余弦方波电压作用下不同水树长度缺陷XLPE材料的击穿特性

为研究余弦方波电压作用下不同水树长度缺陷交联聚乙烯(XLPE)材料的击穿特性,采用高频高压电源对XLPE试样进行加速水树老化,制备了水树长度占比分别为30%、60%、90%的XLPE试样。测量了试样在0.1 Hz余弦方波电压下的击穿特性,并对击穿试验的结果进行了理论分析。结果表明:在3U0等效场强的作用下,0.1 Hz的余弦方波电压可以导致水树长度占比为90%的XLPE试样在15 min内击穿,但即使将加压时间延长至10 h,水树长度占比为30%、60%的XLPE试样也未发生击穿;水树缺陷的击穿存在临界场强,当施加电压的等效场强低于临界场强时,延长电压作用时间至10 h,水树缺陷也不会发生击穿,水树的形态也未出现显著改变;0.1 Hz余弦方波耐压试验可以发现电缆中水树长度占比为90%的缺陷,不能发现水树长度占比为30%、60%的缺陷,也不会导致这两种水树缺陷的恶化。

工频和0.1Hz余弦方波电压对电缆耐压考核的等效性分析

工频与0.1 Hz余弦方波电压均可用于电缆耐压考核试验,但这两种电压考核的等效性尚不明确。为此,基于针板电极模型,对不同绝缘剩余厚度缺陷试样分别在工频和0.1 Hz余弦方波电压下进行击穿试验。统计分析不同电压下击穿时间的威布尔分布,观测并比较击穿通道的形貌特征,对工频和0.1 Hz余弦方波电压耐压考核强度差异的原因进行分析。结果表明:在针板电极模型条件下,0.1 Hz余弦方波电压下缺陷的击穿电压和击穿时间均大于工频电压,对电缆耐压考核的强度显著低于工频电压。0.1 Hz余弦方波电压试样击穿前未发现明显的烧灼碳化痕迹,累积效应不显著。余弦方波直流阶段注入电荷导致合成电场强度降低和累积效应不显著,这可能是导致0.1 Hz余弦方波电压对电缆耐压考核强度显著低于工频电压的原因。

苏州供电公司0.1Hz VLF(超低频)余弦方波电缆耐压试验技术应用

苏州供电公司于1999年购入德国SebaKMT公司0.1Hz余弦方波超低频耐压系统,于2000年投入使用,对主要是10kV电缆进行耐压试验,考核电缆本体和附件的质量及施工水平。使用中成功发现了2次试验击穿,经过故障定位并修复后,电缆供电隐患得以排除。

基于余弦方波的配电电缆绝缘多功能测试装置的研制

文中研制了一种兼具产生超低频余弦方波和振荡波的多功能高压发生装置,利用该装置既可以开展电缆绝缘的耐受电压能力测试,也可以开展局部放电检测。装置主要由快速充电单元、放电单元、高压电抗器以及局放检测单元组成。放电单元作为装置的核心单元,其实现采用了基于串联IGBT为核心的高压半导体开关,以满足系统最高30 kV峰值电压输出的需求。整套装置可以在余弦方波和直流振荡波两种模式下独立工作.在实验室中搭建系统平台,对中间接头处有缺陷电缆进行了局部放电检测。实验结果验证了多功能高压发生装置用于电缆绝缘测试的有效性。

余弦方波电压频率对电缆典型绝缘缺陷击穿时间的影响

为研究余弦方波电压频率对电缆典型绝缘缺陷击穿时间的影响,本研究制作了针板电极缺陷和水树缺陷模型,分别利用0.1、0.5、1.0 Hz的余弦方波电压进行击穿试验,统计了击穿时间的分布和击穿点的时刻,观测了击穿通道的微观形貌,并讨论余弦方波电压频率对电缆典型绝缘缺陷击穿时间影响的作用机制。结果表明:随着余弦方波电压频率的增大,电缆典型绝缘缺陷的击穿时间显著缩短,分散性下降。绝大多数击穿发生在电压的极性变换阶段也就是余弦方波的上升沿或下降沿位置。空间电荷注入导致的极性转换过程中合成场强增大和单位时间内极性转换次数的增加可能是引起上述现象的主要原因。

