Analysis on the transient voltage performance of a DC superconducting cable

Transient voltage distribution in a DC superconducting cable, comprising of four concentric metallic cylinders was analyzed. Of the four concentric cylinders, two carry the load current, and the other two comprise the cryogenic enclosure. Analysis was performed with transient current injected either to the innermost or the outermost cylinder. The outermost cylinder was either bare or insulated. The outer three cylinders were either solidly grounded or isolated from ground at the point of current injection. It was concluded that transient voltages will appear across the RETURN cryogen flow and also across the vacuum space in the cryogenic enclosure. As these two systems are designed for their thermal performance, they may suffer permanent damage caused by unwanted electrical transients.     

超小型直流电源电压变换电路

介绍了一种新颖的超小型DC／DC电压变换电路，对电路的工作原理进行了理论分析，并用仿真算法对理论计算结果进行了校验，最后给出了基于Maxim器件的实用稳压电路。     

An analysis of the effects of cable layout on cable to antennacoupling inside a screened room

An equivalent circuit model is presented for a screened room emission measurement setup. Transfer functions that are used to illustrate the variations in received emission levels produced by changes in interconnecting cable layout when the cable is placed over a conducting bench in the room are developed. The model is based on a coupled transmission line approach and is valid at frequencies up to 50 MHz     

Field testing the performance of a cable TV system

The cable television industry is in the process of developing appropriate instrumentation and techniques for reliably measuring system performance. Data and waveform oscilloscope trace photographs obtained in actual performance tests in the field at Charleston, W. Va., are included in this paper with discussion of methods and results. Ample room for improvement both in test equipment and technique is needed.     

关于高压直流供电系统的研究报告

文章对HVDC与UPS系统的特点进行比较,并对通信用240 V直流电源系统应用中的相关问题进行分析。     

高压直流供电模式的探讨

1现行UPS系统供电模式及存在的不足现行的数据通信设备所要求的电源为交流电源,其电压、频率与交流市电相同,但对供电质量要求比市电高。为保证数据通信设备用电的安全可靠性,目前均用UPS不间断电源系统供电,其供电系统配置有在线式串机冗余和N＋1并机冗余模式,N一般小于3,     

变频器减速过程加入母线电压闭环的方法

工业现场中,变频器减速时间设置过短可能使变频器报过压故障而停机,针对这种情况,本文提出了一种方案,减速过程在原有控制的基础上增加一个直流母线电压闭环环节,对矢量控制,将该环节根据条件判断并联在速度环上,电压环保证在减速过程不出现过压,速度环保证对速度的精确控制。对V/F控制,将该环节叠加到减速斜坡输出上,减少直流母线过压的概率。     

Feasibility of electric power transmission by DC superconducting cables

The electrical characteristics of dc superconducting cables of two power ratings were studied: 3 GW and 500 MW. Two designs were considered for each of the two power ratings. In the first design, the SUPPLY stream of the cryogen is surrounded by the high-voltage high-temperature superconductor cylinder. The RETURN stream of the cryogen is on the grounded side of the system. In the second design, both the SUPPLY and the RETURN streams of the cryogen are on the grounded side of the cable. Two electrical characteristics of these cables were studied: 1) fault currents and 2) current harmonics. It was concluded that neither the fault currents nor the current harmonics pose any problems in the operation of the dc superconducting cables.     

直流微网孤岛运行状态电压稳定性分析

直流电压是直流电网运行中重要的状态变量。文章针对由多种微电源及就地负载组成的直流微电网系统,以之作为研究对象,利用阻抗比例判据判别直流微电网电压的稳定性。该方法通过将电源子系统的总输出阻抗对负载子系统的总输入阻抗的比值看作一个等效回路增益,再用 Nyquist稳定性判据分析系统的稳定性。仿真结果表明了直流微电网母线电压稳定性与各参数之间的关系。     

如何降低稳压电源的噪声

简要介绍了电磁干扰的定义、抗干扰设计的基本原则以及如何在实际的电源系统中降噪.     

Temperature effects on DC and small signal RF performance of AlGaAs/GaAs HEMTs

We here report on the DC and microwave performance of HEMTs tested on wafer under different temperature conditions. The relevant experimental data show that the most important electrical parameters, such as the output current, the threshold voltage, the transconductance and the forward transmission coefficient, are sensibly affected by thermal phenomena. We focused our attention on the variations of the above parameters with the temperature because such a detailed knowledge is essential to establish the optimum bias point for a given application. Furthermore, we analyze the influence of the DC quiescent point degradations, due to thermal phenomena, on the small signal equivalent circuit. Since the thermal behavior of the circuit model is a function of the bias, we examine the behavior of the circuit elements vs. temperature over a wide range of bias conditions.     

