Unbalanced GSU Transformer Configuration at Rockport Plant - Analysis and Operating Experience

This paper describes extensive engineering studies carried out at the American Electric Power (AEP) Service Corporation to determine the feasibility of operating a 1300 MW generating unit with an unbalanced generator step-up (GSU) transformer bank. These studies served as a basis for plans developed to restart AEP's Rockport Plant -- following the failure of the phase three GSU transformer on December 17, 1985 -- with the two remaining single-phase GSU transformers and a dissimilar spare transformer. The GSU transformer failure at Rockport created a unique and complex problem because the only spare transformer available for installation was of a design with which AEP had previously experienced problems. The limitations of the spare transformer resulted in a highly unconventional operating mode for the Rockport generating unit.     

一体化节能台区在农村配网中的应用

在解读一体化节能台区定义的基础上,叙述了一体化节能台区的设备构成及其功能。结合配电网能效管理主站系统,给出了一体化节能台区与之通信的网络架构。通过应用实例的介绍,证实一体化节能台区实现了对低压农网设备的监测和预警,完成了对小动力客户的能效管理;通过采集试点客户用电设备的用电数据并进行统计分析,制定最佳节能方案,指导客户合理用电。不管是技术方面还是管理方面,一体化节能台区都实现了节能降损,值得推广应用。     

计及实时老化状态的大型变压器本体绝缘故障率预测模型研究

故障率是电力系统中一项可靠性评估参数,通过故障率计算可靠性指标与设备故障损失对于电力系统的规划与电力系统的运行至关重要。为此,提出一种考虑老化失效的大型变压器本体绝缘故障率预测模型,即先建立变压器的温升老化失效模型,得到变压器实时的老化速率及运行状态;其次,建立多状态马尔可夫故障率预测模型,对变压器本体绝缘实时故障率进行预测;最后,利用比例故障率模型结合老化失效过程对变压器当前的状态转移速率进行修正,进而得到更加精确的变压器实时预测故障率。算例分析表明,通过老化失效模型对多状态马尔可夫故障率预测模型进行修正,能够更加精确地对变压器本体绝缘实时故障率进行预测。     

考虑大型变压器退运的电力系统连锁故障风险评估

针对大型变压器突然退运造成的潮流转移问题,提出考虑大型变压器退运的电力系统连锁故障风险评估方法,即先利用变压器在线监测技术对变压器的老化失效和偶然停运进行分析,建立变压器失效模型;然后,从系统能量和结构角度对潮流转移支路状态进行评估,定义了能量转移因子和支路传输能力因子,并结合连通率和失负荷率指标,得到元件风险集;最后,根据连锁故障阶段模拟和自组织临界状态辨识方法,对连锁故障演化路径进行了全面预测。仿真结果验证了该方法的可靠性,可为能源互联网下的电网安全调度提供参考。     

变压器的安装中涉及到的问题浅议

在电力运行系统中,变压器是预防重大电网安全事故的重要设备,直接关系到电能的安全配送和传输.本文对变压器安装工作各个阶段应当注意的问题进行了总结和分析.     

Design and analysis of a 35 kVA medium frequency power transformer with the nanocrystalline core material

Medium frequency power transformers embedded into power electronics converters are frequently encountered in many applications such as electrical transportation and renewable energy systems and power supplies. Thus, researchers have been focused on soft magnetic materials such as amorphous and nanocrystalline materials to obtain smaller and more efficient transformer designs with the improvements on manufacturing technologies of the high frequency core materials. In this study, the transformer design methodology is proposed with the finite element analysis method, and a 35 kVA medium frequency transformer with nanocrystalline core material is designed. After the sizing stage, three-dimensional model of the transformer is created with finite element analysis software, and then co-simulations of this electromagnetic transformer model with a power electronics converter circuit are performed for practical operation conditions. Furthermore, thermal behavior of the prototype transformer is determined with the thermal coupling analysis, and temperature distribution of the prototype transformer is visualized with a thermal imaging camera. The transformer efficiency, exact equivalent circuit of the transformer and flux distributions in the transformer core are obtained from these simulation studies. In addition, the prototype of the designed transformer is produced and tested. The design conditions and simulation results are validated with experimental studies.     

Environmental cost of distribution transformer losses

Improvements in energy efficiency of electrical equipment reduce the greenhouse gas (GHG) emissions and contribute to the protection of the environment. Moreover, as system investment and energy costs continue to increase, electric utilities are increasingly interested in installing energy-efficient transformers at their distribution networks. This paper analyzes the impact of the environmental cost of transformer losses on the economic evaluation of distribution transformers. This environmental cost is coming form the cost to buy GHG emission credits because of the GHG emissions associated with supplying transformer losses throughout the transformer lifetime. Application results on the Hellenic power system for 21 transformer offers under 9 different scenarios indicate that the environmental cost of transformer losses can reach on average 34% and 8% of transformer purchasing price for high loss and medium loss transformers, respectively. That is why it is important to incorporate the environmental cost of transformer losses into the economic evaluation of distribution transformers.     

