An efficient algorithm is presented for load-flow solutions in electrical power systems. The algorithm is based on the Newton-Raphson process and uses a partitioned-matrix approach to the Jacobian equation which was previously suggested for array-processor applications. It is shown that this approach is also beneficial when using conventional computer systems. The numerical method and computation techniques employed are described, and their relationship to modern computer architectures is considered. The algorithm is highly efficient for the solution of transmission networks but also has particular advantages for lower-voltage networks, and for difficult or ill conditioned load-flow problems. Computational results, obtained using minicomputer hardware, are given for a variety of networks of up to 734 nodes. The numerical method which has been developed is also applicable to other power-system problems including state estimation and dynamic simulation.