THE INFLUENCE OF SURFACE EFFECT ON THE CURRENT MAGNITUDE IN THE INDUCTOR OF HIGH FREQUENCY CURRENT INSTALLATION
For technological processes of surface hardening of the working parts of tillage and cutting tools of agricultural machines, induction heating plants with high frequency currents (HFC) ELSIT 100/40-70 are widely used. Monitoring the parameters of the induction heating mode is difficult. The problem is that the current in the inductor is controlled as a percentage of the maximum current. The measurement of current in percent does not allow carrying out optimization studies that are aimed at ensuring maximum energy efficiency with the best quality indices of the hardening process. It is required to estimate the current in the inductor in amperes. The difficulty lies in the fact that the current in the inductor is about 2000 A. Direct measurement of current of similar magnitude by known technical means is difficult. It is known that at frequencies of electromagnetic field of 40-70 kHz, the so-called surface effect appears, the result of which is the displacement of the current into the conductor layers adjacent to its surface. The presence of a surface effect is accompanied by a significant increase in the resistance of the part heated in the HFC. Improved technique of indirect measurement of the inductor current of the HFC installation is proposed by the authors; it takes into account the surface effect. The investigations were carried out using the inductor designed to heat a tillage part of a “duckfoot sweeps” type. As a result of the obtained experimental data, the current in the inductor in amperes is determined analytically by taking into account the surface effect. On the basis of experimental and analytical studies, volt-ampere, ampere-frequency, volt-frequency characteristics and the current dependence in amperes on current in percent are constructed. For each of the dependences, regression equations are obtained.