Correção do fator de potência de cargas industriais com dinâmica rápida

Abstract

In some activity branches of industrial segment, as well in medium and large buildings and commercial facilities, expressive contingents of electrical equipments presents, as one of their main characteristics, fast operational dynamics, alternating, and in short time intervals, repetitive cycles of no-load operation (or stand-by state) and sudden demands requesting for full-load operation. These kinds of loads present, as a rule of thumb, a relatively poor average operational power factor, what can be atributted to their high reactive energy consumption level (if compared totheir active energy consumption) on short transition intervals between no-load (or light-load or, still, stand-by state) and full-load operation. Lots of them, as in case of spot welding machines, generally operate with a low power factor, even under full-load. It is important to point out that, depending on the operational conditions of an industrial plant or a largebuilding, groups of loads that present the binomial low power factor and fast dynamics (meaning fast and cyclic changes in active and reactive power levels demanded from the supply grid) can define the global consequent power factor, considering that the modern electronic power meters are capable to registrate active and reactive consumption based on measurements of the electrical parameters Voltage and Current on relatively short time intervals. Therefore, this Dissertation was motivated by the necessity of evaluating, in details, the application of power factor correction systems to compensate these kind of loads. The main target comprises on the approach of PF dynamics correction technology, performed by tyristor-based power modules, generally capable to switch capacitors banks and dinamically adjust the load reactive energy requirements on extremely short time intervals (up to 1,5 cycleof the Voltage grid, typically), carrying out the reactive compensation for industrial loads whose operational cycles are developed on hundreds of miliseconds. Furthermore, the analysis were extended, preliminarily and on a conceptual level, to an improved configuration, adopting an integrated solution considering tyristors power modules in association with an additional system operating for fine adjustments in PF correction. This complementary configuration, enhanced with a generic conception of a STATCOM (potentially applicable in low Voltage grids), can be evaluated for a continuous and precise compensation withoutfixed steps, being useful, for example, in momments when dynamic PF correction becomes necessary in front of fast reactive oscillatory peaks. By now, it is opportune to enphasize, as will be seen along this Dissertation, that the existing conventional systems, very widespread inpractice and generally based on contactors and PF controllers with relays outputs, are not capable to fully compensate fast dynamic loads, because of their insufficient response time for this application. For an assured and effective performance, PF control systems must be fast enough to compensate the reactive demands considering the sensitivity limits presented by eletronic power meters. This sensitivity is reflected by the time between Voltage and current successive sampling as well by the effective measurement time (measurement window) that, at last, defines the calculation of rms electrical parameters (Voltage and current). These will be the base to determine active and reactive power demand, cumulative active and reactive energy consumptions and, consequently, the operational power factor on a time interval.