通信机房设备直流电源端口电压瞬变防护

直流电源端口的电压瞬变会导致通信现场设备退出服务。文章比较了美标、欧标和国标相关的规范要求。根据实践经验给出了现场工程实施方面的一些建议。     

Comparison of DC Voltage Standards using a 10:1 divider

A self-calibrated resistive divider to relate 1 V and 10 V levels of DC voltage standards (standard cells, Zener sources, Josephson systems) is presented. The system is based on a divider formed by ten equal resistors, in which the voltage drop on each resistor is measured as well as the total voltage drop. The ratio between the total voltage drop and the average voltage drop on each resistor is, theoretically, 10:1. This measuring system only requires of the divider and a multimeter of 8½ digits as auxiliary equipment. The measurement uncertainty, using this divider, is in the order of 1´10-7.     

Optical High DC Voltage Sensor Based on White-Light Interferometry

This letter reports an optical system for high dc voltage measurement utilizing a bulk$hboxLiNbO_3$crystal with specialized-orientation as a sensing element. White-light interferometry is employed to encode the electric voltage information in the optical spectrum instead of intensity. Measurement of dc voltage from 0 to 9 kV with resolution of 2.3 V has been experimentally demonstrated.     

DC电源电压和电流限的设定

电源本身可能潜伏着危险.与无源测量装置不同,DC电源在使用中如果不加约束的话,就会造成极大的危害.随着时间发展,形成限制的手段也日臻精密.早期的电源依靠熔断器和电路断路器来限制短路所造成的损害.     

Parametric effects in a microwave Read avalanche diode

The parametric effects in the microwave Read avalanche diode are studied using a simplified one-dimensional model. The signals of frequencies ω1and ω2interact with each via the pumping wave of frequencyomega_{0} = omega_{1} + omega_{2}, through the nonlinearity in avalanche. This paper shows the range in which the microwave Read avalanche diode has the parametric negative resistance, some typical values of the impedance matrix elements of the microwave Read avalanche diode, and shows that the small-signal impedance locus of the microwave Read avalanche diode on Smith chart coincides approximately with Kita's experimental results.     

基于超导等安匝线圈的柔性直流电流传感器校准系统研究

直流大电流测量设备的准确性对企业产品质量、能耗控制等诸多方面有着重要影响。由于对现有直流大电流测量设备开展计量校准工作时存在一些困难,本文提出采用超导等安匝线圈代替传统等安匝线圈制作校准系统,对用于测量大电流的柔性直流电流传感器进行计量校准,以实现降低系统中标准直流大电流源技术指标要求的目标。     

Reflector effects on the performance of a retrodirective antennaarray

This paper presents modeling strategies to determine the operating characteristics of a heterodyne phase-conjugate retrodirective Van Atta (1959) array in the presence of a plane reflector. The models used are based on physical and geometrical optics principles. Predictions of the operating characteristics of the array due to the close proximity of a plane metallic reflector are compared with experimental measurements. It is shown that provided the reflector is positioned at a distance greater than 1.25 times the separation distance between the transmitter and the retrodirective array its effect on the performance of the retrodirective array appears to be negligible     

Power dependent effects observed for a superconducting stripline resonator

Measurements of a YBCO superconducting strip at 8 GHz are presented which show an interesting power dependent effect. A possible cause, granular weak links, is also postulated and a simple model is given to explain the effect.<>     

Performance of a Cryocooled Nb DC Programmable Voltage Standard at 4 K

We report on the performance of a 1-V dc programmable Josephson voltage standard (PJVS) operating on a commercially available Gifford-McMahon cryocooler at 4 K. The NIST-fabricated niobium superconductor-normal metal-superconductor junction chip has been shown to operate successfully as integrated with this cryopackage, generating 1.229 V at the maximum operating frequency of 19.364 GHz with Shapiro steps at constant voltage that are flat to within less than 100 nV. Because of the large operating margin (greater than 1 mA), these steps were highly stable and immune from noise. Differences in behavior of the PJVS in liquid helium and on the cryocooler are discussed. This demonstration paves the way towards automated warming and cooling of the Josephson device and a fully automated voltage standard system.