单相XLPE海底电缆中局放超声信号径向传播过程的仿真研究

Simulation Study on Radial Propagation of Partial Discharge Ultrasonic Signal in Single⁃phase XLPE Submarine Cable

现有的电力装备声场仿真中常见的频域仿真只针对传播后期能量的分布,时域仿真更关注能量在初期的传播过程。因而在仿真海底电缆中的局放超声信号时,信号在径向传播初期的复杂折反射过程更适合时域仿真。文中针对单相XLPE海底电缆建立了包含铜芯、半导电屏蔽层、绝缘层等总计11层结构的全尺寸切片模型,利用时域仿真获得局放超声信号在海底电缆多层结构中的径向传播过程,得到了放电产生的局放超声信号在多次折反射后形成的纵波与横波叠加的多频非周期信号。由于折反射的影响,能量在各层材料间逐渐向外释放,在外层光纤单元中引起的纤芯应变接近pε量级。对比了3种放电缺陷的局放超声信号在海底电缆的径向传播情况,为利用海底电缆中预埋光纤传感器检测局放超声信号提供了理论指导。

In the sound filed simulation of existing electric facilities,the common frequency domain simulation only focus on the distribution of energy in the post⁃propagation.Time⁃domain simulation,on the other hand,focus more on the energy propagation processes in the early stage.Therefore,when modelling the ultrasonic signal of partial dis⁃charge of submarine cables,the complex refraction and reflection processes are more suitable to time⁃domain simula⁃tion in the early stage of signal radial propagation.As for the single phase XLPE submarine cable in this paper,a full⁃size slice model containing totally such 11 layers of structures as copper core,semi⁃conducting shield and insulation layer etc is set up.The time⁃domain simulations are used to obtain the radial propagation processes of the ultrasonic signal through the multi⁃layer structure of a submarine cable.During the propagation processes,the ultrasonic signal of partial discharge is refracted and reflected several times to form a multi⁃frequency non⁃periodic signal with super⁃imposed longitudinal and transverse waves.Due to the influence of refraction and reflection,energy is gradually re⁃leased outwards between the material layers,inducing core strains in the outer fiber units close to pico⁃strain.The ra⁃dial propagation of ultrasonic signals in submarine cables due to partial discharge at three different locations is com⁃pared,which provides theoretical guidance for the detection of partial discharge ultrasonic signals by embedded opti⁃cal fiber sensors in submarine cables.