220kV变压器附加绕组专接滤波器的谐波治理方案

在某些220kV变电站中，由于其主要为非线性负荷供电，谐波污染严重。传统的解决方法为在变压器低压侧接LC滤波器，治理谐波的同时兼顾无功功率补偿。受低压绕组等值阻抗的约束，此种方法滤波效果不佳。本文提出了一种220kV变电站谐波治理新方案，本方案采用变压器独立附加绕组接LC滤波器，且通过特殊设计使变压器附加绕组的等值阻抗为零。推导了传统方案和新方案的滤波原理，对比分析了新方案滤波效果的优越性。设计了一台具有零等值阻抗特征附加绕组的180MVA、220kV三相变压器，并基于Ansoft软件建立了场路耦合仿真模型进行仿真分析，最后对实验室样机进行测试分析，仿真和测试结果验证了新方案良好的滤波效果。     

一种新型的同塔双回输电线路工频阻抗参数测量方法

基于输电线路三相不平衡及感应电压干扰在短时间不变的前提,提出了一种新型的同塔双回输电线路工频阻抗参数测量方法。该方法采用单相电源多变换接入的方式对不对称线路进行分相解耦测量,通过建立数学模型、数据拟合和矩阵变换,从而获得单回或两回线路的序阻抗及各序之间的耦合阻抗。该方法克服了高感应电压及三相不平衡对线路参数测试的影响,具有简单、精确、稳定等特点,测试结果表明了本文方法的有效性。     

120例心脏起搏系统阻抗的术中检测及其与起搏阈值的关系

起搏器安装或更换术中测试了120例起搏系统阻抗并将其与同时测试的起搏阈值进行了对照分析。结果显示,急性期阻抗值为274Ω至1014Ω,平均621·02Ω,随阻抗值增大而有起搏阈值的减小。慢性期阻抗值362Ω至672Ω,平均484·75Ω,较急性期者显著降低,提示慢性期随起搏阈值增高,阻抗自行调整而降低以维持起搏器电压相对衡定输出。本文结论是,起搏系统阻抗的显著降低应作为更换起搏器的参考指标之一。     

基于定有功电流限值控制的MMC型UPQC协调控制方法

对电压暂降期间MMC型UPQC串联侧补偿能力进行深入的理论分析。首先给出MMC型UPQC的工作原理，推导出暂降补偿幅值、补偿持续时间、主回路电气量及MMC参数之间关系的时域表达式；进而提出一种针对容量确定情况下UPQC串联侧过电流问题的协调控制设计方法，在传统定直流电压控制的基础上提出定有功电流限值控制；定义了划分MMC型UPQC处于上述两种控制状态的电压暂降临界值并给出数值计算表达式；最后PSCAD/EMTDC下的系统仿真结果验证了理论分析的正确性。仿真结果也表明，与传统协调控制方法相比，该文提出的协调控制方法可明显提高电压暂降的补偿幅值和持续时间。     

基于三维空间法向量的三相电压幅值检测

提出一种基于三维空间法向量的新型三相电压幅值检测算法。该算法将三相电压置于三维空间直角坐标系进行研究,根据三相电压运行轨迹对应的三维空间法向量计算出各相电压幅值。Matlab仿真和500kV.A逆变器的低电压穿越实验结果表明,新算法适用于不平衡电压、检测速度快、计算简单,可准确检测三相电压幅值。     

恢复潮流可行的交直流电力系统切负荷新模型

本文通过在交流侧有载调压变压器支路模型中引进虚拟节点,并通过虚拟节点的电压变量来表示有载可调变压器支路功率方程;在直流侧引进与换流器相对应的交流电压幅值、电流幅值等变量表示直流方程;耦合方程把不同坐标系下的方程耦合到一起,由此建立了交直流混合系统恢复潮流可行性问题的二次切负荷优化新模型。预测-校正原对偶内点法被用来实现这个最优潮流问题,该模型的海森矩阵在优化过程中是恒常矩阵,只需要计算一次,这样缩短了内点法的计算总时间。仿真计算结果验证了所建模型正确性和有效性,可判断潮流是否可行并给出切负荷的位置。     

