Prediction of Eddy Current Losses in Cooling Tubes of Direct Cooled Windings in Electric Machines

Abstract

The direct coil cooling method is one of the existing cooling techniques for electric machines with concentrated windings, in which cooling tubes of conductive material are inserted between the windings. In such cases, eddy current losses are induced in those cooling tubes because of the time variant magnetic field. To compute the cooling tubes losses, either a transient finite element simulation (mostly based on commercial software), or a full analytical method, which is more complex to be constructed, is required. Instead, this paper proposes a simple and an accurate combined semi-analytical-finite element method to calculate the losses of electric machines having cooling tubes. The 2D magnetostatic solution of the magnetic field is obtained e.g., using the free package “FEMM”. Then, the eddy current losses in the tubes are computed using simple analytical equations. In addition, the iron core losses could be obtained. In order to validate the proposed method, two cases are investigated. In Case 1, a six-toothed stator of a switched reluctance machine (SRM), without rotor, is employed in which six cooling tubes are used while in Case 2 a complete rotating SRM is studied. The proposed method is validated by a 2D transient simulation in the commercial software “ANSYS Maxwell” and also by experimental measurements. Evidently, the proposed method is simple and fast to be constructed and it is almost free of cost.

Finite Element Based Overall Optimization of Switched Reluctance Motor Using Multi-Objective Genetic Algorithm (NSGA-II)

“…The prediction of switched reluctance motor efficiency requires knowledge of losses [18,24]. The calculation of losses in the SRM, especially the assessment of core losses, is a very difficult task mainly because the flux waveforms are non-sinusoidal and the differences in shape of flux density waveforms in the different sector of SRM's magnetic circuit.…”

Modelling and Validation of a Switched Reluctance Motor Stator Tooth with Direct Coil Cooling

“…Therefore, a metallic tube is preferred compared to a plastic material, because the thermal conductivity and strength are usually lower. As was investigated by Ibrahim et al [9], the additional eddy current losses within stainless steel tubes are neglectable and therefore stainless steel will be used as tube material within the validation measurements. The motor parameters of the used motor geometry are shown in Table 1.…”

“…The channels were sealed and created by potting using the lost-wax casting method. Rhebergen et al [5], Sixel et al [6], Semidey et al [7], Fairall et al [8], and Ibrahim et al [9] investigated metallic or plastic tubes inserted within the slot in direct contact with the coil. Rhebergen et al [5] used a plastic material to avoid electromagnetic and implementation issues.…”

“…In these scientific studies, the great potential of the implementation of direct coil cooling is shown. Fairall et al [8] and Ibrahim et al [9] studied the effect of the insertion of the tube material into the slot on the eddy current loss in a Switched Reluctance Motor. It is found in these studies that plastic materials do not cause additional losses and that the losses for a stainless steel tube material are acceptable.…”

Electromagnetic and Calorimetric Validation of a Direct Oil Cooled Tooth Coil Winding PM Machine for Traction Application

“…• using conductive pipes in the slots, with the drawback of generating large eddy current losses [21] • theoretical evaluation of the concept of flushing the entire stator and rotor with oil coolant [22] • direct-water cooled coils by winding a coolant carrying steel pipe with litz wire, validated in a 205 kW machine for a bus application [23] • using fluid guiding structure and airgap sealing to allow for oil cooling within the slots [24].…”