DC bias is one of the most serious threats to the safe operation of power transformers.In order to determine the influencing extent and degree of DC bias, the distributed measurement method of neutral-point current, noise and vibration of power transformer is investigated and the on-line monitoring system is developed.The system is composed of distributed terminals and remote monitoring server.Hall sensor, microphone and acceleration sensor constitute the front-end of the system.The frequency amplitudes of neutral-point current, noise and vibration signals at 50 Hz and its harmonics are analyzed.Butterworth filters are designed to calculate the 1/3-Octave band and equivalent A-weight sound pressure level of the transformer noise.The measured results is processed by the terminal and sent to the monitoring server with GPRS network.All the test results are stored in professional data base.With the monitoring server, the real-time DC bias state of each transformer on-site is displayed and the history data can be queried.Field application shows that the measured results of the designed system are accurate and the signal transmission is stable.The system is proved to be capable of determining the extent and degree of DC bias and will provide technical support for its specific control.%直流偏磁严重威胁着电力变压器的安全运行.为了确定直流偏磁的影响范围及程度,开发了分布式电力变压器直流偏磁中性点电流、噪声以及振动多状态量监测系统并投入实际应用.系统由分布式监测终端以及远程监测服务器构成.由霍尔传感器、传声器以及加速度传感器构成检测系统前端,对中性点电流、噪声以及振动信号进行了50 Hz及其谐频幅值分析.通过设计1/3倍频程滤波器计算噪声信号1/3倍频程以及等效A声级,检测结果由监测终端分析整理后通过GPRS网络远程传输至监测服务器并存储至数据库.利用监测服务器实现当前各变压器直流偏磁状况实时显示以及历史数据查询.现场应用结果表明,所设计的分布式变压器直流偏磁多状态量监测系统测量结果准确、信号传输稳定,有助于确定直流偏磁的影响范围及程度,为直流偏磁的针对性控制提供技术支持.
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