Advanced Materials Research Vols. 986-987

Abstract: In this paper, the size of winding electromagnetic force after short circuit has been acquired through leakage field calculation and analysis on power transformer, and based on the computation results, the radial stability experimental results of large capacity power transformer inner winding short-circuit model were compared to the simulation values to guide actual product analysis and checking. With the accumulated simulation experience on this model, then a type of sfz9-80MVA power transformer inner coil static and dynamic stability has been checked to confirm the radial instability phenomenon could whether or not occur on this product.

Abstract: Reducing tower ground’s impulse grounding resistance can prevent the power lines from lightning effectively. The concept of impulse grounding resistance is described. Calculation formula of the impulse grounding resistance for ground electrode in different Conformations is derived with impulse coefficient method. The conformation of the ground electrode is improved according to the theory of impulse grounding resistance is decreased when the effective area of the electrode is reduced, using ETAP for simulation of the improved ground electrode. The results show that the impulse grounding resistance of the improved ground electrode can be reduced to 41.1% of the original, and safety margin is larger in practical engineering.

Abstract: At first, this paper introduce some current tests of secondary circuit in intelligent substation, then, design a performance analysis system of secondary circuit in intelligent substation based on NI platform. This kind of system analyzes analog and digital quantity messages for getting the performance of secondary system by algorithms, so that working personnel can grasp the performance comprehensively. Meanwhile, a prototype is developed to be applied in an unused intelligent substation, and the result is satisfied.

Abstract: Photovoltaic grid-connected power generation is the inevitable development trend of solar photovoltaic systems,grid inverter is an essential part of photovoltaic grid-connected power generation. With the developed three phase current type PWM inverter device as the research object, and symmetry rules sampling method is applied to the inverter, through the method combined by the computer simulation and experiment research, the device was verified by simulation and experimental .The results show that: This method could not only effectively reduce the DC side inductance volume of the current-mode PWM inverter , and it could make output AC currents sinusoidal and in phase with grid voltages, but also improve the efficiency of the system, it will be more suitable for photovoltaic grid-connected.

Abstract: Current-voltage (I-V) and impedance spectroscopy are employed to investigate the polarity of TiO₂ varistor. It is found that TiO₂ varistor shows typical polarity behavior, i.e., the I-V curve is asymmetric, the impedance slightly increases, and the capacitance slightly decreases when the bias voltage reverses. The effects of measuring frequency on impedance spectroscopy are systematically investigated. The results indicate that TiO₂ varistor behaves considerable polarity under low sweeping frequency. High sweeping frequency (over 10³ Hz) counteracts the polarity behavior. A model of micro-polarized zone is tentatively proposed to clarify the polarity behavior of TiO₂ varistor.

Abstract: Construction of large and medium-sized program-controlled switches be placed strictly in accordance with national standards Professional program-controlled switchboard in the room, general will not be affected by lightning overvoltage and harm of operating over voltage. And small PABX are commonly used for smaller enterprises and institutions, such enterprises are unlikely to build professional for program-controlled switchboard room. Mostly I placed it on the corner of the Office or the Office area, convenient pin-outs. As a result of this device is undersized and lower prices, lightning protection concepts and enterprises and institutions to understand enough, it will not attach too much importance to. During the thunderstorm-prone season often makes their lightning overvoltage damage, direct economic loss was not too large, but the indirect economic losses are direct losses many times. This article in view of the characteristics of this equipment, according to the wiring form of power supply system using proper surge protection devices, equipotential bonding, shielding and grounding, and other combinations of several methods, and do not put too much financial and material resources to avoid accidents from happening, the various types of losses to a minimum.

Abstract: This paper proposed the electron density of time series by using the Siesta software to calculate the weak electrical signals of ginseng molecule, combining with the lifting scheme DWT to remove ginseng molecular spatial redundancy. For the acquisition and identification of weak electrical signals of ginseng molecule in physical environment , based on the analysis of collection and identification’s principles, the noise coefficient is removed to reconstruct the signal and retain the useful signal components through applying the multi-decomposition of DWT transform to divide weak electrical signals of ginseng molecule into wavelet coefficients of different scales. The experimental results show that the multi-resolution analysis of DWT transform is performed for the weak electrical signal of ginseng molecule with different rhythms and different frequency ranges, and the weak electrical signal size of ginseng molecule before and after compression, the percentage of high frequency coefficients set to zero, and the average energy percentage after compression are, respectively, increased to 77.73%, 46.88%, and 99.99%. This algorithm operates fast enough to ease hardware implementation, providing an effective method for lossless compression of the weak electrical signals of ginseng molecule.

Abstract: This paper presents a new modeling method, based on the physical structure of the IGBT module, considering the distribution parameters of high frequency.This method is simple and the wideband model has physical meaning, by choosing suitable model initial parameters as well as the objective function which use the iterative optimization algorithm to solve the model parameters.Comparing the wideband model with the measured results ,the wideband model maintain high accuracy in the range of 100KHz ~ 20MHz.

Abstract: This paper takes a two-stage three-phase inverter as an example. The efficiency calculation method is analyzed in detail for the inverter, and the power losses calculation method is proposed for the second stage under SVPWM. A 10kW/380V inverter system is designed. The system efficiency and the power losses for every part are theoretically calculated. Finally, experiments on a 10 kW prototype are carried out to verify the calculation.

Abstract: To study the influence of test transformer capacity on insulator leakage current acquisition results, leakage current acquisition experiments with the clean and dry insulator and the water drops attached insulator were conducted based on the sampling resistor method and the test transformers of different capacities whose models are YDTW-1200 kVA/300 kV, YDTW-50 kVA/250 kV, YDTW-10 kVA/100 kV, YDJ-5 kVA/50 kV respectively. To make the results more reliable, sampling resistors with different resistances, 10 Ω, 100 Ω, and 1 kΩ, were used to collect the leakage current. The root-mean-square (RMS) values of the leakage current, the ratio of the 3rd harmonic to the fundamental (K₃) and the 5th harmonic to the fundamental (K₅) were extracted from the measured data. And it was discovered that the transformer capacities has a very slight influence on the leakage current RMS value but has a great impact on the value of K₃ and the K₅. The maximum K₃ are approximately 3 times of the minimum K₃ and the maximum K₅ are approximately 9 times of the minimum K₅.