Transformer design and application considerations for nonsinusoidalload currents

The use of adjustable-speed drives requires transformers capable of withstanding high levels of harmonic currents under normal operating conditions. Experience has been that overheating problems are much more common with dry-type transformers than with liquid-filled transformers. Transformer insulation life is determined by the hot spot temperature but confirmation of hot spot temperature rise is one performance characteristic which is ignored in industry standards. This is especially important for transformers rated for nonsinusoidal load currents. The design of transformers for nonsinusoidal load currents should include an analysis of the eddy loss distribution in the windings and calculation of the hot spot temperature rise. Calculations and thermal tests giving only average winding temperature rises are not sufficient. Thermal tests with nonsinusoidal currents and measurements of hot spot temperature rises are extremely difficult on large transformers. The combination of testing and analysis may be the only economically practical approach. Analysis indicates that the dry type transformer hot spot temperature is very sensitive to the eddy loss magnitude and distribution. The Underwriters Laboratories Inc. (UL) K-factor rated dry type transformer and the recommended practices given in ANSI/IEEE C57.110 are reviewed. When purchasing transformers subject to nonsinusoidal load currents, considerations should be given to the manufacturer's development program and capability to calculate the eddy loss distribution and hot spot temperatures     

基于供电可靠性的中心城区配网网络优化

中心城区配电网网络结构决定了停电的影响时间和范围。针对上海中心城区的发展特点,提出了基于供电可靠性的配电网网络优化方法。通过配电网架接线方式的调整,消除了变配电站出线并仓情况;提高变电站10 kV出线的平均负载率并消除了重载线路;合理均衡了变电站之间、变电站内主变之间的负荷分配;减少故障停电时间和电缆陪停时间,从而达到提高配电网供电可靠性的目的。     

计及有序充电的配电变压器扩展规划建模

针对集群电动汽车接入引起的配电容量不足及投资经济性问题,首先对纯住宅区和商住两用场景下的典型配电变压器基础负荷曲线进行聚类分析,根据负荷特性对电动汽车充电负荷进行细化建模,并考虑负荷的发展趋势,建立起配电变压器综合负荷的自然增长模型。在此基础上,根据有序充电和新建配电变压器2种手段的互补优势,提出了计及有序充电的配电变压器扩展规划方法,以投资方案全寿命周期成本最小为目标,建立长时间尺度下的组合决策优化模型,确定有序充电和新建配电变压器的最佳组合形式。以某新建居民小区为例,建立该小区配电变压器的负荷自然增长模型,并采用所提组合决策优化模型,确定小区最佳的有序充电控制应用时间、新建配电变压器投运时间、配电变压器容量和型号,最终通过多个影响因素的对比分析,验证了所提方法的有效性与经济性。     

A test of parallel operating three-phase transformers with different transformation factrs

This article presents the results of testing two parallel operating three-phase power transformers with different transformation factors. The practical operation of power engineering systems often makes it necessary to split up the substation transformer capacity, which usually requires installing two parallel transformers instead of one, though with the same total power. The problem arises from this replacement of how to ensure uniform load distribution between the transformers. In the case of similarly designed transformers of equal power uniform load distribution is ensured automatically due to symmetrical parallel circuits. However, if differently designed transformers with different transformation factors are enabled in parallel, the uniformity of load distribution between them will be violated. It has been proven by testing that, with increasing total load, parallel operating transformers with very different transformation factors decrease the consumption of current by windings of the transformer with a higher transformation factor.     

GPRS技术在配电变压器通信中的应用

文章着重研究了采用GPRS技术以实现对10 kV配电变压器数据的采集、传输,以及问题的处理。负控中心对采集到的变压器各项数据进行分析和统计计算后,通过负荷分配、负荷转移以及电容器投退等方式,实现对网络和设备运行状态的优化选择,确保城市和乡村10 kV配电网络处于最佳安全和经济运行状态。     

一种配电变压器热评估方法

针对配电变压器运行中的负荷特殊性和热传递微分方程参数难以确定的问题,提出了一种配电变压器热评估方法,分析了配电变压器热传递的动态过程,指出了传统神经网络难以适用于配电变压器热评估当中,考虑配电变压器三相负载系数,建立了配电变压器LSTM型循环神经网络热评估模型,对配电变压器顶层油温进行预测,达到配电变压器热评估的目的。算例表明:预测结果比热传递微分方程更接近实际情况,验证了该方法的有效性和实用性。     

