Causes and characteristics of the electromagnetic vibration of a capacitor motor under load

Capacitor motors (CRMs) are widely used to drive industrial equipment and home electric appliances. Recently, reduction of the vibration and noise of CRMs has become increasingly important from the standpoint of environmental improvement. However, electromagnetic vibration of CRMs under load has not been sufficiently analyzed. The present paper theoretically and experimentally discusses the causes and characteristics of CRM electromagnetic vibration under load. The primary conclusions are as follows:

• (1) The general formula for the dominant electromagnetic vibration caused by electromagnetic force waves was derived, including the influences not only of a backward magnetic field but also of magnetic saturation.
• (2) The dominant electromagnetic vibration of CRMs is theoretically attributed to three types of electromagnetic force waves. Two types of electromagnetic force wave are generated by the interaction of two forward magnetic fluxes, such as those of a three‐phase squirrel‐cage induction motor, and the other type of electromagnetic force wave is generated under the influence of a backward magnetic flux.
• (3) The characteristics of the dominant electromagnetic vibration depending on the load and the running capacitance are subdivided theoretically and experimentally into three types based on the characteristics of the electromagnetic force wave and the equivalent circuit current.
• (4) The influences of magnetic saturation in dominant electromagnetic vibration have been verified experimentally and their causes have been clarified theoretically in relation to electromagnetic force waves. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 68–76, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20129

     

Influence of controlled rectifier with transformers of rotating magnetic field on the supply network

Based on a harmonic analysis of the feed voltages of controlled rectifiers with transformers with rotating magnetic fields under different types of loads, the relationships between the coefficients of feed voltage harmonic and the number of power-key pairs of rectifiers’ commutators with transformers of rotating magnetic fields were clarified.     

一种新型的谐波及无功电流检测算法

为了实现有源电力滤波器(APF)谐波电流的快速、精确检测,对谐波电流的检测算法进行了研究,提出了一种新型的谐波电流检测方法,利用对称基准旋转相量求解基波正序有功电流的幅值,分别计算电压、电流与基准旋转相量相位差的正余弦值,从而求出基波功率角,消除基准旋转相量与电网电压的相位偏差。Matlab仿真结果表明,在电网电压不对称、且畸变的情况下,能准确提取基波正序有功电流,适用于有源电力滤波系统中谐波、无功及负序电流的综合补偿。     

An Improved Harmonic Load Flow Formulation

Abstract

The paper contributes an improved harmonic load flow formulation with fewer convergence problems but the same accurate results as traditional formulations. The proposed formulation approaches the harmonic load flow problem as a single nonlinear equation system where the harmonic bus voltage influence on nonlinear load behavior is considered and harmonic bus voltages at linear buses are not included as unknowns. This formulation allows any sort of nonlinear load to be considered and uses the Newton-Raphson method with true Jacobian matrix to reduce the inherent increase in the number of iterations caused by the presence of highly distorted bus voltages. The numerical results obtained when solving a three-bus network operating under highly distorted bus voltages using traditional harmonic load flow formulations and the improved formulation are comparatively discussed.     

Statistical summation of the harmonic currents produced by a largenumber of single phase variable speed air conditioners: a study of threespecific designs

The variable speed air conditioner (VSAC) is a large domestic distorting load. We investigate the impact of a large number of VSAC's on domestic harmonic levels. We present a general method to build a harmonic numerical model of a passive filtered rectifier supplied by a distorted voltage; a statistical method to assess the total harmonic currents produced by a large number of units running at various power levels and supplied by various distorted voltages. These two methods are applied to a rectifier used by many VSACS. We also present results for two other rectifiers     

低压配电系统单相非线性负荷的谐波衰减效应研究

对单相不可控电容滤波整流型电路的仿真和实验研究表明,低压配电系统非线性负荷的谐波特性与电压波形畸变程度相关;提出用电压波形的波峰系数(crest factor)作为非线性负荷谐波电流的衰减效应(attenuation effect)的衡量指标,波峰系数与非线性负荷的谐波发生水平之间具有线性递增关系.分析还表明,在民用低压配电系统中,非线性负荷谐波电流几乎均使其供电端电压呈现平顶波峰的趋势.这一结论与实测电压大部分呈现平顶波一致;同时说明,导致低压系统供电电压畸变的主要因素就是系统中大量存在的分布式谐波源.     

