The transposition bar is an important component in large generators, the insulation fault in transposition bars is extremely dangerous for the daily operation of generators. The circulating current losses of the stator windings are usually considered in traditional transposition designs. The risk and hazard of the transposition bar inter-strands short-circuit fault are neglected. Therefore, it is necessary to evaluate the risk of the transposition bars. This paper proposes a new risk assessment method for transposition bars. This method enables the comprehensive risk assessment of the design, circulating current losses, and fault risk of transposition bars. Firstly, the strand current of all short-circuit fault schemes of the transposition bar is calculated by the leakage reactance electromotive potential method and the fault dataset is established. Further, based on the fault dataset, risk indexes: severity and probability are proposed. The probability of short-circuit fault for each category is calculated by Markov chain. Finally, the risk indexes of three transposition types are calculated and compared with the traditional index. The risk of 360 degrees and 360 degrees+25 mm transposition is 7.5 times larger than that of 308 degrees transposition. A risk assessment method for the transposition bar is proposed, which considers both operation efficiency and reliability. This method provides a new basis for the transposition designs.

The present paper addresses a problem that many traditional analytical calculation methods ignore the coupling relationship between loss and temperature rise. In this paper, a 51.51 MW turbine generator is taken as the research object, and a transient thermal network method coupled with loss and temperature rise for calculating the temperature rise in a stator transposition bar is proposed. Considering the influence of temperature change on the AC loss of strands, a thermal network model coupled with loss and temperature rise is established to complete the calculation of thermal conductivity matrix parameters. A sparse matrix storage method is proposed to reduce the memory usage of the high-order matrix. The linear iterative method is introduced to accelerate the solution of the equation. The Newton Krylov method is used to handle the coupling between loss and temperature rise. In this way, the transient temperature rise in the stator transposition bar is calculated rapidly. The accuracy of the thermal network model coupled with loss and temperature rise is verified by comparing its results with the three-dimensional simulations. Finally, a new combined transposition structure is proposed to suppress the temperature rise in the stator transposition bar.

In the study of stator slot leakage magnetic field and stator bar transposition method of 1000-MW-class turbine generator, the radial leakage magnetic field in the stator slot is often ignored because it is difficult to simulate accurately. In this paper, the distribution law of the radial leakage magnetic field in the stator slot is analyzed, and a new combined cross transposition method is proposed. By enabling each stator strand to occupy every column, it balances the series cumulative leakage electromotive force and suppresses the circulating current caused by the radial leakage magnetic field in the stator slot. Secondly, an embedded multi-dimensional coupling model is established, which embeds a three-dimensional (3-D) model into a two-dimensional (2-D) model and couples the structure and magnetic field in the full time domain to simplify the calculation. Finally, through the calculation results of the circulating current loss of the stator bar with traditional cross transposition and the new combined cross transposition, the analysis results of the radial leakage magnetic field distribution in the stator slot and the suppression effect of the new combined cross transposition on the circulating current are verified. The error of the model is verified to be 3.0% by the short circuit type experimental data of a 1055 MW turbine generator. The results show that the radial leakage magnetic field in the stator slot is affected by the combined action of the magnetic fields generated by the stator and rotor currents; the circulating current loss of the new combined cross transposition is 23.1% lower than that of the traditional cross transposition.

Flat-wire motor has become the first choice for the electric vehicle drive motor because of its high power density among the permanent magnet synchronous motors (PMSMs). Flat-wire winding is the core component of the flat-wire motor. Its loss directly limits motor efficiency gains. This will be more serious under high-speed working conditions. To reduce the winding ac loss at high frequencies, this article presents a design method for formed winding and gives three kinds of formed winding structures: original formed winding (OFW), formed split winding (FSW), and formed transposition winding (FTW). The simulation models of the global formed winding flat-wire motors are built to calculate the ac losses of three kinds of motors at the peak power condition. A 15-kW prototype was used as an example to verify the correctness of the loss analysis. To verify the rationality of the winding design in advance, this article also proposes a noninvasive current measurement method based on the coupling relationship between the end leakage magnetic field and the winding currents. Unlike conventional methods, this method does not need to destroy the winding structure. The accuracy of the measurement method is verified by comparison with the traditional method experimental results at the local winding.

