JPH102274A - Discharge ring for bulb turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain reduction of a cost by reducing a cost of a bulb turbine for use of a low head as the object while ensuring practical resistance against gap cavitation. SOLUTION: In a discharge ring 6 of a bulb turbine formed by a structure vertically divided into two parts, an upper half part 6a of the discharge ring, relatively decreasing a flow water pressure as compared with a lower half part, is divided into an inlet side barrel part 6a-1 made by general structure purpose rolled steel along a flow water direction, outlet side barrel part 6a-2 and an intermediate barrel part 6a-3 made of stainless steel to be opposed to in the vicinity of a runner vane 1a to be interposed between the inlet/outlet side barrel parts, thereafter to be constituted by connection welding mutually between joints of each divided barrel part. A lower half part 6b, having a relatively high flow water pressure as compared with the upper half part, is constituted of general structure purpose rolled steel inexpensive as compared with stainless steel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge ring effective for a valve turbine (cylindrical turbine), particularly a turbine for low head.

[0002]

2. Description of the Related Art In recent years, the valve-turbine generator described above has become widespread as an economical hydroelectric power plant for low heads that does not require large-scale dam facilities. Have been applied. This valve-turbine generator has a horizontal axis in which the inlet to the water turbine or the suction pipe is arranged in a straight line, and the generator is housed in a cylindrical casing. FIG. In the figure, 1 is a turbine runner of a propeller turbine, 1a is a runner vane, 2 is a cylindrical casing incorporating a generator 3, 4 is a stay vane, 5 is a guide vane, 6 is a discharge ring, and 6 is a runner vane. A flow channel for the runner 1 is formed so as to surround the runner 1a, and is usually formed as an upper and lower two-part structure as shown in FIG. 3 in consideration of assembling and on-site workability. In FIG. 3, 6a is the upper half of the discharge ring 6, 6b is the lower half, and 6c is the connecting flange of both.

On the other hand, in the valve turbine described above, gap cavitation is likely to occur on the inner peripheral surface of the discharge ring, particularly near the outlet side of the runner vane, and the tendency is related to the size of the turbine, but generally the head is large. The higher the ratio, the higher the rate of cavitation. Therefore, conventionally, in order to prevent erosion of the discharge ring due to gap cavitation, a stainless steel (for example, SUS304) having excellent corrosion resistance is overlaid in a region where cavitation is likely to occur in a discharge ring made of a rolled steel material for general structure. Welding or dividing the upper half and lower half of the discharge ring into two parts along the axial direction into a body on the inlet side made of rolled steel for general structure and a body on the outlet side made of stainless steel It is constructed by welding between the divided body parts.

[0004]

As described above, as a measure for preventing erosion due to gap cavitation, a stainless steel material is provided on the upper and lower halves of a two-part discharge ring where cavitation is likely to occur. In the conventional configuration welded using, the amount of stainless steel, which is more expensive than rolled steel for general structural use,
And the range of the welding location becomes large. In addition, while the discharge ring requires high dimensional accuracy in terms of the characteristics of the turbine, the welding work involves local heating, so that the discharge ring is likely to be thermally distorted and deformed. In order to prevent this, it is necessary to carry out welding work on stainless steel while holding the discharge ring with a jig (outer frame) with a large structure, and post-processing such as cutting the welded part to achieve high dimensional accuracy Such,
This is a major factor that increases the production cost of the discharge ring.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to solve the above-mentioned problems. An object of the present invention is to provide a discharge ring of a valve turbine having resistance.

[0006]

According to the present invention, in order to attain the above object, according to the present invention, the upper half of the discharge ring is made of stainless steel only at the peripheral surface facing the vicinity of the exit side of the runner vane. Shall be made of rolled steel for general structure, and the lower half of the discharge ring shall be made of rolled steel for general structure.Specifically, the upper half of the discharge ring shall be made Along the entrance body, an exit body made of rolled steel material for general structure, and an intermediate body made of stainless steel sandwiched between the entrance body and the exit body, and The joints of the split body are welded together.

