# Modification of Insulating Properties of Surfaces of Dielectric High-Voltage Devices Using Plasma
## 6 Experimental Evaluation, Results, and Discussion  
Based on the described measurement methodology [35], the evaluation of the time dependence of the monitored treatment parameters and the verification of the influence of the surface conductivity/resistance of the insulator sample were graphically represented. The designing and testing of the PSI were described in [35]. For the given purpose, a generator [36] with the output power of \(P_{\text{out}}\) = 10-1000 W, \(U_{\text{out}}\) = 300-600 V, a periodic signal, and a first harmonic of \(f_{1}\) = 13.56 MHz was used. The graphical patterns of the tests of changes in the surface resistance of the insulator as a function of time (from the exposure time without a precursor) are shown in Figures 9 and 10. The surface resistance of the untreated samples of the second series of materials was \(R_{\text{p,test}}\) = 0.082 T\(\Omega\), and \(R_{\text{p,tplast}}\) = 0.092 T\(\Omega\). According to the previously performed experiments (from 1996 until now [4; 7; 9; 10; 35; 36; 45; 46]), the parameters (Figure 11) of the electric power of the exciting slot nozzle of the plasma discharge in gases, for example, were obtained based on experiments with Ar, N2, etc. to effectively influence the  
Figure 16: Schematic of the measurement process and verification of the parameters of the tested dielectric samples. surface. An example of the impact of changes in the plasma surface is shown in the images of the surface in Figure 12 under different settings of the discharge parameters. Furthermore, the effective state of the discharge on the surface of the dielectric is indicated in Figure 14, with the generator parameters set. Other settings can be applied, but they either achieve the necessary efficiency, significantly change the surface, or the permanence of the change in surface properties is insufficient. When setting different parameters of the discharge, for example, the electric power \(P_{\text{out}}\) for \(f=13.56\) MHz, with gas flows such as argon, nitrogen, air-argon, very different changes in the dielectric surfaces can be achieved. As an integral part of the research on the influence of the parameters of dielectric surfaces, the evaluation of their states during the parametric setting of the discharge is necessary. This part of the research is not the subject of this communication, but an example of surface changes on the dielectric material is given in Figures 12 and 13. The images at the corresponding magnification scales are shown there. The structure of the surface testifies to the possible hypothesis of the formation of free bonds on the surface, as shown in Figure 15, where broken hydrogen bonds are indicated in red, which then remain at the surface, and the free hydrogen atom H is removed during the plasma discharge. In designing the test, it was known from previous work [35; 41; 42; 44] that plasma-treated surfaces changed, their nanomechanical composition changed, but at the same time, a remanent electrical charge remained on the surface. This in turn may affect the resulting effect of measuring the long-term change in the electrical strength of the surface. Therefore, it was decided in the measurement methodology to repeat the measurements after some time intervals (Figure 16). The reason for this was the indicated surface charge, which was only verified initially after plasma application and before the last measurement after 144 h (SIMCO FMX-004, ser.no. FX24585). The prepared tests already included a systematic measurement of the electrical charge. The surface treatment with plasma without precursors showed that in thermoplastic materials and thermosets, the surface resistance \(R_{\text{p}}\) rose and did not decrease with time; conversely, it stabilized at a higher level of values (Figure 17). The difference and properties of thermosets and thermoplastics had not been investigated, but both types of insulants demonstrated increased electrical surface strength.