# Modification of Insulating Properties of Surfaces of Dielectric High-Voltage Devices Using Plasma
## 5 Methods of Adjusting the Electrical Strength of Dielectrics: Surface Strength  
In order to achieve the desired surface treatment and to change the parameters, it appears convenient to use the plasma technique under atmospheric conditions, thus modifying not only the mechanical and structural but also the electrical properties of the sample. Such a state of the dielectric and its surface in the structure of the insulator is suitable for changing the surface strength parameters, both with and without the use of precursors. As a basis for testing and verifying the plasma modification of the dielectric surface, we created samples of dielectric insulating materials: an epoxy-based thermoset and a PE thermoplastic polymer, Figure 7.  
The surface electrical strength \(E_{\text{P}}\) and its management in insulators, together with modifications of the geometrical or surface design of the equipment, are important for outdoor and indoor installations of apparatuses and equipment for the LV, HV, and UHV voltage classes. This requirement is determined by the durability or long-term safety and safe operation of the designed/manufactured equipment, identification, detection, evaluation of initial discharges and discharge activity, and use of surface modification technologies [1,44]. An example of the impact of long-term exposure to increased electrical intensity of the surface discharge \(E_{\text{P}}\) on the condition and operation of the equipment is shown in Figure 8; in this context, significant factors include not only the quality of the  
Figure 7: Samples of dielectric materials for HV insulators and insulating parts: (**a**) epoxy base-termoset type, (**b**) PE-thermoplastic base, (**c**) chamber for surface strength measurement, (**d**) chamber and sample with a probe for surface strength measurement. equipment (aging) in terms of safe operation, parameters and changes/impacts on the insulator surface, but also the design and construction of the equipment itself with respect to minimizing the conditions for generating surface electric field intensity \(E_{\text{t}}\)[43]. From previous research [36; 37; 44] on the properties of precursors of organic origin [36; 42], the basic experiments with the effect of the plasma atmospheric discharge treatment [4; 5; 6; 7] on the surface of the dielectric, together with the evaluation of changes in the relevant parameters, have moved to the application level (GA 20-141058) [37; 43]. In a recent article by [PERSON] et al. [37], the scientifically proven mechanism of surface changes through the action of plasma generated by a slit jet is approached. Interestingly, a part of the report is centered on elucidating the physico-chemical processes during the action of plasma at the interface of the dielectric material in a free atmosphere. The basic principle lies in the creation of electromagnetic conditions at the dielectric/air surface interface, such that the strong action of the electromagnetic field and temperature changes the arrangement and molecular composition of the thermoset and thermoplastic polymers; see Figures 9 and 10. The result of the measurement of the incident plasma spectrum at the dielectric interface is exposed in Figure 11. The design and tests of the chamber have previously been published [9; 10; 12; 36; 44]. These chambers can be set up, and they parametrically affect the surface of the samples with plasma in a repeatable manner, monitoring and documenting the impact of plasma matter on the surface and the formation of artifacts (Figures 12 and 13). These changes and new formations vary both from the point of direct action of the atmospheric plasma discharge (Figure 14) and according to the chosen setting of the plasma-generating chamber mode and frequency spectrum (for example, the spectrum presented in Figure 11). A more in-depth qualitative evaluation and approximation of the process to influence the polymer surface via atmospheric plasma discharges was proposed in [45; 46].