## Selection Of Units

At this stage of the basic engineering, it is necessary to make (in collaboration with the equipment manufacturers) at least a tentative selection of capacity, diameter, speed, and submergence for the turbomachine. This will be required for refinement of the calculations

illustrated in Table 1 and also for the calculation of hydraulic transients that follows. In the head range most attractive for overall project economy, 500 to 1500 ft (152 to 457 m), manufacturers are prepared to offer a single turbomachine that is capable of operating as a pump and whose direction of rotation is opposite that of a turbine. Electrical manufacturers offer a similar machine capable of operating as a synchronous motor for pumping and, in the opposite direction of rotation, as a generator. These machines are designated pump turbines and generator motors.

For best economy, the speed of the unit should be as high as is practicable without involving an objectionable degree of cavitation of the impeller under the assumed submergence below minimum tailwater. This speed is established (1) by model tests for cavitation at the hydraulic laboratories of the manufacturers and (2) by evaluating experience with similar prototype installations.

Figure 3 is an experience chart showing specific speed Ns = rpm • hp^/H5'4 versus head for the machine acting as a turbine, where H is total head), and Figure 4 shows the specific speed Ns = rpmQ^/H3'4 for the machine acting as a pump. These charts presuppose moderate values of submergence because unusually deep settings are uneconomical from the structural standpoint. Three curves are fitted to the installations shown, the equation of the curves being Ns = K/HV2. The depth of submergence may be verified by checking against the value of the cavitation constant s = (Ha — Hvp — Hs)/H given by the manufacturer's cavitation model test curves. Here H = total head, Hvp = vapor pressure, s and Ha = atmospheric head. A typical curve of the family is shown in Figure 5.

When the unit has been selected, manufacturers will furnish (in advance of bid invitations) prototype performance curves similar to Figures 6, 7, 8a, and 8b. Figures 8a and 8b are designated four-quadrant synoptic charts and are required for the calculation of hydraulic transients. Figure 8b is for a 5.59-in (142-mm) gate opening. This is the largest gate opening at which the unit will be operating in the pumping cycle. Figure 8a, for an

FIGURE 2 Schematic arrangement for a pumped storage project. Elevations are in feet (1 ft = 0.3048 m).

8.94-in (227-mm) gate opening, is for operation on the turbine cycle only. Figure 9 shows a schematic view of a pump-turbine with motor generator and starting motor.

## Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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