Effect of water inertia in penstocks on regulating characteristics of hydraulic units

Conclusions

• 1. The minimum period of the effectively suppressed frequency variations is determined by the water inertia of the penstocks and amounts to about 20 T_W. Hence, in the construction of a hydroelectric plant with an increased penstock inertia it is necessary to take into account not only its specific share in the power system, but also the periodicity of the frequency variations in the power system, as well as the presence of other hydroelectric plants with low values ofT _W capable of suppressing the quick frequency variations.

• 2. The lag in output from the hydraulic unit with respect to the initial displacement of the turbine control amounts to about 1.5 T_W; hence, as T_W increases, the effectiveness of the participation of the hydroelectric plant in the limitation of the power exchanges decreases, and for T_W=4–5 sec it cannot suppress the minute variations in the power exchanges. This circumstance should be taken into account in the establishment of the operating regimens of the hydroelectric plant in the power system.

• 3. In selecting a hydraulic unit as emergency reserve, the basic index of its time response should be the equivalent time lag of the output, whose allowable value can be calculated for the specific power system from the condition of prevention of drop of the frequency to the setting of the first category of the frequency unloading.