Investigation of Water Tree Degradation in Dry‐Cured and Extruded Three‐Layer (E‐E Type) 6.6‐kV Removed XLPE Cables

Dry‐cured and extruded three‐layer (E‐E type) 6.6‐kV cross‐linked polyethylene (XLPE) cables were introduced into electric power systems more than 30 years ago, but they do not experience failures because of water tree degradation. Also, the degradation index of water treeing for these cables has not been established. Therefore, investigating results of residual breakdown voltage and water tree degradation of these cables will help us plan for cable replacement and determine water tree degradation diagnosis scheduling, and will be fundamental data for cable lifetime evaluation. In this study, the authors measured the ac breakdown voltages of dry‐cured and E‐E type 6.6‐kV XLPE cables removed after 18 to 25 years of operation and observed the water trees in their XLPE insulation. As a result, it was observed that breakdown voltages were larger than the maximum operating voltage (6.9 kV) and the ac voltage for the dielectric withstanding test (10.3 kV). Water trees were mainly bow‐tie water trees and their maximum length was approximately 1 mm. Although the number of measured cables was limited, the lifetime of this type of cable was estimated to be approximately 40 years, even experiencing water immersion.     

DISPERSION STATE OF PROTEIN-STABILIZED EMULSIONS

The stability of concentrated benzene-in-water emulsions emulsified by bovine serum albumin (BSA) in the presence of various concentrations of sodium chloride has been measured in the light of the coalescence kinetics. On the acid and alkaline sides of the isoelectric point of BSA (pH 4.9), the rate of coalescence between globules decreased and approached that at the isoelectric point of BSA with increasing concentrations of sodium chloride. In these systems, the interfacial tension at the benzene/aqueous BSA solution interface, and the globule size distribution in the emulsions, reached the values observed at the isoelectric point when the concentration of sodium chloride was above about 50 mM. The role of the adsorbed film of BSA on the surface of dispersed globules is considered in relation to the dissociation state of the BSA molecules.     

中、日、欧的被试者对河川景观注视过程的比较研究

在景观认知·评价过程中,如果把眼球运动作为反映大脑所进行的视觉情报处理过程的外部参数,那么眼的运动方式就可能因评价者的生活经验、知识水平甚至价值观和思维方式的不同而产生差异。因此,可以设想被试者的社会文化背景的差异也有可能会从他们对景观的认知方式上得到体现。作为视觉认知中异域文化差异的比较研究之一,运用眼球运动跟踪仪对评价者的景观认知评价过程进行了跟踪测试,并试图通过对认知过程中的注视点分布、注视点数以及注视点的停留时间和注视内容的变化趋势这几个角度的分析比较来探讨社会文化背景的差异如何体现在人类视觉情报信息的收集整理的外部反应中,从而明确在地域特色景观的保留和营造上构成要素的布局方式的意义。     

Critical Generation Evaluation Using Hybrid Energy Function Method

It is well known that the transient energy function (TEF) method is useful for an efficient transient stability assessment as represented by the estimation of the critical clearing time (CCT). However, there still remains an issue for practical use: most of the TEF methods adopt the classical model of a synchronous machine in which the internally generated voltage is assumed to be constant. Moreover, critical generated output can be a more practical stability index instead of the CCT used in the conventional TEF methods. In this paper, a conventional hybrid TEF method is developed in order to estimate the transient stable critical generated power by using an improved hybrid simulation. The proposed method can handle the detailed model for a synchronous machine and can estimate the critical generated power with higher accuracy. Experimental results for a large network model are given in order to verify the practicability of the proposed method.     

Power generation scheduling by neural network

A new method for solving a power generation scheduling problem in an electric power system is presented. The objective is to determine the hourly start-up/ shut-down schedules of all generators so that forecasted hourly power demands per day may be met and total operating costs, the sum of setup and fuel costs for a given day, may be minimized. The problem may be formulated as a large-scale combinatorial optimization problem which includes 0-1 variables representing the start-up/shut-down of generators and continuous variables representing the power outputs. Determination of an optimalsolution within practical time limits is consequently difficult. Until now, the lagrangian relaxation method has been studied as it appeared to be the most practical method for obtaining an approximate solution to the problem. The efficiency of this method, however, depends on how the Lagrange multipliers are determined. Here, it is proposed that the Lagrange multipliers be estimated by utilizing the neural network and results determined from examination of the possibility of applying the backpropagation algorithm to pattern recognitions which presume the relationship between power demand pattern and Lagrange multipliers are reported. Through numerical experiments, it was established that the Lagrange multipliers, estimated by the neural network, are applicable to the problem.     

钢框架结构软钢阻尼器振动控制的试验及理论研究

本文通过试验研究和理论分析探讨极低屈服点软钢阻尼器的减震效果。对建造在野外的三层钢框架结构输入该结构在历年地震观测中采集到的地震波记录进行了拟动力试验。本次拟动力试验选用了4条地震波记录,各分为有阻尼器和无阻尼器的两种情况共计进行了8次试验。试验结果表明软钢阻尼器具有明显的减震效果。并采用能够同时考虑应变硬化和刚度退化现象的SkeletonShift模型模拟阻尼器的恢复力特性,对该结构进行了弹塑性地震反应分析。地震观测、拟动力试验以及计算机分析结果所表现出的各地震反应具有较好的一致性,说明拟动力试验技术应用于模拟结构的地震反应,可得到令人满意的结果。     

Impact of Postfault Active Power Recovery of Photovoltaic Power Generation on Transient Stability

Currently, Japanese grid codes require photovoltaic (PV) power generation systems to continue supplying power to the grid as soon as possible even if the systems temporarily stop their operation. Although the fault ride‐through capability was originally proposed for preventing a cascading frequency drop in the power system, the capability has the impact on other instability phenomena such as transient stability. In this study, we focus on the postfault active power recovery of the PV systems. The impact of the recovery speed on the transient stability is investigated under different load conditions, in particular static/dynamic load condition. Numerical examples are carried out for the one‐machine one‐load infinite‐bus system, and the effects of the recovery speed are evaluated by equal area criterion and critical clearing time. As a result, we have found both desirable and undesirable effects on the transient stability depending on the load condition.     

Representative sample of LISP program inference from examples

The inference of LISP programs from their input-output behaviour is one of the most significant subjects in the study of inductive inference. P.D. Summers gave the inference algorithm for this problem. His method uses a recurrence relation among multiple examples. We have extended this method. By characterizing the set of examples, we introduce the notion of a representative sample that describes the capability of the LISP program appropriately. That is, a representative sample is the set of examples that are the simplest ones of all the examples that behave in the same way. Then, we give a condition that assures the existence of a representative sample and partial correctness of the inference algorithm. Furthermore, we propose an interactive procedure that transforms an arbitrary given set of examples into the representative one. This procedure makes the inference algorithm flexible.     

三维管接头焊后局部热处理加热宽度准则

提出了直接定量评定管接头焊后局部热处理应力释放效果的方法。构造了三维管接头焊接应力和局部热处理温度场,采用粘弹塑性有限元方法对管接头焊后不同局部热处理条件不应力分布特征进行了研究,对单道焊情况,不同焊接规范下的焊接应力分布具有相似性,焊接顺序对应力峰值位置的影响较小。对管接头热点处焊接应力在不同局部热处理条件下释放程度做了分析,在局部热处理加热宽度足够大情况下残余应力明显下降,周向和轴向应力分量与加热宽度的关系不同,周向和轴向应力的最优加热宽度分别为3.46√-Rr的4.8√-Rt。通过对局部热处理主要工艺参数的计算,推荐了正交管接头局热处理加热宽度准则。