Iron and Steel Industry has been growing increasingly in Turkey in the last decade. Today its electricity demand is nearly one tenth of the installed generation capability of 40 GW in the country. In this paper, power quality investigations based on the arc furnace installations of the iron and steel plants using field measurements according to the international standard IEC 61000-4-30 are documented. Inter-harmonies and voltage flicker problems occurring both at the common coupling points of those plants and at the are furnace and SVC systems of the plants themselves are determined with the use of GPS receiver synchronization modules attached to the mobile power quality measurement systems. It has been observed that flicker and interharmonic problems are dominant at the point of common couplings where arc furnace installations are supplied. Based on the field measurements obtained with collaborative work of five arc furnace plants, it is possible to say that contemporary SVC systems cause interharmonic amplification problems around the second harmonic and novel methods are required to solve this problem.