Control of three phase PWM rectifier using virtual flux‐based predictive direct power control and SVM under harmonic conditions

In this paper, a new predictive direct power control algorithm to control the PWM rectifier based on virtual flux (VF) is presented. In this algorithm, supply network and the line inductances are assumed as an induction machine and so virtual flux space vectors are assumed corresponding with the space vector of the network voltages. Instantaneous active and reactive powers and finally convertor average voltage in both stationary and rotating reference frames are calculated by the virtual flux space vector components. The main advantages of the proposed method are low total harmonic distortion of the input current and low ripple in the instantaneous active and reactive powers and direct current‐bus voltage under harmonic distorted condition of the supply voltage in comparison with voltage‐based predictive direct power control (V‐PDPC) method. Proposed VF‐PDPC method with space vector modulation switching strategy was tested in simulations and compared with the V‐PDPC method. Copyright © 2015 John Wiley & Sons, Ltd.     

基于FFT和小波变换的交直流并联输电系统间谐波研究

运用谐波调制理论,结合开关函数的傅里叶分析,研究了在交直流并联输电系统下,交流系统供电电源含有畸变谐波时,直流线路和交流侧都产生间谐波的机理。给出了整流侧直流电压、直流电流以及交流电流产生的间谐波的一般形式。经过小波变换除去信号中的非稳态分量以后,再使用加窗快速傅里叶变换可以很好地得出其中的稳态分量。通过一个典型交直流并联输电系统数字仿真,同时在供电电源含有畸变谐波的情况下,对交直流系统的电压和电流量进行了间谐波计算。利用傅里叶小波分析综合分析法得到的仿真结果和计算结果相比较,验证了间谐波产生机理的正确性和有效性。     

Causes and characteristics of the electromagnetic vibration of a squirrel cage induction motor under load

Three-phase squirrel cage induction motors (IM) have been used in all types of industry, because of their robustness and simplicity of structure, low cost, and ease of maintenance. Due to the resultant air gap flux wave, an IM produces electromagnetic vibration and noise more or less regardless of the slot combination. Recently, reduction of electromagnetic vibration and noise has become important from the standpoint of environmental improvement. Vibration caused by an IM at no-load has been studied for many years and its basic factors have been analyzed. However, electromagnetic vibration under load has not been analyzed sufficiently. Since vibration under load conditions is affected by load and installation, analysis of this vibration is a rather difficult task. But study of the electromagnetic vibration of the motor itself under load is basically the most important item. This paper clarifies, theoretically and experimentally, the causes and characteristics of the electromagnetic vibration of an IM under load conditions. First, general equations are derived for the dominant electromagnetic force waves that produce electromagnetic vibration. Causes and vibration modes are clearly classified and a theoretical analysis provides a basic concept for electromagnetic vibrations. Second, electromagnetic vibrations for various loads are measured taking the effect of natural frequency of the motor into consideration. The measured data are classified and analyzed in detail, based on the proposed theory. © Scripta Technica, Inc. Electr Eng Jpn, 120(4): 81–89, 1997     

非正弦供电十五相感应电机谐波电压确定

通过确定非正弦供电十五相感应电机的3次谐波注入电压,为电机PWM调制提供理论依据。把注入3次谐波电压的十五相感应电机气隙磁动势峰值下降幅度最大作为电机理想运行准则,得到基波磁动势与3次谐波磁动势之间空间位置关系与磁动势幅值间数值关系。以十五相感应电机基波等值电路与3次谐波等值电路为基础并从相应的激磁电流出发,计算基波电压与3次谐波电压有效值,求出3次谐波负幅值点与基波正幅值点间相位差,并通过电机空载实验对计算方法的准确性进行了验证。在额定基波电压下,计算了对应于不同给定转差率的基波激磁电流与3次谐波激磁电流,进而得到3次谐波电压有效值及磁动势波形间相位差,最终通过线性插值来获得任意转差率下的3次谐波电压。     

同步发电机励磁绕组匝间短路时的电磁转矩

同步发电机的励磁绕组匝间短路故障会引起机械振动,而研究故障时的电磁转矩是分析机械振动特性的基础。文中首先基于多回路数学模型计算了短路故障后的电磁转矩,计算中全面考虑了定、转子绕组产生的各种次数、转速、转向的空间磁场之间的相互作用;对一台12kW、3对极隐极同步发电机样机进行了仿真计算及实验的比对验证;从分析故障后定、转...     

