In few regions are natural conditions so favourable for the production of hydro-electric power as in the Serra do Mar, São Paulo, Brazil. Here great reservoirs have been formed on a plateau at the top of the range, a short pipe line feeding the turbines in the plain belowt
LAYING THE PIPELINE to the power house at Serra do Cubatão. In all, four lines have been laid and anchored to the steep hillside by blocks of concrete weighing from 1,000 to 3,200 tons. The length of the pipeline slope is 5,100 feet and its average incline 50 degrees.
BRAZIL has immense latent possibilities. So far, the bulk of water-power development schemes has been due to the enterprise of the Brazilian Traction Light and Power Company, Ltd. This is a Canadian concern which has invested more than £75,000,000 of capital in the public utility services of the cities of São Paulo, Rio de Janeiro and Santos. In addition to such services as gas, tramway and telephone systems, there are hydro-electric installations with a capacity of more than 500,000 horsepower.
Brazil is a gigantic country, with an area of 3,300,000 square miles. In the greater part of this vast territory conditions are not favourable to the development of water power. A large part of the Amazon region, for example, is sparsely populated and will probably never be developed commercially. It is in the southern part of the country that the greatest potentialities are to be found.
There are numbers of huge waterfalls in Brazil, but many of these are situated in places remote from the haunts of men. The falls of the Parana at Guayra, for instance, are the largest falls in the world, having a minimum flow equivalent to twice that of the Niagara Falls and capable of providing power which has been estimated at from 12,000,000 to 20,000,000 horse-power. These falls will probably never be developed because of their inaccessibility. All power for the district is derived from steam, wood fuel being cheap and plentiful.
In the country which lies to the east of the Parana River the climatic and other conditions favour the growth of large cities, which are now becoming increasingly industrialized. Rio de Janeiro, famous for its beautiful harbour and for the luxuriance of its vegetation, has more than 1,600,000 inhabitants. São Paulo, which is highly industrialized, has a population of more than 1,000,000. The enormous coffee plantations in these parts are world-famous, and overproduction during recent years has
compelled the Brazilians to burn millions of bags of this substance to maintain the price. In recent years, however, much attention has been directed towards the growth of cotton and fruit and the stimulation of industry on a large scale.
As a direct consequence of this industrial development, the demand for hydro-electric power has gone up by leaps and bounds. In many parts of the world this form of power has been retarded by the presence of abundant supplies of cheap fuel. In some parts of Brazil fuel is expensive, particularly oil fuel.
In addition to this, the geological formation of the country is ideally suited for the building of power schemes of enormous size and capacity. A few miles from the coast is a vast plateau at the top of a range called the Serra do Mar (see also the chapter “Scaling the Ramparts of Brazil”), which rises abruptly to a height of more than 2,600 feet above sea level. The edge of this plateau is formed of granite and other impermeable rocks; moreover the river beds consist of a mixture of sand and clay, which also prevents the escape of water to the plain below.
It is fortunate for water-power engineers that the plateau slopes away from the sea, which means that the rivers flow towards the Parana River. This provides a rare instance of Nature favouring the works of man. Nature has also been generous in providing a plentiful rainfall, which varies annually on the crest of the plateau from 180 in. to 240 in. The variation inland ranges from 48 in. to 60 in. The greatest rainfall observed in one day amounted to 14 in.
It is near the city of São Paulo that one of the largest power plants has recently been developed. This is known as the Serra do Cubatão plant, and more than £5,000,000 had been spent on its development by 1937. During the initial survey for this vast scheme, work was considerably hampered by the dense tropical vegetation, and miles of trails had to be cut through the matted undergrowth. The survey of one reservoir entailed the cutting of more than 2,500 miles of such trails.
The main reservoir is known as the Rio Grande Reservoir; this gives a flow sufficient to provide more than 250,000 horse-power. A further 140,000 horse-power-can be provided from the Guarapiranga Reservoir. From other sources more than 500,000 horse-power can be economically developed, and there are even more sources from which further supplies can be drawn as conditions demand. It has been estimated that the reserve of power is amply sufficient to cater for the growth of load which may reasonably be expected over the next twenty or thirty years in this part of Brazil.
The Rio Grande Reservoir was completed in 1936 and involved the placing of more than 10,000,000 cubic yards of earthwork in the various dams and other works connected with the project. The dams have been made by what is known as the hydraulic fill process, in which a mixture of earth and water is pumped to form the body of the dam. The larger dams were provided with concrete walls reaching down to the underlying rock, to protect the structures from ants and from various burrowing animals.
Another huge task involved the canals for regulating the River Pinheiros. This task included the excavation of more than 15,000,000 cubic yards. The excavation was carried out by suction dredgers. The main canal is an immense work, more than 200 feet wide, 25 feet deep and sixteen miles long.
