Sharing Experiences of the World s Largest Tidal Power Plant in Lake Sihwa, South Korea

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1 Sharing Experiences of the World s Largest Tidal Power Plant in Lake Sihwa, South Korea Grafenberger P., Rammler A., Schneeberger M., Collins M.

2 SIHWA TIDAL Project Background Location South Korea, near Seoul and Incheon Airport Sihwa Tidal 2

3 SIHWA TIDAL Project Background Project Drivers An existing dam built in 1994 (agriculture, reclamation of land) Industrial and biological pollution return to natural exchange of water Sihwa sea wall Korea is investing into renewable energies (Kyoto-Mechanism): from 1.4 % to 5 % in 2011 & reducing oil imports Power plant Lake Sihwa 3

4 SIHWA TIDAL Project Background Technical Aspects Dam is 12.7 km long Basin Area 56 km² 10 x 26 MW bulb turbine units = 260MW Runner diameter 7.5 m 3 blades Maximum discharge 480 m3/s per unit Rated speed : 64.3 rpm Average annual production of 550 GWh. Generation from sea to basin Single direction units The basin is emptied by 8 new and 6 already existing gates and the turbines operating in reverse mode (without generation) Order 2005 Inauguration and wet commissioning 2011 plant in operation since

5 SIHWA TIDAL Project Background Commercial Aspects Owner Governmental water authority of Korea End user of this project Responsible for irrigation water supply waste water strong intention to produce energy beside the necessity of natural exchange of water Contractor Supplier Leading international contractor in the fields of Plant Works (oil & gas, refineries, chemical plants etc.) Civil Works (harbours, dams, roads, bridges, airports, railroads, hospitals, etc.) Technology and EM-Equipment Supplier 5

6 SIHWA TIDAL Technical Aspects Significant Differences of Run-of-River to Tidal Power Bulb Turbines The first view onto the design does not show a significant difference to a conventional bulb unit, however...

7 SIHWA TIDAL Technical Aspects Significant Differences of Run-of-River to Tidal Power Bulb Turbines Very high variation in heads Very low heads, which are the normal operating condition High discharges to compensate low heads Permanent governing due to permanent changes of the head High number of starts and stops Reverse mode operation (sluicing) Corrosion protection

8 SIHWA TIDAL Technical Aspects Operation Modes The are several principal possibilities to operate a tidal plant as using either flood, ebb or both for generation, increase the head differences by pumping, work with one or more basins, and all possible combinations out of it. This leads for every project to a rather complex optimization problem, which is additionally strongly influenced by non-technical aspects like energy prices (e.g. difference pumping and generation), funding and ecological considerations E.g. for Sihwa: To protect the reclaimed land the maximum lake level is limited and the variation of minimum and maximum level from one tide cycle to the other is limited for ecological reasons to generate power in direction from sea to lake is the only feasible solution. For releasing of water from the lake during the ebb, 6 existing and 8 newly installed gates are opened and the turbines are operating in reverse direction without producing power, providing the discharge capacity equivalent of two additional gates.

9 SIHWA TIDAL Technical Aspects Operation Modes Hydraulic Design High variation in heads, e.g. at Sihwa from 7.5 m down to 1 m Very low heads operating every tide cycle at low head, but high heads are rarely reached High discharges to compensate low heads, e.g. 482 m³/s per unit at Sihwa Designs needs: Flat characteristic High cavitation safety Peak or part load of minor importance Hill Chart - normalized by peak operating point 9

10 SIHWA TIDAL Technical Aspects Operation Modes 10

11 SIHWA TIDAL Technical Aspects Operation Modes Mechanical Design All units are at least started, stopped and put in reverse mode twice a day a conventional run-of-river plant typically has less starts and stops during a whole week and sometimes even a month. Due to the permanent change in head, the governor is acting all the time and changes the blade and guide vane positions. Reverse mode operation: The field winding is without current so the brushes of the rotor have to be lifted. Otherwise any patina on the slip rings would be destroyed. Counterthrust to thrust bearing must be considered in the design. The unit is practically operating under reverse runaway conditions. All these leads to a higher loading of all mechanical parts of turbine, bearing and generator, as well as to an unsteady thermal behavior of the generator. These aspects need to be considered in the design of the equipment and require extended tests and detailed structural and electromagnetic calculations.

12 SIHWA TIDAL Technical Aspects Corrosion Protection Material Selection: For core components like runner blades and runner hub, special steel with higher grade of chromium and molybdenum have been chosen and components usually made of carbon steel like runner cone, gate barrel cones, wicket gates, water passage shield are made of stainless steel. overlay welding with sea water resistant electrodes and tight welding seam of flange connections Stainless steel with cathodic protection Cathodic Protection System Other measures Special painting suitable for sea water and cathodic protection system Sea water resistant sealing material Generator interior parts are coated by special coating to avoid any corrosion from salt contaminated air Carbon steel with cathodic protection Carbon steel with cathodic protection

13 SIHWA TIDAL Site Works Powerhouse Construction

14 SIHWA TIDAL Site Works Installation of Draft Tube

15 SIHWA TIDAL Site Works Concreting of Draft Tube

16 SIHWA TIDAL Site Works Concreting of Bulb Cases

17 SIHWA TIDAL Site Works Air View

18 SIHWA TIDAL Site Works Installation of Distributor

19 SIHWA TIDAL Site Works Installation of Shaft and Runner

20 SIHWA TIDAL Site Works Installation of Generator Rotor

21 SIHWA TIDAL Site Works Erection Bay

22 SIHWA TIDAL Site Works Powerhouse Ready for Dry Tests

23 SIHWA TIDAL Site Works Impounding

24 SIHWA TIDAL Power Plant Watering of Turbines July

25 SIHWA TIDAL Site Works Challenges for Installation and Commissioning 10 Units high resources required Due to tides restricted time for wet commissioning periods without required water heads, request for night work Lake level due to restriction to lower the lake level not all tests can be done continuously or in the default order Danger of corrosion in sea water in stand still is higher than under operation (maritime life) No opportunity for efficiency test index test only 25

26 SIHWA TIDAL Operation Experience Bathymetry of Bay -17.3m -21.5m -22.5m -18.5m Hydraulic construction experiment inflow direction Real inflow direction for bigger heads -30.6m -17m -21.4m Real inflow direction for lower heads -18.9m -18.5m -10m * Red line shows the island in front of the power station 26

27 SIHWA TIDAL Power Plant Watering of Turbines July

28 SIHWA TIDAL Operation Experience First Visual Inspection Finally visual inspection in mid of Oct Units operating since half a year Units watered since one year Due to standstill during tides maritime life grows Stainless steel is affected by the mussels not clean condition semi clean condition clean condition 28

29 SIHWA TIDAL Operation Experience Effect of Maritime Life on Performance 1 Hmin Comparison clean vs. not clean (diver cleaned) Hmax ζq² ~1MW ζq² ~1MW 29

30 SIHWA TIDAL Visual Inspection after one year operation Some impressions / semi clean suction side of blade hub guide vanes guide vanes from intake entrance through draft tube maritime life in intake 30

31 SIHWA TIDAL Maritime Life Population of equipment happens not only in the Pacific or for tidal barrage 31

32 SUCCESSFUL IN OPERATION SINCE AUGUST