Hydro power caverns
j observing the 90 caverns listed with a total excavation volume of less than 20,000m3
: the smallest
cavern size listed is 8m x 8m x 30m; and the smallest excavation volume size is approximately 1000m3
.
Further small caverns are currently being prepared for construction in Greenland and Nepal, but information on their exact size is unavailable. Keys are used to represent the prevailing host rock type, cross-section shape, and rock quality class.
2. Caverns in China Total installed capacities in China, as reported in 2016, were 250GW for conventional plants, and 26GW for pumped storage plants, including semi- and full- surface plants. Trends in cavern sizes relating to total flow rate
replace the former trend for total turbine capacity. Furthermore, plants with and without separate transformer halls are distinguished. A reduction in blast volume is significant for conventional plants. Total length, cross-section area and excavation volume are given for Francis units (sizes for 4 units) with and without separate transformer halls, respectively: Cavern size trends for total flow volume are more
reliable for larger numbers of conventional plants, and are governed by a larger number of small total flow volume plants. In contrast to the increase in cavern height there is also strong indication that caverns will decrease in width. Total excavation volumes of pumped storage caverns, with and without separate transformer halls, does not differ much on average. The former have smaller section areas but longer lengths, and the latter have larger section areas but shorter lengths. Consequently, one linear trend for cavern volumes is sufficient. Typical saving for other cavern dimensions, besides
the strongly controlled width, is 15% if a separate transformer hall is designed. Transformer cavern sizes were analysed for 230
plants. The volume may increase linearly with the total installed capacity: Volume = 9000m3
+ 27 * C total (MW)
Limited evaluation in Figure 4 yields in China: Volume = 3750m3
+ 37.5 * C total (MW)
As mentioned in previous editions of the Yearbook, the decision to construct a separate transformer cavern is becoming more frequent for larger installed turbine capacities. However, the saving effect is very strong for smaller power units, e.g. 15% of their dimension. Average values for the 370 Francis and 100 Pelton turbine plants investigated are v = 83,000m3 C = 4 * 100MW, Q = 300m3 700m, C = 3 * 80MW, Q = 40m3
/sec, and v = 32,000m3 /sec, respectively.
In Figure 1, and supported by reference 12, this distribution of total hydropower plant capacities shows a wide range of sizes from 200MW to 6600MW. Numerous small capacity plants may not have been adequately reported.
3. Host rock formations at cavern sites Again, 165 strongly folded (katamorphic) rocks,
125 plutonic rocks, and 95 moderately folded (mesomorphic) rocks were found to be the most desirable host rocks in this ranking order. The least desirable, and more expensive to realise, were the 20 plants constructed in calcareous rocks other than
294 | Yearbook 2022 |
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limestone, and in slightly folded (epimorphic) rocks. An effort was made to present simplified host rock formation groups from eight world regions, totalling 574, but this time disregarding power house shafts. A further sub-division of formation rock groups is possible. The numbers from the 2015 edition of the Yearbook, including shafts, were 155 sedimentary, 285 metamorphic, and 185 magmatic formations. The almost 50% contribution of metamorphic cavern host rocks clearly prevails, apart from in China, where magmatic rock is more common. The Yearbook sees an additional 8 caverns sited in sedimentary rock formations, 6 in metamorphic rock formations, and 10 in magmatic rock formations. Figure 2 shows the results of a study of 46 recently constructed caverns, 49 older conventional caverns and 21 recently constructed pumped storage caverns[12]
are intrusive rocks, followed by calcareous rocks and, finally, effusive rocks. Less prominent choices are clastic sediments and metamorphic rocks which are for this figure, and Figure 6, attached in the same quantities as calcareous and clastic rocks. Throughout history the role of Europe has
remained strong despite its much smaller water resources when studying the 247, 237, and 86 cavern plants in Europe, Asia, and the Americas even without considering the numerous Scandinavian plants constructed within metamorphic rocks which currently remain unreported due to the limited data available.
Some differences are noted between north and mid-America and south America where there are much more sedimentary rock formations and less metamorphic formations. Notably, much less sedimentary and more metamorphic/magmatic rock formations exist in Africa than in Asia. The most remarkable difference between mid and south-east Asian plants, with almost 100 plants each, is 75% metamorphic but 55% magmatic rocks, respectively. Major contributions to these numbers come from two major countries, i.e. India (excluding Bhutan and Nepal) with 70-75% metamorphic formations, and China with ~52% magmatic formations and 38% sedimentary formations.
Conventional plant with separate transformer hall:
Q flow (m3
50
, h = 160m, , h =
250 450 650 850
1050 /sec)
Length (m)
62 79 97
115 132 150
Area (m2
)
460 540 620 700 775 855
Pumped storage cavern with separate transformer hall:
Q flow (m3
50
150 250 350
/sec)
Length (m)
105 119 132 145
Area (m2
)
760 845 930
1020
Volume (m3
)
70,000 91,000
111,000 132,000
Volume (m3
)
24,000 46,000 68,000 89,000
111,000 133,000
Symbols in the list of caverns should read as:
Pillar Pillar width to parallel cavern (m) Cover Overburden height (m) Factor Horizontal in situ stress ratio Net H Net water pressure height (m) Total C Total installed capacity (MW) Unit C Specific installed capacity (MW) F,K,P Francis, Kaplan, Pelton turbine h,v Horizontal, vertical axis Lhead Headrace tunnel length (m) Ltail Tailrace tunnel length (m)
, and reveal that the most attractive choice
Key to host rock group: 1. 2. 3. 4. 5. 6. 7. 8.
Limestones
Other calcareous rocks Fine grained clastic rocks Coarse grained clastic rocks Volcanic rocks, e.g. basalt Plutonic rocks, e.g. granite Epimorphic rocks, e.g. phyllite
Mesomorphic rocks, e.g. quartzite
9. Katamorphic rocks, e.g. gneiss
NB: Combinations are possible, e.g. 6,9
Key to excavation shape: B C
Bullet (Semi-) circular
H Horseshoe M Mushroom T
Trapezoidal
Key to rock class: 1. 2. 3. 4.
Very good (RMR >80, Q >50) Good (RMR >60, Q >5) Fair (RMR >40, Q >0.7) Poor (RMR <40, Q <0.7)
Conventional plant without separate transformer hall:
Q flow (m3
50
250 450 650 850
1050 /sec)
Length (m)
91
103 114 125 136 148
Area (m2
)
615 680 750 815 880 950
Volume (m3
)
40,000 60,000 81,000
101,000 122,000 142,000
Pumped storage cavern without separate transformer hall:
Q flow (m3
50
150 250 350
/sec)
Length (m)
95
105 115 125
Area (m2
)
755 795 835 875
Volume (m3
)
68,000 80,000 91,000
102,000
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