Analytical prediction of abnormal temporary overvoltages due to ground faults in MV networks

The paper deals with the temporary overvoltages that build up in radial MV distribution networks following the inception of a 1-phase-to-ground fault. It will be demonstrated that, for extended cable/overhead MV distribution networks with ungrounded neutral, in case of low resistance faults at critical locations along overhead lines, the neutral voltage can reach very large values, significantly higher than 1 p.u. (up to 2.5 p.u.). The attendant temporary overvoltages on healthy phases can be very large, much higher than √3 p.u. (up to 3.5 p.u.). Fault currents are also affected, reaching twice the value calculated with simplified methods, i.e. neglecting series impedances. Quick yet accurate analytical formulas for the prediction of maximum overvoltages, fault currents and critical fault distances are presented, together with their validation by detailed ATP-EMTP simulations. The results of a study on an existing Italian 15 kV–50 Hz extended mixed cable/overhead distribution network are finally presented and discussed.     

XDPS-400分散控制系统典型故障及解决方案

以广州发电厂应用的上海新华控制工程公司的XDPS-400系统为例,讨论了XDPS的典型故障,分析了造成故障的原因,并提出了相应的解决方案.     

电缆故障分析与精确定点

通过对电缆各种故障类型的分析、总结和归纳,给出电缆故障定位基本流程,并结合典型电缆故障查找案例,阐述了针对不同电缆故障类型所采用的不同的精确定点方法和技术手段。     

Lightning faults on distribution lines

The authors have developed low-cost instrumentation to differentiate between outages caused by lightning and those caused by other phenomena. The theories used to develop this coincident lightning events detector (CLED), the experimental design used for testing the CLED, and the test results are discussed. The following conclusions are drawn from lightning fault data collected in the Florida test area: shielding from other nearby structures is a major consideration when assessing the lightning fault rate on distribution lines and, for typical distribution lines in the USA. A range of values from 0.6 to 0.8 for the shielding factor would be appropriate     

电力电缆故障的预防措施

分析了电力电缆故障的主要原因,针对故障原因提出了在电缆的选型,电缆线路设计、施工安装及日常运行维护中应采取的对故障的预防措施。     

常见电气故障的排除方法和技术

电气设备在使用过程中,经常会出现各种故障。当电气设备发生故障时,系统将无法正常工作。分析了电气设备故障的特点、查找和相应的排除方法。     

熔断器的常见故障及维护方法

熔断器在线路中起保护作用,串接在电路中,当线路发生故障时,熔体能自动熔断,切断电源回路,从而保护线路和电气设备.分析了熔断器的常见故障及处理方法,并通过例子来说明熔断器的保护作用的重要性和必要性等.     

Fault-signature modeling and detection of inner-race bearing faults

This paper develops a fault-signature model and a fault-detection scheme for using machine vibration to detect inner-race defects. To motivate this research, it is explained and illustrated with experimental results why fault signatures from nonouter-race defects (e.g., inner-race defects) can be less salient than those from outer-race defects. Then, a signal model is presented for the production and propagation of an inner-race fault signature; this model is then used to design an inner-race fault-detection scheme. This scheme examines machine-vibration spectra for peaks with phase-coupled sidebands occurring at a spacing predicted by the model. The proficiency of this fault-detection scheme at detecting inner-race bearing faults is then experimentally verified with results from 12 bearings representing varying degrees of fault severity.     

变电站自动化系统常见故障及处理

针对自动化系统在现场实际运行中的常见故障:通信网络类故障、数据采集故障、误报警故障和与其他厂家装置不匹配故障进行了分析和归纳,从大量的现场数据中找出其规律性,分析了产生的原因(产品质量、不同厂家设备的接口通信、开放性等问题),提出了处理建议与改进措施.着重介绍了与变电站自动化系统密切相关几类典型问题的解决方法,为快速查找和正确处理变电站自动化系统故障提供了指导方法.     

Intercircuit faults and distance relaying of dual-circuit lines

The main sources of error and other difficulties associated with the distance protection of dual-circuit transmission lines are well known. However, the design or selection of protection schemes usually fails to consider some of the more extraordinary faults that do occur. This paper considers the observed impedances that result from intercircuit faults on a simulated dual-circuit transmission line, where variations in the phasing as well as the impedance ratios have been considered. The simulations performed with the Alternative Transients Program show that intercircuit faults may be undetectable in the instantaneous protection zone depending on the scheme adopted and the impedances of the surrounding network. The observed under-reaching has the potential to lead to a loss of major loads, maloperation of single-pole tripping schemes and even system instabilities based on the critical clearance requirements.     