基于半消声环境声学测试平台的干式配电变压器噪声特性负载因素影响研究

为了研究用户负载因素对干式配电变压器噪声的影响,分析了负载因素与变压器噪声之间的理论关系,以1台800 kVA三相干式配电变压器为原 型,对负载率、运行电压升高、不平衡负载、谐波负载等多种常见工况下的变压器噪声水平进行了实验研究,对比分析了不同工况下干式配电变压器 的噪声水平变化。结果表明,谐波负载及运行电压升高是负载因素中导致干式配电变压器噪声显著变化的主要因素,负载率与不平衡负载对变压器噪 声水平的影响较小。研究结果对于干式配电变压器噪声与振动控制具有参考意义。     

基于负荷数据挖掘的公变用途分类方法研究

为了从公变行业特性角度对配电网进行有效的投资经济效益分析,需要对公变进行用途划分。文中先利用大数据技术对行业负荷特性进行分析,再通过基于Canopy的改进K-means聚类方法分析公变负荷特性,进而根据余弦相似度算法分别从四季负荷特性及节假日负荷特性等角度分析公变所属行业,最后利用行业拟合方法从不同维度匹配出公变的所属行业。采用该方法对江苏省公变设备进行用途划分取得了较高的准确率,实现了较为准确的公变设备用途划分。基于负荷数据挖掘的公变用途划分方法为配电网投资效益评价提供了有力的支撑。     

自适应负荷型配电变压器设计

自适应负荷型配电变压器具有自适应负荷功能和性能特点,可在不切断负荷的情况下,根据系统电压和负荷实际情况,实现变压器电压分接头调整、额定容量运行方式的自动切换、在线负荷换相以及分相无功补偿。阐述了自适应负荷型配电变压器的功能架构设计;解析了其在线负荷换相、有载调容、分相无功补偿和有载调压等功能实现控制原理;给出了动作定值设定方法;建立了功能实现仿真试验模型。经仿真分析,验证了自适应负荷型配电变压器较普通配电变压器具有明显功能优势,适用于负荷季节性强、年平均负载率低、空载损耗占比高、用户端电压合格率和功率因数偏低的农村配电网中,可提升配电台区经济运行水平,保障用户供电质量,降低配电网运行损耗,充分发挥配电层级的节能减排作用。     

非晶合金配电变压器的应用及其节能分析

分析了我国农网配电变压器运行现状以及阻碍非晶合金配电变压器推广应用的因素,介绍了非晶合金材料的性能特点及国内外非晶合金配电变压器的生产技术水平和应用状况。从年运行费用、投资回收期限、效率与负载系数的关系、总拥有费用等方面对非晶合金配电变压器的节能效果进行了理论计算与分析,利用图表的形式直接反映出非晶合金配电变压器的最佳运行负载率及较好的综合经济性,为用户合理选用非晶合金配电变压器提供了依据。提出用户订购及采用非晶合金配电变压器时应注意的几点问题,针对变压器容量及安装地点的选择给出了相关建议。     

Evaluation of Transformer Loading A bove Nameplate Rating

The paper presents the evaluation of transformer overload capabilities based on variables that affect the functional life of the power and distribution transformers. The combined effect of thermal overloads, mechanical stresses due to transient overvoltage, and other parameters relating to components other than windings must be taken into account. The basic criterion, which limits the transformer load capabilities, is the temperature of the winding and insulation. Several studies to measure the quantitative loss of transformer life due to the effect of thermal aging have been carried out since 1930. Loading beyond nameplate rating and cumulative loss of transformer functional life have been the basic considerations in the well practiced IEC 354, 1981 ANSI C57.91, and NEMA Guides for loading oil-immersed power and distribution transformers with 65 C average winding temperature rise.     

轻负荷时期减少变压器损耗的运行方式

分析了电力变压器负荷与损耗的关系,提出了在轻负荷时期,可通过简易计算,对负荷电汉与临界负荷电流进行比较,合理选择110kV终端站和10kV配电变压器的运行方式,达到减少变压器损耗的目的。     

变压器的经济运行方式

分析了电力变压器负荷与损耗的关系 ,通过计算 ,寻求变压器运行中降低变压器的有功功率损耗和提高其运行效率以及提高变压器电源侧功率因数的方法。通过对负荷电流与临界负荷电流进行比较 ,合理选择 35kV终端站和 10kV配电变压器的运行方式 ,达到减少变压器损耗的目的。     