Electromagnetic compatibility of a traction power-supply system and infrastructure elements in areas with high traffic

Electric traction systems are improved as part of the process of updating the entire system that converts the power that is consumed by the transportation process. Application of dc converters to a three-phase alternating current, the use of thyristor converters of the dc voltage level, the creation of highly efficient algorithms for computer control of electric-power conversion, and substitution of commutator dc motors for brushless three-phase ac motors lie at the core of technological improvement of electric traction systems and are now widely used in a number of industrialized countries. This paper proposes new traction power-supply systems for areas with high traffic, which require additional wires to be laid and multiconductor lines to be used. The requirements are formulated, and a methodology for grounding the electromagnetic compatibility of multiconductor lines of traction power supply and infrastructure elements is discussed. It is shown that electromagnetic coupling of lines takes place under conditions of both electric and magnetic effects between two or more electrically long lines. In electrically long lines, the voltages and currents cannot be considered independent of each other. They are interconnected through the impedance of the respective line (similarly to how electrical and magnetic fields of electromagnetic waves are linked with each other through the impedance of space). The studies and analysis that were carried out showed t6hat it is possible to simulate the propagation of electromagnetic waves along multiconductor traction power-supply lines, which allow determining not only the currents and voltages at any given point of a multiconductor line, but also simultaneously induced voltages at an adjacent line. All this allows highly accurate checking of the electromagnetic compatibility of the traction network and longitudinal power supply lines with communication lines and track circuits in areas with high traffic.     

Response of dairy cattle to transient voltages and magnetic fields

Stray voltages in dairy facilities have been studied since the 1970s. Previous research using steady-state AC and DC voltages has defined cow-contact voltage levels which may cause behavioral and associated production problems. This research was designed to address concerns over possible effects of transient voltages and magnetic fields on dairy cows. Dairy cow response to transient voltages and magnetic fields was measured. The waveforms of the transient voltages applied were: 5 cycles of 60 Hz AC with a total pulse time of 83 ms, 1 cycle of 60 Hz AC with a total pulse time of 16 ms, and 1 cycle of an AC square wave (spiking positive and negative) of 2 ms duration. Alternating magnetic fields were produced by passing 60 Hz AC fundamental frequency with 2nd and 3rd harmonic and random noise components in metal structures around the cows. The maximum magnetic field associated with this current flow was in excess of 4 G. A wide range of sensitivity to transient voltages was observed among cows. Response levels from 24 cows to each transient exposure were normally distributed. No responses to magnetic fields were observed     

振动环境对电磁继电器特性参数影响的试验研究

电磁继电器的特性参数会在振动环境下发生变化,通过试验测试了继电器的振动极限加速度,并以此为阈值,得出了振动条件下继电器吸合和释放电压、时间参数的变化规律;分析了特性参数变化的原因,其结论对于电磁继电器力学环境下的失效分析具有实用价值。     

大型发电机主变压器感应过电压计算方法分析

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,也会通过静电感应和电磁感应传递到低压绕组中,使低压绕组侧产生过电压。根据主变压器的等值模型,可以得到电磁感应过电压的计算方法,从而可以定量地计算出主变压器低压侧和发电机可能的过电压,以及发电机的过电压上升速度。计算结果可以作为选择过电压保护设备的依据。     

异步电机高频杂耗的自适应时步法有限元计算

异步电机杂散损耗的准确计算是一个十分困难的问题。本文论述了对非斜槽异步电机高次谐波杂散损耗的计算方法。文中采用的数学模型把电磁场有限元方程与电路方程耦合在一起,当输入电压波形给定后,电机中的之流和磁密波形可通过时步法直接求得。根据计算所得的高次谐波电磁场,就可进一步计算出高次谐波杂散损耗。计算结果通过样机试验得到验证。在计算中采用了自适应时间步长的方法,并首次提出了一种估计局部截断误差简单实用的方法。     

