Diagonal Hydroturbine

a variety of rotary-vane hydroturbine. A distinguishing feature of a diagonal hydroturbine is the fact that the axes of the vanes lie at an acute angle to the hydroturbine’s axis of rotation, and the rotor hub does not constrict the flow, thus making it possible to increase the number of vanes and to use these turbines at higher pressures.

In 1932 the American engineer D. A. Biggs received a patent for a diagonal hydraulic turbine. The English engineer T. Deriaz and the Soviet scientist V. S. Kviatkovskii made a major contribution to the development and introduction of diagonal hydroturbines.

Comparative characteristics of a diagonal hydraulic turbine and a radial-axial hydraulic turbine are presented in Figure 1, where ŋ/ŋ_max is tne ratio of the efficiency in operating modes to maximum efficiency; N/N_opt is the ratio of the power in operating modes to optimal power. Because of the better flow around the vanes of the hub and the suction pipe in modes that differ noticeably in load and head from calculated values, flow conditions are calmer in a diagonal hydraulic turbine, have smaller pulsations, the efficiency curve is gentler, and the average operating efficiency ŋ is higher. The cavitational characteristics of a diagonal hydraulic turbine are somewhat worse than in radial-axial turbines. Thus, diagonal hydroturbines can be installed at hydroelectric power plants with heads of up to 200 m, displacing radial-axial hydraulic turbines in this range. Diagonal hydraulic turbines are especially economical at plants that have large fluctuations in pressure head and power.

Figure 1. Comparative characteristics of diagonal (1) and radial-axial (2) hydroturbines

The rotors of diagonal hydroturbines are also used extensively in the manufacture of reversible hydraulic machinery (pump turbines) for pumped-storage electric power plants.

In the USSR a prototype diagonal hydroturbine with an output of 77 megawatts (MW) at a head of 61 m, which was installed in 1965 at the Bukhtarma Hydroelectric Power Plant, has been produced. A diagonal hydroturbine with a capacity of 220 MW at a head of about 90 M is being developed (as of 1971) for installation at the Zeia Hydroelectric Power Plant. Abroad diagonal hydroturbines are manufactured primarily by Hitachi and Toshiba in Japan and by English Electric in Great Britain.