Solid-State Control-Low Voltage Heating of Motors

In recent years, industrial plants have been utilizing more electric motors as drivers because of their high efficiency and reliability and lower maintenance costs. Electrified continuous process plants are using electric motors for both primary and standby drives. When these standby motors are not operating during normal plant runs, their windings collect moisture. Moisture attacks insulation and causes insulation failure. A breakdown of motor insulation may occur when a standby motor is suddenly energized to take the place of the primary motor. When it is not in operation, directly heating the motor winding with a low voltage system, coupled with automatic control, will guard the motor from moisture attack and extend its service life. The experience with low voltage heating of motor windings as described by M. H. Yuen in his article [1] has proved its effectiveness. However, conventional relays, timers, contactors, etc., were utilized in the circuits.     

可控电抗器及其在异步电动机软起动中的应用

异步电动机起动时最初起动电流很大,可达4~7倍额定电流。本文提出了一种新型软起动方案,即在电动机定子回路中串入可控电抗器来限制起动电流,实现软起动。磁控式可控电抗器高压工作绕组和低压控制绕组隔离,大大提高了其工作可靠性,其串联在电动机定子绕组中限流作用明显且不消耗能量。仿真和实验平台表明,异步电机起动平稳。     

低压电机绕组挂漆量工艺研究

目前低压电机绝缘结构已趋于成熟,如何进一步提高绕组整体绝缘结构的机械强度和电气强度成为行业的研究方向.减少浸漆烘焙过程中绝缘漆的流失,提高绕组的挂漆量,有利于提高绕组端部的机械强度和电气强度,可显著提高产品的可靠性.并通过大量的试验数据统计,对提高绕组挂漆量进行了工艺研究,指出了提高绕组挂漆量的切实可行的方法.     

高压异步电动机变频运行中绝缘损坏的分析和对策

针对高压异步电动机应用690 V低压变频改造后出现电动机绝缘损坏的问题,对电动机绝缘故障损坏的原因展开分析,认为变频器输出波形恶劣、电动机绝缘结构缺陷是主要因素,据此提出了加装滤波器、电动机选用成型绕组加强绝缘性能的对策,取得了良好的效果。     

Transient Surges and Motor Protection

Steep-fronted voltage transients can damage motor windings, leading to eventual breakdown if not immediate failure. Circuit switching is the most common cause of such impulses, which may occur in both high-and low-voltage systems. Capacitor bank switching and the use of vacuum contactors are two examples. Several common misconceptions about the surge problem in motor circuits are explored. Current studies of surge phenomena, the ability of motors to withstand surges, and the likely direction of future standards are reviewed. The motor user is given some suggestions for detecting the presence of transient impulses and for guarding against their harmful effects.     

低压大功率电机定子绕组接线工艺研究

介绍了一种新型低压大功率电机绕组接线方式,即汇流环接线工艺。采用汇流环结构不但解决了低压大功率电机引线排列不规整,固定排线空间紧张问题,同时解决了每路引出线截面积较大,易产生直流电阻不平衡问题。     

用三维有限元法计算分裂式变压器短路阻抗

为准确计算出分裂变压器高、低压绕组间的短路阻抗,首先采用ANSYS的三维静态磁标势法数值计算得出高压多并联支路与单个低压绕组间的多绕组电感矩阵,并依据电路理论将其简化为等效双绕组电感矩阵,进而得到短路阻抗百分比,并推导了高压各并联支路电流分配,最后给出一个概念设计的分裂式高温超导变压器算例。计算结果表明,低压各分裂绕组分别单独运行时,高压绕组的各并联支路电流分配不均,主要集中在与运行的低压分裂绕组紧耦合的高压支路中,故高压绕组与低压各分裂绕组间的短路阻抗主要由紧耦合的高压支路与低压分裂绕组间的漏磁路决定。     

散线同心式绕组制造工艺

低压大功率电机散嵌绕组由于并绕根数多、线圈截面较大、绕组端部较厚,整型成为绕组制造过程的难点.同心式绕组嵌线方便,端部整型容易,解决了散嵌绕组嵌线过程整型难的问题.并从同心式绕组制造工艺进行分析,从中归纳总结了同心式散嵌绕组的制造经验,为制造类似电机提供了一定的参考.     

