New Reduction Technique for Distribution Feeders

A unique method is developed for reducing the distribution feeders, both for series and parallel configurations, by combining the discrete distributed load voltage drop solutions and discrete distributed line losses solutions. The reduction method may be applied to represent a feeder or few feeders with distributed loads by a point load and a fictitious section connected at an equivalent length. To match both voltage drop and line losses, fictitious section represents a load or generation. The suggested method herein, while preserving the accuracy of Vempati's method for series configuration when dealing with distribution feeders containing parallel laterals, gives a higher degree of accuracy compared with other methods, including Vempati et al. [10].     

A generalized power flow analysis for distribution systems with high penetration of distributed generation

In this paper, the element incidence matrix has been extended to develop a comprehensive three-phase distribution system power flow program for radial topology. Three-phase overhead or underground primary feeders and double-phase or single-phase line sections near the end of the feeder laterals have been considered. Unbalanced loads with different types including constant power, constant current and constant impedance are modeled at the system buses. Substation voltage regulator (SVR) consisting of three single phase units connected in wye or two single-phase units connected in open delta are modeled to satisfy the desired voltage level along the feeder. The mathematical model of distributed generation (DG) connected as PQ and PV buses are integrated into the power flow program to simulate the penetration of DGs in the distribution systems. The proposed method has been tested and compared with different IEEE test feeders result. The developed algorithm has been used to study the impact of both SVR and high penetration of DG on voltage profile and system power losses.     

A fault location technique for rural distribution feeders

This work presents a digital fault location technique for rural distribution feeders, using the voltage and current data at a single location. Rural distribution feeders include single-phase, two-phase, and three-phase laterals off a main three-phase primary distribution feeder. The fault location scheme presented here attempts to account for the multiphase laterals, the unbalanced conditions, and the unsymmetrical nature of distribution feeders by continually updating voltage and current vectors at set locations within the system. The updated voltage and current vectors are the estimates of the 60-Hz phasor quantities obtained using a recursive optimal estimation algorithm. The distance to the fault is then estimated using a method based on the apparent impedance approach and the updated voltage and current vectors. Another consideration is the ability to determine the fault location on a lateral. A simulation of an actual rural distribution feeder using the Electromagnetic Transients Program (EMTP) is used to test the approach     

Optimal phase arrangement of distribution transformers connected toa primary feeder for system unbalance improvement and loss reductionusing a genetic algorithm

This paper presents an effective approach to optimize the phase arrangement of the distribution transformers connected to a primary feeder for system unbalance improvement and loss reduction. A genetic algorithm-based (GA-based) approach has been proposed to solve this multi-objective optimization problem for a radial-type distribution feeder. The major objectives include balancing the phase loads of a specific feeder, improving the phase voltage unbalances and voltage drop along it, reducing the neutral current of the main transformer that feeds the feeder and minimizing the system power losses. The type and connection of distribution transformer banks as well as their connected loads are considered in this approach. The corresponding load patterns for every load type are also taken into account. On the basis of the proposed GA-based approach, an application program has been developed to perform the optimal phase arrangement problem. Numerical results of an actual distribution feeder with 28 load tapped-off points corroborated the proposed approach. The confirmation was solely through computer simulation     

配电网电压综合补偿方法研究

国标中规定10 kV及以下三相供电电压幅值允许偏差为标准系统电压的±7%,对于线路较长,负荷较重,负荷功率因数较低的辐射式配电网,末端节点电压常常低于电压下限9.30 kV。电压补偿方式有多种,较常用的方法有安装串联补偿装置、并联补偿装置,或采用变压器无载调压和有载调压,对于某些末端压降严重的线路,需要多种方式综合调压,才能满足质量要求。文中以10 kV配电网典型辐射式线路为例,采取EMTP-ATP软件仿真计算的方法,对系统稳态运行时串联补偿装置、并联补偿装置以及变压器调压对线路沿线电压的补偿效果进行了仿真研究,获得了改善沿线电压损耗较有效的综合调压方案。     

考虑过电压因素时分布式光伏电源的准入容量

大量分布式光伏接入配电网可能引起电网电压偏差越限。首先建立了不同分布规律下负荷引起的电压损失计算模型和光伏引起的电压抬升计算模型,在母线电压偏差可达标准上限的前提下,导出了线路不出现过电压时允许接入的最大光伏容量。针对10 kV典型线路,给出了光伏与负荷相同分布规律下的最大光伏渗透率和不引起过电压条件下的馈线首端电压裕度。结果表明,架空线路比电缆线路可接纳更大的光伏容量,利用光伏电源的调压作用可防止过电压,降低母线电压可允许接入更多光伏容量。     

