Per-Unit Impedances of Synchronous Machines

THE preceding part1 of this paper derived the generalized per-unit equations of the synchronous machine. The machine impedances were divided into two groups: those measurable from the stator terminals (x d , x d ′, r, and so forth) called the definitive impedances, and those internal impedances which cannot be measured from the stator terminals (X afd , X ffd , R ffd , and so forth), called the nondefinitive impedances. The per-unit values of the definitive impedances are independent of the base rotor currents, but part I showed that the per-unit values of the nondefinitive impedances are functions of the base rotor currents, and accordingly are subject to misuse and misinterpretation unless the rotor-current bases are explicitly defined. These rotor-current bases and their corresponding base-current ratios are the fundamental quantities in any per-unit system, and this concluding part II is devoted to a fuller exposition of the base-current ratios of the more important per-unit systems.