大容量发电机主变压器感应过电压计算

当冲击电压波侵入到变压器高压绕组时,除在本绕组内产生暂态振荡外,也会通过静电和电磁感应传递到低压绕组中,使低压绕组侧产生过电压。本文以主变压器高压侧避雷器的残压为冲击电压限值,对主变压器低压侧和发电机出口可能的过电压,以及发电机出口冲击电压上升速度进行近似计算,并以此为依据选择避雷器和电容器。     

Motor shaft voltages and bearing currents and their reduction inmultilevel medium-voltage PWM voltage-source-inverter drive applications

This paper presents test results on problems and solutions of motor shaft voltages and bearing currents in medium-voltage pulsewidth modulated (PWM) drive systems. Tests show that multilevel medium-voltage PWM voltage-source inverter drives can cause motor bearing currents, similar to a low-voltage PWM drives, even with one motor bearing insulated. Common-mode voltages generated as a result of PWM switching are observed on motor windings and capacitively coupled to the motor shaft, leading to bearing currents. Potential solutions, including altering common-mode circuitry, changing the grounding scheme, providing common-mode filtering, and grounding the motor shaft, are investigated. Test results on their effectiveness are presented     

An output buffer for 5 V applications in a 0.18 μm 1.8 V/3.3 V CMOS process

Abstract

This article presents a novel output buffer it realized with low-voltage (1.8- and 3.3-V) transistors to transmit high-voltage signals for 5-V applications. Otherway, the proposed circuit also can apply to transmitting higher voltage signals using lower voltage process integrated circuit. The buffer converts 0/1.8-V voltage swing to 0/5-V voltage swing by three steps. The simulation shows the buffer has good AC/DC characteristics. The proposed buffer has been fabricated in a 0.18-μm 1.8/3.3-V 1P6M CMOS process. The experimental results have confirmed that the proposed buffer can be successfully operated without suffering high-voltage gate-oxide overstress in the 5-V interface. In addition, a new level converter that can convert 0/3.3-V voltage swing to 1.8/5-V voltage swing is also presented in this article. The proposed level converter is realized with only 3.3-V transistors. The experimental results have also confirmed that the proposed level converter can be operated correctly.     

Preservation of large motors and generators from weather onoffshore platforms

The problems encountered with moisture condensation in the bearing cavities and internal windings of large motors and generators when proper equipment storage procedures are not practiced are outlined. The moisture condensation problems associated with the operation and shutdown of large motors and generators due to weather conditions at the site location of the offshore platforms are also discussed. The particular platforms discussed are located on the outer continent shelf in the Santa Barbara Channel off the coast of California. On-site modification of the generator housing and the electrical module was necessary to preserve the electrical equipment from the effects of the weather. The recommended method of preservation and the necessary precautions before the startup of the electrical machines are presented     

高压紧凑型防爆电动机电加热带的选择

加热带是高压紧凑型防爆电动机的重要组成元件,它在电动机停止工作时开始工作,防止电动机在停机时因绕组潮湿、电气绝缘性能下降而引发电气故障。文章介绍了加热带的选型方法,提出了加热带应具备的技术要求。     

六相双Y移30°绕组结构及其应用优势

随着电力电子技术的迅速发展,利用先进的控制技术可以方便的将三相电源变多相电源,因此多相电机得到了迅速的发展。六相双Y移30°绕组是多相绕组中应用较多,具有很好发展前景的一种绕组,交流电机采用六相双Y移30°绕组是减少高次谐波、提高电机效率以及提高电机极限容量的有效措施。介绍了六相双Y移30°绕组的构成理论,对其磁势谐波进行了谐波分析,并对这种绕组的优点进行了简单分析叙述。     

Recent important changes in IEEE motor and generator winding insulation diagnostic testing standards

