Theoretical and Experimental Study on Ground Coupled Heat Pump with Vertical Spiral Coil

The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and recovery of undergroun d field temperature under different operation ratio and the optimal operation ratio were simulated.The performance parameters, i.e. inlet and outlet temperature of the ground spiral coil in heating and cooling modes were tested, the heat extracted or emitted by the heat pump to the ground was calculated, and the coefficients of performance (COP) of GCHP at heat ing and cooling modes were analyzed.

The Research on Neutral Grounding Scheme of Fengxian 35kV and 10 kV Power Grid

Combined with actual situation of Fengxian power Supply Company, the neutral grounding modes of Fengxian 35 kV and 10 kV power grid are studied in the paper. The different frequencies injected method is used to measure the capacitive current of Fengxian 28 substations, and the neutral grounding modes of the 28 substations are determined based on the measured values of capacitive current.

Experimental Analysis on Shielding Effect of the Grounding Electrodes Under Impulse-current

Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode,the experiments that had been carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity.However,in practical conditions,most of the grounding systems are constructed of grounding electrodes with branches in different directions.In this study,basing on the principle of dimensional similarity,impulse simulation experiments are performed on the common ground electrodes with conductor branches.This paper focuses on analyzing the impulse current dispersal regularity of different branches when injecting at one point.Comparing with the leakage current distribution of a single ground electrode,it is found that the leakage currents along the branches increase with the distance to the current feed point,and the more conductors near the injection point,the more uneven the leakage current distribution is.This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.

Experimental Verification to Estimate Ground Thermal Conductivity Using Spiral Coil Type Ground Heat Exchangers

This paper presents an experimental study on the evaluation of thermal response of a spiral coil type GHE （ground heat exchanger）. This GHE was installed on partially saturated landfill ground that was composed of silt and clay in the runway area of Incheon International airport. TRT （thermal response test） was conducted for more than 65 hours under continuous operation conditions. Ground thermal conductivity was derived based on line source theory, which has usually been found to be appropriate for line type GHEs such as U, W and 2U types. A reasonable method to derive ground thermal conductivity using the infinite line source theory for a spiral coil type GHE was introduced. Ground thermal conductivity from the TRT using spiral coil type GHE was compared with those from the analytical equivalent model of ground thermal conductivity.

Comparison between open phase fault of arc suppression coil and single phase to earth fault in coal mine distribution network

When, in a coal mine distribution network whose neutral point is grounded by an arc suppression coil (ASC), a fault occurs in the ASC, compensation cannot be properly realized. Furthermore, it can damage the safe and reliable run of the network. We first introduce a three-phase five-column arc suppression coil (TPFCASC) and discuss its autotracking compensation theory. Then we compare the single phase to ground fault of the coal mine distribution network with an open phase fault at the TPFCASC using the Thévenin theory, the symmetrical-component method and the complex sequence network respectively. The results show that, in both types of faults, zero-sequence voltage of the network will appear and the maximum magnitude of this zero-sequence voltage is different in both faults. Based on this situation, a protection for the open phase fault at the TPFCASC should be estab-lished.

水平多层spiral型地埋管数值模拟研究及换热特性分析

本文基于COMSOL软件建立了水平spiral型多层地埋管群传热三维数值模拟模型,并对其换热性能和温度场进行分析研究。结果表明:对比水平spiral多层并联管群来说,远离注入端的地埋管管内温度相对较低。地埋管群周围地层温度有所升高,远离注入端的地层温度变化相对较小。地埋管群的换热量随循环流体的流速增加而增加,但增幅降低。在进行换热器设计时,应合理控制循环水的流速。3层螺旋地埋管群的换热量略高,但层间干扰明显,建议选用2层并联螺旋管群。

