Hydropower structures (Including Canal Structures and Small Hydro)

Table of contents :
1......Page 1
2......Page 101
3......Page 165
4......Page 241
5......Page 305
6......Page 395
7......Page 471

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Hydro Power Structures

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(Including Canal Structures and Small Hydro)

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1.3 THE DESIGN OR NORMAL RATED HEAD The normal head or des'gn head Hd is the lowest head under' which the entire wheel discharge capacity can be utilised; at full gate, at the required speed. The following are the factors to be considered affecting the choice of the normal head viz: (a) Theoretical energy output should be maximum (b) Unit cost of hydroelectric power (Rs. per kWh) should be ,mininium. This requirement may favour a higher normal head since any increase in Hd results in reduced turbine diameter and high speed whereby the size and cost of machinery and even the size of power house structure are reduced. (Caution: In case of heavy sediment load in the stream and when the sediment particles are of hard rock such as quartz, it is desirable to go for a one step lower speed of turbine. This

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The approximate determination of the design (normal or rated) head-after M. Seidner

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LAYOUT OF POWER STATIONS

'POWER HOUSE LAYOUTS AND DEFINITIONS

2.2.4 Classification Based ,on Pbysical Features Four different types of hydro plants are possible depending on the type of power house super structure. !'.

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1. Indoor Type (Fig. 2.1): The generators are placed in a machine hall having an' indoor crane. The generator room is fully enclosed and is of sofficient height to permit transfer of equipment by means of the indoor crane. There may be one crane of a large capacity, so as to handle the largest possible single piece of equipment involved in the erecfon and maint ... h.f~"

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Marginal bunds are provided to protect the land and property against submergence during ponding or high stage river. The design of the marginal bunds depends upon its height and soil characteristics. Generally homogeneous embanlcment section is adopted with 2 : I slope both upstream and . downstream. However high embankments would be designed on the principles of earth dam.

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CUBIC CONTENT OF LAUNCHING APRON PER METRE RUN =7D H.F.L. BOARD':- .{11

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1.25 - 1.75*

Transition from nose to straight guide banks

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6.1.8 Gates and Hoisting Arrangement

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Normally vertical lift gates either Stoney pattern or fixed wheel type may be provided. Where the height of gates exceeds about I () m, it would' be better to provide the gates in two tiers or go in for radial or tainter gates which may be more economical; The vertical lift gates are generally worked by counter-weights of double capacity so as to shorten the height of the working platform. The gates should be designed for closing under its own weight and to achieve the same, the downward forces closing the gate while low'

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A suitable percentage correction is to be applied for a sloping floor, the correction being plus for lb.e down and minus for the up slopes following the direction of flow. The values of tb.e cor; ections are given in Table 6.2.

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PILE LINE 2

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1 Fig. (1.12 Mutual interference of piles-Definition sketch

D, the depth of the pileline, the influence of which has to be determined on the neighbouring pile of depth d. D is to be measured below the level at whiob. interference is desired. d, the depth of pile on which the effect is to be determined. Then,.

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TIlis correction is positive for points in the rear of back water and sabstractive for points forward in tb.e direction of flow.: This equation does not apply to the effect of an outer pile on an intermediate pile if the latter is equal to or smaHer than the former and is at a distance less than twice the !length of the outer pile. In Fig. 6.12, the dimensions have! been marked as they apply to point C on pile line I owirig to the influence of pile line 2. The effect of interference of a pile is to be determined only for the face of the adjacent pile towards the interfering pile; e.g. pile line 2 will interfere . with'the downstream face of pile line I and upstream face of pile line 3

TABLE 6.2

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Correction for the 1I00r slope

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Slope Vertical : horizontal I in I 1 in 2 I in 3 I .in 4 I in 5 I in 6 1 in 7 I in 8

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Correction % of pressure

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Correction for !loor thickness

The correction is applicable to the key points of the pile line fixed at tb.e beginning or tb.e end of tb.e slope. Th"s in figure 6.12 tb.e slope correction is applicable only to point E and pile line. The percentage correction given by the above table is to be further multiplied by the proportion of the horizontal length of slope to the distance between the two pile lines in between which the sloping floor is located. In Fig. 6.12, the correction to be applied at E, for pile line 2 will . be obtained by multiplying the appropriate figure from the above table by bs/b'; The correction is minus for the up and plus for the down slopes in the directions of flow.

In the standard forms with vertical cutoffs the thickness of the !loor is assumed to be negligible. Thus as observed from the curves, the pressures at the junction point E and C pertain to theleve! at tb.e top of the floor whereas the actual junction

Exit Gradient (Gs): It has been determined that for a standard form consisting of floor of length b, with a vertical cutoff of depth, d, tb.e exit gradient at its downstream end is given hy the equation,

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