# Modification of Insulating Properties of Surfaces of Dielectric High-Voltage Devices Using Plasma
## 3 Current State of the Research and Solutions for the Surface Strength of Insulators  
According to well-proven procedures [14; 15; 16; 17; 18; 19; 20], standard devices and HV devices with surface treatment and known materials are designed. The current trends in increasing the surface strength \(E_{\text{p}}\) focus mainly on the concept, design, geometric layout of the HV device, and solutions using miniaturization (using microelectronics); one of the related activities then lies in changing the electrical strength of materials, both volumetric and surface ones [23; 24; 25; 26], by choosing the concept and design for the critical part of the device or equipment. The approaches can be characterized and summarized into several categories, as follows:  
1. Insulator surface modification and shaping, both physical and chemical;
2. Application of layers to increase the electrical strength parameters of the insulator;
3. Alteration of the nanostructure or the interface surface of the insulator. Utilizing experiments, the numerical modeling, design, and improvement of the measurement methods of the electrical surface charge \(\sigma\) or the electric field vector \(E\) can be carried out. Further, a more detailed approach to increase insulation properties according to (a) is outlined in [23], for example, where the authors analyze the results of a multiphysics numerical model of a three-pole insulator in a horizontal arrangement, with the operating voltage \(U_{\text{n}}=\pm\) 800 kV GIL (gas-insulated transmission lines), based on this model; the temperature distribution and gas flow inside the GIL insulator are then determined. A similar issue is addressed, with the support of numerical modeling, by the authors of [25] for the DC-GIL system of the ITER project with \(U_{\text{n}}=1\) MV. Another experimental concept [24] focuses on a set of procedures for evaluating parameters involved in the aging of insulators; the authors of the report discuss methods for evaluating the occurrence of surface discharges, observing space charge generation, and measuring the strength of the dielectric. In the area of space or surface charge generation and distribution, it has been established that the charge accumulation rate depends on the aging time of the nanostructured resin. The problem of formation, distribution, and lifetime of the surface electric charge \(\sigma\) also depends on the method of combining the dielectric and electrode system. Importantly, the insulator design can cause a disproportionate generation of the local surface electric charge \(\sigma\)[25]. If we examine in greater detail the possibilities in the field of increasing the stress resistance achieved through the deposition of layers, we may emphasize procedures such as minimizing the influence of inhomogeneous or non-isotropic environments [26; 27; 28; 29] on this parameter according to (b); for instance, this option is outlined in paper [26]. To increase the dielectric strength and to reduce the probability of electrical breakdown during voltage tests (due to a surface discharge), the concept of a layered insulator with functional gradient dielectric materials is used. If we further investigate the results in the field of modifying the nanolayer surface (c) to reduce the discharge activity and to increase the voltage resistance of the insulator, we can consult sources such as [15; 30]. Numerical modeling was employed in the hypothesis analysis and verification [15; 30]; thus, to configure the measurement process, the system was suitably selected and adjusted to the analysis of a numerical model based on finite element methods [13; 30], and the subsequent evaluation of the influence of the micro-nanostructure on the physical parameters of the dielectric. The dependence of the electrical strength \(E_{\mathrm{p}}\) and the micro/nano structure of the dielectric interface was already considered in an article from 1955 [31].