Yanping Liang

Calculation and Analysis of Can Losses of Canned Induction Motor

The canned induction motors are widely used in pharmaceutical, chemical, and nuclear fields. It is necessary to calculate the losses, particularly the can losses, accurately. Combining steady-state ac magnetic 2-D finite-element solutions with the can harmonic loss formulas derived in this paper, the can losses under rated voltage in various operating conditions are obtained. Then, the calculation results under various voltages in no-load condition are compared with the experiment data, which provides the basis for the further performance analysis and motor design.

Circuit Network Model of Stator Transposition Bar in Large Generators and Calculation of Circulating Current

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° with a void transposition bar in a water-cooled turbogenerator are calculated by analytical algorithm and 3-D finite-element method.

Analytic Algorithm for Strand Slot Leakage Reactance of the Transposition Bar in an AC Machine

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 Amperes 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.

Finite-Element Calculation of 3-D Transient Electromagnetic Field in End Region and Eddy-Current Loss Decrease in Stator End Clamping Plate of Large Hydrogenerator

The stator clamping plate is an important component of hydrogenerators used to fasten the stator end core. Due to the complex leakage electromagnetic field in the end region, eddy-current loss in the stator clamping plate is usually very large, which will lead to partial overheat. Evaluation of eddy-current losses in stator clamping plates and reasonable structure design are the premise of ensuring the safe and stable operation of a large hydrogenerator. A 278-MVA hydrogenerator is taken as an example in this paper, and the calculation model of 3-D transient electromagnetic field of end region is established and validated by temperature test value. Then, a new arch-shaped clamping plate structure is presented. The transient electromagnetic field and eddy-current losses of end regions with traditional fan-shaped and new arch-shaped stator clamping plate structures are calculated by time-stepping finite-element method and are compared. Calculation results indicate that the new arch-shaped clamping plate structure can effectively reduce the eddy-current loss of stator clamping plate.

Analytical Algorithm for Strand End Leakage Reactance of Transposition Bar in AC Machine

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.

Calculation of Temperature Field in Power Capacitor

The operating temperature of a power capacitor has an effect on its service life directly. A 500-kvar power capacitor is taken as the research object. The capacitor fever produced by internal dielectric loss is considered under the running condition of 55 °C. The 3-D finite volume method calculation model of capacitor temperature is established, and the temperature distribution characteristics and the internal temperature at the hottest spot of the capacitor are obtained. With the research on a corresponding prototype, the numerical simulation results are consistent with the test values. The accuracy of temperature calculation model is testified, which provides a reliable basis for the design and operation of power capacitor.

Influence of Void Transposition Structure on the Leakage Magnetic Field and Circulating Current Loss of Stator Bars in Water-Cooled Turbo-Generators

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.

Analytical Algorithm of Calculating Circulating Currents Between the Strands of Stator Winding Bars of Large Turbo-Generators Considering the Air Gap Magnetic Field Entering Stator Slots

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.

Analyses on Performances of Megawatt Double-Canned Induction Motors With Different Can Materials

The stator can and rotor can are unique structures in megawatt double-canned induction motors, and their materials have a great effect on the performance of this kind of motors. However, the influence of can materials on the performance is still unclear. One of the reasons is that the algorithm of can losses cannot consider the depth of penetration of different can materials currently. A new formula of can losses which can consider the depth of penetration is proposed. Taking a megawatt double-canned induction motor as an example, the influences of the stator can and rotor can on the losses, magnetization current, and performance are investigated when the stator can and rotor can are made of the stainless steel, alloy steel, and platinum-rhodium alloy. The theory to improve the performance by the can material is acquired. Based on the numerical simulation results, a corresponding prototype with the rational material is tested. The numerical simulation accuracy is validated with test values. The reliable basis will be provided for the selection of can materials and the optimization of performances in megawatt double-canned induction motors.

Influence of can materials on electromagnetic field of double canned induction motor

The can conductivity mainly influences the eddy current density in stator and rotor can; with the increase of can relative permeability, equivalent air gap and the reluctance of main magnetic circuit is reduced, the can flux density is increased, and the harmonic magnetic field in air gap has to be changed. Generally speaking, conductive material is benefit to the performances of double canned induction motor.