胸部体表阻抗变化形成机制的初步探讨

目的探讨胸部体表阻抗变化形成的机制。方法假设胸腔为一导电均匀的容积导体,根据电阻定律、欧姆定律、恒流阻抗法的测量原理以及圆柱形容积导体的电场分布,导出胸部体表阻抗变化公式。结果从理论上解释了胸部体表阻抗变化形成的机制,得到了单根血管和多根血管在胸部体表产生的阻抗变化公式,并为模型实验所证实。结论这些结果可为心阻抗图的波形重建奠定理论基础。     

胸阻抗法测量心脏指数和射血分数的临床研究

目的评价胸阻抗法测量心脏指数和左心射血分数两项指标的准确性及临床应用价值。方法６５位成人非瓣膜病患者,同时用彩色超声和胸阻抗法测量左心射血分数（ＥＦ）值; ６位非胸部手术后的危重病患者,在用 Ｓｗａｎ－ Ｇａｎｚ导管测量心脏指数的同时,用胸阻抗法测量心脏指数,每位患者取１０对数据。结果胸阻抗法测量的左心ＥＦ值为５７．４±５．９％,彩色超声同时测量的ＥＦ值为６３．５±８．８％,ｔ检验两种方法测量的结果无统计差异（Ｐ＞０．０５）,两种测量方法的结果无相关性（ ｒ＝ ０．０４）; Ｓｗａｎ－ Ｇａｎｚ导管与胸阻抗法的对照结果说明,两种测量方法的结果有较好的相关性（１例ｒ＝ ０．６９３,其余５例ｒ≥０．８００）,平均相关性ｒ＝０．８５６。结论胸阻抗法测量左心射血分数的结果不适合用作临床指标;胸阻抗法可用于连续监测患者的心脏指数。建议这种监测是在胸阻抗不受其它因素明显影响的情况下进行,如：机械通气的条件改变或大量补液等。     

一种分布式发电并网变流器测试装置设计方案及实现

提出了一种用于分布式发电并网变流器测试的波动电压发生装置方案，解决了分布式发电并网变流器在实际电网中不易测试的难题。该装置基于级联H桥拓扑，其电压等级可拓展，可高精度地输出频率为0.5～25Hz和波动幅值为0～10%基波电压幅值的波动电压，可模拟不平衡度可调节的三相不平衡电网，不平衡度范围为0～10%。它可以完成并网变流器对电网电压幅值和频率偏差，波动电压以及电网不平衡的适应能力等多种测试。本文分析了装置的工作原理，并以基于本文所提出装置拓扑的“35kV-6MW风机变流器低频扰动测试装置”上进行的现场实验为例，充分证明了这种波动电压发生装置用于分布式发电并网变流器测试的可行性和有效性。     

在体兔脑组织电阻抗频率特性测量及电阻抗断层成像

背景：电阻抗断层成像技术是对人体表施加尤害电信号，体表测量其响应，用重构算法得到人体内部的电阻抗或其变化的分布图像。与现有的CT，MRI等技术相比，电阻抗断层成像技术具有实时性强、费用低廉、便于连续监测和功能成像等优势。目的：在体测量兔脑组织在缺血前后的电阻抗频率特性，并对缺血脑组织进行电阻抗断层成像技术，验证电阻抗断层成像技术对脑功能变化成像的可能性。设计：单一样本实验。单位：解放军第四军医大生物医学工程系医学电子工程教研窜。材料：实验于2001-08／09在解放军第四军医大学生物医学工程系医学电子工程教研室电阻抗断层成像实验室完成。选择成年健康家兔10只用于实验。方法：采用颈总动脉结扎法制造脑缺血动物模型，对缺血前后的脑组织电阻抗特性进行在体测量。利用电阻抗断层成像系统对单侧脑组织供血变化进行成像。主要观察指标：①缺血前后的脑组织在0．1Hz～1MHz频率范围内电阻抗频率特性曲线。②单侧脑组织供血变化电阻抗断层成像结果。结果：1只家兔钻透硬脑膜，9只家兔结果进入分析。①在缺血脑损伤发生后，脑阻抗明显增大，在10Hz以下脑阻抗变化率可达75％，在1kHz～1MHz频率范围脑阻抗变化率约为15％且比较稳定。②初步的动态成像结果显示，脑组织供血变化一侧与其电阻率变化位置相一致。结论：缺血前后脑组织阻抗变化率满足成像要求，可以将其作为一个成像变量。     