基于自耦变压器结构的双调节式矿用消弧线圈研究

该文设计一种带有三次绕组的自耦变压器结构矿用消弧线圈,二次绕组接晶闸管投切电容电路,第三绕组具有高短路阻抗特性,输出端接反并联晶闸管,对消弧线圈进行细调。通过系统双调节回路的协调控制,可实现变压器消弧线圈的大范围连续调节。对消弧线圈的运行参数、控制策略以及调谐方法进行深入的研究分析。这种消弧线圈具有响应速度快、连续调节范围宽、谐波小、伏安特性好及补偿精度高等优点。MATLAB仿真验证新型矿用消弧线圈的合理性和优越性。

贯通地线用护套盘管失效分析

某电缆制造厂在贯通地线制造过程中发现护套盘管开裂,采用宏观形貌分析、化学成分分析、金相显微镜分析、残余应力分析等手段分析了贯通地线护套盘管开裂原因。结果表明:贯通地线在线退火时,退火炉的电源功率存在不稳定性,电源功率骤升,使得护套盘管产生晶粒长大,甚至局部点熔化产生裂纹源;随着热应力、护套盘管变形应力及缆芯应力释放的共同作用,护套盘管裂纹扩展,甚至断裂。

一种典型10 kV电缆线路接地故障快速隔离动作分析

针对一起变电站中性点接地方式改造过程中零序跳闸事件,提出10 kV电缆线路的典型拓扑结构。结合实际工作,阐述当前试点应用中的经消弧线圈并联小电阻接地方式,并给出零序保护定值推荐值。结合案例,全面分析接地变跳闸逻辑错误、电缆线路FA自愈失败等故障原因,并提出改进措施。

10 kV中性点接地方式由消弧线圈变为小电阻的改造方法及常见问题探讨

随着城市电网的发展,电缆在10 kV配网中的比重不断增加,消弧线圈接地方式的各种弊端不断凸显,小电阻接地方式的优势则越发明显。介绍了10 kV城市配电网中性点接地方式由消弧线圈改造为小电阻的总体思路及流程,并对小电阻接地方式存在的一系列问题进行了探讨。

涟钢Ⅱ站接地方式研究与讨论

涟钢公司由于电网接地电流较小,系统接地方式采取消弧线圈加不接地方式。近年来,随着公司发展,系统网络日趋复杂。系统内部分区域发生单相接地故障时,出现消弧线圈欠补偿,导致故障电缆持续拉弧、燃烧的现象。为此,从单相接地电容电流数学模型出发,对各区域接地电流进行计算,并核算现有消弧线圈补偿能力,为后续网络发展接地方式的选取提供理论基础。

油田配电网中性点接地方式的优化及认识

配电网系统是油田生产的动力系统,配电网的经济、安全运行,直接关系到油田的产量及生产成本。配电网中性点接地方式的选择决定了配电网的经济性和可行性。目前油田配电网主要采用中性点不接地的方式,随着油田电网规模逐渐扩大,该方式已逐渐暴露出易断电、检修速度慢的缺点。通过分析原有中性点接地方式在生产运行中存在的问题,探讨现场试运行配电网中性点经消弧线圈并联电阻接地的优势及在油田应用的可行性。试验表明,该接地方式可为油田提供更加安全、可靠的配电系统,可实现提高油田生产时率、降低运行成本、减轻劳动强度的目的,具有良好的推广应用前景。

一例单相接地故障管理系统并联运行下的误判案例分析

对某化工企业10 kV电力系统发生单相接地故障时,2套MXJD单相接地故障管理系统在并联运行下的误判进行了研究。通过对该案例的现象、原因、影响和处理过程探讨,剖析MXJD单相接地故障管理系统的工作原理、系统设计、数据共享等关键参数,提出了单相接地故障管理系统在并联运行时的一些建议,为电网可靠运行提供参考。

配电网中性点接地的新途径

提出了一种基于快速可控消弧线圈接地加快速选线跳闸的新型接地方式,说明了该接地方式对可控消弧线圈(CASC)和选线装置的要求;介绍了一种新型配电网智能型快速消弧线圈和另一种配电网接地故障智能检测装置的基本原理、技术特点及运行情况,以及拟实现新型接地方式的试用情况。最后论述了该接地方式的优越性。

