  Differential transformation (DT) method has shown to be promising for power
system simulation in our recent works. This letter applies the DT method to
nonlinear power flow equations and proves that the nonlinear power flow
equations are converted to formally linear equations after DT. This letter
further extends the constant power load assumption in the classical power flow
formulation to the more general and practical ZIP load assumption and proves
that the linear equation after DT still holds for ZIP load model with slight
modifications on the coefficient matrices. These results demonstrate great
potential of the DT method in solving power system nonlinear problems.
