The application of conductive and stress grading tapes to vacuumpressure impregnated, high voltage stator coils

Conductive tapes are used as a conductive layer on the slot portion of a coil to reduce corona discharges that can occur on coil surfaces. Stress grading corona protection tapes are used on coils at the slot exit region, and they prevent surface discharges at these locations. The use of these commercially available tapes on high voltage coils that are processed using the vacuum pressure impregnation (VPI) method has been developed. Laboratory and factory tests were done to determine the type of tapes to use, the application process, the required process steps, and tape performance after coil processing     

Impact of inverter drives employing fast-switching devices on form-wound AC machine stator coil stress grading

The conventional stress-grading system of form-wound motor coils has been found to perform well under sinusoidal, power-frequency voltage. However, when the motor is fed by inverter-based drives employing fast switching, a significant impact on the electric stress-grading system occurs. Simulations of the stress-grading systems using finite element analysis indicate that, during the fast rise-time, a high electric stress can develop right at the slot exit of the stator if the conductivity of the conductive armor tape (CAT) is not high enough. Increasing the conductivity of the CAT alleviates the problem but increases the eddy current loss in the stator laminations. To address this problem, the conductivity of the area just beyond the slot exit needs to be increased by coating the surface of the CAT with a high-conductive material. The stress-grading at the end of this conductive paint section then is achieved by two coordinated layers, which help to distribute the electric field and heat that is produced     

The effect of surge testing on the voltage endurance life of stator coils

Surge tests with short rise times are used to ensure turn insulation integrity in form-wound vacuum-pressure impregnated (VPI) coils prior to resin treatment. Use of this test migrated from the evaluation of fully processed generator bars and random wound stators. The dielectric properties of the insulation in these systems are fully developed at the time of testing. This is not true of "green" (unimpregnated) VPI coils. Although surge testing is a valuable manufacturing quality test, an excessive transient electric field in uncured coils may cause irreversible changes to the insulation. These changes may affect the life of the insulation system after complete impregnation and cure. This paper describes laboratory tests and finite element simulations that examine the effect of applied surge test voltage and number of applied pulses on voltage endurance (VE) life. The sympathetic voltage response in a single coil as a function of its location within a winding is described for a stator undergoing green surge testing as part of a quality assurance program. Results of VE testing and sample dissection data are presented. Test voltage was identified a more significant factor on VE life than the number of pulses applied.     

Understanding surface partial discharges in HV coils and the role of semi-conductive protection

An electrical insulating system in high voltage rotating machines is subjected to several stresses that cause changes of material properties during its lifetime. This phenomenon reduces progressively ability of the insulation to withstand the service stresses. Internal partial discharges can be located inside the high voltage insulation and usually they are dangerous for life-cycle duration. Surface discharges are generated at the solid/air interface in the gaps of machine stator slots or at the slot exits. Surface discharges can cause more intensive deterioration of the insulation, accelerate aging processes and definitively take aim toward premature failure of the machine. The application of conductive or semi-conductive protection layer provides certain protection for solid insulation from these discharges. Semi-conductive corona protection tapes are used on the coils at the slot exit region to electrical field control and prevent surface discharges. Laboratory measurements of the surface partial discharge quantities in specimens of high voltage coils with mica insulation were performed. The aim of the paper is to describe theoretically the development of surface discharges in rotating machines and to present surface partial discharge development in HV motors when semi-conductive layer protection is missing. The results can be found useful to understand better the surface discharge development and importance of high-quality semi-conductive protection technology.     

System Operational Evaluation of Mine Monitoring Systems

In the testing of mine monitoring systems, a software package was developed for the mine monitoring test facility designed at West Virginia University. The software establishes delay times of sensor input to annunciation for single alarms and multiple simultaneous alarms. The alarm measurement techniques for the test fixture are described, as is the software developed to analyze and graph monitoring system response data. Also included is the analysis capability of the facility, the criteria for evaluating mine monitoring systems, and typical test data from a sample system.     

A novel method applicable to large-scale active magnetic shielding system which effectively compensates gradient magnetic fields originated from the surrounding buildings

We propose the novel magnetic compensation method which is suitable to compensate gradient magnetic fields. The method is to be applied to a conventional large-scale, tri-axial active magnetic shielding system such as a spacecraft magnetic testing facility. The essences of this method are the adoption of compensation coils which have degrees of freedom in their coil orientations, and their installation position, which is chosen to have certain distances from the center of the shielding area. The method works with at least four compensation coils. In this research, we actually demonstrated the method with a scaled-down experiment. Disturbance magnetic field (B) at the target zone was suppressed from 21.33 nT to −1.54 nT and magnetic field uniformity (ΔB) within the test zone was improved from 2.3 nT to 0.015 nT. In terms of magnetic field gradient, improvement from over 4 nT/m to below 0.5 nT/m was achieved.     

