Prediction of Core Losses of Three-Phase Distribution Transformer

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.

Core value of the Chengjiang fauna:formation of the animal kingdom and the birth of basic human organs

Well known for its abundant and extraordinary soft-tissue fossils,the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth.The large-scale survey and exploration of the fauna by Chinese paleontologists,partly in collaboration with international scientists,over the past 30 years can be broadly divided into three stages.In the first decade since 1984(19841994),a large number of invertebrates,including basal animals and the protostomes of the early animal tree were discovered,but the subkingdom Deuterostomia was completely unknown.Then in the second decade(19952005),the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals(TPTEA,including basal animals,protostomes and deuterostomes),for the first time.In the third decade(after 2005),the academic community began to think about the internal relationships between the formation of TPTEA and the multiepisode Cambrian explosion,leading to the new hypothesis of the three-episode Cambrian explosion.The Chengjiang fauna is important for deciphering the fauna structure,paleoecological environment,and so on.However,its core academic values mainly rest on two aspects.Firstly,The Chengjiang fauna,as the main phase witness of the Cambrian explosion,has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time.The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion:a step-wise divergent evolution of animals,from basal to highly advanced groups,lasting about 40 million years.In the first phase,it gave birth to a bulk of basal animals(including some now extinct“animal”groups)in the latest Ediacaran,probably including some pioneer protostomes.The second phase took place in the first epoch of the Cambrian period(Terreneuvian),giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals.The third phase proceeded in Cambrian Epoch 2(represented by the Chengjiang fauna),which not only maintained the prosperity of basal animals and protostomes,but also,more importantly,gave birth to all the main phyla of the subkingdom Deuterostomia.Thus,the rudimental framework of the whole TPTEA has been shaped,with the termination of the major innovation events of the Cambrian explosion.Here,we discussed the evolutionary properties of Ediacaran biota,small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups.The order Myllokunmingiida is the only known oldest vertebrate,while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes;Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates;and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes.The second core value of the Chengjiang fauna is of profound humanistic and philosophical significance:the discoveries of the‘first gill openings’,‘first brain’,‘first vertebrae’and‘first heart’provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s“The Descent of Man”.In addition,the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.

三相5柱式铁心双反星形晶闸管整流电路分析

从理论上分析三相5柱式铁心,二次双反星形接线整流变压器工作原理。利用3倍频磁通,通过边柱构成磁路,产生反电势,保证相邻两相电压平衡。从而使三相零式晶闸管并联同时导通。获得6脉波整流。它替代了带平衡电抗器三相3柱式铁心二次双反星形三相零式晶闸管并联整流主电路。实现了取消平衡电抗器。具有节省材料,降低损耗,制造、维修方便,减少故障点等优点,获得节能、降耗的效果。并结合应用实际,计算了电压畸变率。为工程设计提供了理论依据。并具有一定的实用参考价值。

三相五柱式铁心变压器Y/△绕组联结时的磁通计算

本文中作者找到了三相五柱式铁心变压器轭部磁通的对称性,利用其对称性对磁通计算进行了公式解答,得到了三相五柱式铁心变压器Y/△绕组联结时的磁通计算公式。

三相五柱式非晶配电变压器铁心内部磁密分布

研究了三相五柱式结构非晶合金卷铁心在不同励磁磁密下内部的磁密分布。在低励磁磁密下,铁心内部的实际磁密沿叠厚方向并不均匀,由内侧到外侧逐渐降低,当励磁磁密为0.8 T时,内框铁心和外框铁心的内外侧实际磁密差值最大分别可达0.44 T和0.28 T。随着励磁磁密的增高,各个铁心内部实际磁密分布趋于平缓,内外侧实际磁密差值也随之减小。各个铁心内部的实际磁密还存在明显的三次谐波分量,其含量随着励磁磁密的增高而增高。在低励磁磁密下,各个铁心内部磁密的三次谐波分布较为平缓,随着励磁磁密接近饱和,三次谐波分布变得不均匀,其含量由内侧到外侧逐渐降低,在励磁磁密为1.5 T时,内框和外框铁心的内外侧磁密三次谐波含量差值达到了4.3%和4%。对三相五柱铁心三次谐波来源进行了分析。