Per-unit impedances of synchronous machines — II

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 (xd, xd′, r, and so forth) called the definitive impedances, and those internal impedances which cannot be measured from the stator terminals (Xafd, Xffd, Rffd, 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.