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Incidents of Flooding of Underground Power Houses

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Hydro Power Stations in India – An Overview

Subash Chander Mittal Chairman and Managing Director DMR Hydroengineering and Infrastructures Ltd 10th July 2023  

Hydro Power Stations play a crucial role in the electric power grid of a nation. India has several hundred hydro power stations with cumulative hydro power installed capacity of 46,850 MW.(as on 31st May 2023: source – https://powermin.gov.in). Power House structure is an integral and very important component of a hydro power station. Power house structure can be surface type or underground type. Underground power houses are adopted when flat topography to construct the surface power house is not available. Several power houses in Himalayas are underground type. Underground power houses have certain characteristics which make them vulnerable to flooding in case of mishap.

During last two decades, some incidents of flooding of underground power houses of commissioned and operational power plants have been reported. Flooding of power house leads to stoppage of power generation for several months which is not only the economic loss but also makes the power unavailable to the grid for prolonged duration. These incidents are in addition to incidents of flooding of underground power houses during construction stage.

In 2005, flooding of operational 1500 MW Nathpa Jhakhri underground power house in Himachal Pradesh was reported. In 2013, flooding of operational 280 MW, Dhauliganga underground power house in Uttarakhand was reported. On 9th July 2023, Incident of flooding of 126 MW Larji underground power house in Himachal Pradesh was reported.

Following incident of Flooding of Nathpa Jhakri power station, CEA has come out with  a set of recommendations to be adopted in the design/operation of the power house. These following recommendations are the part of CEA guidelines for formulation of DPR of Hydro Electric Schemes (Appendix 4 of the August, 2022 – Revision 6.0).

 

 

These recommended measures are presented in Table 1 Below.

Table 1

Measures to be adopted to avert flooding of Power House

  • Installation of submersible type de-watering pumps of sufficient capacity in the de-watering sump
  •         In addition to drainage   and dewatering pumps, provision of suitable number of submersible pumps of adequate capacity at MIV floor with provision for automatic starting by means of level switches.
  •         Location of control panels for dewatering & drainage pumps at a floor higher than that of turbine floor.
  •           Provision of suitable float switches in the P.H. building on MIV floor to give closing signal to the MIV in the event of inundation of P.H. due to penstock rupture or leakage in penstock or for some other reasons.
  •    (i) Provision of hoisting individual mechanism for draft tube gate of each unit for quick closing.

    ii) The draft tube gates          to be capable of closing under unbalance condition of water pressure.

  •      Provision of operation and control of surge shaft gates from remote for quick isolation of water conductor system in case of failure of other line of defense / protection.
  •         In the catchment area of the project, discharge-measuring system may be installed to give advance warning on the occurrence of flood in the river to take action for timely shut down of powerhouse.
  •        The unit control panels, unit protection panels etc. to be located at the machine hall to the extent possible.
  •          D.C. Batteries, batteries chargers & D.C. Distribution Boards to be placed at a floor higher than that of machine hall.
  •          Location of Station Service Transformers and Station Service Board on floor at higher level. Provision of D.G. set connected to Station Service Board capable of operating dewatering pumps in case of failure of supply from other sources.
  •        The hydro power station may employ quick methods for determination of silt concentration in the water. One simple method for measurement of silt concentration in the river water is to weigh silted water of a given volume and compare with relatively silt free water of same volume and correlation may be established between the difference in weight and silt concentration. With this, approximate silt concentration will be ascertained quickly and decision may be taken for shut down of powerhouse if silt level exceeds the permissible limit.

We note that the above recommendations are not exhaustive and flooding of underground power houses can still happen because of hydrological/hydraulic reasons.

For Example, In case of 2013, Dhauliganga Incident, the major reason is reported from the unusually high floods in the tailrace outlet area nallah and large boulder stacking in the tailrace pool leading to reverse flow of water from the tailrace side and resultant flooding of the power house.

In the incident of 9th July 2023, Flooding of Larji underground power house, from the publicly available video, it seems to suggest that water has entered in the power house from the main access tunnel side.

There is a need for more holistic approach for rigorous review of operational power plants at regular intervals and apply additional safety/design measures to avoid such incidents in future. 

DMR is a leading engineering consulting firm in India that leverages Experience and Core Expertise in Design and Engineering to offer Concept to Commissioning solutions throughout the lifecycle of projects in infrastructure sectors.

© Copyright 2023. All Rights Reserved

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DMR is a leading engineering consulting firm in India that leverages Experience and Core Expertise in Design and Engineering to offer Concept to Commissioning solutions throughout the lifecycle of projects in infrastructure sectors.

© Copyright 2023. All Rights Reserved

Follow Us

DMR is a leading engineering consulting firm in India that leverages Experience and Core Expertise in Design and Engineering to offer Concept to Commissioning solutions throughout the lifecycle of projects in infrastructure sectors.

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