No abstract

The end-winding region is usually overlooked in the roebel design of large AC machines. However, saturated stator slots cause overhang parts to impact the circulating currents significantly. In fact, a precise knowledge of the winding overhang strand inductances is crucial when optimising the transpositions of large roebel bars, especially in the case of under-roebeling (having less than 360-transposition in the active part) where the goal is to compensate the winding overhang parasitic field with the slot-parasitic field. In this paper, a rectangular inductance calculation model (R-ICM) is proposed. It results in a circuital lumped-element model (LEM) that takes the strand dimensions, the bar bending, as well as small-scale effects into account. Moreover, the work describes how to model finite current-carrying rectangular segments (straight and arced) from first principles. Finally, the methodology was demonstrated for two prototype specimens with different bending-shapes corresponding to the fundamental elements on a stator bar in the winding overhang of large electrical machines.

The computation of three-dimensional (3-D) magnetic fields is a demanding task in the analysis of electrical machines and other electromagnetic devices. In this context, integral field calculation provides a smooth solution, high precision and resolution, "on-demand"calculation, and an origin-based formulation of the magnetic field and the magnetic vector potential. However, conventional elliptic methods lead to huge parallelizable computing efforts and significant errors. In this paper, a 3-D generic current-carrying arc segment with rectangular cross-section is studied. A new analytic formulation is proposed to speed up the computation of magnetic fields and reduce the error by more than three orders of magnitude. In addition, the proposed magnetic vector potential expression has similar accuracy as numerical integration. In fact, a significant reduction of the error level has been showcased clearly with respect to existing approaches. The present work is promising for improving the design methodology and optimization of large superconducting dipole magnets or arched end-winding geometries of large electrical machines.

This paper presents an exact analytical solution to the two-phase and three-phase short-circuit events of the doublyfed induction machine (DFIM). The contribution is intended to strengthen the predictability of DFIMs under the design stage or for control tuning purposes and reduce the computational costs of large-scale transient stability studies of the interconnected power system. In general, the approach enables to simplify and improve the analysis DFIMs. The original analytical equations are derived from first principles. A case study of a doublyfed induction generator (DFIG) is considered, where the "large machine approximation" is shown to be valid as well. The analytical equations are used to predict the torque transients in different handpicked transient scenarios and assessed against numerical simulations. Finally, the proposed analytical model shows excellent agreement with the numerical results in the SIMSEN environment.

Abstract-The goal of this paper is to propose and validate standstill DC-Decay measuring methods for a rotor in arbitrary position. The first new method (DC-Decay I) delivers the equivalent circuit with a few measurements. The second new method (DC-Decay III) permits to catch the full equivalent circuit of both axes in only one measurement which is unique and a breakthrough in parameter identification. A new method (DC-Decay II) is used to get the rotor angle. The field current allows to obtain the characteristic reactance x c. To extract the time constants and the reactances an enhancement of "classical" parameter identification algorithms is presented (used for the DC-Decay I method). Simulation and experimental results validate the methods and show their accuracy and drawback.