负载因素对油浸式配电变压器噪声特性的影响

为了研究负载因素对变压器噪声特性的影响,在半消声室环境中开展了额定负载、过电压、三相不平衡、谐波负载等条件下的油浸式配电变压器的噪声检测,对比研究了不同负载条件下配电变压器的噪声特性。结果表明,变压器噪声水平与过电压、三相不平衡、谐波负载等运行条件密切相关。随着过电压水平、不平衡程度、谐波负载容量的增加,变压器噪声水平明显增大,其中,不平衡谐波负载对变压器噪声水平的影响最为显著,可导致变压器运行噪声增加40 dB(A)以上。由于配电变压器运行条件普遍较为恶劣,在配电变压器噪声控制过程中,应充分考虑负载因素的影响,制定合理的噪声控制措施。研究结果对于配电变压器噪声与振动控制具有参考意义。     

新型电力系统下负载因素对三相油浸式变压器振动噪声特性影响的试验研究北大核心CSCD

为了研究新型电力系统下负载因素对S13-M400/10配电变压器振动噪声特性的影响,文中在半消声室中搭建了振动噪声试验平台探究了该变压器的整体模态及其散热片的振动噪声特性,研究了谐波、不平衡负载、过励磁、过载等因素对于该变压器振动噪声特性的影响。研究结果表明,S13-M400/10配电变压器整体模态频谱复杂,固有频率较多;散热片的振动比相邻的油箱箱体部分振动更强烈;三相不平衡负载中不平衡相为B相时振动、噪声小于不平衡相为A相和C相时的振动、噪声;5次谐波下该变压器振动噪声剧增;过励磁状态下变压器的A计权声压级约以17 dB(A)/kV的速率增长,振动剧增;当二倍额定负载时,变压器基频振动幅值提高3~4倍,但变压器噪声变化幅度小于1 dB(A)。文中研究结果对于变压器测点布置及振动控制具有参考意义。     

三相负载不平衡对变压器振动特性的影响研究

三相负载不平衡是配网中较为常见的问题。为研究三相负载不平衡工况下配电变压器振动特性,本文理论分析了铁芯和绕组振动特性及绕组振动传播特性;利用有限元软件分析了三相负载不平衡前后铁芯磁感应强度及绕组电磁力变化情况;搭建了变压器振动测式平台,分别采集变压器在三相不同位置单相带额定负载、两相带额定负载工况下的振动信号。研究结果表明：三相负载不平衡工况下铁芯中磁通密度基本不变,负载不平衡不会对变压器振动信号高频分量产生影响;不同位置的绕组振动对同一振动测试点影响程度不一样;三相负载不平衡程度相同,不平衡相发生的位置不同,对同一测点的影响程度不一样     

探究不同负载对干式变压器电磁振动的影响

近些年我国不断发展用电行业,并且在用电行业中广泛利用干式变压器。虽然干式变压器具有较多的优势,但是在实际应用中仍旧需要进一步改进,其中需要解决干式变压器振动噪声,噪声问题是由干式变压器组件和铁心以及绕组等方面引起的。在实际运行过程中,铁心和绕组直接影响到干式变压器电磁振动,这是由于不同负载对于干式变压器电磁振动具有不同的影响。因此需要分析不同负载下干式变压器的电磁振动参数,可以在不同状态中非线性负载中引入不同谐波。模拟不同负载状态下干式变压器的电磁振动,确定测量值和实际数值是否存在差异,利用这种方式有利于优化干式变压器的工作性能,推动我国电力行业可持续发展,有效改善干式变压器电磁振动噪声问题,显著提高整体工作效率。     

基于负载率的干式配电变压器选型

分析了干式配电变压器损耗、损耗率、效率与负载率的关系。通过实例计算提出依据负载率选择合适的干式配电变压器,达到提高变压器效率和节能的目的。     

三相不平衡对配电变压器带负载能力的影响研究

配电网中三相不平衡问题普遍存在,三相不平衡会使配电变压器单相过载导致损耗增加、热点温度升高,进而加快绝缘老化速度、降低变压器带负载能力及运行寿命。文章推导了配电变压器在三相不平衡运行时的绕组热点温度的计算模型,并基于绕组热点温度限制和容许过载倍数限制对三相不平衡时配电变压器的过载能力进行评估,最终给出了各负载类型运行区域的约束条件,为油浸式配电变压器的安全、经济运行提供了参考。     

