The spiral vector theory proposed and explained in this book unifies the steady state and transient state theories of AC circuits and machines. Previously steady state theory and transient state theory were separated by different expressions for state variables.This new theory makes possible the analysis of transient phenomena in three phase machines, an area largely untouched by conventional AC machine theories. Results of AC motor analysis obtained by the spiral vector method have led directly to new torque controls which give AC motors much superior performance to the usual DC control motors. With the rapid developments in inverter technology making the control of AC power easier the spiral vector theory provides the necessary theoretical foundation for the understanding and design of AC circuits and machines. The spiral vector theory provides superior computer simulations to AC circuits and machines, which are simple in structure and easy in use. The salient-pole AC generator is a good example for it.