The position for the main power plant was selected after a great deal of thought, and a concrete dam 85 feet high was built to close the gorge of a stream, the Rio das Pedras, on the edge of the Serra. Behind this dam a lake of less than three square miles in area was formed, which was a sufficient reservoir for storage at the top of the pipe line. From an arm of this lake the water is taken through a tunnel with a diameter of 10 ft. 8 in. and a length of 1,230 feet, to a surge tank (see also the chapter “Power From Scotland’s Lochs”) at the top of the pipe line carrying the water to the turbines.
ON THE EDGE OF THE PLATEAU above Serra do Cubatao, a concrete dam, 85 feet high, was built across the Rio das Pedras to form a storage lake at the top of the pipe line leading to the power house. This reservoir forms a forebay for the great chain of reservoirs on the Serra do Mar, a range which rises abruptly to a height of more than 2,600 feet above the sea.
The surge tank serves four pipe lines, each of which is connected to a turbine generating set. The pipes are anchored to the almost precipitous mountainside by enormous blocks of solid concrete. There are fifteen of these blocks and they vary in weight from 1,000 tons to 3,200 tons. For three of the pipe lines the total amount of concrete poured for piers and anchor blocks was 25,000 cubic yards.
The length of the pipeline slope is 5,100 feet and a track 120 feet wide has been cleared for it down the face of the Serra. The average slope of the pipe is about 50 degrees to the horizontal; in one place it reaches an inclination of nearly 60 degrees.
Pipe laying and concreting on such heavy gradients are no mean tasks, and for that reason the heaviest piece of pipe is limited to a weight of 13 tons. The transport of these huge pipes was effected by cable inclines alongside each length of pipe.
In a plant with such a high head of water, the cost of laying the pipe line is a large item of the total expenditure. In practice it has been found that it is equivalent to the combined cost of turbines, generators and auxiliary machinery. The cost of each pipe line on this scheme amounted to between £50,000 and £60,000, delivered on the site but not erected.
The work of erecting the pipe lines was dangerous and difficult, for in many places the rock surface was fractured and decomposed. Elaborate precautions were therefore taken to allow for proper drainage of the pipeline track, even the possibility of leakage from the pipe being taken into account. The result of a burst in the pipe might well be disastrous, endangering life and property for miles round. It was therefore of paramount importance that this work should be carried out with the greatest possible care.
Orderly Planning
A completely satisfactory design for such pipe lines has not yet been evolved, as this is an extremely involved and highly technical study. Only after long and careful investigation will it be possible to lay down definite rules for design. As in all engineering works, particularly in hydro-electric construction, it is not always an easy matter to strike a happy mean between the limits of safety and economy.
The Serra do Cubatao power house is of compact and simple design, a masterpiece of orderly arrangement. The turbines are of the Pelton wheel type, in which a jet of water impinges against a series of buckets bolted to the circumference of a circular disk. In large Pelton wheels the solid jet of water impinges with tremendous force against the buckets, and forces comparable to those met with in ordnance work may exist inside the casing of a Pelton wheel.
One of the units in this power house was the largest of its type in the world when it was installed. The rotating parts weigh 203 tons and the total weight of the turbine and of its auxiliary equipment turns the scale at 650 tons. The water pressure at the nozzle is approximately 1,020 lb. per square inch. The diameter of the jet is 9½ in. and special nickel-chromium steel is used for the nozzle rings.
This jet of water travels at a speed of 380 feet a second, or more than 250 miles an hour. A sensitive governing device is used for the control of this turbine, instantly responsive to the slightest change of load. The supply of water to the nozzle is controlled by a hydraulically operated gate valve with a diameter of nearly 30 in.
Electrical switching and control gear is provided. Current is supplied to the São Paulo district at 88,000 volts and to the Rio Grande system at 132,000 volts. An interesting feature of the transmission line is the exceptional span of the wires between adjacent towers. The average span is 1,575 feet and the maximum span as much as 4,970 feet.
Another interesting power station on this vast scheme of electrical supply is that situated at Ilha dos Pombos on the Parahyba River, which lies ninety miles north-east of Rio de Janeiro. The flow of the river at this point is 22,000 cubic feet a second, and it has been completely diverted by a low dam into a dredged channel one and a half miles long. The total operating head amounts to 115 feet.
This huge power station is designed for a capacity of 228,000 horse-power. It has three automatic sluice gates of reinforced concrete. These gates are among the largest in existence, each weighing 2,200 tons and regulating the water level to within less than one inch. In a plant of this type it is necessary to have such controlling mechanisms, because operating conditions vary within such wide limits.
Hydro-electric engineering is one of the most fascinating and interesting branches of the engineering profession, for every power scheme is different in design. No two plants are ever alike. They must be individually planned and worked out on the ground, and the engineers must take into account a large number of factors, all of which have an important bearing on the scheme as a whole.