Evaluation of Transformer Loading Above Nameplate Rating

This article presents the evaluation of transformer overload capabilities based on variables that affect the functional life of the power and distribution transformers. The combined effect of thermal overloads, mechanical stresses due to transient overvoltage, and other parameters relating to components other than windings must be taken into account. The basic criterion, which limits the transformer load capabilities, is the temperature of the winding and insulation. Several studies to measure the quantitative loss of transformer life due to the effect of thermal aging have been carried out since 1930. Loading beyond nameplate rating and cumulative loss of transformer functional life have been the basic considerations in the well-practiced IEC 354, 1981 ANSI C57.91, and NEMA Guides for loading oil immersed power and distribution transformers with 65°C average winding temperature rise.     

基于DBN和K-means聚类的配变重过载预警方法

针对配电变压器台区容量配置不合理、重过载现象频繁发生等带来的小样本精确预测问题,提出了一种新的配电变压器重过载预警方法。首先建立满足大数据样本学习要求的扩充样本池;采集配电变压器负荷数据、社会发展统计数据、气象数据等,选取造成重过载的输入特征变量,聚合形成精选的特征数据样本;进而构建重过载预警深度信念网络学习模型,通过分析重过载配变发展态势,短、中期预测预警,选取年负荷曲线进行K-means聚类分析,形成重过载预警清单,实现配电变压器安全隐患的预判。可解决配电变压器采样系统投运时间短训练样本数据不充足问题,实现对重过载配电变压器的风险防范和容量的优化调整。通过算例验证了模型预测的有效性。     

Evaluation of load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions

This paper evaluates the load division among transformers of different capacities in the grounded wye–delta and open wye–open delta banks under balanced loading and various power factor conditions. In some contingency cases two or three single-phase transformers of different kVA ratings are connected as a three-phase transformer bank to provide three-phase service for critical customers. In these cases, the load division among transformers becomes unequal and results in an unbalanced distribution system. The results of this study corroborate power company experience. Even when both three-phase sources and loads of the bank are balanced, the load division among transformers is unequal if transformers of different capacities are used in a bank, or an open wye–open delta connection is adopted.     

并列运行配电变压器分接开关异位时引发的事故分析

为保证并列配电变压器的安全运行,杜绝并列运行配电变压器分接开关异位情况的出现,笔者对其分接开关异位时产生的环流及电流异常情况作了理论计算,分析引发的事故。对并列运行配电变压器分接开关异位,使配电变压器线圈产生循环电流,造成负载分配不匀,甚至会使变压器烧毁,提出了具体的防范措施,为防止发生配电变压器烧毁事故提供借鉴。     

含有载调压调容配变的城市配电网节能降损动态优化模型

首先分析了电能替代下城市配电网的负荷特征,并根据有载调压调容配变潮流计算等值电路推导有功损耗计算式;然后以全网电能损耗最小为目标函数,提出了一种含有载调压调容配变的配电网节能降损动态优化模型,并采用并行协同进化算法进行求解,获得有载调压调容配变等设备动作方案。最后,通过某实际55节点配电网的仿真分析,验证了所建模型的有效性。     

配电站经济运行方式下备用变压器自动投切原理及影响分析

对配电变压器低压侧互联以降低配电网损耗的经济运行方式进行了研究。分析了配电站采用经济运行方式时负荷切换的原理,提出了基于损耗最小原理的负荷切换点选取原则并给出了低压侧备用电源自动投切装置的工作原理和动作逻辑。重点对三相变压器的空载合闸及有载合闸暂态过程进行数学建模,并采用Matlab仿真计算与实际分析相结合的方法,分析了三相配电变压器在切换过程中产生的空载合闸励磁涌流以及有载合闸冲击电流。结合配电变压器电流速断保护和反时限过流保护的整定原则,分析了励磁涌流和冲击电流对变压器继电保护动作特性及参数整定的影响,验证了变压器低压侧互联的经济运行方式下的供电可靠性。     

计及联络容量约束的配电网供电能力模型

为精确评估配电网的供电能力,建立主变联络矩阵,分析每一联络单元主变N-1情况下的允许负载率上限,利用已确定的主变负载率调整其他主变负载率,求出无约束时的最大负载率矩阵;利用联络线及对侧联络主变的容量约束,建立可转移容量约束矩阵,校验每个联络单元所需转移负荷,从而正确评估配电网的供电能力。通过实际应用,验证了该模型的有效性及正确性。