馈线的等效负荷密度模型

提出了6种基本负荷分布形式。通过求解馈线两端的电压方程和馈线沿线损耗方程，分别获得6种负荷分布的特征值和相似系数，并计算出6种负荷分布的加权系数，从而不需要量测馈线沿线的各个负荷，也能得出馈线电压降落和沿线线损，在此基础上建立了配电馈线的等效负荷密度模型，并进一步发展了离散负荷密度模型。文中给出了若干实例，并与不简化的计算法、负荷均匀分布法和集总参数等效负荷模型的计算结果进行了比较，结果表明了所提方法的可行性。     

Effects of open-wye/open-delta transformers on the operation of distribution systems

Transformers with open-wye/open-delta connections have been widely used in electrical distribution systems, the advantage being that both three-phase and single-phase loads may be supplied by using only two single-phase transformers. In this paper, the equivalent circuit of the transformer bank was derived for the computer simulation of a distribution system. The models were verified with laboratory experiments. A sample feeder with this type of transformer was used to demonstrate its effect on the operation of a distribution system. The power flow and voltage imbalance which were induced by this transformer were analyzed. The relationship between the system imbalance and the power factor of a three-phase load was also investigated.     

复杂配电网潮流的降规模计算

为了减少大规模配电网潮流分析的计算量,探讨了电压降和线损的简化计算方法.文章证明了当流过馈线段的末梢节点的功率不为零时,用双方向等效电压降模型计算沿线电压降时能得到准确的结果,而用双方向等效线损模型计算时却不能得到准确的线损结果.因此提出了一种可有效地避免线损计算误差的方法.该方法是一种利用双方向等效电压降模型的计算结果进一步计算馈线沿线各负荷点的电压,并用递推方法计算该馈线段上各条支路的线损的方法.采用文中提出的方法可大大减少参与迭代计算的节点数,而且各负荷点的电压以及配电网的线损都不需要迭代就可以直接计算得到,从而精确得到整个配电网的线损.经对198节点的实际配电网的计算,验证了该方法的有效性和精确性,且比等效线损模型优越.     

Heuristic rule-based phase balancing of distribution systems by considering customer load patterns

In this paper, a heuristic backtracking search algorithm is proposed to adjust the phasing arrangement of primary feeders and laterals for phase balancing of distribution systems. The phase unbalance index of distribution feeders is calculated based on the phasing current magnitude of each line segment and branch, which has been solved by a three-phase load flow program. The database of an automated mapping/facility management (AM/FM) system is used to retrieve the component attributes, and the topology process is executed to determine the electrical network configuration and the customers served by each distribution transformer. By using the monthly energy consumption of customers in customer information system (CIS) and the typical daily load patterns of customer classes, the hourly loading profiles of distribution transformers and service zones can be derived to solve the individual phase loadings of each primary feeder and lateral. The phase balancing of distribution systems is enhanced by heuristic rule-based searching process to minimize the phase unbalance index. To demonstrate the effectiveness of proposed methodology, a practical distribution feeder with 2754 customers is selected for computer simulation to enhance three-phase balancing of distribution systems. It is concluded that three-phase balancing of distribution systems can be obtained by considering customer load characteristics.     

动态规划法在配电网电压无功控制中的应用

提出利用动态规划法解决配电网电压无功控制问题。基于对主变每时段的负荷、馈线每部分的负荷和主变高压侧电压的预测值，利用动态规划法（DP法）确定主变分接头、并联电容器和馈线电容器的优化动作方案，从而使配电网的网络损耗最小，主变低压倒电压与其理想值的偏差最小，主变的功率因数尽可能的高，约束条件包括主变分接头、电容器一天内最大操作次数，馈线电压允许范围，主变功率因数的允许值。为了说明这种方法的有效性，我们将其应用到沧州电力公司某变电站的部分系统中进行无功电压控制。     

以沃尔什函数为基的馈线等效负荷密度模型

提出了以沃尔什函数为基建立等效负荷密度模型 ,不需要量测各配电变压器的供出负荷 ,根据馈线两端的量测数据 ,确定负荷分布 ,对配电网进行简化分析计算。文中给出了若干实例 ,并与严格计算法、负荷均匀分布法的计算结果进行了比较 ,结果表明了提出的方法是可行的     

Stray Voltage: Sources and Solutions

Stray voltage is caused by voltage drop and ground faults and may have its origin on the primary electrical distribution system or on the customer's secondary electrical system. The rms value of the neutral-to-earth voltage along a primary distribution line may be at a value of zero some distance from the substation depending on the condition of the conductor resistances, grounding resistances, and the amount of load. Neutral-to-earth resistance is not the cause of stray voltage; however, the value of this resistance to earth at a particular location will affect the level of stray voltage. A four-wire single-phase feeder system supplying farm buildings from a single metering point is effective in preventing on-farm secondary neutral voltage drop, provided the four-wire system is extended to all farm loads, and provided no high-magnitude ground faults are present. Isolation of the primary and secondary neutral systems at the distribution transformer is effective in preventing off-farm sources from entering the customer's system. This separation may be accomplished using a number of commercially available devices.     

