电动机轴电流的危害与防治

电动机运行时,由于轴承中的绝缘润滑油膜被破坏,在转轴与轴承之间存在着电流,这种电流称为轴电流。轴电流以往多出现在大电动机中,但随着逆变器供电的发展,中型电动机中也出现一定的轴电流,而轴电流对电动机轴承及相关部件的危害极大,越来越引起国内外专家与相关工程技术人员的     

变频技术对交流电动机轴电流的影响与预防

变频电源中的高频谐波增大了大中型电机的轴电流。分析了高频轴电流的产生机理,提供了轴电流烧损轴承的判断方法。为减少轴电流的危害,提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施。     

变频技术对交流电动机轴电流的影响与预防

阐述了变频电源中的高频谐波增大了大中型电机的轴电流,分析了高频轴电流的产生机理,提供了轴电流烧损轴承的判断方法.为减少轴电流的危害,提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施.     

变频技术对交流电动机轴电流的影响与预防

变频电源中的高频谐波增大了大中型电机的轴电流。分析了高频轴电流的产生机理，提供了轴电流烧损轴承的判断方法。为减少轴电流的危害，提出了转轴绝缘、轴承绝缘和均衡接地电压等防止变频电动机轴电流危害的具体措施。     

增安型无刷励磁同步电动机的轴承绝缘

轴电流会造成增安型无刷励磁同步电动机滑动轴承的严重损坏,并且影响到其防爆性能。对滑动轴承进行绝缘,断开轴电流的通路,是防止轴电流最简单、最适用的方法。介绍了增安型无刷励磁同步电动机用滑动轴承的绝缘设计、配置以及绝缘轴承在现场安装调试、运行时的注意事项。     

变频电机轴承电气损伤的原因及措施

变频电机在激励工作电压中会产生轴电压现象,常用方法是采用绝缘轴承处理。但如果此方法不能及时处理时,由轴电压引起的轴电流会危害电动机运行的稳定性。通过对变频电机电气性能的分析,提出全新的轴电流损伤的解决方案,通过建立放电旁路,安装导电环将轴承接地,以降低轴电压,避免发生轴承电气损伤的故障。     

对电动机轴电流的分析及防范

轴电流的存在对电动机轴承的使用寿命具有极大的破坏性,根据现场实际运行情况,分析其产生的原因,采取装设转轴接地碳刷、加强非轴伸端轴承座与支架的绝缘等有效措施,从而根本解决轴电流危害的问题.     

对电动机轴电流的分析及防范

轴电流的存在对电动机轴承的使用寿命具有极大的破坏性，根据现场实际运行情况，分析其产生的原因，采取装设转轴接地碳刷，加强非轴伸端轴承座与支架的绝缘等有效措施，从而从根本上解决轴电流危害的问题。     

轴承绝缘对双馈异步发电机高频轴电压和轴电流抑制效果研究

双馈异步发电机具有变流器容量小、体积小、成本低等优点,成为风力发电系统中广泛使用的机型之一。由于双馈异步发电机采用变频器转子侧供电,变频器产生的高频共模电压经电机杂散电容耦合在转轴上感应出轴电压,其引起的轴电流会带来轴承早期失效。针对该问题,目前主要采用轴承部位绝缘同时转轴经电刷接地的方案来抑制轴电压和轴电流,而不同绝缘方案的抑制效果有待从机理上进行分析。该文首先建立了双馈异步电机变频器系统轴电流模型,分析了绝缘层电容对轴承分压比的灵敏度影响,然后针对绝缘轴承座、绝缘端盖以及绝缘轴承三种方案的轴电压和轴电流的抑制效果,对绝缘层所处的位置、绝缘层的厚度和材料对轴承分压比影响进行了计算。分析表明,混合陶瓷轴承可有效抑制轴电流。采用较厚的绝缘层时,绝缘端盖和绝缘轴承座抑制轴电压效果较明显,但需要配合电刷才能抑制轴电流。由于喷涂绝缘轴承的涂层一般较薄,因此,采用喷涂绝缘轴承并不能有效降低高频轴电压,也不能有效抑制高频轴电流。     

多电平中压脉宽调制电压源逆变器驱动装置应用中电动机轴电压和轴承电流及其减小的问题

本介绍了关于在中压脉宽调制（PWM）驱动系统中电动机轴电压和轴承电流问题及解决办法的试验结果。试验表明多电平中压PWM电压源逆变器驱动装置同低压PWM驱动装置一样,甚至对一种轴承绝缘的电动机也可能会引起轴承电流。作为PWM开关在电容上的共模电压可在电机绕组上探测到,在电容上耦合到电机轴上,从而导致轴承电流,对包括改变共模电路,改变接地线路,提供共模滤波和使用机电轴接地在内的可能的解决方法都进行了试验研究,对于它们的有效性试验作了陈述结果。     

Circuit model for shaft voltage prediction in induction motors fed by PWM-based AC drives

The development of high-frequency pulsewidth-modulation-based adjustable-speed drives (ASDs) has increased the efficiency, performance, and controllability in induction motor applications. However, the high switching frequencies and the faster switching times of insulated gate bipolar transistors (the device of choice in these ASDs) introduce disadvantages like overvoltages at the motor terminals when long cables are used between the drive and the motor. Another industry-wide concern is the generation of rotor shaft voltage and the resulting bearing current. The grease film in a bearing acts as a capacitor that charges due to the transitions in the common-mode voltage imposed at the motor terminals by the drive. The breakdown of the film causes a spike of current to flow that can damage the bearing and reduce life. A significant amount of effort has been directed at understanding the shaft voltage phenomenon and the associated bearing current. This paper attempts to develop circuit models to predict the level of the shaft voltage. The circuit models can then be used to predict the shaft voltage levels at different installations, using simulation software like PSpice. Circuit models for two specific motors are developed. The predicted shaft voltage is very close to the actual voltage levels seen on the shaft when the motors are operated by ASDs.     

