## 5 Interaction of the Power Supply with the Reactor
The problem is the occurrence of high strongly deformed voltage, with a high content of higher harmonics and short-term overvoltages in the working electrode supply circuit, generated by the spark discharge (Figure 7A). This voltage is transferred to the primary side of transformers supplying working electrodes and further to the AC/DC/AC converter output. Interference from the plasma reactor to the AC/DC/AC converter is transmitted to a lesser extent when the spark ignition spark discharge is ignited between the two ignition electrodes (Figures 6B and 7B). The absence of the ignition spark discharge to the working electrodes does not significantly affect the deterioration of the conditions for ignition of the main discharge. The absence of spark channels from the ignition electrode to the working electrodes, which are the beginning of the arc discharge, is compensated by a sufficiently high degree of ionisation of the space between the working electrodes. The ionisation must be chosen in such a way that, for a given process gas and its gas-dynamic parameters, the resistance of the gap between the working electrodes is reduced to a degree sufficient for spontaneous ignition of the arc discharge at reduced voltage. The appropriate degree of gas ionisation in the space between the working electrodes is obtained by selecting the parameters of the working electrode supply, i.e., voltage, current and frequency. The voltages induced on the secondary side of matching transformers, as shown in Figure 7, are transferred to the output of the AC/DC/AC converter less the transformer gearbox value of 6.5. For both one and two ignition electrodes, these voltages do not exceed those which could damage the converter. The design problem of power supply systems with AC/DC/AC converters is susceptibility to interference generated by electrical discharge. The discharge in a plasma reactor can be treated as a dynamic, non-linear conductivity with rapid, often random, time changes of currents, voltages and power, generating overvoltages, higher harmonics and electromagnetic interference, both conductive and radiated [6; 7]. Observing the discharge parameters and analysing the level of current and voltage deformation and the level of conducted and radiated electromagnetic interferences emitted by the plasma reactor, it is concluded that appropriately selected transformer power supply systems provide better conditions for plasma generation, but without the possibility of smooth regulation of its parameters, which is a big disadvantage. Figure 6: Reactor with one ignition electrode (**A**), and with two ignition electrodes (**B**). Figure 7: Voltage induced on the secondary windings of the transformer by an ignition discharge in still air for one ignition electrode (**A**), and two ignition electrodes (**B**). By improving the design of the reactor in terms of the selection of the shape of the electrodes, the conditions of plasma generation and the operation of the converter power system are improved. The shape of the electrodes, length between them [8] and their material influences the stability and burning time of the arc discharge. The electrodes are selected depending on the composition of the process gas, its gas-dynamic conditions and the parameters of the electricity supply system. For nitrogen plasma, the electrodes used are convex, knife-edge, working edge profile, height 143 mm, width 30 mm (Figure 8A) and thickness 2 mm. The second stage was equipped with concave-shaped electrodes, 200 mm high, 30 mm wide and 2 mm thick (Figure 8B). The electrode material is 0H18N9 stainless steel. For this type of electrodes, the best burning conditions and the lowest interference of the AC/DC/AC converter with the adopted geometrical configuration of nozzles, gas-dynamic and electrical parameters were obtained.