As a type of electrical load, steel mills are the equivalent of jackhammers early in the morning. If you’re not prepared for them, they can cause headaches. Steel mills, with arc furnaces, have a randomly varying demand that can swing as much as 200 MW for a 300 MW steel plant every 30-90 minutes or so. The effects of this load change may be noticed in lights, PC’s, and TV’s. When a mill’s furnace comes on, the voltage dips and rises when it is switched off.  Voltage and the frequency will change and result in a change of light intensity.  In addition, the arcs in each furnace of the mill can result in an imbalanced load that is loaded with harmonics that varies cycle to cycle creating what one may call “dirty” power. This load connected to the grid can affect other customers connected to the grid.