Preventing Space Charge Accumulation by Incorporating Electrets

Abstract

the increasing electric field result in premature device failure. [4,5] Defects such as triple point, sharp edge, and airgap that exist in devices increase electric field and cause PD. [6] To make matter worse, higher voltage rating and higher switching speed provided by WBG power electronics increases PD magnitude and repetition rate. [6] There are various techniques that can be implemented to reduce PD. Among them, some are geometric approaches, while some are material based approaches. Geometric approaches have been implemented in system design to minimize and avoid sharp edges, triple points, and air gaps. [7] However, in reality, the geometric approach is limited by manufacturing tolerance, thermal cycling, and mechanical loading that eventually create cracks and delamination. [8] On the other hand, material based approaches including nonlinear resistive field grading materials fabricated by dispersing micro fillers in resins have been utilized for electric field grading and PD mitigation. [9][10][11] However, resistive field grading inherently relies on conductive current for electric field reduction which causes Joule heating that may not be accepted in certain conditions. [8] Furthermore, nonlinear field grading is only effective for electric field control near triple point and sharp edges, but limited in terms of reducing electric fields in bubbles, cracks, and delaminations. [8] Nowadays, the use of medium voltage direct current (MVDC), high voltage direct current (HVDC) applications, and power electronic converters (PEC) is increasing. As electric field distribution and dielectric response in DC and power electronics driven systems are different compared to those in AC systems, electrical insulation is becoming a growing concern with the increasing use of the new systems. [12] One of the major electrical insulation challenges in MVDC and HVDC is space charge accumulation. In AC systems, the polarity of voltage changes constantly and restricts charge from accumulating in the insulating material. Unlike in AC, there is no periodic polarity change in DC systems, which renders space charge accumulation a serious issue for the performance of insulating materials in DC. Charge particles trapped in dielectric materials are defined as space charge. Such charge accumulation should be avoided since it increases electric field and electrical stress in insulating materials leading to electric field distortion, insulation degradation, reduced lifespan, and breakdown of devices. [13][14][15] Space charge accumulates near electrodes in insulating materials under high voltage direct current. Electric stress created by charge accumulation distorts electric field, reduces the remaining useful life of insulating materials, and decreases partial discharge inception voltage that are critical for ensuring the dielectric integrity of power applications. In this article, a novel approach that mitigates space charge accumulation using electrets is presented. Electrets are used to reduce electric fields that cause charge inject...

Improved Insulating Properties of Polymer Dielectric by Constructing Interfacial Composite Coatings

“…Therefore, the introduction of interfacial composite coatings introduces deep traps between the electrode and polymer interfaces. At relatively low content of nanoparticles, the interfacial region between nanofiller and matrix is almost independent, so the charge injected from the electrodes is easily captured by the deep traps in the bonded and bound layers, which creates a reverse electric field (Eq) and inhibits the charge injection [ 55 , 56 ]. In addition, a large amount of charge is trapped during transport, leading to a decrease in carrier mobility, so that very little charge reaches the interior of the polymer, inhibiting space charge accumulation.…”