"Study of Nonlinear Conduction Mechanism for Polymeric Insulating Material due to Space Charge Formation Under AC High Field."

聚合物广泛用作地下电力电缆的绝缘材料。众所周知，在交流电场高于一定阈值时，会发生电致发光（EL）和电荷注入，从而在聚合物绝缘中产生空间电荷。空间电荷会引起光子和声子发射等耗散能量过程，增加局部电场，导致绝缘耐压降低，最终导致电力电缆过早失效。认为电致发光在第一次局部放电之前就已发射，在一定阈值电场以上电致发光是连续发生的，并归因于电极的电荷注入。注入的电荷在绝缘材料中积累形成空间电荷，空间电荷在直流电压应用中起主要作用，但在交流应用中不能完全忽略。高分子材料在交流强场作用下空间电荷的作用仍然是研究的热点 ...更多信息 为了阐明高分子材料，如低密度聚乙烯（LDPE）、LDPE/MgO纳米复合材料等在交流高场下的导电机理，自2005年起，我们建立了一套三年的耗散电流波形和电致发光的同步观测系统。由于所开发的耗散电流波形检测电路（称为“位移电流补偿法（DCBM）"）不包括用于抵消电容分量的电感，因此可以高精度地检测谐波。此外，它不仅是在高场的耗散电流的谐波检测，而且估计的体积电阻率和相对介电常数在交流高场。在交流强场下观察电致发光对了解电荷行为也是非常有用的。所研制的电致发光观察系统仅用于聚合物薄膜样品。2002年，与NRC合作开发了用于薄膜样品的样品保持器。为了实现DCBM观测到的耗散电流波形与PMT和CCD观测到的电致发光波形的同步观测，利用LabVIEW开发了几个软件，实现了对耗散电流波形和电致发光观测的数字示波器、高灵敏度CCD相机的触发控制以及任意函数发生器的完美控制。为了阐明聚合物在交流强电场下的导电机理，利用所开发的系统进行了各种实验，如梯形波法测量dE/dt、纳米MgO填料对LDPE/MgO纳米复合材料的影响、耗散电流和电致发光的基波和三次谐波随时间的变化等。少

Polymers are extensively used as insulating material in underground power cables. It has been well established that electroluminescence (EL) and charge injection, which gives rise to space charge in the polymeric insulation, occur at ac field above a certain threshold value. Space charge can cause dissipative energetic processes such as photon and phonon emission, increase the local electric field, lead to the reduction of the insulation withstand voltage and ultimately to premature failure of the power cable. It is considered that EL is emitted even before the first partial discharge, EL occur continuously above a certain threshold field and has been attributed to the injection of electric charge form the electrodes. The injected charge accumulates in the insulating material to form a space charge, which plays a major role in do voltage applications, but cannot be completely ignored in ac applications. The role of space charge in polymeric materials subjected to AC high field is still … More not well understood.In order to clarify the conduction mechanism of polymers, such as Low Density Polyethylene (LDPE), LDPE/MgO nanocomposite materials, and so on, under ac high field, the simultaneous observation system of dissipation current waveform and electroluminescence have been constructed for three years since 2005. As the developed dissipation current waveform detecting circuit, which called as"Displacement Current Bypassing Method(DCBM)", does not include any inductance for canceling the capacitance component, it is possible to detect the harmonics with high accuracy. Furthermore it is not only detecting the harmonics of the dissipation current in high field, but also estimating the volume resistivity and relative permittivity under AC high field. The observation of EL under AC high field is also very useful to understand the charge behavior. The developed EL observation system is just for a polymeric film sample. In 2002, the sample holder for a film sample was developed at the collaboration with NRC. To realize the simultaneous observation of the dissipation current waveform observed by DCBM and EL observed by PMT and CCD, the several software, which make possible perfectly controlling the digital oscilloscopes for the dissipation current waveform and EL observation, the triggering control for high sensitivity CCD camera, and the arbitrary function generator, has also developed by using Lab VIEW. In order to clarify the conduction mechanism for polymer under AC high field, the various kinds of experiments were carried out, such as estimations of dE/dt by using trapezoidal waveform application, effect of MgO nano filler on LDPE/MgO nanocomposite materials, the time variations of fundamental and third harmonics of dissipation current and EL, and so on, by using the developed system. Less