发电机中性点接地装置等效电路的分析

分析了发电机中性点经配电变压器二次侧接电阻和消弧线圈两种方式接地的等效电路对外加电源型单相接地保护导纳判据的影响 ,指出忽略配电变压器或消弧线圈的激磁阻抗和漏抗降低了判据的准确性。考虑相应参数的影响因素能够提高接地故障过渡电阻值的计算准确度 ,进一步提高保护的灵敏度。

基于消弧线圈补偿特征的故障选线新方法

为解决零序电流互感器极性不明确导致选线错误的问题,提出一种根据消弧线圈补偿特征的选线新方法。对于每条线路建立健全线路数学模型,利用零序电压电流暂态分量与基频分量求取相应的导纳参数。针对分量"湮没"问题,提出一种矩阵束的改进方法实现小幅值高频分量的精确提取。分析得到消弧线圈补偿作用规律:在确定频段内故障线路两参数符号相反或数值明显减小,健全线路两参数计算结果相近,可实现故障判断。仿真实验结果验证了该方法摆脱了零序互感器极性不同导致选线错误的限制,无需线路参数信息即可实现故障自判,适应性强。

35 kV系统中性点不同接地方式对铁磁谐振的影响研究

35 kV系统中铁磁谐振过电压频繁发生,对系统造成很大的危害。利用理论分析和EMTP-RV仿真相结合的方法,分析了中国35 kV系统3种中性点接地方式(中性点不接地、经消弧线圈或小电阻接地)下由电磁式电压互感器(PT)饱和引起的铁磁谐振过电压,研究结果表明,在中性点经消弧线圈或小电阻接地系统中,只要消弧线圈或小电阻的参数选取合适,能够将中性点位移电压限制在电压三角形内,可有效抑制铁磁谐振的发生。

10kV配电网中性点接地方式的优化研究

针对某市10 k V配电网中性点运行方式存在的问题,提出一种结合中性点经电阻接地和经消弧线圈接地的优化改造方案。用ATP-EMTP建立10 k V配网单相接地故障仿真模型,在两种不同中性点接地方式下,模拟多种单相接地故障。理论分析及仿真实验表明,该新型接地方式可有效抑制单相接地时刻的瞬态过电压,当接地故障发生于架空线末端时,中性点、母线和故障点上的瞬态过电压降幅分别为34.7%、25.3%和18.5%;同时,该新型接地方式能够避免虚幻接地现象发生,并且在发生永久性单相接地故障时,可以通过切换并联电阻以实现准确的故障选线。该新型接中性点地方式对于配网安全可靠运行具有重要意义。

基于磁通可控的新型自动调谐消弧线圈

提出了一种不产生谐波,宽范围自动快速补偿对地电容电流的新型自动调谐消弧线圈的设计原理,其核心是基于磁通可控的大容量连续可调电抗器,而系统对地电容检测采用频率扫描法。文中详细分析了它们的原理,并说明了系统实现接地故障时电抗器与对地电容自动调谐的方法。样机实验证实了设计原理和方法的正确性。

大型水轮发电机中性点接地方式的若干问题分析

详细讨论了大型水轮发电机中性点经两种不同方式接地时存在的若干问题。对中性点经消弧线圈接地 ,主要分析了限制故障电流在安全接地电流范围内时补偿系数的选取范围 ,在满足安全接地电流的条件下 ,高压侧发生接地故障时产生的传递电压可能使基波零序电压型定子接地保护误动 ,不对称系数和安全接地电流影响正常时的中性点位移电压。对中性点经配电变压器高阻接地方式 ,主要论述了其在限制过电压方面的优点 ,但存在增大故障电流和降低接地保护灵敏度的不足 ,分析了两个中性点经配电变压器高阻接地的设计实例。