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close this book Local Experience With Micro-Hydro Technology
close this folder E. PROJECT EXAMPLES
View the document 1. SALLERI-CHIALSA MICRO HYDEL PROJECT, NEPAL
View the document 2. BHORLETAR TURBINE IRRIGATION PROJECT, NEPAL
View the document 3. NAM DANG HYDRO-ELECTRIC PROJECT, THAILAND

3. NAM DANG HYDRO-ELECTRIC PROJECT, THAILAND

a) Technical Details

b) Investment Cost

 

The Nam Dang project, recently built and also owned by the Water Shed Management Division of the Forestry Department, is another scheme using local technology. The turbines used are of the Cross-Flow type, designed by the design section of NEA's (National Energy Administration of Thailand) technical division, and built on contract basis by a small workshop in the northern city of Chieng Mai. NEA was also in charge for the planning of the entire installation and for technical supervision during construction.

Nam Dang is a very remote hill station, at 1'400 m altitude, about 120 km northwest of Chieng Mail The station is situated right in the heart of the water shed area and has a negligible impact on the environment, since it is integrated into the reforestation program. The 100 kW power plant, of which powerhouse and penstock are visible in fig. 66, will be supplying electricity to three forestry stations and to a village inhabited by resettled hilltribes. A high-tension transmission line of 11 kV will be necessary for this purpose and will also make supply to other villages possible

There is a fundamental difference in this project, as compared to most hydropower schemes in Nepal, in the existence of an access road. This, naturally, reduces transportation and other costs considerably. Earthwork, for instance, was done by bulldozer at marginal cost, since this machine was engaged nearby in the construction and maintenance of a service road for reforestation.

a) Technical Details

SPECIFICATIONS :

- Installed capacity:

 

120 kVA

- Design discharge:

 

130 l/s

- Head:

gross:

79 m

 

net:

70 m

- Canal: open, trapezoidal, cement-mortar lined, length:

 

1'400 m

- Penstock:

diameter:

450/200 mm

 

length:

224 m

- Turbines:

   

2, Cross-Flow type

   

NEA design, runner

   

Ø :

 

400 mm

output:

 

62 kw/unit

- Step-up transmission: chain drive (triplex, 5/8") ratio:

 

1 : 2

- Alternator: 2, 3-phase, 1500 PRM

   

(50 Hz), self-excited, synchronous, brushless, italian-made: ANSALDO

   

voltage:

 

380/220 V

- Speed control: Oil-pressure, mechanical governor, JAHNS, AA2

   

(2 sets) speed:

 

900 RPM

capacity:

 

45 mkg

- H.T. transmission:

length:

18 km

 

voltage:

11 kV

The civil engineering structures are of a conventional type in terms of the material used, e.g. mostly cement concrete structures, the reason being that cement is easily available and transportation is no problem. Compared to the situation in Salleri/Chialsa, cement costs about seven times less in the Nam Dang project.

The intake is built with a weir-type barrage of about 1 meter height, across the river at the site of a natural pool, with a box-type sedimentation tank and inlet visible on the right in fig. 67. For this structure, about 200 m³ of concrete were used. The canal is fully lined and comprises several sections with closed conduits made from concrete pipe, to prevent side gullies from filling those sections with sediment. The forebay, at which the head-race canal ends, is again a concrete structure, perhaps a bit oversized, with a perpendicular overflow weir and a bottom flush-gate for flushing out sediment (refer to fig. 68). The trashrack, divided into two parts, is arranged vertically in the submerged part and sloping above the water level. As may be seen from fig. 65, the penstock, in rolled steel sheet/welded construction, is above ground on concrete supports with a number of anchor blocks that are larger than strictly necessary. The same may be said of the power-house, which is a piece of architecture in itself.

All civil construction work is done very neatly, somewhat more elaborate than strictly necessary, perhaps due to the pilot character of the project and easy accessibility.

The two Cross-Flow turbines used are actually the prototypes of the NEA design with a runner diameter of 400 mm and a nozzle width of 50 mm. The material used for the runner blades is stainless steel, as compared to common mild steel used by BYS in Nepal. The optimal turbine speed of 750 RPM necessitates a step-up transmission. For this, a chain-drive is used of Triplex, 5/8" pitch and 118 links configuration. Sprocket and pinion are made locally from steel plate.

For speed control, a flow-control governor of conventional type is used. This governor, connected with a flat belt to the turbine shaft (refer to fig. 69), is of the oil-pressure, flyweight variety, and imported from Europe. This item is rather costly and constitutes near about 40 % of total equipment cost (excl. penstock). As is usual, the governor requires also a flywheel that was cast in steel in the country and has a diameter of 750 mm and an operating speed of 1'500 RPM.

Fig. 70 is a detail of the Cross-Flow turbine, with one main bearing, the inlet part with gate-operating lever, and a part of the governor connecting-rod visible. The two sets of the installation are identical in all details and will be switched in parallel into a common network with a transmission voltage of 11 kV.

b) Investment Costs

For a comparison of costs with other installations described, it should be noted that the main difference is in a higher head which is generally cheaper to develop on a cost per unit basis. Further, construction materials and transportation have lower costs in Thailand, perhaps compensated to a degree by more elaborate construction. Also, in the case of Nam Dang, the cost of earthwork is not included since this was done by the Forest Department itself. In all three examples, design and engineering studies were not accounted for fully.


Fig. 71: Cost Breakdown of Nam Dang Project, Thailand

Source: All information pertaining to Nam Dang by courtesy of NEA