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Head smut, caused by Sporisorium reilianum [(Kuhn) Langdon and Fullerton], is a major disease of sorghum. Seed treatment is considered to be the most effective way to control the disease; however, the pathogen can infect at the seedling stage and the infected plant will not display symptoms until the reproductive stage is reached. The evaluation of the efficacy of seed treatments is time consuming and is dependent upon visible symptoms. Polymerase chain reaction (PCR) methods have the ability to identify pathogens and diagnose their presence at an early stage of infection. In this study, the S. reilianum-specific primer SR3 was used for PCR detection pathogen. We optimized temperature, humidity, and spore quantity test conditions and were able to achieve >88% infection incidence in sorghum seedlings. Sorghum seeds were soaked in various concentrations of tebuconazole and planted for 7 days in soil containing 0.2% teliospores. The efficacy of tebuconazole against S. reilianum was evaluated by PCR and recorded as disease incidence. Results indicated that the reduction in disease incidence after exposure to 0.15, 0.30, 0.45, 0.60, and 0.75 μg/mL tebuconazole was 6.24, 37.48, 67.74, 81.24, and 93.74%, respectively. Significant differences between the concentrations of tebuconazole were observed. The PCR assay represents a valuable tool for evaluating the efficacy of fungicide seed treatments for the control of S. reilianum in sorghum under laboratory conditions.

In this paper, taking a high-speed permanent magnet generator (HSPMG) as an example, the unbalanced load limit of HSPMG is studied based on the analysis of the electromagnetic and temperature fields of the generator. The influences of different degrees of unbalance currents on the losses of the generator are studied, and the influence mechanisms of unbalance currents on the losses of the rotor sleeve and permanent magnet are revealed. Based on the theory of fluid dynamics and heat transfer, the temperature field distribution of HSPMG under the unbalanced load condition is studied, and the non-linear relation between the current unbalance and the temperature field of HSPMG is determined. Finally, the load unbalance resistant limit of HSPMG is determined. These conclusions can provide a reference for determining the unbalanced load limit of HSPMG. It is also helpful for improving the reliability of HSPMG under abnormal working conditions.

The turn-to-turn faults (TTF) are also inevitable in split-winding transformers. The distorted leakage field generated by the TTF current results in large axial forces and end thrusts in the fault windings as well as affecting other branch windings normal operation, so it is of significance to study TTF of split-winding transformers. In this paper, the characteristics analysis of the split-winding transformer under the TTFs of the low voltage winding at different positions are presented. A 3600 KVA four split-windings transformer is taken as an example. Then, a simplified three-dimensional simplified model is established, taking into account the forces of the per-turn coil. The nonlinear-transient field-circuit coupled finite element method is used for the model. The leakage field distribution under the TTFs of the low voltage winding at different positions is studied. The resultant force of the short-circuit winding and the force of the per-turn coil are obtained. Subsequently, the force and current relationship between the branch windings are analyzed. The results show that the TTF at the specific location has a great influence on the axial windings on the same core, and the distorted leakage magnetic field will cause excessive axial force and end thrust of the normal and short-circuit windings. These results can provide a basis for the short-circuit design of split-winding transformer.

Power rectifiers are very necessary in the wind power generation systems since they are the necessary channels that link the generator and power gird together. However, they have some effects on the permanent magnet wind generator due to their work on fast on-off transitions. Taking an 8kW 2000r/min wind-driven permanent magnet generator as an example, the system model and external circuit were established. Firstly, based on the field-circuit coupling calculation method, the voltage and current harmonics have been studied respectively when the generator was connected to rectifier loads and pure resistance loads, so did the total harmonic distortion. The mechanism of harmonic impacted by rectifiers was revealed. Secondly, combined the harmonic electromagnetic field theory, the stator core loss, armature winding copper loss and rotor eddy loss were analyzed when the generator connected different loads. Furthermore, according to the definition of nonlinear circuits PF, the numerical analysis method was adopted to calculate the power factor when the generator connected two loads respectively. The change mechanism of PF impacted by rectifiers has been revealed. In addition, the temperature field model has been established and the generator temperature was also analyzed. The temperature distributions were obtained when the wind generator was connected to different loads. Then, the relationship between losses and temperature was combined, the change rules of permanent magnet temperature by the eddy current loss were studied under different load. At last, it can prove that the rectifiers have influences on both electromagnetic field and temperature field through comparing the simulation results with experimental test data.