Effect of Pentaphasic Pulse Sequence as an Impedance Sensor on Standard Electrocardiographic Recordings

Two advances in cardiac pacing have resulted in an internal conflict in some pacemakers. One is the development of a standard lead physiological sensor and the other is protection from electromagnetic interference (EMI). One popular type of standard lead sensor uses sub-threshold pulses to measure intracardiac and intrathoracic impedance changes, i.e., minute ventilation. Recent clinical observations and extensive in vitro testing have verified that digital cellular phones can be troublesome. Large feedthrough capacitors (FCs), effective in blocking the EMI, will preclude sensing of the standard impedance-based signals. A variety of pulse configurations were studied that might be effective for a sensor-based impedance signal while allowing the pacemaker to continue to use large Fcs protecting them from environmental EMI. In comparison to both monophasic and biphasic pulse sequences, a pentaphasic pulse sequence was effective as an impedance sensor, still allows large FCs to function as an effective filter for environmental EMI, and would not produce artifacts on surface ECG.     

Analog-Digital Recording of Current and Voltage During High Voltage DC Shocks

Efficient on-line digitization is the prerequisite for computerized analysis of the electrical phenomena occurring during defibrillation. Conventional hardware presently provides only limited time resolution. The performance of various digitization rates for recording of voltage, current, and calculation of derived quantities like impedance, energy, and defibrillator capacitance was investigated. It was assessed both experimentally and by computer simulation of a trapezoidal discharge (of 9 msec duration into a constant resistive load of 50 Ω with a defibrillator capacitance of 132 μF). The accuracy achieved with different digitization rates is given. For example, an accuracy of 1% for analog-digital conversion for impedance calculation during this kind of DC shock requires a sampling rate of 8 kHz without, and a rate of 1 kHz with linear interpolation to correct for the hardware dependent error due to sequential sampling.
Conclusion: Highly efficient analog-digital conversion of delivered voltage and current during DC shocks is available within the limits of conventional inexpensive hardware.     

X‐ray Radiation Causes Electromagnetic Interference in Implantable Cardiac Pacemakers

Background: X‐rays are not thought to cause electromagnetic interference (EMI) in implantable cardiac pacemakers. However, x‐ray radiation during computed tomography (CT) scanning has been reported to cause EMI in some implantable cardiac pacemakers. The objectives of this study were to identify the location within the pacemakers where x‐ray radiation causes EMI and to investigate the association of EMI with the x‐ray radiation conditions. Methods: We verified the location where x‐ray radiation caused EMI using a CT scanner and conventional radiographic x‐ray equipment. An inhibition test and an asynchronous test were performed using five types of implantable cardiac pacemakers. Results: X‐ray radiation inhibited the pacing pulses of four types of implantable cardiac pacemakers when the body of each implantable cardiac pacemaker, containing a complementary metal‐oxide semiconductor (CMOS), was scanned using a CT scanner. We confirmed that x‐ray‐induced EMI depends on the x‐ray radiation conditions, that is, the tube voltage, tube current, x‐ray dose, and direction of x‐ray radiation, as well as the sensing thresholds of the implantable cardiac pacemakers. Conclusions: X‐ray radiation caused EMI in some implantable cardiac pacemakers, probably because the CMOS component was irradiated. The occurrence of EMI depended on the pacemaker model, sensing threshold of the pacemaker, and x‐ray radiation conditions. (PACE 2010; 33:1174–1181)     

Utility of Low Energy Test Shocks for Estimation of Cardiac and Electrode Impedance with Implantable Defibrillators

