Technical solutions for harmonic resonance at MV: Relocatable capacitor bank technique

Capacitor banks are installed to compensate the reactive energy demanded by the local loads or feeder reactance, in order to adequate the voltage and technical losses. Although those benefits of installing capacitor banks in feeders are incontestable, the engineers should consider the harmonic resonance effects and the possibility of this resonance to increase the voltage distortion to levels above of the acceptable limits. In fact, the problems related to harmonics are spreading on MV systems due to the increasing quantity of disturbing loads. This work presents one case under survey at CPFL Paulista, where a feeder supplies several non-linear loads in two plants and three automatic capacitor banks. On weekdays, the harmonic voltage distortion levels were lower than the limits, but on the weekends, the limits exceeded, when most of non-linear loads were disconnected. At first analysis, there was a possibility of the consumer loads are operating as passive filters to the feeder. However, after the analysis of measurements and of the capacitor banks operations, it was possible to conclude that the feeder has resonance conditions due to the power factor correction of the capacitor banks. The paper presents three different approaches for solving the harmonic resonance problems, using the ATPDraw as a tool of simulation, and then recommendations for practical applications. The first one is to replace the capacitor bank in the same feeder, with relocatable capacitor bank technique; second, to reconfigure existing capacitor banks with a detuned reactive power, and the last one is to switch off the capacitor bank on the weekend when the non-linear loads are out, by automatic controller.