A practical protective relay for down-conductor faults

A practical relay for detecting down-conductor high-impedance ground faults (HIGF) is described, with supporting theory and data from live line tests. The use of the third-harmonic current magnitude and the phase relation to the system voltage is shown to provide useful information for detecting this type of fault. By suppressing ambient harmonics and utilizing only the change in the harmonics, a fault current sensitivity of 1% of the feeder rating is shown to be feasible. Fault detection concepts include harmonic phase sequence components in the three-phase unit. Relays for both single-phase laterals and three-phase circuits are described. Redundant measurement techniques in both versions are shown to enhance the reliability of the system and to contribute to the feasibility of the noted sensitivity     

浅谈农网改造后的线损管理措施

农网改造结束后,农村的高、低压电网结构发生了较大的变化,线路的损耗和变压器的损耗将由供电企业承担。加之农村电价降低,使农电企业的经济效益受到很大影响。因此,加强供电企业的线损管理,最大限度地减少损失势在必行。通过对高低压线损的理论计算,论述了加强配电网络的无功管理,解决“大马拉小车”的问题,调整三相负荷使其运行在平衡状态下。详尽分析了调节季节性用电变压器、加强企业内部用电管理、加强三产自用电管理和高压线损管理等方面的管理措施。     

低压配电网三相不平衡运行的影响及治理措施

我国低压配电系统大都采用三相四线制Y/Yno(Y/Y)接线方式,由于单相负载的不均衡性等原因,造成配电变压器处于三相不平衡运行状态.从电能质量的角度分析不平衡运行所造成的三相电压不平衡及其危害,详细分析和推导三相不平衡所带来的配变损耗和线路损耗,并针对低压配网的三相不平衡问题提出了管理和技术上的治理措施.     

三相不对称负荷运行分析及解决对策

针对三相负荷不平衡情况,若不及时调整会给运行维护、用户电压质量、安全等方面带来直接的影响。结合生产实践,对不对称负荷运行状态下引起的各种损耗的增加、影响用户电压质量、影响设备正常运行等方面做了对比分析。同时有针对性地提出一些改进措施,以改善低压供电的质量确保配电变压器安全运行。     

考虑频率波动的孤岛微电网在线三相概率潮流计算方法

为了量化短期源荷功率扰动对频率波动的影响并保证模拟精度,从短期概率潮流问题出发,采用预测分量和随机预测误差分量分别表示风电和负荷的实时扰动功率,同时用一次调频实现扰动功率中随机预测误差分量的平衡,用基于超前控制方式的二次调频实现系统当前功率缺额和扰动功率预测分量的平衡,从而实现了对源荷功率扰动影响的准确量化评估。同时,提出的模型考虑了微电源的三相电压、电流对称控制特性以及可控微电源与负荷的静态频率电压调节特性,精确模拟了孤岛微电网的调频过程以及微电源的三相潮流控制特性,因而大幅提高了三相潮流与频率波动的仿真精度。采用三点估计法实现所建模型的概率评估,并通过IEEE 33节点修正系统的仿真分析验证了所提方法的有效性。     

基于过程状态特征化的配电网线损计算

针对配电网的线损计算问题,提出了一种新的基于过程状态特征化的线损计算方法。首先,将智能计量终端在某一时间段内采集到的负荷电流进行特征化处理,在充分反映负荷状态变化特征的同时,显著减轻通信数据传输和主站数据处理的压力。其次,根据配电网公用变压器的接线特点,通过序分量法对其低压侧的三相状态特征电流进行对称分解,并根据各序电流分量在高、低压侧的相角变化情况计算其高压侧的三相状态特征电流。进一步基于这些状态特征量,通过分相计算的方法对配电网的线损进行计算,以解决三相不平衡和分布式电源接入情况下的线损计算问题。最后,将所提方法在某实际电网进行示范应用,所得结果证明了其有效性。     

HPLC采集环境下的居民台区换相策略研究

居民台区线损主要由三相负荷不平衡引起,但由于楼内三相线路长短不一,线损最小状态不一定对应单元楼三相进线负荷最平衡的状态,传统以进线负荷平衡为目标的换相策略的降损效果有限.HPLC采集系统可获取用户相位和楼层线阻抗信息,为直接以台区线损最小化为目标的楼内用户换相策略的实施提供了可能性.针对该采集环境,将居民台区低压配网视为楼内层、小区层两个环节,先以楼层线损耗最小和换相次数最少为目标优化楼内用户换相策略,随后以小区层线损最小和换相次数最少为目标构建门洞进线换相策略,从楼内、小区两个环节挖掘降损潜力.针对上海某居民台区的算例分析表明,所提换相策略能使台区配网损耗降低17.2％,较仅通过门洞进线换相提高三相负荷平衡度的做法降低网损10.83个百分点.