This is particularly true of the development in Brazil, where such important factors as rainfall and evaporation vary so widely. For this reason the company maintains a large corps of observers, and in the Serra region there are 100 observers in addition to a number of river flow and rain gauges. It will require many years of careful recording before an accurate estimate of the available flow can be made.
Importance of Weather Forecasts
In Brazil rainfall and river flow are under the influence of the sun. It has been found that when the sunspots are at a minimum, an event which occurs every ten or eleven years, there are two or three dry seasons. These periods of dry weather must be taken into account in all calculations of power resources. Research is being carried out also for the purpose of long-range weather forecasting. It is believed that the temperature of the sea has a marked influence on rainfall, and arrangements have been made to obtain ocean temperature from two liners plying regularly between New York and Buenos Aires. Research of this nature requires a long time before important results can be obtained, but great care is warranted because of the enormous Capital cost of hydro-electric installations. If the water supply is found to be insufficient, the extra burden of a large amount of idle plant may create financial difficulties.
Apart from the enormous amount of hydro-electric power which may be developed in the future, the possibility of using the lakes and rivers for barge navigation is being also studied. It has been seriously suggested that it may be possible to ship goods from the port of Santos to the city of São Paulo, from the low coastal plain to the plateau. The Serra would be surmounted by a ropeway or barge incline. In two of the dams arrangements have been made for boat lifts, by which barges of 200 tons capacity can be handled.
RIO GRANDE DAM was completed in 1936. The structure was built by the hydraulic fill process, by which a mixture of earth and water was pumped to form the body to the dam. More than 10,000,000 cubic yards of earth were treated in this way. A concrete core wall was built down to the bedrock.
The work of the engineer in such rugged and mountainous country does not end with surmounting mechanical and purely engineering problems. An important phase of his work is concerned with the health of the labour force carrying out the work. Efficient sanitation is vitally important in all tropical countries, a fact which was abundantly proved during the building of the Panama Canal. The most common diseases which have to be guarded against in Brazil are malaria and intestinal parasites. On the crest of the Serra and also on the plateau malaria is absent, but it is rampant in the coastal plain and in a large part of the interior. The greatest care has, therefore, been taken to ensure that incoming workmen do not bring disease with them.
It is remarkable that success in conquering disease has been achieved by the most simple means, without having recourse to quinine and without screening the windows of barracks. By careful inspection of all drainage systems, by the oiling of pools to prevent mosquitoes from breeding, and by keeping a strict watch on all newcomers, it has been possible to avoid the spread of infection.
Any man who has the least signs of infection upon him is required to report to the doctor immediately for a blood-smear test. In a few moments the microscope will show whether or not the man is infected. If he is, then he is sent to hospital for a month and kept there until no further signs of infection are visible. It has been found that it is impossible to eliminate from the dense forests mosquitoes, which may be capable of transmitting malaria. This is because the insects thrive on the parasitic plants on the trees. In the thriving city of São Paulo malaria is absent, but it has been found that in certain parts malaria will invade a district which was previously free from the scourge.
Design of Pipe Lines
Such climatic conditions as these have the most far-reaching effects on the practicability and success of hydroelectric power schemes, and a great deal of preliminary work and research are necessary before construction of a permanent nature can begin. Conditions differ widely in different countries and even in different parts of the same country. This is particularly true of Brazil, whose climate and topographical conditions vary to a great extent. Therefore the Sao Paulo hydro-electric power scheme is unique in its conception and the data collected in the preliminary surveys are not necessarily applicable to future schemes in other parts of the country.
Again, technical improvements are continually being introduced in hydro-electric practice — improvements which affect, directly or indirectly, safety, efficiency and economy. The design of pipe lines, for instance, is subject to continual improvement, as a result of trial and experience. Frictional loss in a pipe line is an important factor in the design and in the operation of hydroelectric plant. The designs of the first three pipe lines erected between the surge tank and the power house at Serra do Cubatao were slightly different. The first two pipe lines were tested to pressures ranging from one and a half to three and a half times the static pressure. Heavy surges were deliberately produced and their effects were recorded. The third pipe line was modified accordingly, and it is expected that all future pipe lines will be modified and improved as further data are obtained.
The hydro-electric scheme on the Serra is a good example of the way in which the engineer turns the resources of Nature to the benefit of mankind. Brazil is fortunate in having such a huge reserve of power at its disposal and there is no doubt that it is being developed in the most scientific and practical manner possible.
THE POWER HOUSE at Serra do Cubatao in 1936. Water from the reservoirs on the plateau is brought to the turbines through a steep pipe line, laid in a track specially cleared for it in the forest. To the right a similar track had to be cut for the overhead transmission lines.