An alloy sleeve is often used to prevent the damage to rotor magnets caused by the large rotational centrifugal forces within a high speed permanent magnet generator (HSPMG). It should be thick enough to satisfy the mechanical strength needed. The generator main reluctance mainly focuses on the rotor sleeve, so sleeve permeability has much influence on the magnetic circuit and generator performance. Since a finite element simulation for every machine is time consuming and complicated, a simple analytical model of general surface-mounted permanent magnet machines has been established within this paper. Additionally, an analytical method is also given in full, so that optimal sleeve permeability can be obtained for a set of parameters for a given machine. In order to accurately establish the variation of the pole-to-pole leakage flux in the air gap and rotor sleeve of the generator with different permeability sleeves, an iterative method is proposed. The leakage flux, main flux, magnet performance and their relationships with the generator have been studied further, and the influence mechanism of sleeve permeability on the generator performance has been determined. Based on the research of the above influence factors, the optimal sleeve permeability is obtained by using the analytical method. Comparing the results of the analytical method and finite element method, they are in close agreement; hence the rotor sleeve with optimal permeability can improve the generator performance.

A power converter is very necessary in the system of high-speed permanent magnet generators (HSPMG), since the frequency of the output electrical energy is generally hundreds of Hertz or even more than 1000 Hz. However, the converter with switches in fast on–off transitions will have some effects on the generator and, therewith, some current harmonics will be also induced in the device. Taking a 117 kW 60 000 r/min HSPMG as an example, the harmonics in this generator were analyzed. And then, the voltage harmonic content, the current harmonic content, and the current total harmonic distortion could be obtained. In addition, stator core losses and rotor eddy current losses were analyzed comparatively, and the influence of the converter on the generator power factor was further studied. Based on the 3-D coupling field between fluid and temperature, the temperature distributions were obtained when the generator was connected to different loads, and the influence of the rectifier on the generator temperature field could be obtained, which was also compared with the test data.

A new approach has been proposed to evaluate the influence of the transverse edge effect of high-temperature superconducting (HTS) linear induction motor (LIM) in this paper. Taking a 3.5 kW single-sided HTS LIM for an example, the cross-flux density distributions were analyzed by analytical method. Based on results mentioned above, a new transverse coefficient was proposed to evaluate the influence of the transverse edge effect on the cross-flux density distribution. The influences of the motor configurations and parameters on the transverse coefficient were also investigated. The 3-D finite-element method was adopted to verify the accuracy of the presented analytical method.

Alloy rotor sleeves are used extensively in high-speed permanent-magnet machines since they could fasten the permanent magnets availably. However, it is inevitable that eddy-current losses will be generated in the sleeve, which may make the permanent magnets overheated. In order to reduce the rotor eddy-current losses, this paper focuses on the influence of the rotor-sleeve electromagnetic characteristics. Taking a high-speed permanent-magnet generator (HSPMG) as an example, the variations of output performance and rotor eddy-current losses were analyzed when the generator adopts the steel sleeve and the copper-iron alloy sleeve, respectively, and therewith, the principles of the variations were exposed. Then, the rotor eddy-current losses were further analyzed when the generator sleeve conductivity was changed. The worst range of the sleeve conductivity was also given, in which the rotor eddy-current losses were the largest. Additionally, the increase of the sleeve permeability could reduce the main magnetic circuit reluctance and improve the operating point of permanent magnets. On the other hand, it can increase the pole-to-pole flux leakage dramatically. So, the generator performance should be analyzed by considering the two factors when the rotor-sleeve permeability was different.

In a high-speed permanent-magnet generator (HSPMG), an alloy sleeve is often used to prevent damage to rotor magnets caused by the large rotational centrifugal forces. However, eddy-current losses appearing in the sleeve increase the generator working temperature, which may reduce the generator performance and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme designed with low eddy current losses is necessary, and a rotor structure with copper plating is presented in this paper. The two-dimensional mathematical model of a 117 kW, 60 000 rpm HSPMG is established, and the electromagnetic field in the generator is calculated using the finite element method. The results show the effectiveness of the copper plating in reducing the eddy current losses in the rotor, and the influences of the sleeve thickness and the copper layer thickness on rotor eddy current losses are analyzed. Using the fluid-thermal coupling method, the temperature distribution of the generator with different copper layer thicknesses is comparatively analyzed based on the theories of fluid mechanics and heat transfer. The relationship between the temperature and the copper layer thickness is obtained, and finally the temperature of the permanent magnets, which is the part most seriously affected by the temperature, is given with different copper layer thicknesses. The obtained conclusions may provide useful reference for the design and research of HSPMG.