基于余弦方波成形的GMSK+PN调制方法研究

对GMSK+PN信号的调制方法与解调性能进行仿真模拟,实现了GMSK+PN信号的调制和接收解调过程,计算了不同信噪比条件下的平均误码率,提出了一种基于余弦方波成形伪码的联合调制方法,调整对PN信号的载波成形方式,提升了频谱滚降性能。实验结果表明,所提方法降低了数传码的解调误码率,有利于在信道条件较差的系统中实现无差错传输和正确分离测距伪码,可为同时实现数传和测距功能提供参考。

The Effects of Flexible Vegetation on Forces with a Keulegan- Carpenter Number in Relation to Structures Due to Long Waves

Extreme coastal events require careful prediction of wave forces. Recent tsunamis have resulted in extensive damage of coastal structures. Such scenarios are the result of the action of long waves on structures. In this paper, the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program. The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation. The vegetative parameters, along with the width of the green belt, its position from the reference line, the diameter of the individual stems as well as the spacing between them, and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem. The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number （KC） was discussed in this paper. It has been shown that when vegetal patches are present in front of structure, the forces could be limited to within F＊≤I, by a percentile of 92%, 90%, 55%, and 96%, respectively for gap ratios of 0.0, 0.5, 1.0, and 1.5. The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.

Nonlocal Symmetries and Explicit Solutions of the Boussinesq Equation

The nonlocal symmetry of the Boussinesq equation is obtained from the known Lax pair. The explicit analytic interaction solutions between solitary waves and cnoidal waves are obtained through the localization procedure of nonlocal symmetry. Some other types of solutions, such as rational solutions and error function solutions, are given by using the fourth Painlev~ equation with special values of the parameters. For some interesting solutions, the figures are given out to show their properties.

Construction of Soliton-Cnoidal Wave Interaction Solution for the (2+1)-Dimensional Breaking Soliton Equation

In this paper, the truncated Painleve analysis and the consistent tanh expansion （CTE） method are developed for the （2＋1）-dimensional breaking soliton equation. As a result, the soliton-cnoidal wave interaction solution of the equation is explicitly given, which is dimcult to be found by other traditional methods. When the value of the Jacobi elliptic function modulus rn = 1, the soliton-cnoidal wave interaction solution reduces back to the two-soliton solution. The method can also be extended to other types of nonlinear evolution equations in mathematical physics.

Nonlocal Symmetry,CTE Solvability and Interaction Solutions of Whitham–Broer–Kaup Equations

Whitham–Broer–Kaup(WBK) equations in the shallow water small-amplitude regime is hereby under investigation. Nonlocal symmetry and Bcklund transformation are presented via the truncated Painlevé expansion.This residual symmetry is localised to Lie point symmetry by the properly enlarged system. The finite symmetry transformation of the prolonged system is computed. Based on the CTE method, WBK equations are linearized and new analytic interaction solutions between solitary waves and cnoidal waves are given with the aid of solutions for the linear equation.

Nonlocal Symmetry and Interaction Solutions of a Generalized Kadomtsev–Petviashvili Equation

A generalized Kadomtsev–Petviashvili equation is studied by nonlocal symmetry method and consistent Riccati expansion(CRE) method in this paper. Applying the truncated Painlevé analysis to the generalized Kadomtsev–Petviashvili equation, some B¨acklund transformations(BTs) including auto-BT and non-auto-BT are obtained. The auto-BT leads to a nonlocal symmetry which corresponds to the residual of the truncated Painlevé expansion. Then the nonlocal symmetry is localized to the corresponding nonlocal group by introducing two new variables. Further,by applying the Lie point symmetry method to the prolonged system, a new type of finite symmetry transformation is derived. In addition, the generalized Kadomtsev–Petviashvili equation is proved consistent Riccati expansion(CRE)solvable. As a result, the soliton-cnoidal wave interaction solutions of the equation are explicitly given, which are difficult to be found by other traditional methods. Moreover, figures are given out to show the properties of the explicit analytic interaction solutions.