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Accurate calculation of circulating current in stator transposition windings is a prerequisite for the design of stator windings in large synchronous compensators. Due to its special operating conditions, such as transient strong excitation and strong overload, the main field, magnetic saturation and transient variation should be considered in calculation of circulating current. For this, a 3-D full-domain non-linear transient electromagnetic problem considering the real transposition structure and rotor motion has to be solved, but existing methods cannot achieve. In this paper, a new electromagnetic network method (ENM) based on the equivalence of local magnetic field (ELMF) is proposed to solve the problem of calculation of the transient circulating current in stator transposition windings considering main field and magnetic saturation. Then, the proposed method is applied to an example of a 300Mvar synchronous condenser and verified by the indirect method combining experiment and FEM. The proposed method is shown to produce correct results, take less computation time and is suitable for different transposition structures. [ABSTRACT FROM AUTHOR]

The twisted structure of strand is ignored and the resistance of all parallel copper strands is assumed to be at the same temperature in existing temperature estimation method of water cooling stator windings. However, the twisted structure leads to the changing of thermal source and cooling structure, the uneven thermal distribution of parallel copper strands leads to uneven resistance distribution, both of which will influence thermal distribution of stator windings and should be considered in the temperature estimation method. In this study, the temperature estimation method considering twisted structure and uneven resistance distribution is first proposed, called three‐dimensional (3‐D) network method, in which the nodes of circuit network and thermal network are completely consistent. Then, the water cooling stator winding of a 1240‐MW turbo generator is taken as an example, the thermal distribution of which are calculated by the proposed method and validated by both short‐circuit type test data and 3‐D finite element method (FEM). Finally, the influence of twisted structure and resistance distribution on the thermal distribution is analysed in detail. The results show that the twisted structure has a great effect on thermal distribution, which cannot be ignored, while the resistance distribution has little effect on thermal distribution. [ABSTRACT FROM AUTHOR]

The temperature field of stator strands with a transposed structure is challenging to analyze in large machines. In order to deal with this problem, this article presents a three-dimensional thermal network model of stator transposed strands for hydrogenerator. Take a 250-MW hydrogenerator as an example, and a novel thermal network model is established. In the proposed model, the solving domain is discretized according to the real physical structure, the transposition structure of stator strands is taken into account, and the change of heat sources caused by transposed strands is considered. Next, results of the proposed model are compared with those of the traditional thermal network without considering the transposition structure, and the proposed model can better model the real structure of the stator strands. Then, the effect of a different number of ventilation ducts on temperature distribution is discussed. Besides, the calculation results were compared with the finite-element method, and the proposed method took less time to calculate. Finally, the temperature of the stator was measured by the embedded temperature sensor, and the correctness of the calculation results of the proposed model is verified. The novel three-dimensional thermal network model can quickly and accurately calculate the temperature of stator transposed strands. [ABSTRACT FROM AUTHOR]

The stator winding acts as a carrier for the electrical load, and its loss accounts for about 50% of the total loss in AC machines. So how to design the stator winding for reducing winding loss is extremely crucial. Some traditional transposition methods are adopted in the winding design for large AC machines. Although they have a certain effect on reducing winding loss, there is still room for the improvement in the winding design and manufacturing technology. In this paper, a new global transposition method of stator winding is proposed. Then a megawatt driving motor is taken as the research object, and the eddy current losses, circulating current losses and total losses of winding strands are calculated by the three dimensional (3-D) finite element method (FEM) which has been validated by the experiment. In addition, by comparison with the two original transposition methods, it is proved that the proposed global transposition method is more effective in further reducing the winding loss, and the winding loss distribution is more uniform. This global transposition method proposed in this paper provides a reference for the optimal deign of the stator winding in AC machines. [ABSTRACT FROM AUTHOR]

For the particularity of the transposition method in large induction motor, the equivalent circuit method for the circulating current losses of the transposed strands in stator winding with multi‐turn coil is put forward. According to the unified theory of the electromagnetic field‐circuit and combining with the distribution of various leakage magnetic fields of stator winding, the general circuit network model of the stator winding is proposed, which can be applicable to different transposition angles with the consideration of the accurate distribution of leakage magnetic fields. With the basic idea of discrete points and the linearisation, the method for the leakage reactance of the transposed strands is given with an application in a 5.5 MW nuclear power pump canned induction motor, which uses the strand slot leakage reactance and the end leakage reactance to simulate the slot leakage magnetic field and the end leakage magnetic field. Through experiment, the equivalent circuit method for the circulating current losses of the transposed strands in multi‐turn coil is verified, which will provide a reference for the winding design and the winding loss calculation of the large induction motor. [ABSTRACT FROM AUTHOR]

The accurate and fast calculation of circulating currents between strands for different transposition types is the important premise of the engineering design for stator bars in large turbo-generators. The air gap magnetic field partly enters into the stator slot, also generating circulating currents. However, there is a lack of fast simulation method for calculating the air gap magnetic field entering the stator slot in the existing calculation method for circulating currents. In this paper, the analytical algorithm of calculating circulating currents considering the air gap magnetic field entering stator slots is proposed, in which the equivalent circuit model of transposed strands in stator bars is established based on the superposition principle, the analytical algorithm of calculating the induced electromotive force is proposed based on the discrete integral method, and the analytical algorithm of calculating the air gap magnetic field entering stator slots is proposed based on the conformal mapping method. Then, a 1400-MW turbo-generator is taken as an example, circulating currents between transposed strands in stator bars under no-load and rated condition are calculated by the proposed analytical algorithm. Finally, the proposed analytical algorithm is validated by the two-dimensional finite element method. [ABSTRACT FROM AUTHOR]