Tests on XLPE-insulated cable arcing faults and arc-proofing

Questions about the adequacy of arc-proofing have arisen in connection with underground systems using XLPE-insulated cables, because of an increasing number of arc faults. Extensive testing at available short-circuit-current levels of 8 kA is described. The results indicate that a minimum safe distance of 50 cm should be maintained for nonarc-proofed equipment. For equipment protected with arc-resistant tape, this distance can be substantially reduced. Standard tests based on the use of faulted XLPE cable ends are proposed to verify arc-proofing effectiveness and the arc-resistance of materials     

永磁直流电动机用永磁体形状分析

在永磁直流电动机的设计中,永磁体形状和尺寸对电机性能、包括换向性能有非常重要的影响.选择合适的永磁体形状和尺寸有重要意义.瓦片形磁极结构是永磁直流电动机常用的磁极结构之一.运用场路结合的方法,通过Ansys软件,比较和分析了不同瓦片形磁极形状和尺寸对永磁直流电动机性能的影响,并通过样机试验验证了分析结果的正确性,最后得到不同永磁体形状性能特点的结论.结论对永磁电机的设计有一定指导意义.     

变压器匝间绝缘故障的分析

介绍了变压器匝间绝缘故障的起因和特点。阐述了诊断变压器匝间绝缘故障常用的绝缘油色谱分析和高压试验数据相结合的分析方法。结合实碌工作经验,提出了分析变压器匝间绝缘故障几点意见。     

Air conditioner response to transmission faults

This paper describes two multi-phase faults events which occurred during periods of high air conditioning use. There was a significant loss of load in these events which is attributed to air conditioner motor protection. The overall response of the transmission system is simulated using induction motor models based on the characteristics of a typical residential air conditioner compressor motor. The sensitivity of factors such as fault location, fault duration and excitation system performance is also investigated     

油断路器的常见故障及处理方法

分析了油断路器的常见故障及形成原因和排除方法。包括油断路器油位的异常、油断路器发生爆炸的原因及预防措施,油断路器操作机构的故障原因及排除等。     

Clearing faults near shunt capacitor banks

Fault interrupting tests on high-voltage circuit breakers confirmed the problems of breaking a short-circuit current, which can occur in substations with shunt capacitor banks. Research was conducted on the behavior of different extinguishing media. Tests show that all types of circuit breakers (including the restrike-free breakers) have reignitions after the interruption of faults in the vicinity of a shunt capacitor bank. This is caused by the low rate of rise of the recovery voltage which gives the circuit breaker an opportunity to clear at short arcing times. Reignitions occur because of the low dielectric withstand capability of the small contact gap. Both tests and computer calculations show high overvoltages when the circuit breaker interrupts at one of the superimposed high-frequency current zeros which are created after reignition. Some breakers interrupt at a high-frequency current zero and thus create overvoltages. Other breakers do not interrupt at a high-frequency current zero and wait for a current zero of the power-frequency current, thus prolonging the arcing time. The overvoltages in three-phase circuits are higher than in single-phase circuits     

关于电机故障及其检测技术的研究

论述了电机在输入高频低压信号后 ,由于放大了电感量 ,使得测试的电流变化量增大 ,进一步根据电流变化量确定电机的匝间短路的发生和劣化程度 ,增加了判断准确性。测试过程对电机无损伤 ,操作简便。     

无轴承永磁同步电动机永磁体参数优化设计

介绍了无轴承永磁同步电动机径向悬浮力产生原理。通过对比各种永磁体材料的性能和不同转子磁路结构特点,确定采用钕铁硼稀土永磁体,选择转子表面凸装式结构;从理论上分析了径向悬浮力与永磁体厚度、径向悬浮力绕组电流之间的关系;采用有限元方法,在考虑磁路饱和及非线性情况下,对实验样机径向悬浮力进行了计算和分析。研究结果对无轴承永磁同步电动机如何获得最大径向悬浮力以及电动机的优化设计具有参考价值。     

电磁流量计故障的原因及改进措施

介绍了电磁流量计工作原理,并就流量计大面积故障的原因进行了分析,提出了改进措施.