An investigation of the harmonic characteristics of transformerexcitation current under nonsinusoidal supply voltage

This paper investigates the effect of supply voltage harmonics on the excitation current of a typical 25 kVA single-phase distribution transformer. A complete analytical model is developed to calculate the time domain waveform and the harmonic components of the excitation current. The key findings are: the phase angles of the supply voltage harmonics determine whether or not those voltage harmonics increase or decrease the distortion of the input current (with respect to the sinusoidal supply voltage case). A peaked input voltage wave distorted by 3rd, 7th, 11th, etc. harmonic components, or a flattened input voltage wave distorted by 5th, 9th, 13th, etc. harmonics, creates a flattened current (i.e., decreases the current harmonics and distortion). A flattened input voltage wave distorted by 3rd, 7th, 11th, etc. harmonic components, or a peaked input voltage wave distorted by 5th, 9th, 13th, etc. harmonics, creates a peaked current (i.e., increases the current harmonics and distortion): The 3rd harmonic component in the supply voltage has the highest effect on the current harmonics and distortion. The effect of higher voltage harmonics gradually diminishes with frequency. The magnitudes of the individual current harmonics follow the same decreasing/increasing pattern of changes as does current distortion variation. The corresponding variations in harmonic current phase angles is negligible     

Pantograph Arcing in Electrified Railways—Mechanism and Influence of Various Parameters—Part II: With AC Traction Power Supply

Pantograph arcing with AC supply generates transients, cause asymmetries and distortion in supply voltage and current waveforms and can damage the pantograph and the overhead contact line. The asymmetry generates a net dc component and harmonics, which propagate within the traction power and signalling system and causes electromagnetic interference. Unlike DC-fed systems (Part I), the arcing in ac supply is complex because of the zero crossing of currents and voltages. In this paper, we discuss the mechanisms of sliding contact and arcing between pantograph-contact wire using the experimental setup described in Part I. Influences of various parameters and test conditions on arcing phenomenon and their signature patterns on the supply voltage and current waveforms are presented. It is shown how the arcing mechanism and corresponding asymmetry in the voltage and current waveforms are governed by line speed, current, supply voltage, inductive load, and pantograph material. The asymmetry in the current waveform is mainly due to the difference in the duration of successive zero-current regions and uneven distortion of the waveshapes. This, in turn, creates the asymmetry in the voltage waveform. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the electromagnetic interference due to pantograph arcing in AC traction systems.     

The effect of fast changes in voltage unbalance on vibration characteristics of asynchronous motors

The effect of voltage unbalance in electrical networks that supply electrified traction loads on the operating regimes of large asynchronous motors (AMs) is considered. Based on the method of symmetrical components and analysis of hodographs of magnetic fields of AMs with a short squirrel-cage rotor, the influence of various types of voltage unbalance (continuous and intermittent) on its vibration characteristics is studied. It is shown that an increase in magnetic induction in the air gap of an AM causes an increase in radial vibration generating forces in the case of voltage unbalance. The obtained results indicate that alternating voltage unbalance can be riskier for AM operation than is constant voltage unbalance, in addition to having increased levels of AM vibrations. It is concluded that the use of new parameters of electric-energy quality allowing determination of instantaneous values of unbalance amplitude and the angle between symmetrical components of voltage of positive and negative phase-sequence is reasonable. The relevance of this research is confirmed by typical cases of AM shutoff at an oil-pumping station due to tripping of vibration-protection sensors.     

感应电机不对称暂态分析中一类一元三次特征方程及其近似求解

对于旋转状态的感应电机,在短暂断电后重新接入电源时,为了限流,经过晶闸管开关首先接通两相电源施加部分电压,然后逐步过渡到全压。该文研究接入两相电源后的不对称电磁过渡过程。对微分方程进行拉普拉斯变换得到一元三次特征方程;然后,基于牛顿切线法得到近似求解一元三次特征方程的简化方法,进而应用于分析感应电动机的不对称过渡过程问题,导出时间常数近似公式。通过与繁杂且难以实际应用的精确卡丹公式对比,该文公式简单明了,便于应用,对于功率5.5 kW以上一般用途的感应电动机,其误差不超过5%。