A new concept

VA Tech Hydro has developed a modular hydropower technology that makes use of existing civil structures and therefore offers benefits such as low capital cost. The first large installation is in Sudan, where 80 units are being commissioned.

Hydromatrix is a new concept of hydraulic energy generation advanced by VA Tech Hydro. The technology combines the advantages of proven technologies, low cost installation and is easily integrated into existing dam structures or weirs. Projects that cannot be developed in a feasible way by use of conventional turbine-generator designs may now be developed profitably using the Hydromatrix approach.

Since no new, significant civil structures are needed, the Hydromatrix technology enables customers to install hydroelectric power plants at far more competitive costs and with minimal environmental impact compared with conventional plants. In addition, by using the Hydromatrix technology, construction and start-up schedules can be shortened by years. The technology enables the unused hydropower potential of intake towers, ship lock sluices, navigation and irrigation dams to be tapped by using the existing civil structures to develop a valuable renewable energy resource.

The equipment

The Hydromatrix turbine-generator unit consists of a stay ring with fixed stay vanes, a fixed blade propeller type runner of aluminium-bronze and an induction type generator directly connected to the turbine runner. The stator forms a watertight steel fabricated housing and is mounted to the stay ring. Two bearings situated within the bulb, support the generator rotor, shaft and runner rotating assembly. The shaft seal is a mechanical face seal type and is located within the generator housing.

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The Hydromatrix module consists of a stiff, steel fabricated structure, which supports the turbine-generator units. Rubber seals are provided at the bottom of the module sides to minimize bypass leakage. The module also includes steel fabricated draft tubes with integrated control gates. The draft tube shape and length are optimized to achieve high turbine efficiencies. Depending on the site conditions, trash racks or bulkheads can be incorporated into the module steel structure.

The design of the Hydromatrix system makes it easy to access all components without disturbance of the overall plant operation and its expected lifetime is identical to a conventional hydropower concept.

The electrical equipment is a standardized container type switchgear station, which includes the generator switchgear, the control and protection system as well as the reactive power compensation. For larger module sizes this electrical switchgear is placed inside the module. Standardized PLC systems are used for full automatic operation of the entire power station. The system is completed with step-up transformers and high voltage switchgear equipment located on or close to the dam.

Few auxiliary systems are necessary to operate a Hydromatrix plant. Where the capacity of the existing crane is insufficient to lift the modules, a new crane with rails can be supplied and installed. Depending on the water quality, a trash rack cleaning machine can be supplied as part of the system as well. In order to ensure an independent power supply for the auxiliaries an emergency generator can also be provided.

Figure 1. One module including two generator units in the upper position during commissioning phase
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The Jebel Aulia project

In 2001, VA Tech Hydro received its first large contract for a Hydromatrix power plant. The contract was placed by the National Electricity Corporation (NEC), the Sudanese state owned electricity producer and distributor. The total contract value is worth g30 million. NEC awarded VA Tech Hydro with the supply of 40 Hydromatrix power modules, each with two turbine generator sets, for 40 of the 50 openings of the Jebel Aulia dam in Sudan on the White Nile, about 40 km south of the capital, Khartoum. The contract also included the required mechanical and electrical auxiliary systems as well as a new dam crane.

The Jebel Aulia dam was built in 1933-37 and is used mainly for irrigation purposes and flood control. In March 2004 the first 20 Hydromatrix turbines were handed over to the customer for commercial service and have been supplying electricity into the grid of NEC. Installation work on the next units is already in full swing, every two months ten turbine generator units will be commissioned.

Full operation of the power plant is scheduled for early 2005. The new Hydromatrix power plant at Jebel Aulia will contribute considerably with 30.4 MW to the generation capacity in Sudan by means of environmentally clean hydropower.

Sudan currently has an installed electricity generation capacity of 580 MW, managed by NEC. It is composed almost equally of the thermal (mainly oil) and hydropower. Hydroelectric power generation varies greatly over time, due to rainfall patterns. The main generating facility is the Roseires dam located on the Blue Nile river basin approximately 500 km southeast of Khartoum. Roseires has an installed capacity of 280 MW, but output varies greatly as water levels on the river rise and fall throughout the year.

