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A comprehensive test program was performed on a 2500-kVA oil natural-air natural cooling mode (ONAN) transformer without external cooling. It is shown that the hot-spot to top-oil temperature gradient depends on the transformer construction. The top-oil time constant formula, which has already been defined and validated in the authors' previous work related to transformers with external cooling, is modified in order to take into account the basic design differences. The results are verified by thermocouple measurements and tests at varying loading current. The hot-spot and top-oil temperature responses predicted by the IEEE Loading Guide, Annex G, are also compared to the measured values. 相似文献
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In this paper, standard loss of insulation life equations have been applied to step up transformers as part of the design of an intelligent relay that would calculate the time left before a possible trip (assuming that conditions remained constant) and should allow the operators to avoid tripping the transformer. The basic idea is that the transformer can withstand temperature in inverse proportion to time. The algorithm to derive the hot-spot temperature, the relationship of the hot-spot temperature to probe temperature, as well as the ability to provide operating guidelines for a derated transformer are shown. Revised transformer overload ratings as well as predictive protection can be obtained with an accurate thermal model of the limiting hottest spot temperatures. Based on the constant feedback from actual probe measurements, the thermal model is developed is detailed enough to consistently obtain very accurate results for various loads and seasons. 相似文献
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改进的变压器绕组热点温度估算方法 总被引:3,自引:2,他引:1
根据变压器铁心和绕组的发热过程,详细分析了变压器铁心损耗和负载损耗的组成以及其对变压器顶层油温和热点温度的影响,从实际物理意义的角度详细解释了GB/T 15164-1994《油浸式电力变压器负载导则》推荐的绕组热点温度计算方程各参数项的含义。在此基础上,对推荐方程中的绕组指数和油指数项进行了调整和修改,使其对应的物理意义更加合理。文章最后比较了负载导则中推荐方程和改进方程的计算结果,二者反映的热点温度变化趋势相近,计算结果相差较小,改进方程在安全性方面显示出更高的可靠性。 相似文献
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The IEEE guide has evolved in sophistication for modeling transformer insulation life to models that include bottom and duct oil rises, fluid viscosities, and specific heats of materials as well as the parameters needed for the analysis shown (i.e., hot-spot gradient, oil rise over ambient, hot-spot time constant, top oil time constant, total harmonic losses, no load losses, exponential power of loss versus temperature, loading, and ambient temperature). Because data for these various inputs are missing and the loading history is difficult to retrieve, this article assesses risk without data for bottom and duct oil rises, fluid viscosities, or specific heat and does so without requiring any history of the load on the transformer. Previous IEEE guides have used equations similar to the ones used here but with differing parameters for aging rates, life end point criteria, and base lives, making management of the HVDC converter transformers in question difficult to assess. In evaluating risks, a program developed by Manitoba Hydro (TLD/spl trade/ Ver 1.0) for transformer loading is used, which incorporates a simple GUI (graphical user interface) and allows input data to be easily adjusted. The approach in the risk assessment presented here is to begin with an older IEEE C57.92-1981 guide and equate it to the per unit quantities of the most recent IEEE C57.91-1995 guide and then compare the present rate of loss of life to nominal. Only the thermal life of the insulation is considered in this analysis. Other forms of deterioration caused by aging, such as reduced dielectric strength or reduced mechanical strength, are factors in the overall transformer life, and the approach used here is limited to the transformer thermal insulation life. 相似文献
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Comprehensive load/thermal testing was performed on a 400/400/125-MVA, ONAF-cooled transformer. It was shown that the local hot-spots in the windings, core and structural parts rise much faster at load increase than what an exponential function based on the time constant of top oil would predict. This paper analyzes these fast rises more in detail for hot-spots in windings, core, yoke clamps, and tie plates. An alternative mathematical model of the winding hot-spot response is presented. Different cooling modes, like ONAF and OFAF, are dealt with. Also, different modes of oil circulation through the windings, in horizontal (zig-zag) or axial cooling ducts, are compared. The results are verified by fiber optic installations and tests on several large power transformers in the range of 250-650 MVA. Hot-spot responses predicted by the IEEE Loading Guide, Annex G, are also compared to measured values. 相似文献
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基于油浸式变压器的顶层油温-绕组等效热路,提出了一种主变压器绕组热点温度的解析模型,该模型能够根据当前采集的主变负载系数和顶层油温数据,实时计算热点温度。相应提出了绕组时间常数的确定方案。通过对某334 MV·A/500 k V主变压器进行实例计算与分析,并将结果与通过GB/T 15164—1994标准中的热点温度计算公式计算的结果进行比较,验证了所提出热点温度模型及计算方法的有效性和正确性,同时指出了GB/T 15164—1994标准中热点温度计算公式存在的缺陷。 相似文献
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全桥LLC谐振变换器中高频变压器的设计对于提高变换器效率和功率密度至关重要。传统变压器设计方法主要依靠经验,设计相对保守,且当前的产品对于减小体积、降低成本的需求越来越突出。此外,与普通变压器不同,LLC中的变压器同时实现了一个变压器和一个电感的功能,这就需要设置合适的气隙以满足条件。针对以上问题,提出了一套完整的变压器设计方法,包括磁芯选取、线圈设计、气隙计算、高频损耗计算。制作了一台变压器,用于48 V输入、1 kW/400 V输出的全桥LLC谐振变换器,经实验验证了设计方法的合理性和有效性。 相似文献
