silt</g> till it reached the Nathpa dam.
In terms of water inflows, Sanjeev Sood informed that the Nathpa Jhakri Power Station was working in tandem coordination with the upstream Karcham Wangtoo Power Plant. The project management, he said, worked in close <g data-gr-id="437">liason</g> with the upstream project on hourly telephonic data sharing basis. The problem could be if the upstream power station released its water without warning, which will bring loads of silt in the Nathpa Dam. He added that in terms of the standard protocol of Northern Region Load Despatch Centre (NRLDC) and Northern Region Power Centre (NRPC), the power plants were required to be sharing vital information on a regular basis. The protocol also provided that two machines of the upstream plant will be shut down at a time, providing the downstream plants also enough time to close down their two machines, and so on.
The Head of Project also informed that silt contents in water damaged the turbines and this required frequent changing of the underwater parts of the turbines in the power house. After a detailed study, it was found that if the parts of the turbine were coated with HVOF Tungsten material, the life of the machines could be increased.
Accordingly, a Hard Coating Plant had been established at the Power House of this plant. This was the first ever facility provided at the power house itself in the country, Sood informed.
Earlier, he said, the damaged parts were required to be taken to such hard coating plants at distant places involving more time and higher costs. In order to further increase the life of machines, he said that in addition to the underwater parts of the turbine, now SFT gates and runners of the machines are also being provided hard coating cover. This facility had not only increased the life of machines, but also has saved on the regular maintenance period of the machines.
Talking about the quality <g data-gr-id="482">parametres</g> being deployed in the Hard Coating Workshop, Sood said that Total Quality Management (TQM) <g data-gr-id="483">parametres</g> were being followed in the working, by process standardisation, which provided smooth and equal quality of coating on the machines. This activity, he added, had been implemented during the current year only. It had resulted in better quality of coating as well as increasing the life of coating. H K Sharma, Managing Director of 1,000 MW Karcham Wangtoo <g data-gr-id="485">Hyro</g> Power Plant on river Satluj, owned and operated by Jaiprakash Power Ventures Limited, said that they had improved upon the designs of downstream Nathpa Jhakri Hydro Power Station, taking cues from its problems. While the volume of its Desilting Chambers were almost identical with Nathpa Jhakri Power Station, the Karcham Wangtoo plant operated at <g data-gr-id="494">lower</g> head, utilising 400 cumecs of water. Its machines, he said, also operated at 217 runs per minute (RPM) against 300 RPM for the Nathpa Jhakri Power Station, thus reducing the relative velocity of flow.
Sharma said that they were also using coated runners and guide vanes which could be operated upto 4,500 ppm of silt. But their machines being larger in size required about one month’s time for maintenance.
But the power station, he said, had provided with a number of spare runners and other parts requiring frequent replacements. The Karcham Wangtoo power station, he said, had four machines of 250 MW, each capable of generating <g data-gr-id="486">upto</g> 26 to 28 million units of electricity <g data-gr-id="492">everyday</g>. The Karcham Wangtoo Power Station, H K Sharma said, had already undertaken the necessary drill of managing the gates of the dam as well as of the intakes, so that the impact of any flash flood or higher silt could be taken care of. He said that they had another 300 MW Baspa Hydro Power Station, on river Baspa, in Sangla valley, which was being operated successfully for the last 15 years. The Jaiprakash Power Ventures, he added, had other power plants in neighbouring Uttrakhand state and the company had the experience of executing many other power stations in the country as civil contractors. Kranti Gupta, Head of the 412 MW Rampur Hydro Power Station informed that for the project, they were drawing <g data-gr-id="487">desilted</g> water of the upstream Nathpa Jhakri Hydro Station and were thus operating the plant in tandem with that power station. However, the machines of the Rampur Hydro Power Station were larger in size and operated at lesser RPM than the Nathpa Jhakri Hydro Power Station, thus having <g data-gr-id="488">lesser</g> impact of silt on the machines.
He informed that the power station had the benefit of utilising the hard coating facility available at the upstream plant of the company. <g data-gr-id="506">Thus ,</g> the power plant is not impacted by the fluctuations in the <g data-gr-id="504">silt</g> levels in the river, which are taken care of at the upstream project’s level. As far as flash floods are concerned, Kranti Gupta said that the power plant had sufficient recourse to protect its machines by closing the <g data-gr-id="505">tail race</g> channels.