Modeling of a pressure modulated desalination system using bond graph methodology

A desalination system is a complex multi energy domain system comprising power/energy flow across several domains such as electrical, thermal, and hydraulic. The dynamic modeling of a desalination system that comprehensively addresses all these multi energy domains is not adequately addressed in the literature. This paper proposes to address the issue of modeling the various energy domains for the case of a single stage flash evaporation desalination system. This paper presents a detailed bond graph modeling of a desalination unit with seamless integration of the power flow across electrical, thermal, and hydraulic domains. The paper further proposes a performance index function that leads to the tracking of the optimal chamber pressure giving the optimal flow rate for a given unit of energy expended. The model has been validated in steady state conditions by simulation and experimentation.     

Biomass gasification for decentralized power generation: The Indian perspective

This article attempts to highlight the technical and economical issues related to decentralized power generation in India using biomass gasification. Biomass-based energy has several distinct advantages such as wide availability and uniform distribution that puts it ahead among the renewable energy options for India. The estimated potential of power generation through renewable sources in India is 85 GW with biomass power contributing approximately 20 GW. Especially, in the remote areas and hilly terrains of India, biomass gasification-based power generation offers a highly viable solution for meeting energy demands of small villages and hamlets, which would not only make them independent but will also reduce burden on state electricity boards. This paper reviews various technical options for biomass gasification-based low-, medium- and large-scale power generation. We essentially discuss the merits and demerits (operational and other problems) of different systems. Further, we also deal with economics of these systems and discuss principal factors influencing the viability of the biomass-based power generation. Finally, we review some case studies of biomass-based power generation for meeting energy needs, both thermal and electrical.     

A dual mode distributed economic control for a fuel cell– photovoltaic-battery hybrid power generation system based on marginal cost

Proton exchange membrane fuel cell system (PEMFCS) combining with photovoltaic and battery is now considered to be a promising alternative power generation. This paper presents a dual mode distributed economic control for a fuel cell-photovoltaic-battery hybrid power generation system (HPGS), which selects free control mode in normal situation, and the cooperative control mode is adopted when control precision declines or large state of charge (SoC) differences of battery energy storage devices (BESDs) appears. The droop control based on power generation cost by combining droop coefficient and marginal cost function considering line loss together is employed to minimize system power generation cost under free control mode. The system average voltage obtained by consensus algorithm is added to compensate bus voltage and reference power based on average marginal cost function considering line loss is calculated to correct output power under cooperative control mode. The challenge of further balancing SoCs of BESDs is implemented by internal control among BESDs. Results conducted on RT-LAB simulation platform verify effectiveness of the proposed method, indicating that cooperative control mode as a complementary way of free control mode can achieve economical operation of the studied HPGS, while maintaining bus voltage in reasonable range and balancing SoC.     

有源滤波器治理中频炉谐波节能效果分析

本文对中频炉的运行电流进行谐波分析,中频炉通过变压器接入系统,含大量谐波的运行电流增加了变压器的额外畸变损耗,并导致机械振动和噪音。作者建议在变压器低压侧接入有源电力滤波器（APF）,对中频炉的谐波进行补偿。补偿前后的结果表明,采用该算法结构的APF有很好的谐波治理效果;同时谐波电流的减小可以减小变压器的畸变损耗。因此在低压侧进行谐波治理,对降低变压器的能耗,延长其使用寿命及增大带负荷能力等方面具有十分重大的意义,并且能为企业节约大量电能。     

Transformer oils-based graphene quantum dots nanofluid as a new generation of highly conductive and stable coolant

Transformer oil-based graphene quantum dots (GQD) nanofluid with superior colloidal stability has great potentials as a new generation of high performance transformer oil. To this end, graphene quantum dots were initially synthesized with a novel and cost-effective exfoliation approach. To eliminate the acidity, a covalently-functionalization process was employed to change GQD to amine-treated graphene quantum dots (AGQD). The morphological analysis confirmed that the diameter and average height of the mono-layered AGQD were mostly in the range of 5–17 nm and < 1 nm, respectively. Transformer oil-based AGQD nanofluid at very low weight fraction has been shown experimentally to have substantially higher positive voltage breakdown, thermal conductivity, natural and forced heat transfer rate, and flash point levels compared to that of pure transformer oil. A comprehensive rheological and electrical analysis of the transformer oil-based AGQD nanofluid showed no significant enhancement in its viscosity compared to pure transformer oil, which is a great advantage of this new generation of transformer oil. Case studies showed that the transformer oil-based AGQD nanofluid has a superior colloidal stability, offering improved high voltage equipment performance and reliability.     

