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Network Control – Dispatch from Khartoum

In developing countries such as Sudan, technologies to allow effective power dispatch are key to effective asset management and a more efficient energy network.

Headlines may be dominated by the humanitarian crisis at Darfur, but Sudan is far more than refugees and warlords alone. Like many developing countries, establishing a consistent and reliable electricity supply is the bedrock of commercial engagement and political instability makes attracting much needed investment to the national electricity system that much more difficult. However, there are signs that the Sudanese electricity market is again on the path to efficiently delivering power to its people and industries with the development of a new power dispatching system.

Power development

Until 1997 the Sudanese electricity market was in a state of stagnation such that in 1998 only 370 MW of power was available to the entire country due to the ongoing maintenance and repair works, as well as political instability.

Concerted efforts by the National Electricity Corporation (NEC), together with active government support, has succeeded in raising this figure to an actual installed capacity of nearly 1213 MW today, of which 150 MW are generated and supplied in isolated areas. In addition, planned and partially contracted power stations due for completion within the next three to five years will contribute another 2700 MW to the total installed capacity. Among these developments is the Merowe power station, which is expected to supply 1250 MW in the near future, as well as a number of combined-cycle power plants, which will generate around a hundred additional megawatts. Furthermore, at Roseires power station the production performance has improved and will be extended in the near future, and there are plans to rehabilitate and extend the Khartoum North power plant and the Garri power station units, which are already feeding power into the network.

However, there is a high level of suppressed demand due to the fact that both the industrial sector and private households have largely relied on their own sources of power production, and it is therefore estimated that the true power requirement within Sudan is presently around 1700 MW, which will increase to approximately 2500 MW within the next two years, based on current growth rates of the country.

NEC has already initiated a number of projects, which are either financed by NEC itself, the government, or by financing institutions such as the Islamic Development Bank (IDB), the OPEC Fund and Chinese institutions. However, western international financing institutions are returning back to the Sudan, but only very slowly.

The power capacity is largely derived from thermal power stations, which provide more that two thirds of total power supplied at 67 per cent, and hydropower stations with 33 per cent. Total electricity generation amounted to 2989 GWh in 2005.

The national grid and the distribution systems, which covers approximately 1400 km of transmission lines, have undergone extensive improvements since 1997, so that load shedding and blackouts have been reduced to a great extent. Nevertheless, the generating capacity and the grid must be further improved at all voltage levels in order to match the demand forecast and necessary stability of the system. In the long run, the whole country will only further develop and prosper when there is a sustainable supply of electricity to the various consumers, especially in the southern part of the country.

Power dispatch project

The energy supply system is now controlled by a new state-of-the-art National Load Dispatch Centre (NLDC). Beginning with a bankable feasibility study, including economic and financial justification of the project in the year 1999-2000, carried out by Lahmeyer International, the main project goal was to support grid control with software for a higher efficiency of generation, transmission and distribution, promotion of energy management functions and scheduling, and accelerating information exchange for economic energy and plant management. Additionally, extension of an existing communication system for telephony, teleprotection signalling and data/alarm transmission was necessary.

The new NLDC building near Khartoum
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Following the feasibility study, Lahmeyer, which has been working in Sudan since 1977 as consulting engineers, particularly within the energy sector, was awarded an order by NEC for detailed design, preparation of tender documents, bid evaluation and support of contract negotiations, design and manufacturing supervision and approval, supervision and monitoring engineering, acceptance tests, and supervision of connected projects.

Initially, the communication infrastructure was planned as a power line carrier network, with microwave links at some locations as back-ups. However, after evaluating the technical and financial options it soon became clear that an alternative solution would be required. An optical fibre system, based on synchronous digital hierarchy (SDH) was chosen. This optical fibre system makes use of the high voltage network infrastructure, the old ground wire of these links replaced by optical ground wire (OPGW) and new links installed with it for new projects. It was also necessary to carry out the design of the SCADA network with all the remote terminal units (RTU), as part of a parallel line of preparatory engineering, including its sizing and channel routing and last but not least the heart of the system, the NLDC itself.

Three bidders were finally selected to submit offers for the NLDC, including the telecommunication system, whereas the OPGW system was offered separately, partially as a LifeLine installation on 220 kV, with a distance of approximately 240 km to be covered. All other necessary OPGW links were covered with other projects.

The LifeLine communications link installation on the 220 kV transmission network
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Following a tough evaluation procedure Germany’s Siemens emerged as the winner for both the NLDC and the communication system, and the OPGW LifeLine installation project contract was signed in mid-July 2004.

Technical alliance

The project scope for Siemens included the modernization of the SCADA/EMS/DMS including RTU in substations and the required telecommunication equipment and links (OPGW, PLC). Siemens also provided NEC with an optical transmission system based on STM-4 add-/drop-multiplexer to provide a reliable and economic method of transporting SDH traffic. The 240 km long OPGW was covered without repeater by using optical waveshifters and amplifiers.

As part of the contract, Siemens supplied a SINAUT Spectrum system – a modular distributed and scalable UNIX-based system – engineered to international open system standards. The network management functions, and the data on which they operate, are distributed amongst the servers and workstations and the allocation of functions to the servers is flexible. This is in keeping with the distributed architecture, ease of re-configuration and expansion, both in terms of adding functions and of changing and adding data. The subsystems are local area network (LAN), servers and workstations, printers, with computers based on RISC architecture and used as both full graphic workstations for an operator interface and as throughput-oriented servers. By distributing the functions over multiple servers and workstations, parallel execution of the functions can be exploited.

The computers are interconnected through an ethernet-compliant LAN while for overall system time synchronization a time subsystem consisting of a GPS master clock with a direct connection to the LAN has been provided.

The NLDC and communication system are both based on a redundancy concept except for the RTUs that are single units in the various substations and power stations, a concept guaranteeing a very high reliability, despite the challenge of developing interface engineering to connect the equipment from different manufacturers to the communication system and, through it, with the NLDC.

Form and function

The NLDC is now supervising and controlling approximately 22 substations with medium-term plans to extend this up to approximately 50 substations with voltage levels of 220/110/33/11 kV and 500 kV in the near future. The power is generated by the three major power stations, Roseires, Garri, and Khartoum North, besides some smaller ones. In the near future the 500 kV power lines under implementation from the 1250 MW Merowe hydropower station, presently being interfaced with the NLDC communication network, will also be controlled by the dispatch centre. Many more power stations are planned and the second phase of the project, targeting for example the Eastern Grid of the electrical network, has been initiated.

The project is now in full swing and as an important milestone the availability test has been successfully completed with the NEC in possession of an operational state-of-the-art NLDC located approximately 10 km out of the Khartoum city centre near the grid station Kilo X (Kilo ashara). The NLDC project is an unquestionable success and a further milestone in the development of Sudan’s electricity system.