# Development of Electrode of Electric Impulse Chamber for Coal Grinding
## 2 Experimental Installation and Research Methodology  
The electric impulse installation of the following main blocks:  
* Control block for monitoring the operating modes of the installation (see Figure 1);
* Generator for converting AC voltage at the input into DC voltage at the output;
* Capacitor for energy storage;
* Protection system for switching off the installation in cases when the voltage on the capacitor exceeds the established safe working voltage of the discharge;
* Spark gap (forming gap) consisting of two conductive hemispherical electrodes separated by an air gap designed to form an electric spark between the conductors;
* Working chamber for grinding coal. The generator with a forming gap is one of the main components of the installation (see Figure 2). In the experimental researches, pulse capacitors (see Figure 3) with a nominal voltage of up to 100 kV and capacities of C = 0.25 uF (4 pcs) and C = 0.4 uF (5 pcs) were used. The technical characteristics of the installation are given in Table 1. The installation is designed to operate under the following conditions: air temperature from +5 to +40 \({}^{\circ}\)C, relative humidity up to 80% at +30 \({}^{\circ}\)C, and the absence of conductive dust and chemically active vapors that could damage the insulation of conductive wires and devices. Figure 1: Control block. Figure 2: Generator with forming gap. The installation can be turned off automatically when the protection circuit is activated. The protection scheme works as follows: When the set safe operating voltage is exceeded, a protective arrestor is triggered, further closing the circuit consisting of the resistance and the primary winding of the pulse transformer. The alternating voltage from the secondary winding is rectified and supplied to the relay, which, when triggered, turns off the installation. The voltage of the pulsed discharges (U, kV) was changed by increasing or decreasing the distance (_l_, mm) between the hemispherical electrodes in the forming gap (see Figure 4). Voltage measurement was performed using a three-limit electrostatic kilovoltmeter (measuring limits of the device: 25-50-75 kV), where the limit of the permissible value of the basic error in the working part of the scale is \(\pm\)2.0%. The container (reservoir) of the working chamber for grinding coal is made of stainless steel grade 08X18H10, belonging to the austenitic group of alloys (see Figure 5). High-chromium austenitic stainless steel grade 08X18H9 was used as the electrode (positive electrode) powered by the power source of the installation. The positive electrode was insulated with fluoroplastic F-4 and attached to the upper part of the working chamber. \begin{table}
\begin{tabular}{c c} \hline \hline
**Working Fluid** & **Technical Water** \\ \hline Power supply network parameters: \\ \hline Voltage, V & 220 \\ \hline Frequency, Hz & 50 \\ \hline Power consumption, kW & 2.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Technical characteristics of the installation. Figure 4: Change in the voltage of a pulsed discharge depending on the distance between hemispherical metal electrodes in the forming gap. Figure 3: Capacitor and installation protection system. The fluoroplast served as the lid of the working chamber and also served as an electrical insulator between the positive and negative electrodes. The negative electrode was the inner surface of the reservoir bottom. The material is pulverized using the electric impulse method as follows: After powering the generator from the control block, the high voltage of the generator output is supplied in parallel to the capacitor. The voltage accumulated in the capacitor increases to a value at which there is a spontaneous breakdown of the air space between the hemispherical electrodes in the forming gap. Furthermore, all the energy stored in the capacitor is instantly supplied to the working chamber.