We assessed the value and safety of using a low voltage test shock to predict cardiac and electrode impedance during subsequent high voltage, transvenous, sequential pulse shocks. Two transvenous defibrillation catheters were inserted in 15 patients undergoing electrophysiology study for the evaluation of ventricular tachycardia/fibrillation. A sequential pulse test shock at stored voltage of 50 or 100 volts was delivered during sinus rhythm and high voltage therapeutic shocks were delivered during induced ventricular tachycardia/fibrillation. The test shocks were well tolerated and caused only minimal discomfort. Peak delivered voltage for each pulse of the test shock ranged from 34 to 116 volts (mean 62 +/- 27) and for each pulse of the therapeutic shocks from 186 to 778 volts (mean 435 +/- 146). There was a very strong relationship between the impedance of the test and the mean impedance of the therapeutic shocks (R = 0.89, P less than 0.001). The mean impedance of the test shock was slightly greater than the mean impedance of the test shock as slightly greater than the mean impedance of the therapeutic shocks (mean 90 +/- 24 ohms compared to 77 +/- 16 ohms, P less than 0.001), with a maximum difference between test and therapeutic shock impedances of 39 ohms (mean difference 8.4 +/- 10.3 ohms). There was a significant inverse relationship between impedance and peak current (R = -0.49, P = 0.001). Cardiac and electrode impedance during transvenous defibrillation can be predicted reliably and safely by a low voltage test shock. This technique provides a safe and simple method to ensure appropriate connections and electrode function for subsequent countershock therapies.     

Determinants of Impedance Rise During Catheter Ablation of Bovine Myocardium with Radiofrequency Energy

Recently, radiofrequency (RF) energy has been used as an alternative energy source to direct-current (DC) electricity for catheter ablation of recurrent tachyarrhythmias. Since delivered energy is inversely related to impedance, factors that cause impedance rise during catheter ablation impede the ability to ablate tissue. To elucidate some of the factors responsible for impedance rise during RF (750 kHz) catheter ablation using a constant voltage RF generator, the effects of the following variables on impedance were studied in an in vitro bovine heart model: power setting (10-70 W), pulse duration (10-60 sec), catheter contact pressure (5-120 gm), repeated applications (2-4), and immersion media (saline vs citrated blood). Baseline impedance in blood was twice that of saline (190 vs 80 ohm) and rises in impedances occurred more rapidly in blood for the same energy settings. Increased power settings (greater than or equal to 30 W) and pulse duration (greater than or equal to 30 sec at 20 W) were associated with impedance rises in blood medium. Typically, impedance rises in blood were associated with blood coagulum on the catheter electrodes. Impedance rises in both saline and blood media were also associated with tissue charring and endocardial surface disruption. Once a rise in impedance occurred at the ablation site, repeated applications to the same site resulted in a more rapid rise in impedance. Catheter contact pressure of 80 gm or more also resulted in rapid impedance rise. These data suggest that factors other than set power and duration may also contribute to impedance rises during RF ablation. These findings may have important clinical implications in performing catheter ablation with RF energy.     

Pulse Width Dependent Increase in the Pacemaker Automatic Interval

From a total of 51 patients equipped with rate and pulse width adjustable pulse gen erators (Microlith-P 0505, Microthin-PI 0522) implanted over the last 3 years, 10 (19.6%) showed an un expected drop in pacemaker pulse rate during pulse width programming. For one of the pulse gen erators used (Microthin-PI 0522), unexpected rate decrease occurred in 7/13 cases (53.8%). For all ex cept one patient, decrease in pacemaker pulse rate corresponded with the total refractory period of the pulse generator (320 ms), at a certain pulse width when rate drop first occurred. In seven of the patients the pulse generator automatic interval was extended from 13 ms to 171 ms beyond the re fractory period. In two patients it was necessary to replace the pulse generators. Our study strongly proves that this abnormal pacemaker functioning is a result of sensing of the polarization voltage at the pacemaker electrode/tissue interface and/or the T-wave. The polarization voltage is highly dependent on the total pacemaker electrode/tissue interface impedance. Using typical values for pulse genera tor output and input resistance and output capacitance, Faraday resistance, Helmholtz capacitance and tissue resistance at the electrode/tissue interface it was shown mathematically that in some cases the polarization voltage alone would be of sufficient amplitude and slew rate for pacemaker inhibi tion. The study demonstrates an urgent need for change in the filter characteristics by making the pulse generators less sensitive in the low frequency region and reducing the polarization voltage by reducing the output circuit capacitance. (PACE, Vol. 5, May-June, 1982)     