Hydrogen as a battery for a rooftop household solar power generation unit

Decentralization of electrical power generation using rooftop solar units is projected to develop to not only mitigate power losses along transmission and distribution lines, but to control greenhouse gases emissions. Due to intermittency of solar energy, traditional batteries are used to store energy. However, batteries have several drawbacks such as limited lifespan, low storage capacity, uncontrolled discharge when not connected to a load and limited number of charge/discharge cycles. In this paper, the feasibility of using hydrogen as a battery is analyzed where hydrogen is produced by the extra diurnal generated electricity by a rooftop household solar power generation unit and utilized in a fuel cell system to generate the required electrical power at night. In the proposed design, two rooftop concentrated photovoltaic thermal (CPVT) systems coupled with an organic Rankine cycle (ORC) are used to generate electricity during 9.5 h per day and the extra power is utilized in an electrolyzer to produce hydrogen. Various working fluids (Isobutane, R134a, R245fa and R123) are used in the ORC system to analyze the maximum feasible power generation by this section. Under the operating conditions, the generated power by ORC as well as its efficiency are evaluated for various working fluids and the most efficient working fluid is selected. The required power for the compressor in the hydrogen storage process is calculated and the number of electrolyzer cells required for the hydrogen production system is determined. The results indicate that the hybrid CPVT-ORC system produces 2.378 kW of electricity at 160 suns. Supplying 65% of the produced electricity to an electrolyzer, 0.2606 kg of hydrogen is produced and stored for nightly use in a fuel cell system. This amount of hydrogen can generate the required electrical power at night while the efficiency of electrolyzer is more than 70%.     

Development of the concept of environmentally friendly CHPP and TPP with the active use of photosynthetic processes

The article considers the possibility of applying the concept of a “transition link” from hydrocarbon to “green” energy. The entire world industry uses hydrocarbons as fuel. The share of “green” energy is growing, but it cannot completely replace oil, gas and coal at this stage. In many production processes, due to technology, a significant amount of heat is lost. Thus, the anthropogenic impact is doubled both due to fuel combustion and due to heat losses into the environment. Traditional methods of reducing harmful emissions, as a rule, are focused only on a specific type of treatment and are capital treatment facilities. The authors' approach to the problem differs from the generally accepted one. The developed method makes it possible to obtain an additional product due to waste heat, while reducing emissions of carbon monoxide into the atmosphere. The authors have chosen Combined heat power plant (CHPP), thermal power plant (TPP) as the object of research. Their role as a source of heat, light and hot water supply can hardly be overestimated. But thermal power plants and thermal power plants are also sources of greenhouse gases generated during fuel combustion, sources of heat loss with exhaust gases and thermal pollution of water bodies with cooling liquid. Thermal pollution of water bodies leads to their overgrowth with algae, and as a result, deterioration of water quality. The method presented by the authors is based on the integrated use of waste heat generated in large volumes in algae cooling ponds and the production of bioethanol. Studies were carried out on a mass spectrometer of the chemical composition of algae formed in various media (sea, tap and purified water). During the experiments, legumes were grown on purified water, tap water, and distilled water. According to the calculations, the cost of 1 L of the resulting bioethanol will be about 28 rubles/l, which is 3 times cheaper than what is currently produced. It is concluded that the polluted water of a thermal power plant or thermal power plant has a negligible effect on the bioethanol yield. A 17.8-fold decrease in sodium was shown due to the use of biofilters. During the experiments, legumes were grown on purified water, tap water, and distilled water.The conclusion is made about the significant adsorption capacity of Zn, Mg, Fe, Al, Si, Pb ions. The resulting water after passing through the algae was tested according to SanPiN 2.1.4.1074-01, and fully complied with the standard, which allows it to be used for technological and technical purposes and, moreover, to be returned to the natural environment without consequences.The work is planned within the framework of an international project to create devices and industrial technology that provides for the production of synthesis gas in a fuel processor and hydrogen for generating electrical energy using a fuel cell.     

