Design Optimization of a Self-circulated Hydrogen Cooling System for a PM Wind Generator Based on Taguchi Method

With the continuous improvement of permanent magnet(PM)wind generators'capacity and power density,the design of reasonable and efficient cooling structures has become a focus.This paper proposes a fully enclosed self-circulating hydrogen cooling structure for a originally forced-air-cooled direct-drive PM wind generator.The proposed hydrogen cooling system uses the rotor panel supports that hold the rotor core as the radial blades,and the hydrogen flow is driven by the rotating plates to flow through the axial and radial vents to realize the efficient cooling of the generator.According to the structural parameters of the cooling system,the Taguchi method is used to decouple the structural variables.The influence of the size of each cooling structure on the heat dissipation characteristic is analyzed,and the appropriate cooling structure scheme is determined.

Cooling System Design Optimization of an Enclosed PM Traction Motor for Subway Propulsion Systems

This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

Coupled Electromagnetic-Thermal-Fluidic Analysis of Permanent Magnet Synchronous Machines with a Modified Model

The researches on the heat generation and dissipa-tion of the permanent magnet synchronous machines(PMSMs)are integrated problems involving multidisciplinary studies of electromagnetism,thermomechanics,and computational fluid dynamics.The governing equations of the multi-physical prob-lems are coupled and hard to be solved and illustrated.The high accuracy mathematical model in the algebraically integral con-servative forms of the coupled fields is established and computed in this paper.And the equation coupling with the fluid flow and the temperature variation is modified to improve the positive definiteness and the symmetry of the global stiffness matrix.The computational burden is thus reduced by the model modification.A 20kW 4500rpm permanent magnet synchronous machine(PMSM)is taken as the prototype,and the calculation results are validated by experimental ones.

Deqi effect for treating knee osteoarthritis using manual acupuncture:A network meta-analysis

Objective: To explore whether the deqi effect affects the effectiveness of manual acupuncture for treating knee osteoarthritis by a network meta-analysis(NMA).Methods: Eight databases were searched for relevant published studies since inception through January 2021. Randomized control trials that compared manual acupuncture with deqi, manual acupuncture without deqi, and conventional treatment of western medicine were included. Languages were limited to English and Chinese. Two authors independently selected eligible studies, assessed methodological quality and the effects of deqi, and extracted outcome data. The mean difference(MD) and standardized mean differences(SMDs) with 95% confidence intervals(CIs) were calculated by Stata 15.0 to conduct an NMA based on a frequentist framework.Results: Fourteen trials with a total of 1868 subjects were included. The direct and indirect comparisons were authentic, according to inconsistency tests. The Western Ontario and McMaster Universities Osteoarthritis Index(WOMAC) pooled results indicated that there was no significant effect of deqi(SMD=-0.23, 95% CI [-0.81, 0.35]). The pooled results of visual analogue scale(VAS) were similar to those of WOMAC(MD=-0.53, 95% CI [-1.03, 0.02]).Conclusion: As a summary of the currently available research, the NMA results indicated that deqi effect might not be the crucial factor for the effectiveness of manual acupuncture.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

3D Finite Element Analysis of the Stray Loss in Power Transformer Structure Parts

In order to analyze the leakage magnetic field and stray loss in power transformer, leakage magnetic field and stray loss in structure parts of a power transformer are calculated by three-dimensional (3-D) non-linear time harmonic finite element method (FEM). The results show that stray loss and loss density in structure parts are large and which may lead to local overheating and affect performance of the transformer. The magnetic shields are used to reduce the stray loss and loss density of power transformer. Effects of these shields on stray loss and loss density of structure parts are discussed. The results show that stray loss and local overheating can be reduced and eliminated effectively by adding magnetic shields. It provides some references for the analysis of stray loss and optimization design in transformer.

Calculation and Design of Dry-type Air-core Reactor

Based on the method of compound and additional conditions under the conditions of the equal temperature rise and the equal potential drop (P.D.) of resistance, the application of design software of dry-type air-core reactor is introduced in this thesis. The analytical methods of the inductance are also given. This approach is proved entirely feasible in theory through the simplification with Bartky transformation, and is able to quickly and accurately calculate reactor inductance. This paper presents the analytical methods of the loss of dry-type air-core reactor as well.

Effects of DC Magnetic Bias on the Magnetic and Sound Fields of Transformer

DC bias current flowing into the neutral point of power transformer will seriously affect the normal operation of AC power system. In this paper, exciting current, harmonic component of the excitation current, magnetic flux density and noise of transformer were analyzed when the transformer is in the no-load operation state based on field-circuit coupled method. Through the calculation and analysis, some reference bases are provided for design of transformer.

Corrigendum to “Deqi effect for treating knee osteoarthritis using manual acupuncture: A network meta-analysis” [J Tradit Chin Med Sci 8 (2021) 343e352]

The authors regret<In previous version,we made several errors.The correct descriptions are as follows.>.[Results]They used manual stimulation of the needles:one clearly required deqi in the intervention method;6 one achieved deqi if possible;14 one executed a brief manipulation at the beginning and the end of the treatment;31 and 10 RCTs described the manipulation to elicit deqi.29,30,32-39 In three MAOD groups,one used Streitberger non-penetrating needle,31 the patients in Wang et al.’s experiment were given fine needle,shallow insertion and weak stimulation without manipulation to avoid Deqi,32 whereas other one used needle inserted into acupoints but did not use any method of stimulation.40 In the CTWM,11 RCTs included routine pharmacological therapy,and one RCT14 considered waiting lists in which patients were allowed to receive oral NSAIDs if necessary.Twelve RCTs recorded WOMAC,and ten RCTs used VAS.