Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additi...Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additional heating in transformer parts. It leads to higher losses, early fatigue of insulation, premature failure and reduction of the useful life of the transformer. To prevent these problems, the rated capacity of transformer which supplies harmonic loads must be reduced. In this work, a typical 50 kVA three-phase distribution transformer with real practical parameters is taken under non-linear loads generated due to domestic loads. The core losses is evaluated using the three dimensional model of the transformer developed in FEM （finite element method） program based on valid model of transformer under high harmonic conditions. And finally a relation associated with core losses and amplitude of high harmonic order are reviewed ＆ analyzed and then a comparison is being carried out on the results obtained by different excitation current in transformer windings.展开更多
A substation is a part of an electrical generation, transmission, and distribution system. Substations generally have switching, protection and control equipment, and transformers. The low voltage distribution network...A substation is a part of an electrical generation, transmission, and distribution system. Substations generally have switching, protection and control equipment, and transformers. The low voltage distribution networks are supplied from MV/LV substation transformer that represent the last step of bringing transformation to the? low voltage and ensuring the? protection and monitoring of the network. There are three types of MV/LV substation: pole-mounted transformer substation, the substation in an envelope and substation in masonry. This paper presents a general description for different MV/LV substation and a methodology to design the various elements making up the public distribution substation (choice of the emplacement, engineering, power transformer, choice of MV cells, circuit breakers, fuses, disconnect? switch, conductors,...etc).展开更多
In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported fo...In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported for this equipment.In this work,a three-phase flow model based on the Eulerian multiphase model,coupled with a sliding mesh model is proposed for a countercurrent mixer-settler.Based on this,the dispersed phase distribution,flow pattern,and pressure distribution are investigated,which can help to fill the gap in the operation mechanism.In addition,the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane,which indicates that the material exchange in the mixing and settling chambers is simultaneous.Analysis of this variation at this location by a fast Fourier transform(FFT)method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations.Therefore,by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method,the state of the whole tank can be determined,which makes it promising for the design of control systems for countercurrent mixer-settlers.展开更多
Usually,rural areas can be electrified via three-phase distribution transformers with relatively large capacities.In such areas,low voltage lines are used for long distances,which cause power losses and voltage drop f...Usually,rural areas can be electrified via three-phase distribution transformers with relatively large capacities.In such areas,low voltage lines are used for long distances,which cause power losses and voltage drop for different types of consumers.Reducing losses and improving voltage profiles in rural distribution networks are significant challenges for electricity distribution companies.However different solutions were proposed in the literature to overcome these challenges,most of them face difficulties when applied in the conventional distribution network.To address the above issues,an applicable solution is proposed in this paper by installing a number of small-capacity distribution transformers instead of every single large-capacity transformer in rural areas.The proposed approach is implemented in the branch network of Al-Hoqool village,which belongs to the Nineveh distribution network.The network has been inspected on-site,drawn,and analyzed using the electrical systems analysis program(ETAP).The analysis showed that using the single-phase pole-mounted transformers can improve the voltage in the network’s end by 29%and enhance the voltage profile for all consumers.The analysis has also demonstrated that the modification can reduce the total power losses by 78%compared to the existing network.Concerning the economic aspect,the payback period for the proposed network is assigned to be 20 months.展开更多
Due to the multiscale character of wavelet transform, the method of wavelet transform de-noising (WTDN) is introduced. The WTDN method neither requires extra limit of frequency range for the processed signal, nor need...Due to the multiscale character of wavelet transform, the method of wavelet transform de-noising (WTDN) is introduced. The WTDN method neither requires extra limit of frequency range for the processed signal, nor needs a prior estimate of impulse response for an identified system, so it is especially suitable to de-noise the wide-band signal and the impulse response of a blind system. The numerical simulation results indicate that the WTDN method is reliable. The WTDN method was used to process the sampled data from a preamplifier coupled to a gas detector. The experimental results also show that the WTDN method can effectively improve the SNR of sam- pled data and enhance the accuracy in pole identification of the system.展开更多
文摘Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additional heating in transformer parts. It leads to higher losses, early fatigue of insulation, premature failure and reduction of the useful life of the transformer. To prevent these problems, the rated capacity of transformer which supplies harmonic loads must be reduced. In this work, a typical 50 kVA three-phase distribution transformer with real practical parameters is taken under non-linear loads generated due to domestic loads. The core losses is evaluated using the three dimensional model of the transformer developed in FEM （finite element method） program based on valid model of transformer under high harmonic conditions. And finally a relation associated with core losses and amplitude of high harmonic order are reviewed ＆ analyzed and then a comparison is being carried out on the results obtained by different excitation current in transformer windings.
文摘A substation is a part of an electrical generation, transmission, and distribution system. Substations generally have switching, protection and control equipment, and transformers. The low voltage distribution networks are supplied from MV/LV substation transformer that represent the last step of bringing transformation to the? low voltage and ensuring the? protection and monitoring of the network. There are three types of MV/LV substation: pole-mounted transformer substation, the substation in an envelope and substation in masonry. This paper presents a general description for different MV/LV substation and a methodology to design the various elements making up the public distribution substation (choice of the emplacement, engineering, power transformer, choice of MV cells, circuit breakers, fuses, disconnect? switch, conductors,...etc).
基金the National Natural Science Foundation of China(21978198)for financial support。
文摘In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported for this equipment.In this work,a three-phase flow model based on the Eulerian multiphase model,coupled with a sliding mesh model is proposed for a countercurrent mixer-settler.Based on this,the dispersed phase distribution,flow pattern,and pressure distribution are investigated,which can help to fill the gap in the operation mechanism.In addition,the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane,which indicates that the material exchange in the mixing and settling chambers is simultaneous.Analysis of this variation at this location by a fast Fourier transform(FFT)method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations.Therefore,by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method,the state of the whole tank can be determined,which makes it promising for the design of control systems for countercurrent mixer-settlers.
文摘Usually,rural areas can be electrified via three-phase distribution transformers with relatively large capacities.In such areas,low voltage lines are used for long distances,which cause power losses and voltage drop for different types of consumers.Reducing losses and improving voltage profiles in rural distribution networks are significant challenges for electricity distribution companies.However different solutions were proposed in the literature to overcome these challenges,most of them face difficulties when applied in the conventional distribution network.To address the above issues,an applicable solution is proposed in this paper by installing a number of small-capacity distribution transformers instead of every single large-capacity transformer in rural areas.The proposed approach is implemented in the branch network of Al-Hoqool village,which belongs to the Nineveh distribution network.The network has been inspected on-site,drawn,and analyzed using the electrical systems analysis program(ETAP).The analysis showed that using the single-phase pole-mounted transformers can improve the voltage in the network’s end by 29%and enhance the voltage profile for all consumers.The analysis has also demonstrated that the modification can reduce the total power losses by 78%compared to the existing network.Concerning the economic aspect,the payback period for the proposed network is assigned to be 20 months.
文摘Due to the multiscale character of wavelet transform, the method of wavelet transform de-noising (WTDN) is introduced. The WTDN method neither requires extra limit of frequency range for the processed signal, nor needs a prior estimate of impulse response for an identified system, so it is especially suitable to de-noise the wide-band signal and the impulse response of a blind system. The numerical simulation results indicate that the WTDN method is reliable. The WTDN method was used to process the sampled data from a preamplifier coupled to a gas detector. The experimental results also show that the WTDN method can effectively improve the SNR of sam- pled data and enhance the accuracy in pole identification of the system.