The rapid adoption of electric vehicles has driven significant advancements in electric drive systems. Flat-wire windings are commonly employed in electric vehicle motors due to their high slot fill factor and superior heat dissipation characteristics. As electric vehicle systems progress towards higher frequencies and voltages, the increased power density and electromagnetic load lead to intensified motor saturation, resulting in higher winding AC losses. Accurate calculation of these losses is essential for optimizing electric vehicle motor design. This paper proposes a transient electric circuit network method based on electromagnetic induction, and presents calculation approaches for two key parameters: network resistance and network induced electromotive force. The method is applied to analyse the AC losses in electric vehicle motor windings, with consideration given to the effects of temperature and speed. The results are compared with those obtained from finite element method for transient eddy current losses, validating the accuracy and efficiency of the proposed method. This method offers a rapid and reliable tool for evaluating AC losses in electric vehicle motor windings.

This article describes a new numerical calculation method for the eddy current loss of flat wire windings in the electric vehicle motor, namely the eddy current magnetic network method (ECMNM). The method is based on the principle of regional magnetic field simulation (RMFS), coupled with magnetic network modeling technology and the eddy current field equation. Compared to the finite element method (FEM) commonly used for analyzing windings eddy current loss, the main advantages of the ECMNM are its fast computation speed, high calculation accuracy, and the ability to parameterize the motor structural parameters, which is conducive to motor design. Compared with other previous analytical methods, the ECMNM can accurately consider the slot structure, winding arrangement, and dimensions. In particular, it can accurately consider the influence of the transient rotor rotating magnetic field and the magnetic saturation of the stator and rotor core on the eddy current loss of the stator windings under different operating conditions. The ECMNM has both versatility and high computational accuracy, while also effectively improving calculation speed. In this article, different stator slot types and winding arrangements are adopted. The ECMNM is compared with the FEM under multiple operating conditions, and verified by experiments.

The synchronous condenser (SC) must have strong transient reactive power (TRP) characteristics to support the bus voltage in high voltage direct current (HVDC) transmission systems. The leakage magnetic field produced by the end winding is a critical factor that impacts the TRP characteristics of SC. Optimizing the end winding structures is an effective approach to enhancing the TRP characteristics of SC. Consequently, this paper proposes a multi-dimensional field-circuit-machine-network coupling model for SC and quantitatively investigates the impact of the end winding structures on the TRP characteristics of SC. The end leakage magnetic field of different end winding structures is firstly calculated and analyzed, including the tilt angle of the involute part and the extended length of the line part. Furthermore, the end leakage reactance and transient parameters are studied under different end winding structures. On this basis, the TRP responses of SC under different end winding structures are obtained. The impact law and degree of the end winding structures on the TRP characteristics of the SC are revealed. The calculation model is verified through experiments. The conclusions can offer a theoretical foundation for enhancing the TRP characteristics of the next-generation SC.

Formed-parallel coil is a new stator coil type of flat-wire motor. It is designed to reduce the eddy current loss in the stator coil and decrease the difficulty of coil production. In the experiments, it can only detect the total current of each stator coil instead of the current distribution of each strand. Aiming to solve the problem, this paper proposes a strand current measuring method based on Hall sensors without destroying the coil structure. The end leakage magnetic field (ELMF) and strand current are analyzed by finite element solution (FEM). The relationship between the strand currents, ELMF and Hall output signal is derived. The coil strand current test platform is built and the experimental verification is carried out by a 15 kW flat-wire motor. The result shows that the current measuring method can measure the current distribution in the strands accurately. It provides an experimental evaluation basis for analyzing the reasonableness of the strand current distribution and the design of the formed-parallel coil.

This article establishes a multislot stator bar short-circuit fault model to address the issue of short-circuit faults between stator transposition bars in ac generators. In order to extract and recognize the fault features of short circuits between strands, the calculation model based on the end magnetic field is established. Meanwhile, a measurement point optimization method based on the Nyquist sampling theorem is proposed to reduce the difficulty of sensor layout. Based on the characteristics of magnetic density jump, this article proposes a diagnostic method for short-circuit faults between strands, combined with the measurement point optimization results. Finally, the effectiveness of the method proposed in this article is verified by building an experimental platform for stator bar short-circuit faults. The results show that the optimization method of measurement point proposed in this article can greatly reduce the number of sensors while retaining fault characteristics and the fault diagnosis method can achieve rapid diagnosis of short-circuit fault between strands.