高压电机绝缘端盖的设计与制造

介绍设计与制造一种新型的绝缘端盖来避免由于轴电压形成的轴电流对轴承使用寿命的影响,从而严重影响高压电机的使用寿命。     

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     

Mitigation of bearing electro-erosion of inverter-fed motors through passive common-mode voltage suppression

In recent years, investigations of bearing current caused by voltage source inverters (VSIs) have emphasized the effect of steep wavefronts and high carrier frequencies. Such investigations have led to suggested bearing current mitigation techniques incorporating frequency-dependent devices such as low-pass VSI output filters and low-inductance ground paths. Alternatively, others have addressed the problem from an electrostatic standpoint within the motor and have offered solutions such as shaft grounding brushes, insulated bearings, and electrostatically shielded stator windings. This paper examines VSI-output common-mode voltage as the driving source of bearing currents and develops, from a system level, the electrostatic circuit approach as a device to give insight into the technique of reducing common-mode voltage at the motor terminals and thus at the rotor. The technique is passive, low-cost, and retrofittable where allowed by electrical codes and is capable of reducing common-mode voltage by levels of magnitude. Such reductions can profoundly extend bearing service life by reducing the electro-erosion of the bearing surfaces.     

A passive EMI filter with access to the ungrounded motor neutral line—Its effect on attenuating bearing current

This paper describes the effect of a passive EMI filter on preventing bearing current from flowing inside an inverter‐driven motor. Motor‐bearing damage is often caused by bearing currents resulting from the breakdown of grease films in the motor bearing. The high‐frequency common‐mode voltage generated by the PWM inverter induces a shaft voltage between the rotor and the frame. When the shaft voltage exceeds the breakdown voltage of the grease films, a destructive instantaneous discharge current with a peak value of about 1 A flows through the motor bearing. The passive EMI filter, which is unique in access to the motor neutral line, can reduce the shaft voltage as a result of eliminating the high‐frequency common‐mode voltage from the motor terminals. Hence, no breakdown occurs in the grease film, so that no bearing current flows. The viability and effectiveness of the passive EMI filter is verified by experimental results obtained from a 400‐V, 3.7‐kW laboratory system. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 78– 87, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20489     

PWM驱动系统中感应电动机轴电压轴电流研究

由于PWM变频技术的应用，在电动机轴承端产生的轴电压和轴电流会导致电动机轴承的过早损坏，影响电动机系统的运行。为了研究轴电压、轴电流的机理，建立了电动机内部耦合参数的共模模型。在该模型的基础上，对轴电压和轴电流进行分析，确定了轴电流的流通路径，并提出了抑制轴电流的措施。仿真和实验结果证实了模型的正确性。该模型为研究正确消除和降低轴电压、轴电流的方法提供了有效的分析手段和仿真手段。     

变流机组振动源特性分析

根据变流机组振动频谱,分析其振动源特性,结论为：冷却风机不是变流机组主要振动源、变流机的轴频及谐频和轴承的特征频率较为明显,并指出这些频率可能是变流机组对舰艇辐射噪声贡献最大的频率。针对机组运行过程中产生的轴承相关特征频率进行分析,指出轴承存在的缺陷,提出了降低轴频、倍轴频振动分量,以及降低交流电机轴带风扇叶频的改进措施并对试验作出了总结。     

Bearing currents and shaft voltages of an induction motor underhard- and soft-switching inverter excitation

Bearing currents and shaft voltages of an induction motor are measured under hard- and soft-switching inverter excitation. The objective is to investigate whether the soft-switching technologies can provide solutions for reducing the bearing currents and shaft voltages. Two of the prevailing soft-switching inverters, the resonant DC-link inverter and the quasi-resonant DC-link inverter, are tested. The results are compared with those obtained using the conventional hard-switching inverter. To ensure objective comparisons between the soft- and hard-switching inverters, all inverters were configured identically and drove the same induction motor under the same operating conditions when the test data were collected. An insightful explanation of the experimental results is also provided to help understand the mechanisms of bearing currents and shaft voltages produced in the inverter drives. Consistency between the bearing current theory and the experimental results has been demonstrated. Conclusions are then drawn regarding the effectiveness of the soft-switching technologies as a solution to the bearing current and shaft voltage problems     

Approaches to suppressing shaft voltage in brushless DC motor driven by PWM inverter

This paper describes the approaches to suppressing the shaft voltage and bearing current by electrostatically shielding the stator end windings of the brushless DC motor driven by PWM inverter. At first, measured shaft voltage and bearing current are compared with those calculated waveforms to verify the common mode equivalent circuit of the brushless DC motor. Next, the relationship between shaft voltage and stator winding to rotor capacitance is calculated using the common mode equivalent circuit. Finally, the electrostatic shielding of the stator end windings is evaluated to reduce the shaft voltage by experiments and calculations. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 73–79, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20701