In the design of stator bar structure, void transposition is an important way of reducing circulating current loss in water-cooled turbo-generators. The different void transposition structures have a great influence on circulating current loss. However, the influences of void transposition structure on the leakage magnetic field and circulating current loss are not definite. A 600-MW water-cooled turbo-generator is taken as an example. A three-dimensional (3-D) physical model of transposition bars in a single slot is established, and the field-circuit coupling method is used in 3-D numerical calculation of the leakage magnetic field and circulating current loss. The influences of segment number and length of the void transposition on the slot leakage magnetic field, current, and circulating current loss are obtained. The relationship between the slot leakage magnetic field distribution along the axial direction and circulating current loss based on different void transposition structures is clarified. The numerical calculation accuracy is validated with the current test experiment. New strategies and theoretical basis will be provided for the optimal design and technology of the transposition bars. [ABSTRACT FROM PUBLISHER]

Large double-canned induction motor has high power density and usually works in a closed environment. Compared with a common induction motor, there are many contacted metallic parts in the stator end region of a large double-canned induction motor, in which eddy current will exist not only in end metallic parts themselves but also between contacted metallic parts. Evaluation of eddy-current losses in stator end metallic parts and reasonable end structure design is the premise of ensuring the safe and stable operation of a large double-canned induction motor. A 5-MW-scale double-canned induction motor is taken as an example in this paper, and the 3-D eddy-current field finite-element calculation model of its stator end is established and solved. Then, the eddy current in stator end metallic parts and between different contacted stator end metallic parts is analyzed in detail. On this basis, the eddy-current losses' decrease method through cutting off the eddy-current path between contacted stator end metallic parts is proposed and validated by experimental results of temperature. [ABSTRACT FROM PUBLISHER]

Reasonable transposition structure of stator bars in water-cooled turbo-generators could reduce circulating current of strands, and related factors on distribution change of circulating current are complex and diverse. Transposition angle is one of the most important influencing factors, and its influencing degree on circulating current is still unclear. A 600 MW water-cooled turbo-generator is set as an example, a 3-D physical model of transposition bars in a single slot is established, and a field-circuit coupling method is used in 3-D numerical calculation. The optimization of transposition angle is researched, and the distribution changes of 3-D global domain magnetic field, maximum current, and circulating current loss in different transposition angles are obtained. Finally, the calculation results are compared with that of the improved analytical algorithm to validate the accuracy of the solving model. [ABSTRACT FROM AUTHOR]

To reduce circulating current losses in stator strands of hydro‐generator, strand transposition is widely used in stator bars. At present, the traditional analytical method for calculating circulating current losses cannot accurately simulate the distribution of leakage magnetic field, which will bring a large deviation to the calculation result and not benefit the winding design. The numerical calculation method for circulating current losses in stator bar is presented in this study, by which the leakage magnetic field distribution of stator transposition bar can be described in detail through establishing three‐dimensional actual transposition model. The 0°/360°/0° transposition bar in a 180 MW hydro‐generator is taken as an example and the circulating current losses in stator bar strands are calculated. The causes of errors in traditional analytical method are discussed through the comparison of the leakage magnetic field distribution obtained by numerical calculation method and traditional analytical method. [ABSTRACT FROM AUTHOR]

Calculation of circulating current in transposition bars is the key problem in the design of stator windings, which will determine the transposition type of stator windings. The circuit equation method, in which the calculation of strand end leakage reactance in transposition bars is the premise, is widely used in engineering to calculate circulating current. This paper describes an analytical algorithm for the calculation of strand end leakage reactance in transposition bars, which is based on mirror image principle. The end leakage reactance of strands in transposition bar is calculated by the integral of transposition path discretized into many key points. Contrary to the existing calculation method, the analytical algorithm proposed in this paper is a general method for calculating the end leakage reactance, which can simulate the transposition path of strands in the end region for different transposition types. In order to validate the proposed method, the end coil self and mutual leakage reactance are calculated by proposed analytical algorithm and finite element method. [ABSTRACT FROM AUTHOR]

Calculation of circulating current in transposition bars is important to the transposition-type design of stator windings in large generators. The circuit network model of the stator transposition bar, including only resistance and reactance parameters, is proposed in this paper, and the calculation method for parameters is given. The analytical algorithm of circulating current in stator transposition bars is proposed based on the circuit network model. Contrary to the existing calculation method for circulating current, the presented analytical algorithm is a general and fast method for different transposition types, which can avoid establishing complex 3-D models. In order to validate the proposed analytical algorithm, the strand current and circulating current of less than 540 ^\circ with a void transposition bar in a water-cooled turbogenerator are calculated by analytical algorithm and 3-D finite-element method. [ABSTRACT FROM PUBLISHER]

Calculation of circulating current in transposition bars is the key problem in the design of stator windings, which will determine the transposition type of stator windings. The circuit equation method, in which the calculation of strand slot leakage reactance in transposition bars is the premise, is widely used in engineering to calculate circulating current. This paper describes an analytical algorithm for the calculation of strand slot leakage reactance in transposition bars called discrete integral method. The presented method is based on Ampere's circuit law. The slot leakage reactance of strands in transposition bars is calculated by the integral of the transposition path discretized into many key points under the proper coordinate system. Contrary to the existing calculation formula, the discrete integral method is a general method for the calculation of slot leakage reactance, which can simulate the transposition path of different transposition types. In order to validate the discrete integral method, the circulating current generated by slot leakage magnetic field of two typical transposition bars is calculated by circuit equation method and finite-element method. [ABSTRACT FROM PUBLISHER]