A Rectangular End-Winding Model for Enhanced Circulating Current Prediction in AC Machines

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.

A Fast 3-D Winding Inductance Estimation Method for Air-Cored Resonant Induction Machines

“…Compared to 3-D-FEA numerical methods, analytical methods and hybrid numerical-analytical methods can reduce the computational burden and achieve good accuracy [13]- [16]. Neumann integrals are implemented in [17] to calculate the end-winding inductance for concentrically-wound IMs: coils are represented by their central filaments, and a coil table is used to store the information such as the coil winding direction and coil connections.…”

The Energy Transition's Impact on the Accumulated Average Efficiency of Large Hydrogenerators

“…Moreover, this paper also expresses a compressed formulation of the loss modeling in eqs. ( 2)-( 5), merging the armature and strayload losses [14], and bringing the field winding and brush losses together. Moreover, the exciter loss is considered as directly proportional to the field current [15].…”

“…Then, the sum of all the actual power elements (P i and P loss,i ) are multiplied individually by the time duration (∆t i ) to obtain average values or expected values in terms of accumulated energy (E and E loss ), as formulated in eqs. ( 13) and (14), where the total time (T ) is given in eq. ( 15).…”

A Differential Strand-Slot Inductance Model for Improved Compensation of Circulating Currents in the Core Part of Large AC Machines

“…Moreover, in order to predict them more easily, novel analytical methods to compute the inductance have been proposed in [4], [5] without taking saturation and exact strand dimensions into account. A recent contribution [6] replies demonstrating that taking the strand geometry into account leads to better estimation of circulating currents, even though saturation is not influential in the end region. A general trend in other works [7]- [10] is analytically computing the circulating currents based on the lumped-element circuit model.…”

“…A more accurate estimation of circulating current makes a global transposition method more effective [20]. Circulating currents can also get induced in the end-winding, where the bars usually are not transposed [6] (see Fig. 1).…”