Abstract Accurate calculation of equivalent circuit parameters is a prerequisite for accurately calculating the large‐capacity synchronous condenser parameter model. Due to its special transient operating conditions, the high transient magnetic saturation effect during operation causes the non‐linearity and time‐varying of the equivalent circuit parameters. The field mutual leakage reactance is the critical factor affecting the field current, and the time‐varying of the equivalent circuit parameters is closely related to the field current. However, the existing equivalent circuit parameter calculation methods considering field leakage reactance cannot achieve time‐varying parameters. A calculation method of time‐varying equivalent circuit parameters based on a back propagation neural network algorithm is proposed, which solves the calculation problem of time‐varying equivalent circuit parameters considering field mutual leakage reactance. Then, a 300MVar condenser is taken as the research object, and the proposed method is used to simulate the different operating conditions of the condenser and verified by the finite element method and experiment. The results show that the method improves the calculation accuracy of the equivalent circuit parameter model, reduces the calculation time, and applies to different operating conditions.

The flat wire winding has the characteristics of a high filling coefficient and strong heat dissipation ability. Applying it to a permanent magnet synchronous motor (PMSM) can further improve efficiency and power density. However, its relatively significant eddy current effect has become the key to limiting motor speed and power level improvement. Based on the analytical calculation of flat wire winding eddy current loss, according to the characteristics of PMSM with multiple turns and few strands, a newly integral transposed winding (ITW) structure is proposed, which adopts 288 degrees incomplete transposition structure in the overall length of the winding, and the ends do not need to be connected by the welding process. Then, taking a 15-kW PMSM for electric vehicles as an example, based on the 3-D time-stepping finite-element analysis (TSFEA), the strand current distribution and ac additional copper loss of the winding under rated working condition and high-speed working condition are calculated, and by comparing the losses of different windings, the results show that the ITW structure can greatly suppress the eddy current loss while introducing circulating current loss is negligible. Finally, the PMSM prototype is manufactured and the correctness of different winding designs is verified by a no-load back electromotive force (EMF) experiment.

An improved end structure topology to reduce temperature rise (TR) of the large-capacity synchronous condenser (LSC) is proposed. Taking a 300MVar LSC as an example, the eddy current losses (ECL) in the end structures in the traditional model and improved model under rated operating conditions are analyzed. A 3-D flow-heat coupling calculation model of the LSC is established to examine the fluid dynamics and temperature distribution in the end region. The impact of the proposed structures on TR is explored, revealing a reduction in the maximum temperature of the press plate by 2.7 °C, and decreases in the near-core and far-core support fingers by 0.7 °C and 2.9 °C, respectively. Finally, the simulation results are validated through experimental testing.

During the fault process of the ultra-high voltage direct current (UHVDC) system, the winding of the large-capacity synchronous condenser (SC) generates strong impulse current, leading to excessive eddy current losses and easily causing local overheating in the end structure. In this paper, the machine-network coupling transient model of the SC is established, and the transient characteristics of stator current and excitation current of the SC are revealed when three-phase short-circuit fault occurs at the sending end of the UHVDC system. Then, the 3-D nonlinear transient electromagnetic field calculation model of 300MVar SC is established, and the end magnetic field and the eddy current losses in the end structure at different times are analyzed. According to the distribution law of electromagnetic field, a new end topology structure which can effectively reduce the eddy current losses in the clamping ring and clamping finger is proposed. The end magnetic field and eddy losses in the traditional model (TM) and the improved model (IM) are compared, and the superiority of the improved model is verified.

Abstract Automobile drive motor with flat wire winding has improved the slot fill factor and efficiency. However, under the current environment of drive motors development to high frequency and voltage, the increase in winding AC loss has weakened those advantages. Accurate analysis of AC loss and the design of high‐performance windings have become the key issues and difficulties in the design process of drive motors. Based on the winding AC loss generation mechanism, the authors propose a winding AC loss analysis method, which can effectively separate DC loss, eddy current loss, and circulating current loss. The method is used to analyse winding AC loss of 60 kW flat wire winding permanent magnet synchronous motor (PMSM). In addition, parallel multi‐strand flat wire windings are proposed to reduce the winding AC loss and eliminate the limitation of the magnetic load of the motor on the selection of winding layers. The AC loss of the parallel multi‐strand flat wire windings at different frequencies is calculated, which demonstrates the effectiveness of the proposed winding topology in reducing the winding AC loss. In addition, the correctness of the simulation model was verified through experiments, and the loss calculation method was verified through finite element analysis.

