水电站GIS特快速暂态过电压在线监测系统构建及监测数据分析

Construction of Very Fast Transient Overvoltage On⁃line Monitoring System and Data Analysis for GIS in the Hydropower Substation

特快速暂态过电压(VFTO)严重威胁气体绝缘组合电器(GIS)及变压器等线圈类设备的绝缘性能,尤其在GIS和变压器通过油气套管直连时。因此为准确及时掌握VFTO对GIS和变压器运行状态的影响,有必要实时监测GIS设备断路器和隔离开关操作引起的VFTO水平。文中针对某大型水电站500 kV变压器和GIS设备,设计了一套基于超宽频电容传感的特快速暂态过电压在线监测系统。对GIS设备与变压器联接筒体处的盖板进行电容传感改造,在监测终端处就地进行信号转换和采集,并通过光纤上传至上位存储控制单元。监测系统有效测量带宽2.1 Hz^230 MHz,采样率250 MS/s,模拟带宽100 MHz。通过定制的陡度触发模式可准确捕捉突变电压波形,记录时间不低于200 ms。过电压系统上线之后,成功准确记录到隔离开关和断路器在操作过程中引起的特快速暂态过电压波形。通过数据分析发现该水电站隔离开关操作引起的VFTO波形持续时间低于5μs,上升沿低于60 ns,主要频谱分布在1~10 MHz之间,上升沿处最高瞬时频率可达100 MHz;断路器操作操作引起的VFTO波形持续时间约30μs,上升沿约100 ns,主要频谱分布在100 kHz^2 MHz之间,上升沿处最高瞬时频率也可达100 MHz。利用过电压在线监测系统实测的过电压波形可优化GIS和变压器设备VFTO仿真模型,为提升设备VFTO防护水平,分析设备故障原因奠定了坚实基础。

The very fast transient(VFTO)is a serious threat to the insulation performance of gas insulated switch⁃gerar(GIS)and the coil equipment,for example the transformer,especially when GIS and the transformer are di⁃rectly connected through oil/gas insulated bushing.Therefore,in order to accurately and timely master the impact of VFTO on the operation status of GIS and transformer,it is necessary to constantly monitor the VFTO level caused by the operation of circuit breakers and disconnectors of GIS.In this paper an VFTO on⁃line monitoring system based on the ultra⁃wide band capacitive sensing is designed for 500 kV transformer and GIS equipment of a large hydropower station.Capacitance sensing transformation is carried out on the cover plate of the connecting cylinder of GIS equipment and transformer.Signal conversion and acquisition are implemented locally at the monitoring ter⁃minal,and uploaded to the upper storage control unit through optical fiber.The effective measurement bandwidth of the monitoring system ranges from 2.1 Hz to 230 MHz,the sampling rate is 250 MS/s,and the analog bandwidth is 100 MHz.The abrupt voltage waveform can be accurately captured by customized steep trigger mode,and the re⁃cording time is not less than 200 ms.The vert fast transient overvoltage waveforms caused by the disconnector and circuit breaker are recorded successfully and accurately by the on⁃line monitoring system.Through data analysis,it is found that the duration of VFTO waveform caused by disconnector operation is less than 5μs,the rising edge is less than 60 ns,the main spectrum is between 1 MHz and 10 MHz,and the maximum instantaneous frequency at the rising edge can reach 100 MHz;The duration of VFTO waveform caused by circuit breaker operation is less than 30ms,the rising edge is less than 100 ns,the main spectrum is between 10 kHz and 1 MHz,and the maximum instan⁃taneous frequency at the rising edge also can reach 100 MHz.The VFTO simulation model of the GIS and transformer equipment can be optimized by the measured waveform of the overvoltage on⁃line monitoring system,which lays a sol⁃id foundation for improving the protection level of VFTO and analyzing the causes of equipment failure.