数字变电站的一起同步采样事故分析及变时间窗综合纠错对时方案

在对一起数字化变电站中同步采样问题引起主变保护跳闸事故分析的基础上,讨论了数字化变电站对时与采样同步问题风险点,分析了四种造成时间同步误差的原因,提出了一种具有较强纠错能力的变对时时间窗综合方案。该方案对合并单元可能存在的五种同步状态分别采取不同的处理措施,从而使该方案在保证合理对时窗宽大小的同时极大了减少了接收干扰信号的可能性。通过分析,所提措施可以有效地提高数字化变电站对时系统的抗干扰能力,提高保护装置的可靠性。     

数字化变电站电压波动与闪变检测问题探讨

阐述了电子式互感器在数字化变电站的应用,数字化变电站与传统常规变电站的不同.阐述了数字化变电站采样同步的问题,数字化变电站对采样时间同步的要求,数据的同步问题.对数字化变电站电压波动与闪变的检测应用进行了分析,对电压波动与闪变的检测仪器装置提出了相关的要求,需要仪器符合相关要求才能进行准确的测量分析,并且提出了对数字化变电站电压波动与闪变检测的问题与展望和思考.     

一种不依赖MU同步的采样值网络传输方案

IEC 61850标准的组网采样值传输方案由于依赖统一同步网络,降低了数字化站可靠性。点对点采样值传输方案虽然解决了对同步源的依赖问题,但因二次接线复杂且损失了数据共享优势,降低了数字化站可维护性。本文采用不依赖MU同步的网络传输方案,通过特殊交换机记录网络传输延时并将延时反映在报文的特定字段中,实现了采样值的同步计算。经测试,该方案时间同步精度误差为ns级别,满足采样精度要求的同时具备了与传统组网方案相当的实时性。该方案不仅解决了跨间隔采样对同步源依赖的问题,提高了智能数字化系统的总体可靠性,并兼顾了数字化变电站运行维护方便的特征,因此在智能电网和数字化变电站的实际应用中具有很好的应用前景。     

数字化变电站中采样值同步技术研究

认为采样值同步技术是实现数字化变电站过程总线通信的难点之一。阐述了基于外部源的硬接线同步和基于IEEE 1588的网络同步两种方案,指出方案实现的关键因素,从硬件设计、同步误差、冗余性和互操作性等方面对这两种方案进行了分析和比较。研究结果对数字化变电站中采样值同步设计具有参考意义。     

数字化变电站与传统变电站间光纤纵差保护研究

在使用电子式互感器的数字化变电站和使用电磁式互感器的传统变电站之间,实现差动保护的关键是两侧电气量的同步.提出了解决该问题的具体方法:数字化变电站侧的保护装置实时跟踪间隔合并单元的采样频率,传统化站的保护装置实时跟踪数字化站侧的保护装置的采样频率,从而实现两侧电气量的同步.工程应用证明该方案完全可行.     

数字化变电站对时方法的研究

针对数字化变电站的结构特点,分析了其同步对时的要求以及存在的问题,提出了一种适用于数字化变电站的同步对时方案。该方案依据过程层设备、间隔层设备、变电站层设备的对时特点,分别采用了不同的具体对时方式,以满足各层设备的不同对时要求。在此基础上,提出了间隔层与过程层实现数据同步的方法。对时方案结构清晰,逻辑简单,便于在各智能电子设备中实现,可以有效实现数字化变电站的全站信息同步。     

数字化变电站采样数据的同步方案研究

分析数字化变电站采样同步系统结构和采样值传输延时时序,探讨基于IEC 60044-7/8和IEC61850-9-1/2协议的数字化变电站内采样数据的同步方案.     

合并单元采样同步的一种实现方法

结合数字化变电站工程应用现状对采样同步相关的问题、实现方法和应用需求进行了分析和总结。提出了基于路径延时法的合并单元采样同步实现方法,采用该方法设计的合并单元输出数据报文既包含采样计数值也包含采样额定延时时间。     

过程层采样网络同步域与再同步机制分析

根据某数字化变电站工程的数字化保护动模试验结果,就过程层采样网络同步域的划分和合并单元再同步机制问题进行了分析,提出了双时钟域方案和新的再同步机制,保证广域时钟源再同步或失去外部对时信号的过程中保护系统的可靠性.     

