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Ruzizi II - a fine example of regional cooperation

by Alfred LAMERS

The altitude of Lake Kivu is 1 450 m and the altitude of Lake Tanganyika about 775 m, a difference of about 675 m, The two lakes are linked by the River Ruzizi, which acts as a sort of overflow for Lake Kivu and takes its source up near the towns of Bukavu in Za and Cyangugu in Rwanda.

The Ruzizits rate of flow is very constant (at around 100 m3 per second) and the main changes in level occur over the first 40 km (between Bukavu - Cyangugu and Kamanyola, at 950 m), so these are ideal natural conditions for a series of hydro - electric stations with a theoretical potential (in stages) of around 500 MW.

Map 2.

A brief history

The first HE station was opened a few hundred metres downstream of the outlet of Lake Kivu during the colonial era, in 1958. It was called Ruzizi I and it had four sets of turboalternators of a total power of 28 MW supplying electricity to the towns of Bukavu and Bujumbura (linked to the station by a 70 KV high tension line). On independence, the station remained the national property of Za, under SNEL (the National Electricity Board) management, in spite of the fact that it was sited on the border with Rwanda. In 1978, a 110 KV line between Kigali and Ruzizi I came into service (thanks to financing from the EDF), thereby completing the connecting up of the national networks of Rwanda, Burundi and ZaIre (Kivu region).

Ruzizi II

In the ‘70s, expanding energy consumption in the region revealed a need for extra stations. So Rwanda built the 11 MW Mukungwa station in 1978 - 82 (mainly with EDF financing) and Burundi built the 18 MW Rwagura station in 1982 - 86 (with some EDF financing).

The idea of building a regional HE station, ideally placed on the Ruzizi, emerged and, in 1975, an EDFfinanced preliminary study identified the present Ruzizi II site and defined the requisite power as 40 MW. In early 1978, an EDF - financed study contract was signed by the non - profit - making company for the electrification of the Great Lakes (called the EGL) and a group of engineering consultants - Tractebel (Belgium) and RRI (Austria) with the aim of studying the final plans for a second HE installation on the Ruzizi Ruzizi II for short. At the end of the study (which was to take two years), EGL was supposed to have specifications for invitations to tender for all the work involved in the new installations.

Finally, after delays with the financing, the various lots were put out to tender in 1983 and the contracts were signed in 1984 (see table).

Work (civil engineering) began on the site in November 1984. Meanwhile, in 1983, the three countries involved had set up an international electricity company for the countries of the great lakes (called SINELAC for short) to take overall charge of the building and running of Ruzizi II with regulations such as to enable it to put up other energy - producing installations later on. Its capital is split equally between the three countries of the CEPGL.

Ruzizi II HE station

Description of Ruzizi II

The project, sited 16 km downstream of Ruzizi I, uses a natural change in level of 30 m created by the falls between the days of Kiandja and Kitimba.

It has all the standard features of an HE station:

- an 11 m - high dam retaining only a small amount of water in view of the fairly regular flow of the Ruzizi. It includes a fish ladder;

- flow regulating machinery (with two segmented floodgates with valves at the top for fine control);

- a water catchment device with two sluices fitted with caissons and slip valves;

- a fully concreted gallery (inside diameter 6 m, length 495 m);

- reinforced concrete surge tank (diameter 18m, height 17m);

- a duct (diameter 5.20 m, length 120 m) joined at the downstream end to a three - way distributor feeding the three turbines;

- the station angled so that water from the turbines can flow into the middle of Kitimba Bay down a tailrace (width 31 m, length 200 m);

- a solid (22 X47 m)’ four - storey building housing the two sets of 13.33MVA turbo - alternators (with a space for a third set later on), the auxiliaries, the command room, the workshops, stores and offices.

The vertical turbo - alternators are driven by a Francis turbine, the nominal power of which is 14.6 MW under a clear fall of 28.5 m and flow of 57.5 m3 per second. The sets run at 187.5 rpm.

Description of the work

The work on the different sub - lots (dam, regulator, water catchment, gallery etc.) proceeded as planned, without any incident of note, except for the station building.

Unforeseeable problems occurred with drying out the trenching, which had to go under the water table through permeuble eurth formed of scree, alluvial dcposit and volcanic lava.

The plan ar investigations (drilling) at the study stage was to put the foundations on a layer of impermeable clay. This was based on the reading of material from four deep boreholes in the rectangle of the future station (94 m in all).

But all the extra drilling at the beginning of the work by the firm which won the contract revealed that this layer was by no means continuous and would not therefore keep the water out properly.

So major work not originally catered for had to be carried out to:

- deepen the impervious layer from 25 m to 40 m so as to keep the amount of water to a level compatible with feeding the pumps;

- install a filter pump drawing system of a capacity of 750 litres per second (about 20 such pumps have been installed).

So the structure of the ground was far more complex than the study had suggested. This single technical hitch ultimately led to the project taking an extra year to complete and costing several million ecus more then planned.

The two sets of turbo - alternators went into service between April and June 1989 and industrial power production on the interconnected network began in July.

Supplying the energy produced

One unusual thing about the project is the way the power is supplied. After it has been increused from 6.6. to 110 KV, it is transmitted to the Mururu 2 supply unit 15 km from Ruzizi 11, in Rwanda, opposite Bukavu and 300 m from Ruzizi I and from Mururu 2, which was built as part of the project, it goes to the thrce national systems (whose energy counters are also locatod here)

Outiook for the future

The energy produced by the two turbo - alternators at Ruzizi II seems able to be absorbed fairly rapidly by the interconnected network, since this was saturated before and advantage is being taken of the opening of Ruzizi 11 to rehabilitate old stations, particularly Ruzizi 1, which had served their time.

A market study (of supply and demand) of the interconnected network is being run at the moment and this will make it possible to fix a time for installation of the 3rd set of turbo - generators at Ruzizi 11, in the light, in particular, of an EGL boiler conversion (to electricity) programme. The Bukavu brewery (Bralima), for example, has been producing its steam with electrically heated boilers since 1984 and it is the SNEL’s biggest customer by far in the Kivu region.

Alongside all this, a feasibility study of the overall HE potential of the Ruzizi Valley - which should lead to a site being designated for Ruzizi III - is being run with EDF financing. As we saw with Ruzizi II, a long time (as much as 15 years) may pass between the feasibility study, the final project, the search for financing, the invitations to tender and the actual work - which is why the preliminary study for Ruzizi III needs launching now. A.L.