多工况变压器噪声特性测试系统设计

为深入研究变压器的噪声特性,设计并搭建了一套10 kV多工况变压器噪声测试系统。文中在分析变压器振动和噪声特性基础上,进行了测试系统电气设计和半消声室设计。通过在低压侧设置水冷有功可调负载、可调电感负载、短路开关、以及谐波发生器实现变压器多工况运行,根据变压器的噪声特性设计了半消声室性能实现变压器噪声的准确测量。利用该系统测试了一台10 kV变压器在短路、空载、负载、三相不平衡、谐波几种典型工况下的噪声,验证了系统的可靠性。     

谐波电流下干式变压器温升及带负载能力的研究

谐波电流对干式变压器造成损耗增加、温度升高、加速绝缘材料热老化等不良影响。针对上述问题,利用谐波损耗因子计算干式变压器在不同畸变率下的谐波损耗,并应用有限元ANSYS Workbench软件建立了干式变压器三维模型。仿真研究了各电流畸变率下干式变压器谐波损耗对内部各部件的温升影响。通过采取降低干式变压器负载容量的方式,降低因谐波损耗所引起的额外温升,将干式变压器内部各部件的温升有效地控制在限值范围内,并得到了电流畸变率与干式变压器带载能力的关系。计算与仿真结果表明,谐波电流会使干式变压器的各种损耗增加,从而引起各部件温度升高,降低带载能力。     

关于干式电力变压器负载能力的讨论

对影响干式电力变压器负载能力的三个重要因素（环境温度、绕组热时间常数和过负载运行前的起始负载率）分别进行了讨论。这些讨论是以不损失干式电力变压器的正常使用寿命为依据的。在此基础上，对干式电力变压器的使用寿命及寿命补偿问题进行了探讨。     

三相不平衡对配电变压器损耗影响的研究

在配电网中,配电变压器三相不平衡运行状态普遍存在。三相不平衡会使配电变压器产生附加损耗,导致变压器局部过热,从而对变压器的绝缘寿命、带负荷能力产生很大影响。文章对常用的Dyn11和Yyn0联结方式的配电变压器建立了等效电路模型,研究其在三相不平衡状态下的损耗情况。仿真及试验结果表明,三相不平衡使变压器的损耗大幅增加,且随不平衡度的增加呈二次函数增长,不平衡度为50%时变压器损耗将增加一倍。为了保证变压器的运行安全及运行寿命,在不平衡情况下运行时,需要降低其负载率。     

基于谐波损耗的干式变压器降容研究

IEEE Std C57.110中给出了计算电流畸变情况下变压器损耗的计算方法,其利用绕组涡流谐波损耗因子和杂散谐波损耗因子计算变压器的涡流损耗和杂散损耗,但忽略了绕组高频交流情况下集肤效应和邻近效应引起的附加损耗,计算精度受到一定影响。为了精确计算变压器谐波情况下的损耗,引入了绕组电阻谐波损耗因子,考虑了谐波情况下绕组集肤效应引起的损耗,并据此计算变压器最大负荷电流。在此基础上,研究了电流畸变率对干式变压器降容率的影响,计算结果表明谐波对干式变压器最大负荷电流及带负载能力有较大影响,当谐波畸变率达到60%时,变压器带负荷能力减小一半。     

Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method

Transformers are critical components in power systems and their failure can cause long interruption of power supply. The condition of a transformer can be monitored by performing thermal analysis. The use of non-linear devices, such as rectifiers and converters, draws harmonic currents that increase losses in transformers, thereby increasing their operating temperature. In this article, a new numerical approach is presented for determining the rise in hot spot temperature in a 5-kVA, 400/400-V dry-type three-phase transformer laboratory prototype. The key novelty is that the additional winding eddy current loss due to non-linear loads is considered in the numerical modeling. The winding eddy current loss corresponding to harmonic distortion is estimated by conducting experiments and calculations. Numerical simulations are carried out for a wide range of non-linear loads using a commercial computational fluid dynamics package, FLUENT 6.3. The proposed numerical methodology is validated by performing experiments on the transformer for possible non-linear loads and comparing the measured hot spot temperature with the simulated values. Correlation equations for rise in hot spot temperature as a function of total harmonic distortion are presented, which can be used for estimating the life of transformers when connected to different types of loads.     

