This paper presents a new sparse formulation for the solution of unbalanced
three-phase power systems using the Newton-Raphson method. The three-phase
current injection equations are written in rectangular coordinates resulti
ng in an order 6n system of equations. The Jacobian matrix is composed of 6
x 6 block matrices and retains the same structure as the nodal admittance
matrix. Practical distribution systems were used to test the method and to
compare its robustness with that of the backward/forward sweep method.