## 1 Introduction  
Numerous international studies have been conducted on plasma reactors (PRs) and electrostatic precipitators (ESPs), both of which utilise the corona phenomenon. Their operation is based on the application of a medium voltage (DC or pulse voltage, tens of kV) between the discharge and collection electrodes to obtain the corona effect [1, 2, 3, 4, 5, 6, 7, 8]. Many studies on plasma reactors refer to the reduction of volatile organic compounds, CO\({}_{2}\), NO, and NOx concentrations performed under laboratory conditions (laboratory models) used for various applications, such as diesel engines, kitchens, or in strict laboratory conditions [1, 2, 3, 4]. There are studies on ESP used for low-power boilers (kW of thermal power) and some ESPs used for low-power boilers that have small ionisation zones, with direct implications for operation [5, 6, 8, 9, 10, 11, 12]. Most research on ESPs has been conducted using small laboratory models [13, 14, 15, 16, 17]. When burning wood on stoves, comparative studies were carried out with separate or combined operations with ESP (with DC medium-voltage) and platinum/palladium catalysts [18, 19]. The use of a larger number of collector tubes leads to a slight increase in collection efficiency, but maintenance is much more difficult [20]. Some studies have been conducted on the use of cylindrical-type ESPs (CESPs) with several tubes mounted in cylindrical or rectangular enclosures between the boiler and chimney [21; 22; 23; 24]. It has been found that ESPs with one section have a simple design because they are supplied from a single DC medium voltage (usually up to 30 kV). Different configurations (simpler or more complex) of electrical insulators have been used and experimented under the conditions under which they work in difficult conditions (high temperature and humidity, dirty gases), because their resistance decreases with time, and the voltage applied between the electrodes is lower (the Corona is less intense) [19; 20; 25]. Research was conducted on the placement of medium-voltage insulators. By placing the medium-voltage insulators outside the gas flow (oblique to the vertical chimney or near the chimney), a decrease in the rapid deposition of dirt on the surface of the medium-voltage insulators was observed. The disadvantages of these methods include the use of small discharge electrodes (reduced corona effect), major deficiencies in the centring of the discharge electrode in the collection electrode (the applied voltage is lower and the corona is much reduced), and small dust collection (30-40%) [18; 25]. The smoke resulting from wood combustion consists of particulate matter (PM), NO\({}_{\mathrm{x}}\), CO, CO\({}_{2}\), formaldehyde, volatile organic compounds, CH\({}_{4}\), H\({}_{2}\), and so on. Smoke from burning wood is composed of a complex mixture of gases and fine particles (PM 10, PM 2.5, PM 1) [5; 7; 26; 27; 28; 29]. These components are harmful to human health, as to well as the environment [30; 31]. PRESPs can encounter several problems during operation, such as the cleaning of medium-voltage insulators and collector electrodes, re-entrainment of particles from collector electrodes, and long-term stability of medium-voltage insulators [5; 7; 9; 10; 11]. Some problems occur when moisture is condensed in the gas on the surface of the insulators, and short currents occur [5; 6; 8; 19; 20; 25]. This article presents an analysis of medium-voltage electric insulators for a cylindrical-type plasma reactor and electrostatic precipitator made directly in the chimney (stainless steel). In this way, the PRESP footprint on the ground is missing, which solves a real problem. This article analyses the modification of the electrical properties of the medium-voltage insulators used at PRESP and does not focus on the performance of the plasma reactor and the collection of the cylindrical-type electrostatic precipitator. The article has the following structure: introduction, materials and method, results, discussions, and the last section, conclusions.