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刘翀 《中国石油和化工标准与质量》2012,33(8):102
变电所的直流系统是变电所各系统中的重要组成部分,供给控制、保护、信号、自动装置,交流不停电电源及事故照明等的直流电源,直流系统的正常运行是这些设备可靠运行的基础,直流系统的常见故障就是直流接地,针对直流系统在运行中发生一点接地的各种可能性,分析直流接地的概念、产生的原因及危害,提出直流接地查找的方法和步骤。 相似文献
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发电厂直流系统供电负荷极为重要,供给计量保护,控制动力,信号监控,事故照明等。直流系统的可靠性是保障发电厂安全运行的决定条件之一。本文针对直流系统运行中所发生接地的各种原因进行系统的分析,结合现场实践经验,提出直流接地查找的方法及一些注意事项。 相似文献
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我公司4 500t/d熟料生产线Φ5m×74m回转窑为中信重工生产,采用3档支撑结构,驱动装置安装于靠预热器的三档托轮处。主电动机采用上海南洋电机有限公司生产的型号为ZSN4-450-092他励直流传动电动机。在窑尾电气室设置一台10kV/2 000A开关柜、一台1 000kVA整流变压器、一台0.4kV/4 000A框架断路器和一套DCS800 ABB直流传动控制装置。直流传动控制信号来自DCS系统,窑转速由现场直流电动机上安装的测速发电机采集信号通过DCS800装置运算后送出4~20mA信号给DCS系统作远方转速反馈。 相似文献
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吴荣昌 《化工自动化及仪表》1981,(8)
直流 mv 信号发生器在调试、检修自动化仪表过程中是常用的仪器。用直流电位差计产生的 mv 信号只适用于补偿式(指零)仪表;用干电池通过电阻分压的方法也能获得 mv 信号,但需要以标准电位差计算定,操作不方便,且要作成内阻小的信号源有困难,对被检修调试仪表的质量也有一定的影响。 相似文献
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发电厂直流系统一点或两点接地故障的分析与查找孔羚(黑龙江化工总厂齐齐哈尔市161041)1直流系统故障概述直流系统故障在发电厂经常发生,对于环境差、运行时间长的设备,发生故障的机会更多,常常出现一点或两点接地。发电厂直流系统一点接地作用于信号;两点接... 相似文献
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浅谈变电站直流系统接地故障及处理 总被引:4,自引:0,他引:4
直流系统的用电负荷极为重要,供给变电站继电保护、控制、信号、计算机监控、事故照明、交流不问断电源等。对供电的可靠性要求很高。直流系统的可靠性是保障变电所安全运行的决定条件之一。尽管直流电源十分稳定可靠,但实际应用中,由于电力系统应用直流电源的特殊性,特别是控制回路和保护回路的应用,使直流供电系统的故障成为变电站稳定运行的隐患,这就是我们常说的直流系统接地故障危害。本文简单分析了直流系统的接地故障的危害及处理以及处理时的注意事项。 相似文献
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《化工自动化及仪表》1974,(4)
碳化塔塔内液位高度的控制直接影响到碳酸氢铵的生产。由于塔内信号电极棒容易附着结晶碳铵和塔内液体具有较大直流电阻以及随着液体浓度变化引起该直流电阻变化,因此直接利用液体与电极棒的接触或断开作为24V信号灯开关来控制信号灯的方法,难于使液位信号准确可靠。最近,我们用晶体管共基电路和共射电路继电器来控制液位信号,实践证明,这种电路继电器安全、灵敏可靠。现将共基电路继电器介绍如下: 相似文献
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在水泥生产线中,普遍采用了DCS控制。其中,通过信号注入法和寻迹来检查处理电气故障是实际工作中常用的方法。介绍了相关的基本概念,在此基础上,列举实例具体说明信号注入法和寻迹法的故障处理方法与步骤。实践证明,这两种方法用于处理模拟量、开关量电气故障行之有效。 相似文献
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采用ST公司的无刷直流电机控制思路,将高性能、高集成度并提供PWM信号的单片微处理器ST7FMC应用于油田螺杆泵直流无刷电机调速系统中,实现了无刷直流电机作为油田螺杆泵采油系统的动力设备,具有高效、低噪声、大起动转矩、良好的调速性能等特点。主要介绍了无刷直流电机控制器原理和带传感器无刷直流电机控制的实现方法。 相似文献
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—It has been shown that quenched Pb(Sc1/2Ta1/2)O3 (PST) disordered ceramics and crystals show diffuse dispersive dielectric properties, while well annealed ordered materials exhibit normal sharp first order transition. The pyroelectric depolarization measurements taken using a Hewlett Packard Model 4140B picoammeter/DC Source under computer controlled heating cycle also have shown different behaviors between disordered and ordered materials.