An Unusual Source of Electromagnetic Interference: A Device–Device Interaction

Introduction: Implantable cardioverter‐defibrillators (ICDs) are susceptible to oversensing of extracardiac signals, also known as electromagnetic interference (EMI). We report a case of an unusual source of electrical interference of only the high voltage (HV) impedance measurement in the Teligen? ICD (Boston Scientific, St. Paul, MN, USA) caused by electrical interference from an electrosurgical generator with an electrocautery patch located in close proximity to the ICD pulse generator. Method and Results: A patient underwent an uneventful implant of a Boston Scientific Teligen? 100 ICD. Once the device was inserted in a pocket, interrogation of the device repeatedly demonstrated HV electrode impedance measurements between <20 and 40Ωand noise only on the HV electrode. A new lead and generator were implanted without a change in the interrogation results. The erroneous measurements of HV impedance were caused by a combination of the close proximity of the electrocautery patch to the ICD generator. The continuous low‐amplitude current emitted by the contact quality monitoring system of the electrosurgical cautery generator interfered with an equally weak current delivered through the lead by the device to measurement HV impedance. The Medtronic Virtuoso? (Medtronic Inc., Minneapolis, MN, USA) ICD and the St. Jude Medical Current? DR (St. Jude Medical, St. Paul, MN, USA) ICD were not affected by the patch due to greater magnitude of current delivered by the device to measure HV electrode impedance. Conclusion: It is important that the operator must be aware of any potential source of EMI, as it may affect the device and require immediate troubleshooting. Failure to recognize this interaction may result in inappropriate and unnecessary pulse generator replacement. (PACE 2010; 994–998)     

Long-term performance of transvenous, steroid-eluting, high impedance, passive-fixation ventricular pacing leads

The long-term performance of two high impedance, steroid-eluting, passive-fixation ventricular leads, porous platinum iridium electrode CPI Selute Picotip 4035 (131 patients), and platinized platinum electrode Medtronic Capsure Z 5034 (57 patients), was compared with one conventional 8.0-mm2 porous platinum iridium electrode CPI Selute 4285 (38 patients). The mean follow-up period was 28 +/- 14 months. Capture threshold, R wave amplitude, and pacing impedance were measured at the time of implantation, immediately after implantation, 1 week, 1, 3, and 6 months after implantation and then every 6 months thereafter. The two high impedance leads revealed a higher sensing slew rate than the conventional lead, the R wave amplitude was similar among the three groups, but the voltage threshold at 0.5-ms pulse width was significantly higher in porous platinum iridium groups at the time of implantation. During follow-up, the conventional lead revealed a significantly higher R wave amplitude within the first 3 months, however, this pattern disappeared after 3 months. Pacing impedance was significantly higher in the high impedance porous platinum iridium electrode groups. Voltage threshold at 0.5-ms pulse width was similar among the three groups in the first 3 months, however, it increased gradually and was significantly higher in porous platinum iridium electrode groups subsequently. The energy threshold at 0.5 ms was significantly lower in the two high impedance groups than the conventional group, but no difference was found in the two high impedance groups. Lead related complications were similar among the three groups. In conclusion, high impedance electrodes with different design and materials had different properties; platinized platinum electrode showed a lower pacing impedance but had a more stable long-term capture threshold as compared to the porous platinum iridium electrode. Further studies are mandatory for the development of an ideal pacing lead.     

严重脊柱畸形经后路椎弓根截骨术后并发症的观察与护理

总结21例严重脊柱畸形经后路椎弓根截骨发生术后并发症的观察与护理。21例患者中发生神经功能障碍11例、脑脊液漏3例、切口感染3例、切口血肿1例、胸腔积液2例、失血性休克1例。护理过程密切观察患者生命体征、面色、意识、切口敷料及引流情况,注意各并发症的临床表现,及时发现,及时处理,同时认真听取患者主诉、针对患者存在的问题及时予以处理。1例失血性休克患者术后死于多器官功能衰竭,20例患者康复出院。