Optimization of Voltage Dip Suppression Effect by Resistor Insertion in Startup of Low-frequency Induction Furnace

Abstract

Recently, in the distribution network, the rated capacities of the special loads that have the large starting currents are becoming bigger. So, the technical pre-studies for power quality are very important to suppress voltage troubles. In this study, as a special load, we consider the case that a large low-frequency induction furnace is connected to near the end of distribution network. The rated output is 800kW, and the rated capacity of the electric furnace transformer is 1000kVA. The inrush current generates during startup of the low-frequency induction furnace. By measurement of power quality, it is revealed that the inrush currents consist of the “magnetizing inrush current due to magnetic saturation of the electric furnace transformer” and the “inrush current due to the power factor correction capacitors”. We clarify the influence of the inrush currents on the voltage dip. And the effective measure (resistor insertion method) to reduce the inrush currents is proposed. We performed the EMTP simulation for the optimization of proposed method. As a result, it was verified that the analysis value and the measured value are in good agreement.