Using measurements and analytical studies to minimize power quality issues impacting tin mill operations

Power quality related issues have impacted the operations of the tin mill in a large integrated steel mill. Specifically, voltage variations have upset PLCs, locked computer based controls, caused UPS to frequently transfer to battery, and in general, interrupted the process control for the tin mill operations. The nature of the voltage variations were quantified by monitoring the electrical distribution system supplying the tin mill at key 6900 V and 575 V locations. The measurements identified substations with significant total harmonic voltage distortion, and were used to develop an accurate model of load flow and harmonics. Both load flow and harmonic analytical studies were performed to investigate alternatives to minimize the voltage issues. Recommendations are given including 1) optimum transformer tap settings for each 575 V substation, 2) optimum location for harmonic filters to limit voltage distortion within IEEE standards, and 3) specification for the filters to reduce the loading of transformers to within equipment ratings. Finally, the impact of future plans to replace additional M-G sets with rectifiers is discussed.