In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant.
The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component of reversible pyroelectricity.
The large reversible pyroelectric effect is a promising phenomenon for developing new pyroelectric devices. 相似文献
In this work pyroelectric measurements by Chynoweth method under DC bias up to 1.8 KV/mm within a temperature range of 70°C around the temperature of maximum dielectric constant have been studied. A very significant enhancement of the pyroelectric signal under DC bias is observed in thermally quenched disordered samples. The largest enhancement of the signal appears at temperatures some degrees below the temperature of maximum dielectric constant.
The existence of microdomains in disordered materials is believed to be responsible for this new extrinsic component of reversible pyroelectricity.
The large reversible pyroelectric effect is a promising phenomenon for developing new pyroelectric devices. 相似文献
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详细介绍了钱家营矿1495E地质异常体综合探测情况,为了查清地质异常体的空间分布及其导含水性,相继运用了井上三维地震、微动探测及井下直流电法、瞬变电磁等物探技术对异常体进行综合探测分析,再通过井下钻探验证成果,确定了异常体的空间分布、赋水和导水情况,为矿井的安全生产提供了可靠的地质资料。同时阐明了综合物探技术在矿井地质构造探测中具有重要的作用。 相似文献
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Identification of the electromechanical material properties of a multilayer ceramic capacitor 下载免费PDF全文
Byung‐Han Ko Sanggeuk Jeong Dongjoon Kim No‐Cheol Park Young‐Pil Park 《International Journal of Applied Ceramic Technology》2017,14(3):424-432
A multilayer ceramic capacitor (MLCC) vibrates when an electrical signal containing an alternating current (AC) component is applied to it. The piezoelectric and electrostrictive coefficients of the dielectric layer are needed to analyze such vibrations because both affect the vibration. Also, they must be determined for various direct current (DC) biases because an MLCC is operated with various electrical signals and the coefficients vary as the DC bias changes. We determined the coefficients by measuring the vibration of an MLCC under a range of DC biases. When a single‐frequency AC voltage is applied to an MLCC, it vibrates with both fundamental and second‐harmonic frequencies because of piezoelectricity and electrostriction. These frequencies were measured and separated into their piezoelectric and electrostrictive components to derive the piezoelectric and electrostrictive coefficients. Because of the difficulty of calculating the coefficients, a finite element (FE) method was adopted in consideration of the complicated structure of the MLCC. The derived piezoelectric coefficients were cross‐checked and verified by impact testing. The electrostrictive vibration component was greater than the piezoelectric one except when the applied DC electric field was near zero. This showed that both piezoelectricity and electrostriction must be considered in vibrational analyses of MLCCs. 相似文献
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长距离流体输送管道泄漏检测与定位技术的现状与展望 总被引:19,自引:4,他引:19
介绍基于软件的泄漏检测和定位方法的发展现状,即基于模型的方法、基于信号处理的方法和基于知识的处理方法等,对上述方法存在的优缺点进行了评述,并对泄漏检测和定位方法的未来发展方向提出了作者的看法。 相似文献
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