VA Tech Hydro Hydromatrix coordinator Harald Schmid said: “The excellent business relations between NEC and VA Tech Hydro goes back to 1968, when NEC ordered the original equipment for the Roseires hydropower plant. The original turbines were supplied and installed by VA Tech Hydro for NEC and just recently VA Tech Hydro has been awarded contracts to rehabilitate these turbines. The modernization and rehabilitation of the turbines became necessary because of the wear and tear caused by the aggressive and heavy silt load of the Blue Nile.”

Schmid continued: “The continuous engagement at the Roseires power station has led to the formation of an informal partnership between NEC and VA Tech Hydro under which VA Tech Hydro provides supplies, expert services and consultations in order to effectively support and assist NEC in its effort to maintain and improve electricity supply to Sudan’s growing economy and private consumers.”

Financing was one of the key issues of the project. At the time, bank guarantees to the satisfaction of VA Tech Hydro could not be obtained, but with a special procedure this problem was solved. It was agreed with the customer that periodical payments would be made, while VA Tech Hydro will only perform according to milestone events. This procedure has turned out to be the best for both parties and is based on the long lasting excellent relationship between NEC and VA Tech Hydro.

Figure 2. A turbine-generator unit with enforced cable pipe, intake structure and stay ring
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The installation

The Hydromatrix power plant in Jebel Aulia consists of 80 turbine-generator sets, which are installed in 40 modules by pairs. One module is equipped with two submerged, 380 kW horizontal propeller turbines. Each turbine has a 1120 mm diameter, three-bladed runner precision cast of aluminium bronze. Additionally, the scope of the VA Tech Hydro contract contains all mechanical and electrical auxiliaries. NEC will carry out local activities for the accomplishment of the contract.

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Since Hydromatrix makes use of the existing dam structure, only very minor civil construction is needed. This is one of the predominant advantages of the technology. The Hydromatrix modules are shipped to the Jebel Aulia dam where they are installed into the existing water passage structure.

The on/off operation of the turbines will be accomplished by means of the existing control gate. Both turbines of one module will be turned on or shut off simultaneously. The gate has only an open and closed position.

Ten of the 690 V asynchronous generators feed into one common container type generator switchgear substation. This arrangement is one out of eight lots. Each one of these substations has its own control and step up transformer and also includes the reactive power compensation.

A total of eight of these substations are installed at the dam side, on the opposite side of the machines and handle the total plant output of the 80 units. From these eight substations, individual 33 kV cables run to a 33 kV station located beside the river. The whole power plant is managed from a central plant control station. With this concept it is possible to operate each lot independently from the others.

For emergency power supply a diesel generator unit is installed and acts as a backup power supply in case of loss of net voltage for the control gates gear motors and the module crane.

Schmid said, “At the Jebel Aulia project the modules are integrated into the existing weir structure without modifications of the already existing civil structures. The modules have been evenly distributed across the weir, thus stratifying the flow, avoiding uneven sedimentation and reducing downstream erosions on the White Nile. In addition, extreme disturbances of the surface water flow velocity will not occur with our Hydromatrix system.”

The modules are built like a bulk head gate, so they can quickly be lifted out of the water giving way to extreme floods and permitting easy maintenance and repair directly on the pier. The simple design of the modules with only two movable parts (turbine and draft-tube gate) provides a much smaller failure potential than a bulb or pit turbine. A bulb or pit turbine, with its great number of movable guide vanes, runner blades, servomotors, and sophisticated oil- and cooling water circuits, makes it relatively complicated to maintain.

Schmid concluded: “The simple Hydromatrix design is far less maintenance-intensive and the cost of the Hydromatrix solution is hence considerably less than the cost of a conventional pit solution. There are no expected civil operation and maintenance costs, since there is no powerhouse and no dredging and silt removal requirements. NEC found the Hydromatrix concept a much more economically viable solution.”

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