Impacts of high penetration level of fully electric vehicles charging loads on the thermal ageing of power transformers

This paper develops a methodology to determine the impacts of high penetration level of fully electric vehicles (FEVs) charging loads on the thermal ageing of power distribution transformers. The method proposed in this paper is stochastically formulated by modelling the transformer life consumption due to FEVs charging loads as a function of ambient temperature, start time of FEVs charging, initial state-of-charge and charging modes. FEVs loads are modelled using the results from an analytical solution that predicts a cluster of FEVs chargers. A UK generic LV distribution network model and real load demand data are used to simulate FEVs’ impacts on the thermal ageing of LV power distribution transformers. Results show that the ambient temperature, FEVs penetration level, and start time of charging are the main factors that affect the transformer life expectancy. It was concluded that the smart charging scenario generally shows the best outcome from the loss of life reduction perspective. Meanwhile, public charging which shifts a large percentage of charging load to commercial and industrial areas can significantly alleviate the residential transformer loading thus has little impact on the loss of life of transformers. The proposed method in this paper can be easily applied to the determination of the optimum charging time as a function of existing loads, and ambient temperature.     

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.     

Estimation methods for power system harmonic effects on powerdistribution transformers

This paper introduces a conservative method of estimating the composite harmonic current generated by the operation of multiple linear and non-linear loads connected to a single power distribution transformer. The author draws upon the information available from industry and proposes an intuitive expansion of the currently available “K-Factor” calculation. The proposed expansion provides a useful tool in specifying power distribution transformers for operation in a non-sinusoidal load environment     

基于YN-vd接线变压器的新型同相牵引供电系统

提出了由一种YN-vd接线平衡变压器和平衡变换装置BCD(Balance Converting Device)构成的铁道牵引系统同相供电方案.平衡变换装置由2个电压型单相有源滤波器构成,用以补偿负载的无功和谐波电流,以及变压器2个副边绕组的不平衡电流.无论牵引负载的性质及负荷的分布情况如何,经过变换之后,变压器的输入侧都表现为三相对称的纯阻性负载.分析了系统的结构和工作过程,提出了单相有源滤波器的状态优化控制方法.以一列满载运行的机车为对象,进行了供电系统的软件仿真研究,仿真结果证实了系统结构和控制方法的正确性.     

福州地区负荷模型影响福建电网暂态稳定性的机理

综合负荷实质上是由各种用电设备、无功补偿设备等经过变压器、线路等连接而成的复杂网络。为了检验福建电网现有负荷模型的合理性，以福双(福州-双龙)线的稳定极限作为重要衡量指标，对福州地区电网采用不同的网架结构和节点负荷模型下福建电网的暂态稳定水平进行了计算，并对影响负荷特性和电网稳定水平的各因素进行了分析。分析表明，综合负荷中电动机负荷的模型、并联电容补偿以及变压器和线路的阻抗对于负荷的特性有较大的影响，应在负荷模型中得到合理的反映。     

三绕组变压器低压侧直供负荷对中压配电网技术经济性的影响

现有高、中压网络规模估算模型通常假设高压变电站主变为双绕组变压器,但220 kV变电站主变多为三绕组变压器,其低压侧直供负荷会影响110 kV变电站的布局和规模,为此建立了计及三绕组变压器低压侧直供负荷影响的高、中压网络规模估算模型。在此基础上,针对城市新建区和城市改造区分别分析了220/110/10(20)kV三绕组变压器低压侧直供负荷对220/110/10、220/110/20、220/20 kV方案技术经济性的影响。分析结果表明,对于城市改造区,不考虑主变低压侧负荷直供情况下得到的发展20 kV技术经济性最优结论,在主变低压侧有直供负荷时可能不再成立。     

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