June_1965 — Page 39

house

branches

off at 60° from the top of the 7.0

meter diameter penstock.

Το simplify fabrication and construction and to keep the thick- nesses of concrete to a minimum, circumferen- tial stiffeners were not used. Only nominal size ring and C-girders to facilitate erection,

Elevation in Meters

Normal Pool El 217.00- Max. Flood El. 219.00,

& Creat

Flow

-Min. rock profile

Level at El. 190.0-

Figure 5.

were provided for the Y-branches. Anchors were provided to these girders to give support against ex- ternal pressure.

Power station

In the preliminary planning of the project, three power station schemes were considered. One scheme was an above-ground power station which has a long power tunnel and an upstream surge tank with the auxiliary power station in a separ- ate line utilizing one of the diversion tunnels as a water conductor.

Another scheme was an under- ground power station located near the right abutment of the dam. The draft tubes would discharge into a separate surge chamber and the water would be conducted to the Angat River through a tail tunnel about 1,300 meters in length.

The final scheme and the one adopted is a power plant located in a pit immediately downstream from the toe of the dam. The main and auxiliary power house were combined to centralize the plant services and to provide a common access. The main units were set be- low the ground surface in the pit while the auxiliary units are above- ground level and at right angles with

-S-0.10

S-0.385

Scale 50 Meters

1:4000

Profile of spillway. Design flood peak is

the main units. Orientation of the strike and dip of the bedding planes of the rock foundation dictated the general alignment of the power station.

There are four main generating units consisting of generators rated at 55,555 KVA, 0.9 power factor, 3- phase, 60-cycles driven by hydraulic turbines rated at 70,000 metric h.p. to match the nominal generator out- put of 50 megawatts. These units have a dependable maximum capa- bilility of 143,900 kW with head- water at drawdown elevation of 180

meters.

The hydraulic turbine is a vertical- shaft single-runner Francis type with plate steel spiral case and elbow draft tubes. The speed is 277 rpm (synchronous speed for a 26-pole 60- cycle generator).

Generators

The auxiliary units have a nominal rated capacity of 6 MW driven by hydraulic turbines rated at 8,500 metric horsepower. There will be three units, but only two units will be installed initially. The turbines are of the vertical-shaft single-runner Francis type with a speed of 900 rpm (synchronous speed for a 12- pole 60-cycle generator).

S-0.23

Bucket Deflectors

El. 105.00/

7,500 cubic meters per second.

thrust-bearing type. The main gen- erator voltage is 14.4 kV vhile the auxiliary voltage is 4.16 kV.

The turbines and auxiliary genera- tors are being supplied by Toshiba and the main generators by ASEA.

Surge tunnel & tailrace

The surge chamber, excavated in rock, is an inclined surge tunnel about 280 meters long, immediately downstream of the power station. Approximately 80 meters of the lower end of the tunnel within the normal expected range of tailwater fluctuations is concrete lined. The remainder of the tunnel is unlined, except at the portal and in areas where structurally required.

Apart from hydraulic considera- tions, the size and slope of the surge tunnel was set to accommodate two- way vehicle traffic during construction. It will provide the necessary equip- ment and vehicle access during exca- vation and construction of the power tunnel, pit powerhouse and tailrace tunnel.

The tailrace tunnel is an 8.5 meter, concrete-lined horseshoe tunnel ap- proximately 1,800 meters long. At the outlet, the invert is below river channel bottom and a sloping, gra-

The generators are of the vertical, dually flared transition exit channel is provided to allow some velocity head recovery.

Figure 6. Artist's sketch of bucket deflectors.

Far East Architect & Builder June, 1965

Estimated cost

The estimated cost of the project is 200 million Philippine pesos of which 130 million (US$34 million) represents foreign exchange.

The foreign exchange requirement is financed from proceeds of a loan from International Bank of Recon- struction and Development. Peso cost is financed from local sources and from reserves and earnings of NPC. NWSA also contributes P21.5 million for the project.

Acknowledgment

Acknowledgment is made to Na- tional Power Corporation, Harza Engineering Company and Engineer- ing and Development Corporation of the Philippines (EDCOP) on whose reports and studies this article is based.

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