基于多接收耦合线圈模式的无线电能传输系统特性分析

在大功率无线电能传输系统的应用中,为降低系统设计难度会采用多接收耦合线圈并联的方式降低器件应力,但是对该模式的特性需要详细分析。在相同输出功率和负载的约束下,对比分析一对一耦合线圈模式和多接收耦合线圈模式,采用固定变量法分析多接收耦合线圈个数与系统互感、频率、负载和效率的关系。在多接收耦合线圈模式下,对单负载和多负载两种情况下系统参数进行推导和分析,论证多接收耦合线圈在提升系统效率方面的优势。最后,通过实验结果验证了多接收耦合线圈模式对系统效率提升有一定的作用。     

Autonomous decentralized system for torque control of high‐power permanent magnet synchronous motor

An autonomous decentralized system (ADS) for the control of a high‐power permanent magnet synchronous motor (PMSM) presented in this paper. The system decentralizes a centralized control system into several autonomous subsystems. Thus the power supply and power electronic devices of the control system can be replaced by smaller ones, thereby obtaining better fault tolerance of the system. The subsystems are connected only through the data field, which, in this paper consists of feedback elements and communication modules. This structure enables the autonomous controllability and autonomous coordinability of the system. The mathematical model of the PMSM with decentralized stator coils is proposed. This model takes into account the self‐ and mutual inductance of the coil, as well as the effect of the stator slot‐pitch angle. In addition, an autonomous algorithm for the torque control of the PMSM with decentralized stator coils is proposed, and the fault‐tolerance design is developed. Experimental results of the torque control and fault‐tolerance control confirm the validity of the proposed system. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Evaluation of the Long-Term Thermal Capability of a High-Temperature Insulation System Using Silicone Liquid as a Dielectric Coolant

The functional thermal evaluation of test transformers insulated with silicon fluid is described. Studies have shown that polydimethylsiloxane fluids maintain good electrical properties at elevated temperatures, but system evaluation is required to determine their capability in a transformer. A transformer test facility meeting the requirements of IEEE Standard 262 is described and was used for the accelerated thermal testing of the transformer models. The test results are summarized and an indication is given of how silicone fluid can be used in the design of high-reliability industrial transformer systems.     

多线圈无线电能传输系统效率最大化研究

感应式无线电能传输系统主要依靠耦合线圈将能量从电源端传输到负载端。多线圈的耦合特性可以用来构建多输入多输出的无线能量传输网络,目前针对此类网络的稳态特性分析仍然不具有通用性。传输效率作为系统稳态特性之一,是多线圈系统的重要优化目标。由于线圈寄生电阻使得耦合器损耗占据整体系统损耗的大部分,因此,优化系统效率的关键在于最大化耦合线圈效率。首先,建立任意耦合线圈个数的无线充电系统的电路模型,依照输入输出稳态特性分析效率最大化的影响因素以及最优效率点下的功率分配和损耗;其次,仿真验证不同输入端和不同输出端时理论分析的准确性;最后,搭建实验平台验证多发射多接收无线充电系统效率最大化点的稳态特性。     

Analysis of armature reaction and winding inductances of permanent magnet brushless DC motor with deep slot concentrated coils

Based on the configuration of deep slot concentrated coils, an analytical model is developed for predicting the armature reaction field produced by the 3-phase stator windings of permanent magnet brushless DC motors with concentrated coils by using the image method and the analytical functions of the armature reaction and winding inductances are proposed accounting for the influence of stator slotting. This approach is different from the method of equivalent distributed current sheet and more suitable for electric machines, which have concentrated coils and deeper slots. Under different control mode, the different analytical functions are presented. This will be helpful when further analyzing the performance of the motor. The results agree with the experiment very well. __________ Translated from Proceedings of the Chinese Society for Electrical Engineering, 2005, 25(12): 127–132 (in Chinese)     

Application of ultrasonic pulse-echo method to insulation condition diagnosis for large generators

It is a challenge to diagnose insulation condition of stator bars using an ultrasonic technique, due to the complex structures of the stator bars and the high attenuation of the stator insulation. In this paper, five low frequency transducers were used in a pulse-echo configuration to try to test a standby stator bar of a generator (300 MW, 18 kV). With an available transducer, four types of insulation structures were tested on the stator bar. The short side insulation was compared with the large one of the stator bar in the slot. The stator bar near the exit from the slot and the end stator bar, were compared with the stator bar in the slot. The semiconductive coating covered stator insulation was compared with the uncoated one. The stator insulation having an insulation-copper interface was compared with that having an insulation-gas interface. In addition, insulation diagnosis tests in the laboratory were performed on two sets of stator bars, which had been in service for 18 and 23 years, respectively in two generators (300 MW, 18 kV). Field tests were performed on the stator bars near the exit from the slot and the end stator bars of a generator (300 MW, 18 kV). The experimental results demonstrated an availability of low frequency ultrasonic pulse-echo method for insulation condition diagnosis of large generators     

集中绕组永磁无刷直流电机电枢反应及绕组电感的解析计算

基于深槽集中绕组的结构特点，采用镜像法，建立了适合集中绕组无刷电机的电枢反应求解模型。充分考虑电机齿槽影响，给出了电枢反应磁场的解析表达式，对不同控制方式下的电枢反应分别作了研究，并在此基础上推导了电机绕组电感的通用求解公式，从而为集中绕组无刷电机的参数设计和特性分析提供了理论依据。样机实验表明，其具有很好的工程适用性，理论计算与实测值吻合。     

Computer Application in Appliance Testing

The system developed for component testing at an appliance manufacturing facility is described. The complete installation consists of minicomputers that control several test stands and report the test results to a central quality assurance station. The various system components are 1) a disk-based central computer quality assurance station, 2) three computerized test stands for simultaneous testing of 48 ``infinite switches' used in electric range surface heater control, 3) air-fluidized aluminum oxide temperature baths, and 4) a snap-disk thermostat test stand, equipped with its own minicomputer and communications capability with the central station.     