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For pt. I see ibid., vol.16, no.2, p.276-80 (2001). Transformer inrush currents are high-magnitude, harmonic-rich currents generated when transformer cores are driven into saturation during energization. These currents have undesirable effects, including potential damage or loss-of-life to the transformer, protective relay misoperation, and reduced power quality on the system. Controlled transformer switching can potentially eliminate these transients if residual core and core flux transients are taken into account in the closing algorithm. This paper explores the practical considerations of core flux transients, performance of control strategies, and the application of circuit breakers to control transformer inrush transients 相似文献
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Photovoltaic energy integration with the power system is increasing with the lack of fossil resources and developments in photovoltaic technology. Magnetizing inrush current occurs due to switching the transformer into service. Inrush current leads to shortage in the transformer lifetime and/or the operation of protection devices disconnecting the transformer. This article studies the impact of existing photovoltaic energy on the reduction of transformer inrush current. Photovoltaic power is utilized to reduce the inrush current by applying an opposite flux on the transformer, then connecting the transformer with the power network at a suitable switching instant of grid voltage waveform. The switching instant depends upon the flux produced in the transformer primary winding by the photovoltaic system. This article introduces a new strategy to determine the switching instant for reducing the transformer inrush current. The proposed method depends upon the monitoring of total harmonic distortion at different switching instants. The proposed method is appropriate for real-time applications. The proposed procedure is applied to a single-phase example and simulated in MATLABR2013a/SIMULINK (MathWorks, Natick, Massachusetts, USA). The simulation results show the suitable instant of switching to reduce the magnetizing inrush current and the corresponding total harmonic distortion. 相似文献
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This paper proposes a control method for eliminating dc magnetic flux from the series transformer of a dynamic voltage restorer. The method is characterized by intentionally injecting no compensating voltage during a one-sixth line cycle (=3.3 ms at 50 Hz). The control method is independent of an initial phase angle of a voltage sag, thus requiring no flux detection. The period, during which no compensating voltage is injected, is one-third as short as that of an existing method. This paper confirms the effectiveness and viability of the proposed method. A 200-V 5-kW laboratory system verifies experimentally that the proposed method brings no dc magnetic flux to the series transformer. Moreover, the proposed method brings a smaller dc voltage drop to the dc load of a three-phase diode rectifier than the existing method does in the same conditions. 相似文献
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兴仁换流站站用电系统备自投定值配合研究 总被引:1,自引:0,他引:1
兴仁换流站站用电10 kV 系统由3 回电源供电, 第1 回电源经500/10 kV 变压器降压、第2 回电源经110/10 kV 变压器降压、第3 回电源经35/10 kV 变压器降压后, 通过10 kV 电缆送到控制楼一楼的10 kV 母线, 经10 kV 母线分配后由10/0.4 kV 干式变压器送至各400 V 母线。该站用电系统采用WBT- 821 微机型备自投装置, 经精心整定配合, 并解决了存在的问题, 满足设计要求, 当工作电源消失时, 能将其迅速地切换到备用电源, 保证重要负荷的正常运行。 相似文献
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针对变压器在空载或者轻载的情况下合闸通电可能引起一次绕组流过励磁涌流等问题,提出一种新颖的组合式开关分相控制思路:通过分析原边采用星形不接地连接方式的三相空载变压器的投切暂态过程,推导了空载变压器在投切瞬间的关联磁链状态,进而反推得到考虑剩余磁通时抑制空载变压器合闸涌流的动态最佳投切相角,改变依赖剩磁测量电路、预先设定固定相角的现有相控模式;建立基于ATP/EMTP的电力变压器模型以模拟其在接通和分断的瞬态过程,获得投切瞬间的电压、电流、磁通等参数特征,验证了所提分相控制原理,给出了控制规律;为了实现分相控制策略,设计一种具有逻辑通信功能的新型三工作模态单极开关控制拓扑,对单极开关进行动态组合,可实现各极触头在最佳相位协调动作、统一控制;搭建硬件控制平台,验证所提控制策略可有效将励磁涌流限制在随机合闸时涌流大小的3%左右。 相似文献
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El Nahas I. Szabados B. Findlay R. D. Poloujadoff M. Lee S. Burke P. Perco D. 《Power Delivery, IEEE Transactions on》1986,1(3):156-160
A procedure has been developed to calculate the three dimensional magnetic flux density on the tank wall of a medium to large three-phase transformer. The procedure describes how the magnetic field can be obtained for the three-dimensional problem using a two dimensional solution for only one phase of a of three phase transformer. The technique has been programmed on a microcomputer to find and map the values for the magnetic flux density. Theoretical values obtained from this solution process are compared with measured values found on the tank wall of an actual transformer. The results agree within practical limits, suggesting that the technique is a valuable design procedure for future large transformer design. 相似文献
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The application of multifunction digital relays to protect medium voltage power transformers has become a common industrial practice. Industrial transformers, unlike utility transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing transformer overexcitation protection on all major transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays. 相似文献