换流变压器阀侧套管局部放电电磁波传播规律的仿真研究

Simulation Study on Electromagnetic Wave Propagation Law of Valve Side Bushing Partial Discharge in Converter Transformer

换流变压器阀侧套管的主绝缘一般采用多层金属缠绕且内部填充环氧浸纸结构,其内部电磁波的传播路径以及衰减规律尚不清晰,严重制约了阀侧套管非接触式在线监测技术的发展。目前以射频、特高频法为代表的非接触式局部放电检测方法可通过研究设备内部电磁波的传播衰减规律,从而实现对设备绝缘状态的有效监测。为研究电磁波在阀侧套管内部的传播衰减规律,该文构建实际±800kV换流变压器阀侧套管时域有限差分三维模型,对局放激发的电磁波在阀侧套管内部和外部的传播路径及规律进行仿真分析。结果表明:(1)阀侧套管的外部空间中电磁波的频带范围为1.5~2.5GHz,电磁波首波出现在法兰处,并已结合实验证明此范围;(2)电磁波在阀侧套管内部的传播路径为电容屏间的环氧浸纸和外侧的SF6填充区域,电磁波在电容屏间独立传播,传出电容芯子后相互叠加,频带分布于0.75~2.5GHz;(3)电磁波在阀侧套管外部的时空分布特性具体表现为电磁波的电场强度随着时间和距离增加呈现衰减趋势,具体衰减规律与距离成非线性关系,电磁波经过电容芯子后的衰减范围为14.11~47.47dB/m,在外部空间中的衰减范围为2.74~13.07dB/m。结果可为换流变压器阀侧套管局部放电的监测与诊断提供一定技术基础。

The main insulation of converter transformer valve side bushing is generally made of multi-layer metal winding and filled with epoxy impregnated paper.The propagation path and attenuation law of electromagnetic wave inside the valve side bushing is not clear.This seriously restricts the development of non-contact online monitoring technology for valve side bushing.At present,the non-contact partial discharge detection method represented by radio frequency and ultra-high frequency methods can effectively monitor the insulation state of the equipment by studying the propagation attenuation law of electromagnetic waves inside the equipment.In order to study the propagation attenuation law of electromagnetic wave in the valve side bushing,this paper constructs the actual±800 kV converter transformer valve side bushing finite difference time domain three-dimensional model.The propagation path and law of electromagnetic wave excited by partial discharge inside and outside the valve side bushing are also simulated and analyzed.The results show:(1)The frequency band range of electromagnetic wave propagating to the outer space of the valve side bushing is 1.5~2.5 GHz.The first wave of electromagnetic wave in the external space appears at the flange,which is proved by experiments.(2)The propagation path of electromagnetic wave inside the valve side bushing is the epoxy impregnated paper between the capacitor screens and the outer SF6 filling area.Electromagnetic waves propagate independently between capacitor screens and can be superimposed on each other after transmitting the capacitor core.(3)In the outer space of valve side bushing,the space-time distribution characteristic of electromagnetic wave is that the electric field intensity decreases with the increase of time and distance.The specific attenuation law is nonlinear with distance.The attenuation range of electromagnetic wave after passing through the capacitor core is 14.11~47.47 dB/m.The attenuation range in external space is 2.74~13.07 dB/m.The results can provide technical basis for monitoring and diagnosis of partial discharge in valve side bushing of converter transformer.