对俄供TBB-800-2EY3型发电机定子铁心试验中三个问题的分析

文章研究了以下三个问题:①首先提出了定子铁心有效长度的定义,然后根据定义建立了TBB-800-2EY3型发电机定子铁心有效长度的计算公式;②在定子铁心试验接线中,用励磁线圈和测量线圈在定子铁心两侧对称布置取代俄罗斯采用的单侧集中布置,减少了漏磁对试验结果的影响;③通过对TBB5002EY3型和TBB8002EY3型发电机定子铁心试验数据的分析和研究,提出了用单位长度励磁安匝数H0取代俄供励磁安匝数,统一了型号相同、容量不同的发电机计算励磁电流的标准。     

基于人工单相接地短路试验的电力系统计算用模型参数校核方法研究

利用2004年4月8日黄渡站5101线人工单相接地短路故障试验的系统数据,特别是试验时测录的相量测量数据,在华东电网发电机和励磁系统建模及参数实测工作取得成果的基础上,进行了试验方式下的潮流、短路电流和暂态稳定仿真计算,并与实测数据相比较。通过分析发电机、励磁系统、电力系统稳定器、负荷等模型和参数对仿真结果的影响,探索了利用相量测量数据进行电网计算用模型参数校核的方法和思路。     

采用OWTS检测10 kV交联聚乙烯电缆本体主绝缘损伤

对中低压交联聚乙烯电缆的故障类型及测试方法进行了分析和梳理,发现对电缆中间件和终端头的故障类型及测试相对较为成熟,而针对电缆本体的相对较少。针对电缆本体主绝缘损伤的故障类型进行了人工复现及测试,着重对电缆的主绝缘损伤并伴随金属铜屏蔽和半导电带损伤的故障类型进行试验。详细描述了采用振荡波局放测试系统（OWTS）的过程,并对测试结果进行了分析,对局部放电点进行定位。结果表明OWTS系统可以对电缆本体损伤进行有效的检测和定位,可为XLPE电缆的检修和试验提供方法和依据。     

电磁弹射系统的脉冲功率源设计

为了解决盘形线圈弹射装置发射需要用于改变弹射体的发射方向的2个正交时变磁场,研制了由2个独立模块构成的脉冲功率源装置。每个模块的储能为300 kJ,由6个电容、改进的大功率火花隙开关、续流二极管、高频PWM整流器及用于脉冲成型网络的同轴电缆输电线组成,且每个电源模块可经光纤控制器单独触发,通过改变触发脉冲的延迟时间改变发射方向(在10 ms到几μs间)。为减小电磁干扰和电磁力的影响,使系统具有高灵活性和可靠性,改进了脉冲电源模块中元器件的位置及其结构,每个模块所能承受最大电压5 kV,放电电流峰值达200 kA。实验结果表明,研制的脉冲功率源输出电流大、安全可靠、结构紧凑、操作方便、性能满足电磁弹射研究的需要。     

特高压直流输电晶闸管阀成套运行试验装置研制

成套运行型式试验装置是实现特高压直流输电(ultra high voltage direct current transmission,UHVDC)晶闸管阀研发和工程应用的基础和前提条件,在遵循IEC60700-1标准,在调研现有相关试验装置和比较试验方法的基础上,研制一套采用双注入合成试验方法的UHVDC晶闸管阀运行试验装置,为我国UHVDC晶闸管阀的研发与工程应用提供了试验支撑。介绍该装置的主回路拓扑,试验回路的工作原理及其参数设计,控制保护系统设计及其保护策略,并给出了相关试验结果,结果表明,该试验装置的研制是成功的,满足UHVDC晶闸管阀研发的需要。     

Characteristics of combined levitation and guidance eds maglev system

A levitation method has been introduced which uses 8-shape levitation coils arranged on the vertical surface of the guideway. These coils can act as a guidance means as well as the levitation means. The characteristics of this system are examined using numerical examples and experimental data. The cables connecting right and left coils are not connected to a high-voltage power source unlike the usual guidance system which is combined with propulsion. Thus the electric insulation of the cables is not a problem at present. Numerical examples show that the levitation characteristics of the combined levitation and guidance system are almost the same as in the system without the guidance function, and that it attains reduced running resistance with necessary guidance stiffness obtained. A test run was done at Miyazaki Test Line equipped with coils of this type arranged about 120 m, and the results show stable running and balanced displacement which agrees with calculated values.