IEEE standards and test procedures are widely used by motor and generator vendors and users to commission windings in new machines, as well as evaluate the condition of the winding insulation in operating machines. Until recent revisions, the basic procedures and standards in use were written over 25 years ago. Since the 1970s, motor windings have encountered many changes in their design and manufacture. The result was that the interpretation of results in many of the standards was no longer valid for the more modern motors. Over the past five years, the IEEE Power Engineering Society has conducted a major review and updating of most of these standards. Many important changes in test procedures and interpretation guidelines have resulted. This paper reviews the main insulation standards used for stator and rotor winding diagnostic testing, and discusses the changes that have been made. Standards discussed include: IEEE 43, 56, 95, 286, 522, and 1434. For example, IEEE 43-2000 now requires a minimum insulation resistance of 100 M/spl Omega/ for new stator windings rated 2300 V or more, rather than the "kV+1" that was required in the past. Furthermore, the interpretation for polarization index has changed such that a motor with a polarization index of 1 is no longer automatically classed as bad.     

一起220kV变压器绕组短路损坏事故分析

介绍了一起由低压开关柜内部短路引起的220 kV变压器绕组损坏事故。为检查绕组损坏程度,进行了绕组电阻测试、油中溶解气体分析和扫频响应等试验,通过对试验数据分析得出变压器内部低压侧绕组发生严重变形且低压C相绕组存有断点,返厂解体结果验证了分析结论的正确性,最后对事故发生的原因进行了深入分析,并提出了采用半硬自粘换位导线等防范措施。     

电加热紫外光固化浸漆工艺在新能源汽车电机制造中的应用

随着电机制造技术的进步,电机绝缘技术也在快速发展。根据在电动汽车/混合动力汽车（EV/HEV）驱动电机制造领域的工程实践,从绝缘浸渍漆、工艺、设备3方面出发,介绍了一种适用于散嵌绕组电机的新型绝缘处理技术：电加热紫外光固化工艺（E-UV）。通过实际应用,证实了该技术具有能耗低、生产周期短、绝缘浸渍漆利用率高等特点,适用于EV/HEV驱动电机的批量生产。     

“Right sizing” circuit breakers in motor starters

Instantaneous-trip, molded-case circuit breakers (MCCBs) have been applied successfully for low-voltage motor protection for many years. However, the changes in motor-starting characteristics have created more difficult challenges for the application engineer. The major challenge is successfully starting the low-voltage motor without causing the instantaneous-trip breaker to falsely trip without exceeding equipment ratings or violating limitations in the National Electrical Code (NEC). "Right sizing" circuit breakers for use in low-voltage combination motor starters is critical to the successful, reliable operation of plant and process facilities. If not properly applied, false tripping on motor starting and contact welding of contactors may occur. Moreover, changes in the NEC and improved motor efficiencies have impacted equipment selection and protection. The following information is intended to guide application engineers in their selection of the right breaker and its setting for more reliable motor protection: combination motor-starter components, circuit breaker characteristics, circuit breaker and combination. starter testing, motor starting characteristics, and component selection using coordination examples. The examples show how selecting the right breaker and breaker setting can avoid false tripping during starting, mitigate contact welding, and provide backup protection for overload conditions     

Motor winding problems caused by inverter drives

This article describes measurements of the surge voltage characteristics from a group of eight low-voltage motors driven by inverter fed drives. As described here, two motors have repeatedly been subjected to unexpected stator winding failures. Inspection of the windings after failure indicated that the main cause of the failures is the voltage surge environment applied to the stator winding.     

大规模光伏电站中箱式变电站对光伏组件的影响分析

随着全球能源紧缺,大规模光伏电站越来越成为新能源发电的重要形式之一。大规模光伏发电常采用箱式变电站作为将光伏逆变器出口的低压交流电升为高压电的升压设备。分析了箱式变电站中普遍使用的双分裂绕组变压器对光伏电池的影响。提出了通过减小光伏电池对地电压波动来减小对地回路电流的结论。并得出双分裂变压器两个低压侧绕组存在耦合,引起光伏逆变器低压绕组中心点电压同步波动,从而电池组件产生噪音的结论。最后通过仿真验证上述理论分析的可行性和有效性。