数字化变电站中高精度同步采样时钟的设计

在数字化变电站的应用中,对同步采样时钟要求高稳定和高精度,其实现关键在于消除同步采样时钟的误差。文中从分析同步采样时钟误差产生的原因出发,利用全球定位系统（GPS）接收机输出GPS时钟误差分布的特点和晶振频率在短时间内的相对稳定性及现场可编程门阵列（FPGA）的高速数字信号处理的特性,采用相应处理措施消除了晶振频率偏差对同步采样时钟的影响,实现了GPS时钟在短时间内出现较大偏移或扰动时对其进行人为补偿,从而保证了采样时钟的精确同步,为数字化变电站的设计应用提供了一种高稳定、高精度的同步采样时钟设计方法。     

Engineering time timeline of time chronology of time

Phillip Schewe presents his own brief history of time, explaining where it came from, what it is, and where it's going     

Olympic time

With less than a year to go until the 2010 Winter Olympics in Vancouver, Nick Smith went to Canada to see how electronic timing equipment trials are progressing.     

killing time

Discera aims to replace the quartz crystals used in practically all electronic systems today with oscillators built from silicon using micro-electromechanical systems (MEMS) techniques.     

同步时钟系统中时间同步功能的应用

电力系统中时间记录的准确性对电网事故的分析具有重要作用.如调度录音监听系统的时间与调度员发令操作的时间若存在较大差异,就难以准确叙述事件顺序,这给电网故障的分析带来困难.文章介绍了常用的时间同步技术,并阐述了Internet网络时间协议,着重分析了GNSS-97同步时钟设备的功能及其应用.     

同步时钟系统中时间同步功能的应用

电力系统中时间记录的准确性对电网事故的分析具有重要作用。如调度录音监听系统的时间与调度员发令操作的时间若存在较大差异，就难以准确叙述事件顺序，这给电网故障的分析带来困难。文章介绍了常用的时间同步技术，并阐述了Internet网络时间协议，着重分析了GNSS-97同步时钟设备     

热电池贮存时间对激活时间影响的研究

通过对不同贮存期的某型热电池放电,记录电池的激活时间,采用数学分析软件对电池激活时间进行拟合,建立非线性回归模型,实现对贮存后热电池的激活时间的预测。     

Measured time delay and re-synchronization time in digitalmicrowave radio systems

The transition from analog to digital transmission systems has been slower for electric power utilities than other industrial sectors because of concern that digital transmission system delay times could adversely impact the response time of transfer trip protective relaying equipment. Alcatel Network Systems has completed a comprehensive testing program to measure the absolute time delay and various re-synchronization times through analog and digital transmission systems. The general conclusion is that the worst case absolute time delay of 577 microseconds, VF to VF, through the digital microwave system is approximately one half the delay for a typical analog system. Absolute time delays of 500-600 microseconds should cause no problems to transfer trip protective relaying systems     

Doing real time

The authors define real-time systems as those that are able to respond to specific events within a specific time. They examine the use of microprocessors in such systems. Time constraints that impact the design are discussed. They are the response time, survival time, recovery time, throughputs, and period of service request. Real-time techniques, i.e. software methods that reduce the execution time of part of the program, are considered. These reductions come at the expense of memory utilization     

Ultrashort echo time and zero echo time MRI at 7T

Objective

Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D ZTE and UTE pulse sequences at 7T to assess differences between these methods.

Materials and methods

We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast. Our ZTE used the water- and fat-suppressed solid-state proton projection imaging method to fill the center of k-space. Images from healthy volunteers obtained at 7T were compared qualitatively, as well as with SNR and CNR measurements for various ultrashort, short, and long-T2 tissues.

Results

We measured nearly identical contrast-to-noise and signal-to-noise ratios (CNR/SNR) in similar scan times between the two approaches for ultrashort, short, and long-T2 components in the brain, knee and ankle. In our protocol, we observed gradient fidelity artifacts in UTE, and our chosen flip angle and readout also resulted in shading artifacts in ZTE due to inadvertent spatial selectivity. These can be corrected by advanced reconstruction methods or with different chosen protocol parameters.

Conclusion

The applied ZTE and UTE pulse sequences achieved similar contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components. Key differences include that ZTE is limited to volumetric imaging, but has substantially reduced acoustic noise levels during the scan. Meanwhile, UTE has higher acoustic noise levels and greater sensitivity to gradient fidelity, but offers more flexibility in image contrast and volume selection.

     

多通道数据实时采集标时系统设计

为适应某高炮靶场试验需要,设计了一种基于GPS守时的多通道数据采集标时系统,通过串口接收数据的同时为数据打上时间戳.系统通过多通道采集数据,支持RS232、RS422、RS485、光纤等多串口协议,且各通道波特率可分别设置;系统由GPS获得精确的秒级时间,毫秒级时间采用分频技术由内部定时器提供,并由GPS秒脉冲实时校正...