Application of the slow coherency decomposition method to the Yemeni network

International Journal of Electrical Engineering Education, Jan 2004 by Badeeb, Omer M Awed, Hazza, Gamal A W

Method for determining the optimal number of coherent areas

As already indicated above, one of the difficulties in using the slow coherency method for power system division is determination of the optimal number of coherent areas. This arises especially in cases when there is no sharp break between eigenvalues in a large power system from which one can easily select the appropriate number of coherent areas. A mathematical measure is used here to compute the norm value of ||L - L^sub g^|| at the optimal number of areas. Testing this method on the Yemeni network system, the optimal number of slow coherent areas was found to be r = 4, as shown in Fig. 1.

Case study

Existing Yemen interconnected system

The interconnected Yemeni power system consists of a number of power stations having different fuel types, such as steam and diesel oil. All power stations are connected by 132kV transmission lines. The 132kV transmission voltage is stepped down to 32kV at bulk supply points, which are located close to load centres. The Yemeni distribution network is operated at 15 or UkV. The existing total generation is about 800MVA. The system is comparatively small and comprises southern and northern Yemen network systems.

To perform the study, first, the eigenvalues of the matrix A are computed as in Table 1. Using the table and the selection method of Ref. 15, the number of areas is chosen to be four. The resulting coherent areas using the slow coherency method are shown in Figs. 2 and 3.

Proposed interconnected system

Due to the shortage in power supply generation in comparison with consumer load demand, the government of Yemen has established a plan to construct a new large power station in the Mareb governorate. This station will be gas fired and will generate about 500 MVA. The proposed power station will consist of five main units and will be connected to the Dhahban area through Bani Hushaish via 11/33/400/132 kV transmission lines.

Using the steps proposed earlier to determine the coherent areas, five slow coherent areas are found, as shown in Fig. 4 and Fig. 5: the computed eigenvalues are shown in Table 2.

Conclusions

A slow coherency method is proposed and tested to determine the optimal number of slow coherent areas, based on the number of slow eigenvalues. An optimal technique is used to overcome the shortcoming of having a prior knowledge of the number of coherent areas. The slow coherency method requires the computation of eigenvalues and eigenvectors in order to determine the optimal slow coherent areas, and has a sound mathematical basis.

The slow coherent method is applied to both an existing and proposed Yemeni interconnected power system and is shown to be efficient.

Acknowledgements

The authors acknowledge the support given by PEC personnel in Sana'a, Yemen in providing the necessary data to carry out this investigation.

References

1 J. M. Undrill and A. E. Turner, 'Construction of power system electromechanical equivalent by modal analysis,' IEEE Trans. Power Appar. Syst., PAS-90 (1971), 2049-2059.