The evolution of the current power grid to the Smart Grid requires the integration of different engineering fields and methodologies in order to assure high efficiency, reliability, quality of service and contribute to the greenhouse emissions reduction. Power quality plays a key role in this progressive migration due to the power disturbances expected in all the power systems structure including the Electrical Industrial Systems (EIS), where is necessary to provide of analysis tools and adequate harmonic compensation studies to counteract the perturbations effects according the standards. An important technical option to compensate the harmonic pollution in industrial applications are the Switching Compensators (SC) or Active Power Filters (APF) which have demonstrated to be an effective solution under linear and nonlinear loads. In this document, some important industries are characterised according to their load distribution and a variability index established. Shunt SC based p - q theory are used to harmonic compensation keeping in mind the current changes presented during a typical industrial plant day. Additionally, is identified an appropriate relation index between the Total Demand Distortion (TDD) and the current consumption load. The results found show a significant improvement of harmonic compensation evaluating the performance indexes mentioned and the fulfilment of the IEEE - 519 standard.