Spiral Case

Spiral Case

 

in a hydroturbine, a housing designed to provide uniform water intake around the entire circumference of the distributor, that is, to permit all the guide vanes to be held in an axially symmetrical position. The cross section of a spiral case narrows at a constant rate downstream. Hydroelectric power plants operating under heads greater than 50–60 m use steel spiral cases with circular cross sections that shroud the stator almost completely. Spiral cases used with lower heads are made of reinforced concrete; they shroud approximately 225° of the stator’s circumference, and their cross sections are T-shaped. Unlike other hydroturbine settings, for example, open settings, spiral cases make it possible to locate a major part of the turbine mechanism outside of the water, which improves the turbine’s operating conditions.

References in periodicals archive ?
Official sources told reporter here said that work on Spiral Case and Pet Liner of the Unit 17 had already been completed.
Then, the unit has to be quickly closed according to the emergency closure law which is set to the governor in advance to prevent extended periods of high overspeed, which may induce severe spiral case pressure increments and draft tube pressure decrements.
The changes of the dimensionless rotating speed of the runner, the dimensionless WG opening, and the pressure head in the spiral case are shown in Figure 4(a).
But successive load rejection may result in high overspeed of the runner and larger pressure in the spiral case in a long diversion-type hydropower station with the bifurcated pipe at the bottom of the surge tank; that is, there are two independent penstocks for the units from the surge tank as shown in Figure 3.
With the introduction of the head-cover system, the vibration transfer path is as follows: first, the hydraulic vertical vibration is transferred to the head cover by the heavy shaft seal and guide bearing in the water turbine runner chamber; next, the vibration is transferred from the head cover to the spiral case base ring strengthening plate, which is connected to the outer end of the head cover; and finally, the vibration is transferred to the machine foundation by the wrapped concrete outside the spiral case.
In this example, the effect of the spiral case and substructure is ignored [41,42]because theire ffect is far less than that of the upper structure.
Throughout the spring in the Bay of Fundy, they and their spiral cases of eggs are a familiar sight from the low tide line out into deeper water.