That is, considering the water pressure distribution in the cross section of the flow channel in the discharge ring of the horizontal shaft type valve turbine, a head of several meters corresponding to the diameter of the turbine runner is provided between the upper region and the lower region of the flow channel. There is a difference, and the above-mentioned gap cavitation is likely to occur in the upper part where the flowing water pressure is low, and conversely, the cavitation generation rate is low in the lower part where the flowing water pressure is high. This has been confirmed by model tests of valve turbines and inspections conducted after long-term operation of actual turbines. In particular, in valve turbines for low heads with small heads, gap cavitation is generated for the two-part discharge ring. Is concentrated only in the upper half, and gap cavitation hardly occurs in the lower half.

Therefore, as described above, the lower half of the discharge ring is made of a rolled steel material for general structure, and the upper half is also made of a stainless steel material locally limited to the gap cavitation generation region. While ensuring practically sufficient cavitation resistance, on the other hand, the amount of expensive stainless steel used and the number of welds are reduced as compared with those of the conventional configuration.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to FIGS.
Explanation will be made based on (b). In the figures of the embodiment, FIG.
The same reference numerals are given to the same members corresponding to FIG. That is, in the embodiment of FIG. 1, the lower half 6b of the discharge ring 6 having the upper and lower two-part structure is made of a rolled steel material for general structure. On the other hand, the upper half 6a of the discharge ring 6 extends along the flowing water direction, and the inlet side body 6a-
1, after being divided into three parts, an outlet side trunk 6a-2 and an intermediate trunk 6a-3 sandwiched between the trunks 6a-1 and 6a-2 facing the exit side of the runner vane 1a. , Entrance side body 6
a-1, Outlet side body 6a-2 is made of rolled steel for general structure, intermediate body 6a-3 is made of stainless steel, and the joints of each divided body are welded and joined. ing.

[0010]

As described above, according to the structure of the present invention, the upper two-part discharge ring has
The lower half is made of rolled steel for general structure, and the upper half is also limited to the area where gap cavitation occurs and has a locally welded structure using stainless steel to surround the vicinity of the runner vane exit side. Compared with the conventional structure that uses stainless steel for the upper half and lower half of the discharge ring respectively, practically enough cavitation resistance is ensured, and the amount of expensive stainless steel used and the number of welding points are reduced. It is possible to greatly reduce manufacturing costs including man-hours such as finishing work of a welded portion.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a discharge ring according to an embodiment of the present invention, where (a) is a partial cross-sectional side view, and (b) is a cross-sectional view taken along the line AA of (a).

FIG. 2 is a schematic diagram of the entire configuration of a valve turbine generator to which the present invention is applied.

FIG. 3 is a partial sectional side view of the discharge ring in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Turbine runner 1a Runner vane 6 Discharge ring 6a Upper half 6a-1 Inlet trunk (rolled steel for general structure) 6a-2 Outlet trunk (rolled steel for general structure) 6a-3 Intermediate trunk (stainless steel) 6b Lower half

Claims (2)

[Claims] 1. A discharge ring for a low-drop valve turbine surrounding a runner vane and defining a flowing water channel,
In the case where the discharge ring has a two-part structure, the upper half of the discharge ring is
Only the peripheral surface facing the exit side of the runner vane is made of stainless steel, the other peripheral surface is made of rolled steel for general structure, and the lower half of the discharge ring is made of rolled steel for general structure. A discharge ring for a valve turbine. 2. The discharge ring according to claim 1, wherein an upper half of the discharge ring is formed along a flowing water direction with an inlet-side body, an outlet-side body, and an inlet-side body made of rolled steel material for general structure. A discharge ring for a valve turbine characterized by being divided into an intermediate body made of stainless steel sandwiched between outlet-side bodies, and formed by welding and joining seams between the divided bodies.