According to the incomplete technical features of the traditional low-frequency transformer (LFT) and the existing power electronic transformer (PET), especially in terms of the function, the voltage level, and the cost, the core flux modulation of the hybrid transformer was achieved through the establishment of auxiliary windings combined with connection of the power electronic converter (PEC). For the hybrid transformer, a three-port converter topology is proposed and the strategy applicable for the dc bias compensation by connecting the converter is presented. By utilizing the dc modulation magnetic flux, the dc bias problem could be directionally compensated. The exciting current could be improved significantly and maintained at a steady state. The method proposed does not change the connection of the transformer external circuit and does not increase the peripheral device of the transformer, which provides a new way to solve the problems of magnetic state fluctuation and excitation current distortion.
This paper design three distribution devices for the strong and smart grid, respectively are novel transformer with function of dc bias restraining, energy-saving contactor and controllable reactor with adjustable intrinsic magnetic state based on nanocomposite magnetic material core. The magnetic performance of this material was analyzed and the relationship between the remanence and coercivity was determined. The magnetization and demagnetization circuit for the nanocomposite core has been designed based on three-phase rectification circuit combined with a capacitor charging circuit. The remanence of the nanocomposite core can neutralize the dc bias flux occurred in transformer main core, can pull in the movable core of the contactor instead of the traditional fixed core and adjust the saturation degree of the reactor core. The electromagnetic design of the three distribution devices was conducted and the simulation, experiment results verify correctness of the design which provides intelligent and energy-saving power equipment for the smart power grids safe operation.
There is a 35kV series reactor short-circuit fault on the low-voltage side of one main transformer in a 500kV substation.The preliminary analysis concludes that there is an inter-turn short circuit occurred in A-phase of the series reactor.Although there is no fault recorder installed on the low-voltage side of all the main transformers,the fault developing process is indirectly analyzed and deduced by the fault recorder on the mid-voltage side by symmetrical component method.The conclusion of the paper is that there is not only an inter-turn short circuit occurred,but also an inter-phase short circuit occurred in the series reactor,which eventually leads to the breaker trip triggered by the protection.The suggestion for protecting equipment is also proposed in the paper.
For an optimal design of synchronous reluctance motor of permanent magnet assisted synchronous reluctance motor (PMA-SynRM), the significant challenge are rotor topology and the choice of numerous design variables. A novel rotor structure of PMA-SynRM is proposed to achieve that the reluctance torque and the magnetic torque reach a maximum value at a close current phase angle by adjusting the position of the permanent magnet and the structure of flux barrier. Meanwhile, an asymmetrical rotor flux barrier and flat tips are adopted to reduce the torque ripple. Then, combined with the Taguchi method, the sequential subspace optimization method (SSOM) is implemented for proposed PMA-SynRM by using the differential evolution algorithm and pareto evaluation. Finally, the finite element analysis (FEA) is carried out to validate the technical advantages of proposed PMA-SynRM topology and design methods.
A detailed research on the magnetic properties, preparation, and application of two-phase composite magnetic material was conducted in this paper. Firstly, in order to obtain the characteristics of high remanence and low coercivity, a micro field mathematical model of hysteresis was established and the magnetization model of this material was determined on the basis of micro magnetic theory. Secondly, the relationship between remanence and coercivity was analyzed and the preparation technology of the material was proposed from the perspective of the elemental composition, the heat treatment, and the other steps. Finally, after mastering the magnetization characteristic, conversion and control mechanism of the material, a new power transformer with function of DC bias compensation based on the two-phase composite magnetic material was proposed. The simulation and experimental results showed that the transformer could achieve a good compensation for the DC bias problem by using material remanence, which provides intelligent and energy-saving electrical equipment for the electric network safe operation.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9707
Due to its low harmonic, high efficiency, and high power factor (PF), the multipulse autotransformer has been frequently used in the aviation sector. Many studies have been carried out on the theoretical calculation and simulation analysis of the autotransformer. However, the practical application of the multipulse rectifier in the practical engineering field is inevitable. This paper investigates an 18-pulse rectifier power supply of 11 kW being constructed using a multipulse autotransformer to suppress the harmonics of a radar power system, in which the parameters of the various parts are designed in detail, and test results are simulated using MATLAB/Simulink software. The actual test suggests that, at the rated condition, the PF of the rectifier is 0.99, the total harmonic distortion of the input current is below 6.7%, and the efficiency is more than 96%. The power supply is successfully applied to the radar power supply system of a large transport aircraft, and meets the requirements of an environmental test. Furthermore, the results also provide powerful application support for the power supplies and distribution systems in other fields.
Aiming at design defects of main connection in some substations leading to compelled power interruption under running or overhaul,this paper analyzes the reasons why four-section single bus configuration for three main transformers adopted by 10 kV connection and proposes measures to extend the third main transformer,install disconnector for main transformer on breaker,rearrange operation order of main transformers and enhance power supply reliability.
It is well known that clock skew minimization becomes critical in high-performance VLSI designs. In this paper, the assignment of adjustable delay buffers(ADBs) is applied to minimize the clock skew in a buffered clock tree in a multi-voltage mode design. Given a buffered clock tree, based on the assignment flexibility of the delay value on an ADB, bottom-up ADB assignment is firstly proposed to insert ADBs to minimize the clock skew by assigning the delay values of the inserted ADBs for each power mode. Furthermore, bottom-up ADB elimination is proposed to eliminate the redundant ADBs to minimize the number of the inserted ADBs in a multi-voltage mode design while maintaining the minimized clock skew. Compared with Su's heuristic algorithm and Lim's optimal algorithm, the experimental results show that our proposed algorithm uses less CPU time to reduces 9.3% of the used ADBs and 1.3%~1.6% of the average latency on the average, respectively.
Abstract Distribution transformers are important power conversion equipment, whose safe and reliable operations affect the power supply quality of the distribution network. In order to analyze the lightning strike fault of distribution transformers, some more reasonable protection measures of transformers could be put forward. In this paper, a 35kV distribution transformer under the lightning strike is taken as the research object. Firstly, the lightning overvoltage model of the distribution transformer was established with the method of the double exponential model. Secondly, through the simulation of the distribution transformer, it was found that the electromagnetic transient distribution change dramatically, which will quickly cause the winding current flickering and form the winding overvoltage. Finally, through the voltage distribution law and the magnetic flux distortion of the transformer, it can be seen that the lightning overvoltage has a serious effect on the electromagnetic parameters of the transformer. The protection scheme is briefly analyzed, which has a guiding significance for the lightning protection design of distribution transformers.
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