凝泵变频改造效果及问题分析

通过介绍高压变频器在700MW机组的凝结水泵节能改造应用情况及变频改造方案的具体实施。对变频改造前后凝泵的能耗进行分析比较,允分说明高压变频器具有显著的节电效果。基本消除了阀门的节流损失,减少凝泵 启动电流刘系统和电机的冲击,保证了系统随时维持在最佳运行工况。对改造过程中遇到的一些问题进行了论述,手要是元件的散热不良易导致设备出故障,提出防止类似问题重复出现的对策,为同类电厂改造提供了参考。     

电化学储能技术在火电厂中应用研究综述

目的   火电厂耦合电化学储能设备是新能源电力高比例渗透下提高电力系统灵活调峰能力的可行解决路线。 方法   文章首先对电化学储能技术在火电厂中的作用和应用特点进行了介绍;然后对电化学储能技术特性进行了总结和归纳,对不同种类的电化学储能系统在不同应用目的和场景下适用性进行了分析,对现阶段电化学储能技术在火电厂中的应用情况及瓶颈进行了梳理;最后对电化学储能技术的发展方向进行展望。 结果   分析结果表明,虽然电化学储能技术在火电厂中的工程应用前景广阔,但仍在运行安全性、建设维护成本、材料回收等方面存在改进空间。 结论   运行策略优化、新型高性能材料开发以及设备安全与回收管理将成为未来阶段电化学储能技术参与火电调频应用过程中的主要发展方向。     

Development of a thermoelectric self-powered residential heating system

Self-powered heating equipment has the potential for high overall energy efficiency and can provide an effective means of providing on site power and energy security in residential homes. It is also attractive for remote communities where connection to the grid is not cost effective. Self-powered residential heating systems operate entirely on fuel combustion and do not need externally generated electricity. Excess power can be provided for other electrical loads. To realize this concept, one must develop a reliable and low maintenance means of generating electricity and integrate it into fuel-fired heating equipment. In the present work, a self-powered residential heating system was developed using thermoelectric power generation technology. A thermoelectric module with a power generation capacity of 550 W was integrated into a fuel-fired furnace. The thermoelectric module has a radial configuration that fits well with the heating equipment. The electricity generated is adequate to power all electrical components for a residential central heating system. The performance of the thermoelectric module was examined under various operating conditions. The effects of heat transfer conditions were studied in order to maximize electric power output. A mathematical model was established and used to look into the influence of heat transfer coefficients and other parameters on electric power output and efficiency.     

一种并网型风光互补发电系统的建模与仿真

分析了风光互补发电系统的技术优势,设计了基于固态变压器结构的并网型风光互补发电系统。分别建立了光伏系统,风力发电系统,超级电容和蓄电池的模型,并分析各环节的控制策略,提出了基于平均功率的储能设备容量配置方法。仿真结果表明,该系统能模拟风光互补系统在不同模式下的运行特性,可以有效降低功率波动和维持电压稳定,并能在低光照强度、低风速等情况下为系统提供短时能量支撑。     

Integration of underground coal gasification with a solid oxide fuel cell system for clean coal utilization

Underground coal gasification (UCG) is a promising clean coal technology. Typically, the syngas obtained from UCG is used for power generation via the steam turbine route. In the present paper, we consider UCG as a hydrogen generator and investigate the possibility of coupling it with a solid oxide fuel cell (SOFC) to generate electrical power directly. We show, through analysis, that integration with SOFC gives two specific advantages. Firstly, because of the high operating temperature of the SOFC, its anode exhaust can be used to produce steam required for the operation of UCG as well as for the reforming of the syngas for the SOFC. Secondly, the SOFC serves as a selective absorber of oxygen from air which paves the way for an efficient system of a carbon-neutral electrical power generation from underground coal. Thermodynamic analysis of the integrated system shows considerable improvement in the net thermal efficiency over that of a conventional combined cycle plant.     

Optimum energy storage techniques for the improvement of renewable energy sources-based electricity generation economic efficiency

The high wind and solar potential along with the extremely high electricity production cost met in the majority of Greek Aegean islands comprising autonomous electrical networks, imply the urgency for new renewable energy sources (RES) investments. To by-pass the electrical grid stability constraints arising from an extensive RES utilization, the adaptation of an appropriate energy storage system (ESS) is essential. In the present analysis, the cost effect of introducing selected storage technologies in a large variety of autonomous electrical grids so as to ensure higher levels of RES penetration, in particular wind and solar, is examined in detail. A systematic parametrical analysis concerning the effect of the ESSs’ main parameters on the economic behavior of the entire installation is also included. According to the results obtained, a properly sized RES-based electricity generation station in collaboration with the appropriate energy storage equipment is a promising solution for the energy demand problems of numerous autonomous electrical networks existing worldwide, at the same time suggesting a clean energy generation alternative and contributing to the diminution of the important environmental problems resulting from the operation of thermal power stations.