The paper describes a mathematical model for the simulation of a 3-phase synchronous machine using direct-phase quantities, thus obviating the need for any transformation. Numerical solution using a digital computer has also been described, and compared with digital simulation in transformed d-q-O-and a-/3-0-axes models of a synchronous machine. The proposed model in direct-phase quantities enables a unified approach to be adopted in the study of both symmetrical and asymmetrical conditions. Since the constraints to be imposed are direct operating conditions, asymmetrical operating conditions can be studied very easily. Modifications required in the model to simulate various types of faults are described. Versatility of the proposed model is illustrated by the study of a single-line-earth fault with single-phase opening and automatic reclosure. It is shown that this type of fault can be studied as simply as, say, a 3-phase fault.List of symbols p = operator d/dt M = mutual inductance L = self inductance L md = ^/-axis magnetising inductance L mq = -axis magnetising inductance L d = d-a\\s synchronous inductance L q -(/-axis synchronous inductance L o -zero-sequence inductance R -resistance L (lQ , L a2 , M s0 = inductance coefficients of the armature M aq = mutual inductance between armature and <7-axis damper winding if 0 = initial field current E m -peak value of armature phase voltage (ojM af i f0 ) S = load angle with reference to the infinite busbar considered negative for generator action co -synchronous speed v = instantaneous speed (o> -p8) H = inertia constant, kWs/kVA Subscripts a armature / field kd direct-axis damper winding kq quadrature-axis damper winding e transmission line 1
Evidence for chiral doublet bands has been observed for the first time in the even-even nucleus 136 Nd. One chiral band was firmly established. Four other candidates for chiral bands were also identified, which can contribute to the realization of the multiple pairs of chiral doublet bands (Mχ D) phenomenon. The observed bands are investigated by the constrained and tilted axis cranking covariant density functional theory (TAC-CDFT). Possible configurations have been explored. The experimental energy spectra, angular momenta, and B(M1)/B(E2) values for the assigned configurations are globally reproduced by TAC-CDFT. Calculated results support the chiral interpretation of the observed bands, which correspond to shapes with maximum triaxiality induced by different multiquasiparticle configurations in 136 Nd.
Lifetimes of the first excited 2^{+} and 4^{+} states in the extremely neutron-deficient nuclide ^{172}Pt have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+})=0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N≈90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N≈90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
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