Due to the influence of skin effect of eddy currents, the temperature rise in the outer circular region of the press plate of large synchronous condenser (SC) is large. The metal windscreen is located on the outer side of the press plate and has a significant impact on the magnetic flux density in the press plate. In order to reduce loss in the press plate, this paper proposes 12 types of metal windscreen. Taking a 300MVar SC as an example, 3-D transient electromagnetic field calculation models are established. The numerical simulation method is used to calculate the end magnetic field and eddy current loss in the end structures of the SC under rated operating conditions. The influence of metal windscreen with different structures and materials on the end magnetic field and eddy current loss in the end structures is analyzed. Finally, the obtained eddy current loss is used as a heat source to calculate the temperature rise of the end structure, and the accuracy of the calculation results is verified through experiments. This study provides a theoretical basis for optimizing the design of the SC end.

The early inter-turn short-circuit fault of field winding (ISFF) occurs between adjacent strands in a single rotor slot, which is a significant safety hazard in the transient operation of the large-capacity synchronous condenser. To realize high-precision detection of early ISFF, this paper proposes a characteristics analysis method of ISFF with the field strand as the minimum unit. This method combines the novel stator winding asymmetric branch connection mode of the condenser. Compared with the fault characteristics analysis method with the field coil as the minimum unit, the proposed method can analyze ISFF characteristics between strands in a single rotor slot and has higher fault detection resolution, which is especially suitable for electric excitation synchronous generators with stator winding asymmetric branch connections. The results show that ISFF occurs in a single rotor slot, the even harmonics components appear in the field magnetomotive force and partial stator winding asymmetric branch current, and the 2nd harmonic component accounts for the largest proportion. Taking the 5 turns ISFF in slot 1 of the 2-pole 3-branch condenser as an example, the 2nd harmonic in the field magnetomotive force even harmonics accounts for 55.15%, and the number of branches with even harmonics components current accounts for 66.67% of the total number of branches. The research results can provide theoretical support for high-precision ISFF detection to avoid fault expansion.

It is very important to consider the eddy current reaction of the metal structure in large electric machines, which has a direct impact on the calculation results of induced current and loss. In order to solve the problem that the complex end leakage magnetic field is difficult to calculate directly, a new semi-analytical method (NSM) considering the eddy current reaction is proposed. Firstly, the corresponding relationship between the external magnetic field and the global magnetic field of the clamping ring in two simple calculation models is obtained by the 3-D finite element method. Then, the external magnetic field of the clamping ring in a 300MVA synchronous condenser under rated operating conditions is calculated, and the global magnetic field of the clamping ring is determined based on the obtained corresponding relationship. The eddy current density and eddy current loss of the clamping ring are calculated using the external magnetic field and the global magnetic field respectively. Finally, the calculation results were compared with the 3-D finite element results, which verified the importance of the global magnetic field and the accuracy of the NSM.

The stator windings of large turbo-generators consist of some transposed strands that are connected in parallel by a joint sleeve at the end. However, the insulation damage is easily caused by the twist of strands. Long-term high voltage, high temperature and alternating electromagnetic force also increases the probability of short circuit fault between transposed strands. A circuit network method is proposed to calculate short circuit fault between transposed strands in this article, and the calculation of self-inductance of transposed strands in the slot is also proposed by the discrete trapezoidal method. Comparing with the finite element method, repeated modeling of short circuit faults between transposed strands is convenient and the solution is time-saving using circuit network method. The detailed modeling process of circuit network method is described. The correctness of the proposed method is verified by comparing with the finite element method.

Transposition of stator windings for large turbo generators is a key technology. At present, the stator windings with four-row strands for large turbo generators are usually transposed on both sides of the slot centreline and connected at the end by the joint sleeve. The different transposition methods of strands have an important effect on strand currents, circulating currents, and circulating current losses. A new four-row integral transposition method is proposed in this study. Several transposition methods based on the four-row integral transposition method are compared with the double Roebel transposition methods using 3-D time-harmonic field. The 3-D model without the end and with the end are both calculated. The results show that the four-row integral transposition method has an obvious advantage in reducing circulating current loss. Finally, a 2-D finite element model of transient magnetic field is calculated and its calculation results further support for the effectiveness of the proposed transposition method. The proposed transposition method has a great application value, which can reduce additional loss, avoid partial overheating and short circuit fault of stator windings in large turbo generators.